Discrete Dynamical Modeling of Influenza Virus Infection Suggests Age-Dependent Differences in Immunity J. Virol. (IF 4.663) Pub Date : 2017-12-01 Ericka Keef; Li Ang Zhang; David Swigon; Alisa Urbano; G. Bard Ermentrout; Michael Matuszewski; Franklin R. Toapanta; Ted M. Ross; Robert S. Parker; Gilles Clermont
Immunosenescence, an age-related decline in immune function, is a major contributor to morbidity and mortality in the elderly. Older hosts exhibit a delayed onset of immunity and prolonged inflammation after an infection, leading to excess damage and a greater likelihood of death. Our study applies a rule-based model to infer which components of the immune response are most changed in an aged host. Two groups of BALB/c mice (aged 12 to 16 weeks and 72 to 76 weeks) were infected with 2 inocula: a survivable dose of 50 PFU and a lethal dose of 500 PFU. Data were measured at 10 points over 19 days in the sublethal case and at 6 points over 7 days in the lethal case, after which all mice had died. Data varied primarily in the onset of immunity, particularly the inflammatory response, which led to a 2-day delay in the clearance of the virus from older hosts in the sublethal cohort. We developed a Boolean model to describe the interactions between the virus and 21 immune components, including cells, chemokines, and cytokines, of innate and adaptive immunity. The model identifies distinct sets of rules for each age group by using Boolean operators to describe the complex series of interactions that activate and deactivate immune components. Our model accurately simulates the immune responses of mice of both ages and with both inocula included in the data (95% accurate for younger mice and 94% accurate for older mice) and shows distinct rule choices for the innate immunity arm of the model between younger and aging mice in response to influenza A virus infection. IMPORTANCE Influenza virus infection causes high morbidity and mortality rates every year, especially in the elderly. The elderly tend to have a delayed onset of many immune responses as well as prolonged inflammatory responses, leading to an overall weakened response to infection. Many of the details of immune mechanisms that change with age are currently not well understood. We present a rule-based model of the intrahost immune response to influenza virus infection. The model is fit to experimental data for young and old mice infected with influenza virus. We generated distinct sets of rules for each age group to capture the temporal differences seen in the immune responses of these mice. These rules describe a network of interactions leading to either clearance of the virus or death of the host, depending on the initial dosage of the virus. Our models clearly demonstrate differences in these two age groups, particularly in the innate immune responses.
Caenorhabditis elegans as an Emerging Model for Virus-Host Interactions J. Virol. (IF 4.663) Pub Date : 2017-12-01 Don B. Gammon
Since 1999, Caenorhabditis elegans has been extensively used to study microbe-host interactions due to its simple culture, genetic tractability, and susceptibility to numerous bacterial and fungal pathogens. In contrast, virus studies have been hampered by a lack of convenient virus infection models in nematodes. The recent discovery of a natural viral pathogen of C. elegans and development of diverse artificial infection models are providing new opportunities to explore virus-host interplay in this powerful model organism.
Control of the HIV-1 DNA Reservoir Is Associated In Vivo and In Vitro with NKp46/NKp30 (CD335 CD337) Inducibility and Interferon Gamma Production by Transcriptionally Unique NK Cells J. Virol. (IF 4.663) Pub Date : 2017-12-01 Francesco Marras; Anna Casabianca; Federica Bozzano; Maria Libera Ascierto; Chiara Orlandi; Antonio Di Biagio; Emanuele Pontali; Chiara Dentone; Giancarlo Orofino; Laura Nicolini; Lucia Taramasso; Mauro Magnani; Francesco M. Marincola; Ena Wang; Lorenzo Moretta; Andrea De Maria
The size of lentiviral DNA reservoirs reflects the effectiveness of immune responses against lentiviruses. So far, abundant information has been gathered on the control of HIV-1 replication. Understanding the innate mechanisms contributing to containment of the HIV DNA reservoir, however, are only partly clarified and are relevant to guiding interventions for reservoir containment or eradication. We studied the contribution of natural killer (NK) cell functional features in HIV patients controlling replication either spontaneously (HIV controllers [HIC]) or after progression and antiretroviral treatment (progressor patients [PP]). An inverse correlation between HIV DNA copy numbers (either total or integrated) in circulating CD4+ cells and NK cell function was observed. Induced interferon gamma (IFN-γ) production and NKp46/NKp30 activating receptor-induced expression correlated inversely with reservoir size. The correlation was present not only for a homogeneous cohort of HIC patients but also when PP were included in the analysis. Adaptive (NKG2C+ CD57+) NK cell features were not associated with reservoir size. However, a distinct set of 370 differentially expressed transcripts was found to underlie functional differences in NK cells controlling HIV DNA reservoir size. In proof-of-principle in vitro experiments of CD4+ cell infection with HIV-1, purified NK cells with the above-mentioned functional/transcriptional features displayed 10- and 30-fold higher abilities to control HIV replication and DNA burdens in vitro, respectively, than those of other NK cells. Thus, NK cells with a specific functional and transcriptional signature contribute to control of the HIV reservoir in CD4+ cells. Their selection, expansion, and/or adoptive transfer may support strategies to eradicate HIV-1 infection or to safely deescalate antiretroviral treatment. IMPORTANCE The most relevant feature of HIV-1 infection is represented by its DNA reservoir size in the body, which guarantees lifelong infection and resumption of virus replication after antiretroviral treatment interruption. So far, there has been little success in the identification of factors contributing to HIV-1 reservoir containment. In this study, by studying quantitative total and integrated HIV-1 DNA levels and NK cells in HIV-1 patients with either progressive or nonprogressive disease, we observed that inducible IFN-γ and natural cytotoxicity receptor (NCR) expression in a specific subset of NK cells with a characteristic transcriptional signature represents a correlate for HIV-1 reservoir control. This represents an advance in our understanding of the mechanism(s) that controls the lentivirus reservoir. Monitoring, selection, expansion, and adoptive transfer of these NK cells may allow monitoring of treatment efficacy and the likelihood of reservoir control and may support protocols for HIV-1 eradication.
Transcriptome Analysis of the Spodoptera frugiperda Ascovirus In Vivo Provides Insights into How Its Apoptosis Inhibitors and Caspase Promote Increased Synthesis of Viral Vesicles and Virion Progeny J. Virol. (IF 4.663) Pub Date : 2017-12-01 Heba A. H. Zaghloul; Robert Hice; Peter Arensburger; Brian A. Federici
Ascoviruses are double-stranded DNA (dsDNA) viruses that attack caterpillars and differ from all other viruses by inducing nuclear lysis followed by cleavage of host cells into numerous anucleate vesicles in which virus replication continues as these grow in the blood. Ascoviruses are also unusual in that most encode a caspase or caspase-like proteins. A robust cell line to study the novel molecular biology of ascovirus replication in vitro is lacking. Therefore, we used strand-specific transcriptome sequencing (RNA-Seq) to study transcription in vivo in third instars of Spodoptera frugiperda infected with the type species, Spodoptera frugiperda ascovirus 1a (SfAV-1a), sampling transcripts at different time points after infection. We targeted transcription of two types of SfAV-1a genes; first, 44 core genes that occur in several ascovirus species, and second, 26 genes predicted in silico to have metabolic functions likely involved in synthesizing viral vesicle membranes. Gene cluster analysis showed differences in temporal expression of SfAV-1a genes, enabling their assignment to three temporal classes: early, late, and very late. Inhibitors of apoptosis (IAP-like proteins; ORF016, ORF025, and ORF074) were expressed early, whereas its caspase (ORF073) was expressed very late, which correlated with apoptotic events leading to viral vesicle formation. Expression analysis revealed that a Diedel gene homolog (ORF121), the only known “virokine,” was highly expressed, implying that this ascovirus protein helps evade innate host immunity. Lastly, single-nucleotide resolution of RNA-Seq data revealed 15 bicistronic and tricistronic messages along the genome, an unusual occurrence for large dsDNA viruses. IMPORTANCE Unlike all other DNA viruses, ascoviruses code for an executioner caspase, apparently involved in a novel cytopathology in which viral replication induces nuclear lysis followed by cell cleavage, yielding numerous large anucleate viral vesicles that continue to produce virions. Our transcriptome analysis of genome expression in vivo by the Spodoptera frugiperda ascovirus shows that inhibitors of apoptosis are expressed first, enabling viral replication to proceed, after which the SfAV-1a caspase is synthesized, leading to viral vesicle synthesis and subsequent extensive production of progeny virions. Moreover, we detected numerous bicistronic and tricistronic mRNA messages in the ascovirus transcriptome, implying that ascoviruses use other noncanonical translational mechanisms, such as internal ribosome entry sites (IRESs). These results provide the first insights into the molecular biology of a unique coordinated gene expression pattern in which cell architecture is markedly modified, more than in any other known eukaryotic virus, to promote viral reproduction and transmission.
Distinct Mechanism for the Formation of the Ribonucleoprotein Complex of Tomato Spotted Wilt Virus J. Virol. (IF 4.663) Pub Date : 2017-12-01 Yu Guo; Baocheng Liu; Zhenzhen Ding; Guobang Li; Meizi Liu; Dantong Zhu; Yuna Sun; Shishang Dong; Zhiyong Lou
The Tomato spotted wilt virus (TSWV) belongs to the Tospovirus genus of the Bunyaviridae family and represents the sole plant-infecting group within bunyavirus. TSWV encodes a nucleocapsid protein (N) which encapsidates the RNA genome to form a ribonucleoprotein complex (RNP). In addition, the N has multiple roles during the infection of plant cells. Here, we report the crystal structure of the full-length TSWV N. The N features a body domain consisting of an N-lobe and a C-lobe. These lobes clamp a positively charged groove which may constitute the RNA binding site. Furthermore, the body domains are flanked by N- and C-terminal arms which mediate homotypic interactions to the neighboring subunits, resulting in a ring-shaped N trimer. Interestingly, the C terminus of one protomer forms an additional interaction with the protomer of an adjacent trimer in the crystal, which may constitute a higher-order oligomerization contact. In this way, this study provides insights into the structure and trimeric assembly of TSWV N, which help to explain previous functional findings, but also suggests distinct N interactions within a higher-order RNP. IMPORTANCE TSWV is one of the most devastating plant pathogens that cause severe diseases in numerous agronomic and ornamental crops worldwide. TSWV is also the prototypic member of the Tospovirus genus, which is the sole group of plant-infecting viruses in the bunyavirus family. This study determined the structure of full-length TSWV N in an oligomeric state. The structural observations explain previously identified biological properties of TSWV N. Most importantly, the additional homotypic interaction between the C terminus of one protomer with another protomer indicates that there is a distinct mechanism of RNP formation in the bunyavirus family, thereby enhancing the current knowledge of negative-sense single-stranded RNA virus-encoded N. TSWV N is the last remaining representative N with an unknown structure in the bunyavirus family. Combined with previous studies, the structure of TSWV N helps to build a complete picture of the bunyavirus-encoded N family and reveals a close evolutionary relationship between orthobunyavirus, phlebovirus, hantavirus, and tospovirus.
Heterogeneity of the Epstein-Barr Virus (EBV) Major Internal Repeat Reveals Evolutionary Mechanisms of EBV and a Functional Defect in the Prototype EBV Strain B95-8 J. Virol. (IF 4.663) Pub Date : 2017-12-01 Mohammed M. Ba abdullah; Richard D. Palermo; Anne L. Palser; Nicholas E. Grayson; Paul Kellam; Samantha Correia; Agnieszka Szymula; Robert E. White
Epstein-Barr virus (EBV) is a ubiquitous pathogen of humans that can cause several types of lymphoma and carcinoma. Like other herpesviruses, EBV has diversified through both coevolution with its host and genetic exchange between virus strains. Sequence analysis of the EBV genome is unusually challenging because of the large number and lengths of repeat regions within the virus. Here we describe the sequence assembly and analysis of the large internal repeat 1 of EBV (IR1; also known as the BamW repeats) for more than 70 strains. The diversity of the latency protein EBV nuclear antigen leader protein (EBNA-LP) resides predominantly within the exons downstream of IR1. The integrity of the putative BWRF1 open reading frame (ORF) is retained in over 80% of strains, and deletions truncating IR1 always spare BWRF1. Conserved regions include the IR1 latency promoter (Wp) and one zone upstream of and two within BWRF1. IR1 is heterogeneous in 70% of strains, and this heterogeneity arises from sequence exchange between strains as well as from spontaneous mutation, with interstrain recombination being more common in tumor-derived viruses. This genetic exchange often incorporates regions of <1 kb, and allelic gene conversion changes the frequency of small regions within the repeat but not close to the flanks. These observations suggest that IR1—and, by extension, EBV—diversifies through both recombination and breakpoint repair, while concerted evolution of IR1 is driven by gene conversion of small regions. Finally, the prototype EBV strain B95-8 contains four nonconsensus variants within a single IR1 repeat unit, including a stop codon in the EBNA-LP gene. Repairing IR1 improves EBNA-LP levels and the quality of transformation by the B95-8 bacterial artificial chromosome (BAC). IMPORTANCE Epstein-Barr virus (EBV) infects the majority of the world population but causes illness in only a small minority of people. Nevertheless, over 1% of cancers worldwide are attributable to EBV. Recent sequencing projects investigating virus diversity to see if different strains have different disease impacts have excluded regions of repeating sequence, as they are more technically challenging. Here we analyze the sequence of the largest repeat in EBV (IR1). We first characterized the variations in protein sequences encoded across IR1. In studying variations within the repeat of each strain, we identified a mutation in the main laboratory strain of EBV that impairs virus function, and we suggest that tumor-associated viruses may be more likely to contain DNA mixed from two strains. The patterns of this mixing suggest that sequences can spread between strains (and also within the repeat) by copying sequence from another strain (or repeat unit) to repair DNA damage.
Molecular Evolution of Herpes Simplex Virus 2 Complete Genomes: Comparison between Primary and Recurrent Infections J. Virol. (IF 4.663) Pub Date : 2017-12-01 Miguel A. Minaya; Travis L. Jensen; Johannes B. Goll; Maria Korom; Sree H. Datla; Robert B. Belshe; Lynda A. Morrison
Herpes simplex virus 1 (HSV-1) and HSV-2 are large, double-stranded DNA viruses that cause lifelong persistent infections characterized by periods of quiescence and recurrent disease. How HSV evolves within an infected individual experiencing multiple episodes of recurrent disease over time is not known. We determined the genome sequences of viruses isolated from two subjects in the Herpevac Trial for Women who experienced primary HSV-2 genital disease and compared them with sequences of viruses isolated from the subsequent fifth or sixth episode of recurrent disease in the same individuals. Each of the HSV-2 genome sequences was initially obtained using next-generation sequencing and completed with Sanger sequencing. Polymorphisms over the entire genomes were mapped, and amino acid variants resulting from nonsynonymous changes were analyzed based on the secondary and tertiary structures of a previously crystallized protein. A phylogenetic reconstruction was used to assess relationships among the four HSV-2 samples, other North American sequences, and reference sequences. Little genetic drift was detected in viruses shed by the same subjects following repeated reactivation events, suggesting strong selective pressure on the viral genome to maintain sequence fidelity during reactivations from its latent state within an individual host. Our results also demonstrate that some primary HSV-2 isolates from North America more closely resemble the HG52 laboratory strain from Scotland than the low-passage-number clinical isolate SD90e from South Africa or laboratory strain 333. Thus, one of the sequences reported here would be a logical choice as a reference strain for inclusion in future studies of North American HSV-2 isolates. IMPORTANCE The extent to which the HSV-2 genome evolves during multiple episodes of reactivation from its latent state within an infected individual is not known. We used next-generation sequencing techniques to determine whole-genome sequences of four viral samples from two subjects in the Herpevac Trial. The sequence of each subject's well-documented primary isolate was compared with the sequence of the isolate from their fifth or sixth episode of recurrent disease. Only 19 genetic polymorphisms unique to the primary or recurrent isolate were identified, 10 in subject A and 9 in subject B. These observations indicate remarkable genetic conservation between primary and recurrent episodes of HSV-2 infection and imply that strong selection pressures exist to maintain the fidelity of the viral genome during repeated reactivations from its latent state. The genome conservation observed also has implications for the potential success of a therapeutic vaccine.
Differentiated Human SH-SY5Y Cells Provide a Reductionist Model of Herpes Simplex Virus 1 Neurotropism J. Virol. (IF 4.663) Pub Date : 2017-12-01 Mackenzie M. Shipley; Colleen A. Mangold; Chad V. Kuny; Moriah L. Szpara
Neuron-virus interactions that occur during herpes simplex virus (HSV) infection are not fully understood. Neurons are the site of lifelong latency and are a crucial target for long-term suppressive therapy or viral clearance. A reproducible neuronal model of human origin would facilitate studies of HSV and other neurotropic viruses. Current neuronal models in the herpesvirus field vary widely and have caveats, including incomplete differentiation, nonhuman origins, or the use of dividing cells that have neuropotential but lack neuronal morphology. In this study, we used a robust approach to differentiate human SH-SY5Y neuroblastoma cells over 2.5 weeks, producing a uniform population of mature human neuronal cells. We demonstrate that terminally differentiated SH-SY5Y cells have neuronal morphology and express proteins with subcellular localization indicative of mature neurons. These neuronal cells are able to support a productive HSV-1 infection, with kinetics and overall titers similar to those seen in undifferentiated SH-SY5Y cells and the related SK-N-SH cell line. However, terminally differentiated, neuronal SH-SY5Y cells release significantly less extracellular HSV-1 by 24 h postinfection (hpi), suggesting a unique neuronal response to viral infection. With this model, we are able to distinguish differences in neuronal spread between two strains of HSV-1. We also show expression of the antiviral protein cyclic GMP-AMP synthase (cGAS) in neuronal SH-SY5Y cells, which is the first demonstration of the presence of this protein in nonepithelial cells. These data provide a model for studying neuron-virus interactions at the single-cell level as well as via bulk biochemistry and will be advantageous for the study of neurotropic viruses in vitro. IMPORTANCE Herpes simplex virus (HSV) affects millions of people worldwide, causing painful oral and genital lesions, in addition to a multitude of more severe symptoms such as eye disease, neonatal infection, and, in rare cases, encephalitis. Presently, there is no cure available to treat those infected or prevent future transmission. Due to the ability of HSV to cause a persistent, lifelong infection in the peripheral nervous system, the virus remains within the host for life. To better understand the basis of virus-neuron interactions that allow HSV to persist within the host peripheral nervous system, improved neuronal models are required. Here we describe a cost-effective and scalable human neuronal model system that can be used to study many neurotropic viruses, such as HSV, Zika virus, dengue virus, and rabies virus.
Type I Interferon Signaling to Dendritic Cells Limits Murid Herpesvirus 4 Spread from the Olfactory Epithelium J. Virol. (IF 4.663) Pub Date : 2017-12-01 Clara Lawler; Philip G. Stevenson
Murid herpesvirus 4 (MuHV-4) is a B cell-tropic gammaherpesvirus that can be studied in vivo. Despite viral evasion, type I interferons (IFN-I) limit its spread. After MuHV-4 inoculation into footpads, IFN-I protect lymph node subcapsular sinus macrophages (SSM) against productive infection; after peritoneal inoculation, they protect splenic marginal zone macrophages, and they limit MuHV-4 replication in the lungs. While invasive infections can be used to test specific aspects of host colonization, it is also important to understand natural infection. MuHV-4 taken up spontaneously by alert mice enters them via olfactory neurons. We determined how IFN-I act in this context. Blocking IFN-I signaling did not increase neuronal infection but allowed the virus to spread to the adjacent respiratory epithelium. In lymph nodes, a complete IFN-I signaling block increased MuHV-4 lytic infection in SSM and increased the number of dendritic cells (DC) expressing viral green fluorescent protein (GFP) independently of lytic infection. A CD11c+ cell-directed signaling block increased infection of DC only. However, this was sufficient to increase downstream infection, consistent with DC providing the main viral route to B cells. The capacity of IFN-I to limit DC infection indicated that viral IFN-I evasion was only partly effective. Therefore, DC are a possible target for IFN-I-based interventions to reduce host colonization. IMPORTANCE Human gammaherpesviruses infect B cells and cause B cell cancers. Interventions to block virus binding to B cells have not stopped their infection. Therefore, we must identify other control points that are relevant to natural infection. Human infections are difficult to analyze. However, gammaherpesviruses colonize all mammals. A related gammaherpesvirus of mice reaches B cells not directly but via infected dendritic cells. We show that type I interferons, an important general antiviral defense, limit gammaherpesvirus B cell infection by acting on dendritic cells. Therefore, dendritic cell infection is a potential point of interferon-based therapeutic intervention.
Epstein-Barr Virus BKRF4 Gene Product Is Required for Efficient Progeny Production J. Virol. (IF 4.663) Pub Date : 2017-12-01 H. M. Abdullah Al Masud; Takahiro Watanabe; Masahiro Yoshida; Yoshitaka Sato; Fumi Goshima; Hiroshi Kimura; Takayuki Murata
Epstein-Barr virus (EBV), a member of human gammaherpesvirus, infects mainly B cells. EBV has two alternative life cycles, latent and lytic, and is reactivated occasionally from the latent stage to the lytic cycle. To combat EBV-associated disorders, understanding the molecular mechanisms of the EBV lytic replication cycle is also important. Here, we focused on an EBV lytic gene, BKRF4. Using our anti-BKRF4 antibody, we revealed that the BKRF4 gene product is expressed during the lytic cycle with late kinetics. To characterize the role of BKRF4, we constructed BKRF4-knockout mutants using the bacterial artificial chromosome (BAC) and CRISPR/Cas9 systems. Although disruption of the BKRF4 gene had almost no effect on viral protein expression and DNA synthesis, it significantly decreased progeny virion levels in HEK293 and Akata cells. Furthermore, we show that BKRF4 is involved not only in production of progeny virions but also in increasing the infectivity of the virus particles. Immunoprecipitation assays revealed that BKRF4 interacted with a virion protein, BGLF2. We showed that the C-terminal region of BKRF4 was critical for this interaction and for efficient progeny production. Immunofluorescence analysis revealed that BKRF4 partially colocalized with BGLF2 in the nucleus and perinuclear region. Finally, we showed that BKRF4 is a phosphorylated, possible tegument protein and that the EBV protein kinase BGLF4 may be important for this phosphorylation. Taken together, our data suggest that BKRF4 is involved in the production of infectious virions. IMPORTANCE Although the latent genes of EBV have been studied extensively, the lytic genes are less well characterized. This study focused on one such lytic gene, BKRF4, which is conserved only among gammaherpesviruses (ORF45 of Kaposi's sarcoma-associated herpesvirus or murine herpesvirus 68). After preparing the BKRF4 knockout virus using B95-8 EBV-BAC, we demonstrated that the BKRF4 gene was involved in infectious progeny particle production. Importantly, we successfully generated a BKRF4 knockout virus of Akata using CRISPR/Cas9 technology, confirming the phenotype in this separate strain. We further showed that BKRF4 interacted with another virion protein, BGLF2, and demonstrated the importance of this interaction in infectious virion production. These results shed light on the elusive process of EBV progeny maturation in the lytic cycle. Notably, this study describes a successful example of the generation and characterization of an EBV construct with a disrupted lytic gene using CRISPR/Cas9 technology.
Host Noncoding Retrotransposons Induced by DNA Viruses: a SINE of Infection? J. Virol. (IF 4.663) Pub Date : 2017-12-01 Jessica M. Tucker; Britt A. Glaunsinger
Our genomes are dominated by repetitive elements. The majority of these elements derive from retrotransposons, which expand throughout the genome through a process of reverse transcription and integration. Short interspersed nuclear elements, or SINEs, are an abundant class of retrotransposons that are transcribed by RNA polymerase III, thus generating exclusively noncoding RNA (ncRNA) that must hijack the machinery required for their transposition. SINE loci are generally transcriptionally repressed in somatic cells but can be robustly induced upon infection with multiple DNA viruses. Recent research has focused on the gene expression and signaling events that are modulated by SINE ncRNAs, particularly during gammaherpesvirus infection. Here, we review the biology of these SINE ncRNAs, explore how DNA virus infection may lead to their induction, and describe how novel gene regulatory and immune-related functions of these ncRNAs may impact the viral life cycle.
Mutations in the Fusion Protein of Measles Virus That Confer Resistance to the Membrane Fusion Inhibitors Carbobenzoxy-d-Phe-l-Phe-Gly and 4-Nitro-2-Phenylacetyl Amino-Benzamide J. Virol. (IF 4.663) Pub Date : 2017-12-01 Michael N. Ha; Sébastien Delpeut; Ryan S. Noyce; Gary Sisson; Karen M. Black; Liang-Tzung Lin; Darius Bilimoria; Richard K. Plemper; Gilbert G. Privé; Christopher D. Richardson
The inhibitors carbobenzoxy (Z)-d-Phe-l-Phe-Gly (fusion inhibitor peptide [FIP]) and 4-nitro-2-phenylacetyl amino-benzamide (AS-48) have similar efficacies in blocking membrane fusion and syncytium formation mediated by measles virus (MeV). Other homologues, such as Z-d-Phe, are less effective but may act through the same mechanism. In an attempt to map the site of action of these inhibitors, we generated mutant viruses that were resistant to the inhibitory effects of Z-d-Phe-l-Phe-Gly. These 10 mutations were localized to the heptad repeat B (HRB) region of the fusion protein, and no changes were observed in the viral hemagglutinin, which is the receptor attachment protein. Mutations were validated in a luciferase-based membrane fusion assay, using transfected fusion and hemagglutinin expression plasmids or with syncytium-based assays in Vero, Vero-SLAM, and Vero-Nectin 4 cell lines. The changes I452T, D458N, D458G/V459A, N462K, N462H, G464E, and I483R conferred resistance to both FIP and AS-48 without compromising membrane fusion. The inhibitors did not block hemagglutinin protein-mediated binding to the target cell. Edmonston vaccine/laboratory and IC323 wild-type strains were equally affected by the inhibitors. Escape mutations were mapped upon a three-dimensional (3D) structure modeled from the published crystal structure of parainfluenzavirus 5 fusion protein. The most effective mutations were situated in a region located near the base of the globular head and its junction with the alpha-helical stalk of the prefusion protein. We hypothesize that the fusion inhibitors could interfere with the structural changes that occur between the prefusion and postfusion conformations of the fusion protein. IMPORTANCE Due to lapses in vaccination worldwide that have caused localized outbreaks, measles virus (MeV) has regained importance as a pathogen. Antiviral agents against measles virus are not commercially available but could be useful in conjunction with MeV eradication vaccine programs and as a safeguard in oncolytic viral therapy. Three decades ago, the small hydrophobic peptide Z-d-Phe-l-Phe-Gly (FIP) was shown to block MeV infections and syncytium formation in monkey kidney cell lines. The exact mechanism of its action has yet to be determined, but it does appear to have properties similar to those of another chemical inhibitor, AS-48, which appears to interfere with the conformational change in the viral F protein that is required to elicit membrane fusion. Escape mutations were used to map the site of action for FIP. Knowledge gained from these studies could help in the design of new inhibitors against morbilliviruses and provide additional knowledge concerning the mechanism of virus-mediated membrane fusion.
Pathogenic Correlates of Simian Immunodeficiency Virus-Associated B Cell Dysfunction J. Virol. (IF 4.663) Pub Date : 2017-12-01 Egidio Brocca-Cofano; David Kuhrt; Basile Siewe; Cuiling Xu; George S. Haret-Richter; Jodi Craigo; Celia Labranche; David C. Montefiori; Alan Landay; Cristian Apetrei; Ivona Pandrea
We compared and contrasted pathogenic (in pig-tailed macaques [PTMs]) and nonpathogenic (in African green monkeys [AGMs]) SIVsab infections to assess the significance of the B cell dysfunction observed in simian (SIV) and human immunodeficiency virus (HIV) infections. We report that the loss of B cells is specifically associated with the pathogenic SIV infection, while in the natural hosts, in which SIV is nonpathogenic, B cells rapidly increase in both lymph nodes (LNs) and intestine. SIV-associated B cell dysfunction associated with the pathogenic SIV infection is characterized by loss of naive B cells, loss of resting memory B cells due to their redistribution to the gut, increases of the activated B cells and circulating tissue-like memory B cells, and expansion of the B regulatory cells (Bregs). While circulating B cells are virtually restored to preinfection levels during the chronic pathogenic SIV infection, restoration is mainly due to an expansion of the “exhausted,” virus-specific B cells, i.e., activated memory cells and tissue-like memory B cells. Despite of the B cell dysfunction, SIV-specific antibody (Ab) production was higher in the PTMs than in AGMs, with the caveat that rapid disease progression in PTMs was strongly associated with lack of anti-SIV Ab. Neutralization titers and the avidity and maturation of immune responses did not differ between pathogenic and nonpathogenic infections, with the exception of the conformational epitope recognition, which evolved from low to high conformations in the natural host. The patterns of humoral immune responses in the natural host are therefore more similar to those observed in HIV-infected subjects, suggesting that natural hosts may be more appropriate for modeling the immunization strategies aimed at preventing HIV disease progression. The numerous differences between the pathogenic and nonpathogenic infections with regard to dynamics of the memory B cell subsets point to their role in the pathogenesis of HIV/SIV infections and suggest that monitoring B cells may be a reliable approach for assessing disease progression. IMPORTANCE We report here that the HIV/SIV-associated B cell dysfunction (defined by loss of total and memory B cells, increased B regulatory cell [Breg] counts, and B cell activation and apoptosis) is specifically associated with pathogenic SIV infection and absent during the course of nonpathogenic SIV infection in natural nonhuman primate hosts. Alterations of the B cell population are not correlated with production of neutralizing antibodies, the levels of which are similar in the two species. Rapid progressive infections are associated with a severe impairment in SIV-specific antibody production. While we did not find major differences in avidity and maturation between the pathogenic and nonpathogenic SIV infections, we identified a major difference in conformational epitope recognition, with the nonpathogenic infection being characterized by an evolution from low to high conformations. B cell dysfunction should be considered in designing immunization strategies aimed at preventing HIV disease progression.
A Selective Bottleneck Shapes the Evolutionary Mutant Spectra of Enterovirus A71 during Viral Dissemination in Humans J. Virol. (IF 4.663) Pub Date : 2017-12-01 Sheng-Wen Huang; Yi-Hui Huang; Huey-Pin Tsai; Pin-Hwa Kuo; Shih-Min Wang; Ching-Chuan Liu; Jen-Ren Wang
RNA viruses accumulate mutations to rapidly adapt to environmental changes. Enterovirus A71 (EV-A71) causes various clinical manifestations with occasional severe neurological complications. However, the mechanism by which EV-A71 evolves within the human body is unclear. Utilizing deep sequencing and haplotype analyses of viruses from various tissues of an autopsy patient, we sought to define the evolutionary pathway by which enterovirus A71 evolves fitness for invading the central nervous system in humans. Broad mutant spectra with divergent mutations were observed at the initial infection sites in the respiratory and digestive systems. After viral invasion, we identified a haplotype switch and dominant haplotype, with glycine at VP1 residue 31 (VP1-31G) in viral particles disseminated into the integumentary and central nervous systems. In vitro viral growth and fitness analyses indicated that VP1-31G conferred growth and a fitness advantage in human neuronal cells, whereas VP1-31D conferred enhanced replication in human colorectal cells. A higher proportion of VP1-31G was also found among fatal cases, suggesting that it may facilitate central nervous system infection in humans. Our data provide the first glimpse of EV-A71 quasispecies from oral tissues to the central nervous system within humans, showing broad implications for the surveillance and pathogenesis of this reemerging viral pathogen. IMPORTANCE EV-A71 continues to be a worldwide burden to public health. Although EV-A71 is the major etiological agent of hand, foot, and mouth disease, it can also cause neurological pulmonary edema, encephalitis, and even death, especially in children. Understanding selection processes enabling dissemination and accurately estimating EV-A71 diversity during invasion in humans are critical for applications in viral pathogenesis and vaccine studies. Here, we define a selection bottleneck appearing in respiratory and digestive tissues. Glycine substitution at VP1 residue 31 helps viruses break through the bottleneck and invade the central nervous system. This substitution is also advantageous for replication in neuronal cells in vitro. Considering that fatal cases contain enhanced glycine substitution at VP1-31, we suggest that the increased prevalence of VP1-31G may alter viral tropism and aid central nervous system invasion. Our findings provide new insights into a dynamic mutant spectral switch active during acute viral infection with emerging viral pathogens.
Structurally Guided Removal of DeISGylase Biochemical Activity from Papain-Like Protease Originating from Middle East Respiratory Syndrome Coronavirus J. Virol. (IF 4.663) Pub Date : 2017-12-01 Courtney M. Daczkowski; Octavia Y. Goodwin; John V. Dzimianski; Jonathan J. Farhat; Scott D. Pegan
Middle East respiratory syndrome coronavirus (MERS-CoV) is an emerging human pathogen that is the causative agent for Middle East respiratory syndrome (MERS). With MERS outbreaks resulting in over 35% fatalities and now spread to 27 countries, MERS-CoV poses a significant ongoing threat to global human health. As part of its viral genome, MERS-CoV encodes a papain-like protease (PLpro) that has been observed to act as a deubiquitinase and deISGylase to antagonize type I interferon (IFN-I) immune pathways. This activity is in addition to its viral polypeptide cleavage function. Although the overall impact of MERS-CoV PLpro function is observed to be essential, difficulty has been encountered in delineating the importance of its separate functions, particularly its deISGylase activity. As a result, the interface of MERS-CoV and human interferon-stimulated gene product 15 (hISG15) was probed with isothermal calorimetry, which suggests that the C-terminal domain of hISG15 is principally responsible for interactions. Subsequently, the structure of MERS-CoV PLpro was solved to 2.4 Å in complex with the C-terminal domain of hISG15. Utilizing this structural information, mutants were generated that lacked appreciable deISGylase activity but retained wild-type deubiquitinase and peptide cleavage activities. Hence, this provides a new platform for understanding viral deISGylase activity within MERS-CoV and other CoVs. IMPORTANCE Coronaviruses, such as Middle East respiratory syndrome coronavirus (MERS-CoV), encode a papain-like protease (PLpro) that possesses the ability to antagonize interferon immune pathways through the removal of ubiquitin and interferon-stimulated gene product 15 (ISG15) from target proteins. The lack of CoV proteases with attenuated deISGylase activity has been a key obstacle in delineating the impact between deubiquitinase and deISGylase activities on viral host evasion and pathogenesis. Here, biophysical techniques revealed that MERS-CoV PLpro chiefly engages human ISG15 through its C-terminal domain. The first structure of MERS-CoV PLpro in complex with this domain exposed the interface between these two entities. Employing these structural insights, mutations were employed to selectively remove deISGylase activity with no appreciable impact on its other deubiquitinase and peptide cleavage biochemical properties. Excitingly, this study introduces a new tool to probe the pathogenesis of MERS-CoV and related viruses through the removal of viral deISGylase activity.
Porcine Hemagglutinating Encephalomyelitis Virus Enters Neuro-2a Cells via Clathrin-Mediated Endocytosis in a Rab5-, Cholesterol-, and pH-Dependent Manner J. Virol. (IF 4.663) Pub Date : 2017-12-01 Zi Li; Kui Zhao; Yungang Lan; Xiaoling Lv; Shiyu Hu; Jiyu Guan; Huijun Lu; Jing Zhang; Junchao Shi; Yawen Yang; Deguang Song; Feng Gao; Wenqi He
Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurovirulent coronavirus that invades the central nervous system (CNS) in piglets. Although important progress has been made toward understanding the biology of PHEV, many aspects of its life cycle remain obscure. Here we dissected the molecular mechanism underlying cellular entry and intracellular trafficking of PHEV in mouse neuroblastoma (Neuro-2a) cells. We first performed a thin-section transmission electron microscopy (TEM) assay to characterize the kinetics of PHEV, and we found that viral entry and transfer occur via membranous coating-mediated endo- and exocytosis. To verify the roles of distinct endocytic pathways, systematic approaches were used, including pharmacological inhibition, RNA interference, confocal microscopy analysis, use of fluorescently labeled virus particles, and overexpression of a dominant negative (DN) mutant. Quantification of infected cells showed that PHEV enters cells by clathrin-mediated endocytosis (CME) and that low pH, dynamin, cholesterol, and Eps15 are indispensably involved in this process. Intriguingly, PHEV invasion leads to rapid actin rearrangement, suggesting that the intactness and dynamics of the actin cytoskeleton are positively correlated with viral endocytosis. We next investigated the trafficking of internalized PHEV and found that Rab5- and Rab7-dependent pathways are required for the initiation of a productive infection. Furthermore, a GTPase activation assay suggested that endogenous Rab5 is activated by PHEV and is crucial for viral progression. Our findings demonstrate that PHEV hijacks the CME and endosomal system of the host to enter and traffic within neural cells, providing new insights into PHEV pathogenesis and guidance for antiviral drug design. IMPORTANCE Porcine hemagglutinating encephalomyelitis virus (PHEV), a nonsegmented, positive-sense, single-stranded RNA coronavirus, invades the central nervous system (CNS) and causes neurological dysfunction. Neural cells are its targets for viral progression. However, the detailed mechanism underlying PHEV entry and trafficking remains unknown. PHEV is the etiological agent of porcine hemagglutinating encephalomyelitis, which is an acute and highly contagious disease that causes numerous deaths in suckling piglets and enormous economic losses in China. Understanding the viral entry pathway will not only advance our knowledge of PHEV infection and pathogenesis but also open new approaches to the development of novel therapeutic strategies. Therefore, we employed systematic approaches to dissect the internalization and intracellular trafficking mechanism of PHEV in Neuro-2a cells. This is the first report to describe the process of PHEV entry into nerve cells via clathrin-mediated endocytosis in a dynamin-, cholesterol-, and pH-dependent manner that requires Rab5 and Rab7.
Vector Order Determines Protection against Pathogenic Simian Immunodeficiency Virus Infection in a Triple-Component Vaccine by Balancing CD4+ and CD8+ T-Cell Responses J. Virol. (IF 4.663) Pub Date : 2017-12-01 Ulrike Sauermann; Antonia Radaelli; Nicole Stolte-Leeb; Katharina Raue; Massimiliano Bissa; Carlo Zanotto; Michael Krawczak; Matthias Tenbusch; Klaus Überla; Brandon F. Keele; Carlo De Giuli Morghen; Sieghart Sopper; Christiane Stahl-Hennig
An effective AIDS vaccine should elicit strong humoral and cellular immune responses while maintaining low levels of CD4+ T-cell activation to avoid the generation of target cells for viral infection. The present study investigated two prime-boost regimens, both starting vaccination with single-cycle immunodeficiency virus, followed by two mucosal boosts with either recombinant adenovirus (rAd) or fowlpox virus (rFWPV) expressing SIVmac239 or SIVmac251 gag/pol and env genes, respectively. Finally, vectors were switched and systemically administered to the reciprocal group of animals. Only mucosal rFWPV immunizations followed by systemic rAd boost significantly protected animals against a repeated low-dose intrarectal challenge with pathogenic SIVmac251, resulting in a vaccine efficacy (i.e., risk reduction per exposure) of 68%. Delayed viral acquisition was associated with higher levels of activated CD8+ T cells and Gag-specific gamma interferon (IFN-γ)-secreting CD8+ cells, low virus-specific CD4+ T-cell responses, and low Env antibody titers. In contrast, the systemic rFWPV boost induced strong virus-specific CD4+ T-cell activity. rAd and rFWPV also induced differential patterns of the innate immune responses, thereby possibly shaping the specific immunity. Plasma CXCL10 levels after final immunization correlated directly with virus-specific CD4+ T-cell responses and inversely with the number of exposures to infection. Also, the percentage of activated CD69+ CD8+ T cells correlated with the number of exposures to infection. Differential stimulation of the immune response likely provided the basis for the diverging levels of protection afforded by the vaccine regimen. IMPORTANCE A failed phase II AIDS vaccine trial led to the hypothesis that CD4+ T-cell activation can abrogate any potentially protective effects delivered by vaccination or promote acquisition of the virus because CD4+ T helper cells, required for an effective immune response, also represent the target cells for viral infection. We compared two vaccination protocols that elicited similar levels of Gag-specific immune responses in rhesus macaques. Only the animal group that had a low level of virus-specific CD4+ T cells in combination with high levels of activated CD8+ T cells was significantly protected from infection. Notably, protection was achieved despite the lack of appreciable Env antibody titers. Moreover, we show that both the vector and the route of immunization affected the level of CD4+ T-cell responses. Thus, mucosal immunization with FWPV-based vaccines should be considered a potent prime in prime-boost vaccination protocols.
Role of Herpes Simplex Virus 1 γ34.5 in the Regulation of IRF3 Signaling J. Virol. (IF 4.663) Pub Date : 2017-12-01 Richard Manivanh; Jesse Mehrbach; David M. Knipe; David A. Leib
During viral infection, pattern recognition receptors (PRRs) and their associated adaptors recruit TANK-binding kinase 1 (TBK1) to activate interferon regulatory factor 3 (IRF3), resulting in production of type I interferons (IFNs). ICP0 and ICP34.5 are among the proteins encoded by herpes simplex virus 1 (HSV-1) that modulate type I IFN signaling. We constructed a recombinant virus (ΔXX) that lacks amino acids 87 to 106, a portion of the previously described TBK1-binding domain of the γ34.5 gene (D. Verpooten, Y. Ma, S. Hou, Z. Yan, and B. He, J Biol Chem 284:1097–1105, 2009, https://doi.org/10.1074/JBC.M805905200). These 20 residues are outside the γ34.5 beclin1-binding domain (BBD) that interacts with beclin1 and regulates autophagy. Unexpectedly, ΔXX showed no deficit in replication in vivo in a variety of tissues and showed virulence comparable to that of wild-type and marker-rescued viruses following intracerebral infection. ΔXX was fully capable of mediating the dephosphorylation of eIF2α, and the virus was capable of controlling the phosphorylation of IRF3. In contrast, a null mutant in γ34.5 failed to control IRF3 phosphorylation due to an inability of the mutant to sustain expression of ICP0. Our data show that while γ34.5 regulates IRF3 phosphorylation, the TBK1-binding domain itself has no impact on IRF3 phosphorylation or on replication and pathogenesis in mice. IMPORTANCE Interferons (IFNs) are potent activators of a variety of host responses that serve to control virus infections. The Herpesviridae have evolved countermeasures to IFN responses. Herpes simplex virus 1 (HSV-1) encodes the multifunctional neurovirulence protein ICP34.5. In this study, we investigated the biological relevance of the interaction between ICP34.5 and TANK-binding kinase 1 (TBK1), an activator of IFN responses. Here, we establish that although ICP34.5 binds TBK1 under certain conditions through a TBK1-binding domain (TBD), there was no direct impact of the TBD on viral replication or virulence in mice. Furthermore, we showed that activation of IRF3, a substrate of TBK1, was independent of the TBD. Instead, we provided evidence that the ability of ICP34.5 to control IRF3 activation is through its ability to reverse translational shutoff and sustain the expression of other IFN inhibitors encoded by the virus. This work provides new insights into the immunomodulatory functions of ICP34.5.
Three Conserved Regions in Baculovirus Sulfhydryl Oxidase P33 Are Critical for Enzymatic Activity and Function J. Virol. (IF 4.663) Pub Date : 2017-12-01 Wenhua Kuang; Huanyu Zhang; Manli Wang; Ning-Yi Zhou; Fei Deng; Hualin Wang; Peng Gong; Zhihong Hu
Baculoviruses encode a conserved sulfhydryl oxidase, P33, which is necessary for budded virus (BV) production and multinucleocapsid occlusion-derived virus (ODV) formation. Here, the structural and functional relationship of P33 was revealed by X-ray crystallography, site-directed mutagenesis, and functional analysis. Based on crystallographic characterization and structural analysis, a series of P33 mutants within three conserved regions, i.e., the active site, the dimer interface, and the R127-E183 salt bridge, were constructed. In vitro experiments showed that mutations within the active site and dimer interface severely impaired the sulfhydryl oxidase activity of P33, while the mutations in the salt bridge had a relatively minor influence. Recombinant viruses containing mutated P33 were constructed and assayed in vivo. Except for the active-site mutant AXXA, all other mutants produced infectious BVs, although certain mutants had a decreased BV production. The active-site mutant H114A, the dimer interface mutant H227D, and the salt bridge mutant R127A-E183A were further analyzed by electron microscopy and bioassays. The occlusion bodies (OBs) of mutants H114A and R127A-E183A had a ragged surface and contained mostly ODVs with a single nucleocapsid. The OBs of all three mutants contained lower numbers of ODVs and had a significantly reduced oral infectivity in comparison to control virus. Crystallographic analyses further revealed that all three regions may coordinate with one another to achieve optimal function of P33. Taken together, our data revealed that all the three conserved regions are involved in P33 activity and are crucial for virus morphogenesis and peroral infectivity. IMPORTANCE Sulfhydryl oxidase catalyzes disulfide bond formation of substrate proteins. P33, a baculovirus-encoded sulfhydryl oxidase, is different from other cellular and viral sulfhydryl oxidases, bearing unique features in tertiary and quaternary structure organizations. In this study, we found that three conserved regions, i.e., the active site, dimer interface, and the R127-E183 salt bridge, play important roles in the enzymatic activity and function of P33. Previous observations showed that deletion of p33 results in a total loss of budded virus (BV) production and in morphological changes in occlusion-derived virus (ODV). Our study revealed that certain P33 mutants lead to occlusion bodies (OBs) with a ragged surface, decreased embedded ODVs, and reduced oral infectivity. Interestingly, some P33 mutants with impaired ODV/OB still retained BV productivity, indicating that the impacts on BV and on ODV/OB are two distinctly different functions of P33, which are likely to be performed via different substrate proteins.
Insights into the Impact of CD8+ Immune Modulation on Human Immunodeficiency Virus Evolutionary Dynamics in Distinct Anatomical Compartments by Using Simian Immunodeficiency Virus-Infected Macaque Models of AIDS Progression J. Virol. (IF 4.663) Pub Date : 2017-12-01 Brittany Rife Magalis; David J. Nolan; Patrick Autissier; Tricia H. Burdo; Kenneth C. Williams; Marco Salemi
A thorough understanding of the role of human immunodeficiency virus (HIV) intrahost evolution in AIDS pathogenesis has been limited by the need for longitudinally sampled viral sequences from the vast target space within the host, which are often difficult to obtain from human subjects. CD8+ lymphocyte-depleted macaques infected with simian immunodeficiency virus (SIV) provide an increasingly utilized model of pathogenesis due to clinical manifestations similar to those for HIV-1 infection and AIDS progression, as well as a characteristic rapid disease onset. Comparison of this model with SIV-infected non-CD8+ lymphocyte-depleted macaques also provides a unique opportunity to investigate the role of CD8+ cells in viral evolution and population dynamics throughout the duration of infection. Using several different phylogenetic methods, we analyzed viral gp120 sequences obtained from extensive longitudinal sampling of multiple tissues and enriched leukocyte populations from SIVmac251-infected macaques with or without CD8+ lymphocyte depletion. SIV evolutionary and selection patterns in non-CD8+ lymphocyte-depleted animals were characterized by sequential population turnover and continual viral adaptation, a scenario readily comparable to intrahost evolutionary patterns during human HIV infection in the absence of antiretroviral therapy. Alternatively, animals that were depleted of CD8+ lymphocytes exhibited greater variation in population dynamics among tissues and cell populations over the course of infection. Our findings highlight the major role for CD8+ lymphocytes in prolonging disease progression through continual control of SIV subpopulations from various anatomical compartments and the potential for greater independent viral evolutionary behavior among these compartments in response to immune modulation. IMPORTANCE Although developments in combined antiretroviral therapy (cART) strategies have successfully prolonged the time to AIDS onset in HIV-1-infected individuals, a functional cure has yet to be found. Improvement of drug interventions for a virus that is able to infect a wide range of tissues and cell types requires a thorough understanding of viral adaptation and infection dynamics within this target milieu. Although it is difficult to accomplish in the human host, longitudinal sampling of multiple anatomical locations is readily accessible in the SIV-infected macaque models of neuro-AIDS. The significance of our research is in identifying the impact of immune modulation, through differing immune selective pressures, on viral evolutionary behavior in a multitude of anatomical compartments. The results provide evidence encouraging the development of a more sophisticated model that considers a network of individual viral subpopulations within the host, with differing infection and transmission dynamics, which is necessary for more effective treatment strategies.
Comparative Transcriptomics Highlights the Role of the Activator Protein 1 Transcription Factor in the Host Response to Ebolavirus J. Virol. (IF 4.663) Pub Date : 2017-12-01 James W. Wynne; Shawn Todd; Victoria Boyd; Mary Tachedjian; Reuben Klein; Brian Shiell; Megan Dearnley; Alexander J. McAuley; Amanda P. Woon; Anthony W. Purcell; Glenn A. Marsh; Michelle L. Baker
Ebolavirus and Marburgvirus comprise two genera of negative-sense single-stranded RNA viruses that cause severe hemorrhagic fevers in humans. Despite considerable research efforts, the molecular events following Ebola virus (EBOV) infection are poorly understood. With the view of identifying host factors that underpin EBOV pathogenesis, we compared the transcriptomes of EBOV-infected human, pig, and bat kidney cells using a transcriptome sequencing (RNA-seq) approach. Despite a significant difference in viral transcription/replication between the cell lines, all cells responded to EBOV infection through a robust induction of extracellular growth factors. Furthermore, a significant upregulation of activator protein 1 (AP1) transcription factor complex members FOS and JUN was observed in permissive cell lines. Functional studies focusing on human cells showed that EBOV infection induces protein expression, phosphorylation, and nuclear accumulation of JUN and, to a lesser degree, FOS. Using a luciferase-based reporter, we show that EBOV infection induces AP1 transactivation activity within human cells at 48 and 72 h postinfection. Finally, we show that JUN knockdown decreases the expression of EBOV-induced host gene expression. Taken together, our study highlights the role of AP1 in promoting the host gene expression profile that defines EBOV pathogenesis. IMPORTANCE Many questions remain about the molecular events that underpin filovirus pathophysiology. The rational design of new intervention strategies, such as postexposure therapeutics, will be significantly enhanced through an in-depth understanding of these molecular events. We believe that new insights into the molecular pathogenesis of EBOV may be possible by examining the transcriptomic response of taxonomically diverse cell lines (derived from human, pig, and bat). We first identified the responsive pathways using an RNA-seq-based transcriptomics approach. Further functional and computational analysis focusing on human cells highlighted an important role for the AP1 transcription factor in mediating the transcriptional response to EBOV infection. Our study sheds new light on how host transcription factors respond to and promote the transcriptional landscape that follows viral infection.
IKKγ-Mimetic Peptides Block the Resistance to Apoptosis Associated with Kaposi's Sarcoma-Associated Herpesvirus Infection J. Virol. (IF 4.663) Pub Date : 2017-12-01 Louise C. Briggs; A. W. Edith Chan; Christopher A. Davis; Nicholas Whitelock; Hajira A. Hotiana; Mehdi Baratchian; Claire Bagnéris; David L. Selwood; Mary K. Collins; Tracey E. Barrett
Primary effusion lymphoma (PEL) is a lymphogenic disorder associated with Kaposi's sarcoma-associated herpesvirus (KSHV) infection. Key to the survival and proliferation of PEL is the canonical NF-κB pathway, which becomes constitutively activated following overexpression of the viral oncoprotein KSHV vFLIP (ks-vFLIP). This arises from its capacity to form a complex with the modulatory subunit of the IκB kinase (IKK) kinase, IKKγ (or NEMO), resulting in the overproduction of proteins that promote cellular survival and prevent apoptosis, both of which are important drivers of tumorigenesis. Using a combination of cell-based and biophysical assays together with structural techniques, we showed that the observed resistance to cell death is largely independent of autophagy or major death receptor signaling pathways and demonstrated that direct targeting of the ks-vFLIP–IKKγ interaction both in cells and in vitro can be achieved using IKKγ-mimetic peptides. Our results further reveal that these peptides not only induce cell killing but also potently sensitize PEL to the proapoptotic agents tumor necrosis factor alpha and etoposide and are the first to confirm ks-vFLIP as a tractable target for the treatment of PEL and related disorders. IMPORTANCE KSHV vFLIP (ks-vFLIP) has been shown to have a crucial role in cellular transformation, in which it is vital for the survival and proliferation of primary effusion lymphoma (PEL), an aggressive malignancy associated with infection that is resistant to the majority of chemotherapeutic drugs. It operates via subversion of the canonical NF-κB pathway, which requires a physical interaction between ks-vFLIP and the IKK kinase modulatory subunit IKKγ. While this interaction has been directly linked to protection against apoptosis, it is unclear whether the suppression of other cell death pathways implicated in ks-vFLIP pathogenesis is an additional contributor. We demonstrate that the interaction between ks-vFLIP and IKKγ is pivotal in conferring resistance to apoptosis. Additionally, we show that the ks-vFLIP–IKKγ complex can be disrupted using peptides leading to direct killing and the sensitization of PEL cells to proapoptotic agents. Our studies thus provide a framework for future therapeutic interventions.
An Envelope-Modified Tetravalent Dengue Virus-Like-Particle Vaccine Has Implications for Flavivirus Vaccine Design J. Virol. (IF 4.663) Pub Date : 2017-12-01 Akane Urakami; Mya Myat Ngwe Tun; Meng Ling Moi; Atsuko Sakurai; Momoko Ishikawa; Sachiko Kuno; Ryuji Ueno; Kouichi Morita; Wataru Akahata
Dengue viruses (DENV) infect 50 to 100 million people each year. The spread of DENV-associated infections is one of the most serious public health problems worldwide, as there is no widely available vaccine or specific therapeutic for DENV infections. To address this, we developed a novel tetravalent dengue vaccine by utilizing virus-like particles (VLPs). We created recombinant DENV1 to -4 (DENV1-4) VLPs by coexpressing precursor membrane (prM) and envelope (E) proteins, with an F108A mutation in the fusion loop structure of E to increase the production of VLPs in mammalian cells. Immunization with DENV1-4 VLPs as individual, monovalent vaccines elicited strong neutralization activity against each DENV serotype in mice. For use as a tetravalent vaccine, DENV1-4 VLPs elicited high levels of neutralization activity against all four serotypes simultaneously. The neutralization antibody responses induced by the VLPs were significantly higher than those with DNA or recombinant E protein immunization. Moreover, antibody-dependent enhancement (ADE) was not observed against any serotype at a 1:10 serum dilution. We also demonstrated that the Zika virus (ZIKV) VLP production level was enhanced by introducing the same F108A mutation into the ZIKV envelope protein. Taken together, these results suggest that our strategy for DENV VLP production is applicable to other flavivirus VLP vaccine development, due to the similarity in viral structures, and they describe the promising development of an effective tetravalent vaccine against the prevalent flavivirus. IMPORTANCE Dengue virus poses one of the most serious public health problems worldwide, and the incidence of diseases caused by the virus has increased dramatically. Despite decades of effort, there is no effective treatment against dengue. A safe and potent vaccine against dengue is still needed. We developed a novel tetravalent dengue vaccine by using virus-like particles (VLPs), which are noninfectious because they lack the viral genome. Previous attempts of other groups to use dengue VLPs resulted in generally poor yields. We found that a critical amino acid mutation in the envelope protein enhances the production of VLPs. Our tetravalent vaccine elicited potent neutralizing antibody responses against all four DENV serotypes. Our findings can also be applied to vaccine development against other flaviviruses, such as Zika virus or West Nile virus.
Calcitonin Gene-Related Peptide Induces HIV-1 Proteasomal Degradation in Mucosal Langerhans Cells J. Virol. (IF 4.663) Pub Date : 2017-12-01 Morgane Bomsel; Yonatan Ganor
The neuroimmune dialogue between peripheral neurons and Langerhans cells (LCs) within mucosal epithelia protects against incoming pathogens. LCs rapidly internalize human immunodeficiency virus type 1 (HIV-1) upon its sexual transmission and then trans-infect CD4+ T cells. We recently found that the neuropeptide calcitonin gene-related peptide (CGRP), secreted mucosally from peripheral neurons, inhibits LC-mediated HIV-1 trans-infection. In this study, we investigated the mechanism of CGRP-induced inhibition, focusing on HIV-1 degradation in LCs and its interplay with trans-infection. We first show that HIV-1 degradation occurs in endolysosomes in untreated LCs, and functionally blocking such degradation with lysosomotropic agents results in increased trans-infection. We demonstrate that CGRP acts via its cognate receptor and at a viral postentry step to induce faster HIV-1 degradation, but without affecting the kinetics of endolysosomal degradation. We reveal that unexpectedly, CGRP shifts HIV-1 degradation from endolysosomes toward the proteasome, providing the first evidence for functional HIV-1 proteasomal degradation in LCs. Such efficient proteasomal degradation significantly inhibits the first phase of trans-infection, and proteasomal, but not endolysosomal, inhibitors abrogate CGRP-induced inhibition. Together, our results establish that CGRP controls the HIV-1 degradation mode in LCs. The presence of endogenous CGRP within innervated mucosal tissues, especially during the sexual response, to which CGRP contributes, suggests that HIV-1 proteasomal degradation predominates in vivo. Hence, proteasomal, rather than endolysosomal, HIV-1 degradation in LCs should be enhanced clinically to effectively restrict HIV-1 trans-infection. IMPORTANCE During sexual transmission, HIV-1 is internalized and degraded in LCs, the resident antigen-presenting cells in mucosal epithelia. Yet during trans-infection, infectious virions escaping degradation are transferred to CD4+ T cells, the principal HIV-1 targets. We previously found that the neuroimmune dialogue between LCs and peripheral neurons, innervating mucosal epithelia, significantly inhibits trans-infection via the action of the secreted neuropeptide CGRP on LCs. In this study, we investigated whether CGRP-induced inhibition of trans-infection is linked to CGRP-controlled HIV-1 degradation in LCs. We show that in untreated LCs, HIV-1 is functionally degraded in endolysosomes. In sharp contrast, we reveal that in CGRP-treated LCs, HIV-1 is diverted toward and degraded via another cytosolic protein degradative pathway, namely, the proteasome. These results establish that CGRP regulates HIV-1 degradation in LCs. As CGRP contributes to the sexual response and present within mucosal epithelia, HIV-1 proteasomal degradation in LCs might predominate in vivo and should be enhanced clinically.
Novel Role for Interleukin-17 in Enhancing Type 1 Helper T Cell Immunity in the Female Genital Tract following Mucosal Herpes Simplex Virus 2 Vaccination J. Virol. (IF 4.663) Pub Date : 2017-12-01 Puja Bagri; Varun C. Anipindi; Philip V. Nguyen; Danielle Vitali; Martin R. Stämpfli; Charu Kaushic
It is well established that interferon gamma (IFN-γ) production by CD4+ T cells is critical for antiviral immunity against herpes simplex virus 2 (HSV-2) genital infection. However, the role of interleukin-17A (IL-17A) production by CD4+ T cells in HSV-2 antiviral immunity is yet to be elucidated. Here we demonstrate that IL-17A plays an important role in enhancing antiviral T helper type 1 (Th1) responses in the female genital tract (FGT) and is essential for effective protection conferred by HSV-2 vaccination. While IL-17A did not play a critical role during primary genital HSV-2 infection, seen by lack of differences in susceptibility between IL-17A-deficient (IL-17A−/−) and wild-type (WT) C57BL/6 mice, it was critical for mediating antiviral responses after challenge/reexposure. Compared to WT mice, IL-17A−/− mice (i) infected intravaginally and reexposed or (ii) vaccinated intranasally and challenged intravaginally demonstrated poor outcomes. Following intravaginal HSV-2 reexposure or challenge, vaccinated IL-17A−/− mice had significantly higher mortality, greater disease severity, higher viral shedding, and higher levels of proinflammatory cytokines and chemokines in vaginal secretions. Furthermore, IL-17A−/− mice had impaired Th1 cell responses after challenge/reexposure, with significantly lower proportions of vaginal IFN-γ+ CD4+ T cells. The impaired Th1 cell responses in IL-17A−/− mice coincided with smaller populations of IFN-γ+ CD4+ tissue resident memory T (TRM) cells in the genital tract postimmunization. Taken together, these findings describe a novel role for IL-17A in regulating antiviral IFN-γ+ Th1 cell immunity in the vaginal tract. This strategy could be exploited to enhance antiviral immunity following HSV-2 vaccination. IMPORTANCE T helper type 1 (Th1) immunity, specifically interferon gamma (IFN-γ) production by CD4+ T cells, is critical for protection against genital herpesvirus (HSV-2) infection, and enhancing this response can potentially help improve disease outcomes. Our study demonstrated that interleukin-17A (IL-17A) plays an essential role in enhancing antiviral Th1 responses in the female genital tract (FGT). We found that in the absence of IL-17A, preexposed and vaccinated mice showed poor disease outcomes and were unable to overcome HSV-2 reexposure/challenge. IL-17A-deficient mice (IL-17A−/−) had smaller populations of IFN-γ+ CD4+ tissue resident memory T (TRM) cells in the genital tract postimmunization than did wild-type (WT) mice, which coincided with attenuated Th1 responses postchallenge. This has important implications for developing effective vaccines against HSV-2, as we propose that strategies inducing IL-17A in the genital tract may promote more effective Th1 cell immunity and better overall protection.
Epstein-Barr Virus Fusion with Epithelial Cells Triggered by gB Is Restricted by a gL Glycosylation Site J. Virol. (IF 4.663) Pub Date : 2017-12-01 Britta S. Möhl; Jia Chen; Seo Jin Park; Theodore S. Jardetzky; Richard Longnecker
Epstein-Barr virus (EBV) entry into epithelial cells is mediated by the conserved core fusion machinery, composed of the fusogen gB and the receptor-binding complex gH/gL. The heterodimeric gH/gL complex binds to the EBV epithelial cell receptor or gp42, which binds to the B-cell receptor, triggering gB-mediated fusion of the virion envelope with cellular membranes. Our previous study found that the gL glycosylation mutant N69L/S71V had an epithelial cell-specific hyperfusogenic phenotype. To study the influence of this gL mutant on the initiation and kinetics of gB-driven epithelial cell fusion, we established a virus-free split-green fluorescent protein cell-cell fusion assay that enables real-time measurements of membrane fusion using live cells. The gL_N69L/S71V mutant had a large increase in epithelial cell fusion activity of up to 300% greater than that of wild-type gL starting at early time points. The hyperfusogenicity of the gL mutant was not a result of alterations in complex formation with gH or alterations in cellular localization. Moreover, the hyperfusogenic phenotype of the gL mutant correlated with the formation of enlarged syncytia. In summary, our present findings highlight an important role of gL in the kinetics of gB-mediated epithelial cell fusion, adding to previous findings indicating a direct interaction between gL and gB in EBV membrane fusion. IMPORTANCE EBV predominantly infects epithelial cells and B lymphocytes, which are the cells of origin for the EBV-associated malignancies Hodgkin and Burkitt lymphoma as well as nasopharyngeal carcinoma. Contrary to the other key players of the core fusion machinery, gL has the most elusive role during EBV-induced membrane fusion. We found that the glycosylation site N69/S71 of gL is involved in restricting epithelial cell fusion activity, strongly correlating with syncytium size. Interestingly, our data showed that the gL glycosylation mutant increases the fusion activity of the hyperfusogenic gB mutants, indicating that this gL mutant and the gB mutants target different steps during fusion. Our studies on how gL and gB work together to modulate epithelial cell fusion kinetics are essential to understand the highly tuned tropism of EBV for epithelial cells and B lymphocytes and may result in novel strategies for therapies preventing viral entry into target host cells. Finally, making our results of particular interest is the absence of gL syncytial mutants in other herpesviruses.
Differential Inhibitory Receptor Expression on T Cells Delineates Functional Capacities in Chronic Viral Infection J. Virol. (IF 4.663) Pub Date : 2017-12-01 Jeffrey E. Teigler; Gennadiy Zelinskyy; Michael A. Eller; Diane L. Bolton; Mary Marovich; Alexander D. Gordon; Aljawharah Alrubayyi; Galit Alter; Merlin L. Robb; Jeffrey N. Martin; Steven G. Deeks; Nelson L. Michael; Ulf Dittmer; Hendrik Streeck
Inhibitory receptors have been extensively described for their importance in regulating immune responses in chronic infections and cancers. Blocking the function of inhibitory receptors such as PD-1, CTLA-4, 2B4, Tim-3, and LAG-3 has shown promise for augmenting CD8 T cell activity and boosting pathogen-specific immunity. However, the prevalence of inhibitory receptors on CD4 T cells and their relative influence on CD4 T cell functionality in chronic HIV infection remains poorly described. We therefore determined and compared inhibitory receptor expression patterns of 2B4, CTLA-4, LAG-3, PD-1, and Tim-3 on virus-specific CD4 and CD8 T cells in relation to their functional T cell profile. In chronic HIV infection, inhibitory receptor distribution differed markedly between cytokine-producing T cell subsets with, gamma interferon (IFN-γ)- and tumor necrosis factor alpha (TNF-α)-producing cells displaying the highest and lowest prevalence of inhibitory receptors, respectively. Blockade of inhibitory receptors differentially affected cytokine production by cells in response to staphylococcal enterotoxin B stimulation. CTLA-4 blockade increased IFN-γ and CD40L production, while PD-1 blockade strongly augmented IFN-γ, interleukin-2 (IL-2), and TNF-α production. In a Friend retrovirus infection model, CTLA-4 blockade in particular was able to improve control of viral replication. Together, these results show that inhibitory receptor distribution on HIV-specific CD4 T cells varies markedly with respect to the functional subset of CD4 T cells being analyzed. Furthermore, the differential effects of receptor blockade suggest novel methods of immune response modulation, which could be important in the context of HIV vaccination or therapeutic strategies. IMPORTANCE Inhibitory receptors are important for limiting damage by the immune system during acute infections. In chronic infections, however, their expression limits immune system responsiveness. Studies have shown that blocking inhibitory receptors augments CD8 T cell functionality in HIV infection, but their influence on CD4 T cells remains unclear. We assessed the expression of inhibitory receptors on HIV-specific CD4 T cells and their relationship with T cell functionality. We uncovered differences in inhibitory receptor expression depending on the CD4 T cell function. We also found differences in functionality of CD4 T cells following blocking of different inhibitory receptors, and we confirmed our results in a Friend virus retroviral model of infection in mice. Our results show that inhibitory receptor expression on CD4 T cells is linked to CD4 T cell functionality and could be sculpted by blockade of specific inhibitory receptors. These data reveal exciting possibilities for the development of novel treatments and immunotherapeutics.
NLRX1 Mediates MAVS Degradation To Attenuate the Hepatitis C Virus-Induced Innate Immune Response through PCBP2 J. Virol. (IF 4.663) Pub Date : 2017-12-01 Yuwen Qin; Binbin Xue; Chunyan Liu; Xiaohong Wang; Renyun Tian; Qinya Xie; Mengmeng Guo; Guangdi Li; Darong Yang; Haizhen Zhu
Activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. However, attenuation or termination of signaling is also necessary for preventing immune-mediated tissue damage and spontaneous autoimmunity. Here, we identify nucleotide binding oligomerization domain (NOD)-like receptor X1 (NLRX1) as a negative regulator of the mitochondrial antiviral signaling protein (MAVS)-mediated signaling pathway during hepatitis C virus (HCV) infection. The depletion of NLRX1 enhances the HCV-triggered activation of interferon (IFN) signaling and causes the suppression of HCV propagation in hepatocytes. NLRX1, a HCV-inducible protein, interacts with MAVS and mediates the K48-linked polyubiquitination and subsequent degradation of MAVS via the proteasomal pathway. Moreover, poly(rC) binding protein 2 (PCBP2) interacts with NLRX1 to participate in the NLRX1-induced degradation of MAVS and the inhibition of antiviral responses during HCV infection. Mutagenic analyses further revealed that the NOD of NLRX1 is essential for NLRX1 to interact with PCBP2 and subsequently induce MAVS degradation. Our study unlocks a key mechanism of the fine-tuning of innate immunity by which NLRX1 restrains the retinoic acid-inducible gene I-like receptor (RLR)-MAVS signaling cascade by recruiting PCBP2 to MAVS for inducing MAVS degradation through the proteasomal pathway. NLRX1, a negative regulator of innate immunity, is a pivotal host factor for HCV to establish persistent infection. IMPORTANCE Innate immunity needs to be tightly regulated to maximize the antiviral response and minimize immune-mediated pathology, but the underlying mechanisms are poorly understood. In this study, we report that NLRX1 is a proviral host factor for HCV infection and functions as a negative regulator of the HCV-triggered innate immune response. NLRX1 recruits PCBP2 to MAVS and induces the K48-linked polyubiquitination and degradation of MAVS, leading to the negative regulation of the IFN signaling pathway and promoting HCV infection. Overall, this study provides intriguing insights into how innate immunity is regulated during viral infection.
Genesis and Spread of Newly Emerged Highly Pathogenic H7N9 Avian Viruses in Mainland China J. Virol. (IF 4.663) Pub Date : 2017-12-01 Lei Yang; Wenfei Zhu; Xiyan Li; Minmei Chen; Jie Wu; Pengbo Yu; Shunxiang Qi; Yiwei Huang; Weixian Shi; Jie Dong; Xiang Zhao; Weijuan Huang; Zi Li; Xiaoxu Zeng; Hong Bo; Tao Chen; Wenbing Chen; Jia Liu; Ye Zhang; Zhenli Liang; Wei Shi; Yuelong Shu; Dayan Wang
The novel low-pathogenic avian influenza A H7N9 viruses (LPAI H7N9 viruses) have been a threat to public health since their emergence in 2013 because of the high rates of mortality and morbidity that they cause. Recently, highly pathogenic variants of these avian influenza A H7N9 viruses (HPAI H7N9 viruses) have emerged and caused human infections and outbreaks among poultry in mainland China. However, it is still unclear how the HPAI H7N9 virus was generated and how it evolved and spread in China. Here, we show that the ancestor virus of the HPAI H7N9 viruses originated in the Yangtze River Delta region and spread southward to the Pearl River Delta region, possibly through live poultry trade. After introduction into the Pearl River Delta region, the origin LPAI H7N9 virus acquired four amino acid insertions in the hemagglutinin (HA) protein cleavage site and mutated into the HPAI H7N9 virus in late May 2016. Afterward, the HPAI H7N9 viruses further reassorted with LPAI H7N9 or H9N2 viruses locally and generated multiple different genotypes. As of 14 July 2017, the HPAI H7N9 viruses had spread from Guangdong Province to at least 12 other provinces. The rapid geographical expansion and genetic evolution of the HPAI H7N9 viruses pose a great challenge not only to public health but also to poultry production. Effective control measures, including enhanced surveillance, are therefore urgently needed. IMPORTANCE The LPAI H7N9 virus has caused five outbreak waves in humans and was recently reported to have mutated into highly pathogenic variants. It is unknown how the HPAI H7N9 virus originated, evolved, and disseminated in China. In this study, we comprehensively analyzed the sequences of HPAI H7N9 viruses from 28 human and 21 environmental samples covering eight provinces in China that were taken from November 2016 to June 2017. The results show that the ancestor virus of the HPAI H7N9 viruses originated in the Yangtze River Delta region. However, the insertion of four amino acids into the HA protein cleavage site of an LPAI H7N9 virus occurred in late May 2016 in the Pearl River Delta region. The mutated HPAI H7N9 virus further reassorted with LPAI H7N9 or H9N2 viruses that were cocirculating in poultry. Considering the rapid geographical expansion of the HPAI H7N9 viruses, effective control measures are urgently needed.
APOBEC3A Is Upregulated by Human Cytomegalovirus (HCMV) in the Maternal-Fetal Interface, Acting as an Innate Anti-HCMV Effector J. Virol. (IF 4.663) Pub Date : 2017-12-01 Yiska Weisblum; Esther Oiknine-Djian; Zichria Zakay-Rones; Olesya Vorontsov; Ronit Haimov-Kochman; Yuval Nevo; David Stockheim; Simcha Yagel; Amos Panet; Dana G. Wolf
Human cytomegalovirus (HCMV) is the leading cause of congenital infection and is associated with a wide range of neurodevelopmental disabilities and intrauterine growth restriction. Yet our current understanding of the mechanisms modulating transplacental HCMV transmission is poor. The placenta, given its critical function in protecting the fetus, has evolved effective yet largely uncharacterized innate immune barriers against invading pathogens. Here we show that the intrinsic cellular restriction factor apolipoprotein B editing catalytic subunit-like 3A (APOBEC3A [A3A]) is profoundly upregulated following ex vivo HCMV infection in human decidual tissues—constituting the maternal aspect of the placenta. We directly demonstrated that A3A severely restricted HCMV replication upon controlled overexpression in epithelial cells, acting by a cytidine deamination mechanism to introduce hypermutations into the viral genome. Importantly, we further found that A3 editing of HCMV DNA occurs both ex vivo in HCMV-infected decidual organ cultures and in vivo in amniotic fluid samples obtained during natural congenital infection. Our results reveal a previously unexplored role for A3A as an innate anti-HCMV effector, activated by HCMV infection in the maternal-fetal interface. These findings pave the way to new insights into the potential impact of APOBEC proteins on HCMV pathogenesis. IMPORTANCE In view of the grave outcomes associated with congenital HCMV infection, there is an urgent need to better understand the innate mechanisms acting to limit transplacental viral transmission. Toward this goal, our findings reveal the role of the intrinsic cellular restriction factor A3A (which has never before been studied in the context of HCMV infection and vertical viral transmission) as a potent anti-HCMV innate barrier, activated by HCMV infection in the authentic tissues of the maternal-fetal interface. The detection of naturally occurring hypermutations in clinical amniotic fluid samples of congenitally infected fetuses further supports the idea of the occurrence of A3 editing of the viral genome in the setting of congenital HCMV infection. Given the widely differential tissue distribution characteristics and biological functions of the members of the A3 protein family, our findings should pave the way to future studies examining the potential impact of A3A as well as of other A3s on HCMV pathogenesis.
Natural Reassortants of Potentially Zoonotic Avian Influenza Viruses H5N1 and H9N2 from Egypt Display Distinct Pathogenic Phenotypes in Experimentally Infected Chickens and Ferrets J. Virol. (IF 4.663) Pub Date : 2017-12-01 Mahmoud M. Naguib; Reiner Ulrich; Elisa Kasbohm; Christine L. P. Eng; Donata Hoffmann; Christian Grund; Martin Beer; Timm C. Harder
The cocirculation of zoonotic highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 and avian influenza virus (AIV) of subtype H9N2 among poultry in Egypt for at least 6 years should render that country a hypothetical hot spot for the emergence of reassortant, phenotypically altered viruses, yet no reassortants have been detected in Egypt. The present investigations proved that reassortants of the Egyptian H5N1 clade 22.214.171.124 virus and H9N2 virus of the G1-B lineage can be generated by coamplification in embryonated chicken eggs. Reassortants were restricted to the H5N1 subtype and acquired between two and all six of the internal segments of the H9N2 virus. Five selected plaque-purified reassortant clones expressed a broad phenotypic spectrum both in vitro and in vivo. Two groups of reassortants were characterized to have retarded growth characteristics in vitro compared to the H5N1 parent virus. One clone provoked reduced mortality in inoculated chickens, although the characteristics of a highly pathogenic phenotype were retained. Enhanced zoonotic properties were not predicted for any of these clones, and this prediction was confirmed by ferret inoculation experiments: neither the H5N1 parent virus nor two selected clones induced severe clinical symptoms or were transmitted to sentinel ferrets by contact. While the emergence of reassortants of Egyptian HPAIV of subtype H5N1 with internal gene segments of cocirculating H9N2 viruses is possible in principle, the spread of such viruses is expected to be governed by their fitness to outcompete the parental viruses in the field. The eventual spread of attenuated phenotypes, however, would negatively impact syndrome surveillance on poultry farms and might foster enzootic virus circulation. IMPORTANCE Despite almost 6 years of the continuous cocirculation of highly pathogenic avian influenza virus H5N1 and avian influenza virus H9N2 in poultry in Egypt, no reassortants of the two subtypes have been reported. Here, the principal compatibility of the two subtypes is shown by forcing the reassortment between copassaged H5N1 und H9N2 viruses in embryonated chicken eggs. The resulting reassortant viruses displayed a wide range of pathogenicity including attenuated phenotypes in chickens, but did not show enhanced zoonotic propensities in the ferret model.
Susceptibility of Human Endogenous Retrovirus Type K to Reverse Transcriptase Inhibitors J. Virol. (IF 4.663) Pub Date : 2017-12-01 Rafael Contreras-Galindo; Derek Dube; Koh Fujinaga; Mark H. Kaplan; David M. Markovitz
Human endogenous retroviruses (HERVs) make up 8% of the human genome. The HERV type K (HERV-K) HML-2 (HK2) family contains proviruses that are the most recent entrants into the human germ line and are transcriptionally active. In HIV-1 infection and cancer, HK2 genes produce retroviral particles that appear to be infectious, yet the replication capacity of these viruses and potential pathogenicity has been difficult to ascertain. In this report, we screened the efficacy of commercially available reverse transcriptase inhibitors (RTIs) at inhibiting the enzymatic activity of HK2 RT and HK2 genomic replication. Interestingly, only one provirus, K103, was found to encode a functional RT among those examined. Several nucleoside analogue RTIs (NRTIs) blocked K103 RT activity and consistently inhibited the replication of HK2 genomes. The NRTIs zidovudine (AZT), stavudine (d4T), didanosine (ddI), and lamivudine (3TC), and the nucleotide RTI inhibitor tenofovir (TDF), show efficacy in blocking K103 RT. HIV-1-specific nonnucleoside RTIs (NNRTIs), protease inhibitors (PIs), and integrase inhibitors (IIs) did not affect HK2, except for the NNRTI etravirine (ETV). The inhibition of HK2 infectivity by NRTIs appears to take place at either the reverse transcription step of the viral genome prior to HK2 viral particle formation and/or in the infected cells. Inhibition of HK2 by these drugs will be useful in suppressing HK2 infectivity if these viruses prove to be pathogenic in cancer, neurological disorders, or other diseases associated with HK2. The present studies also elucidate a key aspect of the life cycle of HK2, specifically addressing how they do, and/or did, replicate. IMPORTANCE Endogenous retroviruses are relics of ancestral virus infections in the human genome. The most recent of these infections was caused by HK2. While HK2 often remains silent in the genome, this group of viruses is activated in HIV-1-infected and cancer cells. Recent evidence suggests that these viruses are infectious, and the potential exists for HK2 to contribute to disease. We show that HK2, and specifically the enzyme that mediates virus replication, can be inhibited by a panel of drugs that are commercially available. We show that several drugs block HK2 with different efficacies. The inhibition of HK2 replication by antiretroviral drugs appears to occur in the virus itself as well as after infection of cells. Therefore, these drugs might prove to be an effective treatment by suppressing HK2 infectivity in diseases where these viruses have been implicated, such as cancer and neurological syndromes.
p21 Restricts HIV-1 in Monocyte-Derived Dendritic Cells through the Reduction of Deoxynucleoside Triphosphate Biosynthesis and Regulation of SAMHD1 Antiviral Activity J. Virol. (IF 4.663) Pub Date : 2017-12-01 Jose Carlos Valle-Casuso; Awatef Allouch; Annie David; Gina M. Lenzi; Lydia Studdard; Françoise Barré-Sinoussi; Michaela Müller-Trutwin; Baek Kim; Gianfranco Pancino; Asier Sáez-Cirión
HIV-1 infection of noncycling cells, such as dendritic cells (DCs), is impaired due to limited availability of deoxynucleoside triphosphates (dNTPs), which are needed for HIV-1 reverse transcription. The levels of dNTPs are tightly regulated during the cell cycle and depend on the balance between dNTP biosynthesis and degradation. SAMHD1 potently blocks HIV-1 replication in DCs, although the underlying mechanism is still unclear. SAMHD1 has been reported to be able to degrade dNTPs and viral nucleic acids, which may both hamper HIV-1 reverse transcription. The relative contribution of these activities may differ in cycling and noncycling cells. Here, we show that inhibition of HIV-1 replication in monocyte-derived DCs (MDDCs) is associated with an increased expression of p21cip1/waf, a cell cycle regulator that is involved in the differentiation and maturation of DCs. Induction of p21 in MDDCs decreases the pool of dNTPs and increases the antiviral active isoform of SAMHD1. Although both processes are complementary in inhibiting HIV-1 replication, the antiviral activity of SAMHD1 in our primary cell model appears to be, at least partially, independent of its dNTPase activity. The reduction in the pool of dNTPs in MDDCs appears rather mostly due to a p21-mediated suppression of several enzymes involved in dNTP synthesis (i.e., RNR2, TYMS, and TK-1). These results are important to better understand the interplay between HIV-1 and DCs and may inform the design of new therapeutic approaches to decrease viral dissemination and improve immune responses against HIV-1. IMPORTANCE DCs play a key role in the induction of immune responses against HIV. However, HIV has evolved ways to exploit these cells, facilitating immune evasion and virus dissemination. We have found that the expression of p21, a cyclin-dependent kinase inhibitor involved in cell cycle regulation and monocyte differentiation and maturation, potentially can contribute to the inhibition of HIV-1 replication in monocyte-derived DCs through multiple mechanisms. p21 decreased the size of the intracellular dNTP pool. In parallel, p21 prevented SAMHD1 phosphorylation and promoted SAMHD1 dNTPase-independent antiviral activity. Thus, induction of p21 resulted in conditions that allowed the effective inhibition of HIV-1 replication through complementary mechanisms. Overall, p21 appears to be a key regulator of HIV infection in myeloid cells.
A DNA Vaccine That Targets Hemagglutinin to Antigen-Presenting Cells Protects Mice against H7 Influenza J. Virol. (IF 4.663) Pub Date : 2017-12-01 Tor Kristian Andersen; Fan Zhou; Rebecca Cox; Bjarne Bogen; Gunnveig Grødeland
Zoonotic influenza H7 viral infections have a case fatality rate of about 40%. Currently, no or limited human to human spread has occurred, but we may be facing a severe pandemic threat if the virus acquires the ability to transmit between humans. Novel vaccines that can be rapidly produced for global distribution are urgently needed, and DNA vaccines may be the only type of vaccine that allows for the speed necessary to quench an emerging pandemic. Here, we constructed DNA vaccines encoding the hemagglutinin (HA) from influenza A/chicken/Italy/13474/99 (H7N1). In order to increase the efficacy of DNA vaccination, HA was targeted to either major histocompatibility complex class II molecules or chemokine receptors 1, 3, and 5 (CCR1/3/5) that are expressed on antigen-presenting cells (APC). A single DNA vaccination with APC-targeted HA significantly increased antibody levels in sera compared to nontargeted control vaccines. The antibodies were confirmed neutralizing in an H7 pseudotype-based neutralization assay. Furthermore, the APC-targeted vaccines increased the levels of antigen-specific cytotoxic T cells, and a single DNA vaccination could confer protection against a lethal challenge with influenza A/turkey/Italy/3889/1999 (H7N1) in mice. In conclusion, we have developed a vaccine that rapidly could contribute protection against a pandemic threat from avian influenza. IMPORTANCE Highly pathogenic avian influenza H7 constitute a pandemic threat that can cause severe illness and death in infected individuals. Vaccination is the main method of prophylaxis against influenza, but current vaccine strategies fall short in a pandemic situation due to a prolonged production time and insufficient production capabilities. In contrast, a DNA vaccine can be rapidly produced and deployed to prevent the potential escalation of a highly pathogenic influenza pandemic. We here demonstrate that a single DNA delivery of hemagglutinin from an H7 influenza could mediate full protection against a lethal challenge with H7N1 influenza in mice. Vaccine efficacy was contingent on targeting of the secreted vaccine protein to antigen-presenting cells.
Zika Virus Encoding Nonglycosylated Envelope Protein Is Attenuated and Defective in Neuroinvasion J. Virol. (IF 4.663) Pub Date : 2017-12-01 Arun S. Annamalai; Aryamav Pattnaik; Bikash R. Sahoo; Ezhumalai Muthukrishnan; Sathish Kumar Natarajan; David Steffen; Hiep L. X. Vu; Gustavo Delhon; Fernando A. Osorio; Thomas M. Petro; Shi-Hua Xiang; Asit K. Pattnaik
Zika virus (ZIKV), a mosquito-transmitted flavivirus responsible for sporadic outbreaks of mild and febrile illness in Africa and Asia, reemerged in the last decade causing serious human diseases, including microcephaly, congenital malformations, and Guillain-Barré syndrome. Although genomic and phylogenetic analyses suggest that genetic evolution may have led to the enhanced virulence of ZIKV, experimental evidence supporting the role of specific genetic changes in virulence is currently lacking. One sequence motif, VNDT, containing an N-linked glycosylation site in the envelope (E) protein, is polymorphic; it is absent in many of the African isolates but present in all isolates from the recent outbreaks. In the present study, we investigated the roles of this sequence motif and glycosylation of the E protein in the pathogenicity of ZIKV. We first constructed a stable full-length cDNA clone of ZIKV in a novel linear vector from which infectious virus was recovered. The recombinant ZIKV generated from the infectious clone, which contains the VNDT motif, is highly pathogenic and causes lethality in a mouse model. In contrast, recombinant viruses from which the VNDT motif is deleted or in which the N-linked glycosylation site is mutated by single-amino-acid substitution are highly attenuated and nonlethal. The mutant viruses replicate poorly in the brains of infected mice when inoculated subcutaneously but replicate well following intracranial inoculation. Our findings provide the first evidence that N-linked glycosylation of the E protein is an important determinant of ZIKV virulence and neuroinvasion. IMPORTANCE The recent emergence of Zika virus (ZIKV) in the Americas has caused major worldwide public health concern. The virus appears to have gained significant pathogenicity, causing serious human diseases, including microcephaly and Guillain-Barré syndrome. The factors responsible for the emergence of pathogenic ZIKV are not understood at this time, although genetic changes have been shown to facilitate virus transmission. All isolates from the recent outbreaks contain an N-linked glycosylation site within the viral envelope (E) protein, whereas many isolates of the African lineage virus lack this site. To elucidate the functional significance of glycosylation in ZIKV pathogenicity, recombinant ZIKVs from infectious clones with or without the glycan on the E protein were generated. ZIKVs lacking the glycan were highly attenuated for the ability to cause mortality in a mouse model and were severely compromised for neuroinvasion. Our studies suggest glycosylation of the E protein is an important factor contributing to ZIKV pathogenicity.
Protective Humoral Immunity in the Central Nervous System Requires Peripheral CD19-Dependent Germinal Center Formation following Coronavirus Encephalomyelitis J. Virol. (IF 4.663) Pub Date : 2017-12-01 Jeffrey R. Atkinson; Cornelia C. Bergmann
B cell subsets with phenotypes characteristic of naive, non-isotype-switched, memory (Bmem) cells and antibody-secreting cells (ASC) accumulate in various models of central nervous system (CNS) inflammation, including viral encephalomyelitis. During neurotropic coronavirus JHMV infection, infiltration of protective ASC occurs after T cell-mediated viral control and is preceded by accumulation of non-isotype-switched IgD+ and IgM+ B cells. However, the contribution of peripheral activation events in cervical lymph nodes (CLN) to driving humoral immune responses in the infected CNS is poorly defined. CD19, a signaling component of the B cell receptor complex, is one of multiple regulators driving B cell differentiation and germinal center (GC) formation by lowering the threshold of antigen-driven activation. JHMV-infected CD19−/− mice were thus used to determine how CD19 affects CNS recruitment of B cell subsets. Early polyclonal ASC expansion, GC formation, and virus-specific ASC were all significantly impaired in CLN of CD19−/− mice compared to wild-type (WT) mice, consistent with lower and unsustained virus-specific serum antibody (Ab). ASC were also significantly reduced in the CNS, resulting in increased infectious virus during persistence. Nevertheless, CD19 deficiency did not affect early CNS IgD+ B cell accumulation. The results support the notion that CD19-independent factors drive early B cell mobilization and recruitment to the infected CNS, while delayed accumulation of virus-specific, isotype-switched ASC requires CD19-dependent GC formation in CLN. CD19 is thus essential for both sustained serum Ab and protective local Ab within the CNS following JHMV encephalomyelitis. IMPORTANCE CD19 activation is known to promote GC formation and to sustain serum Ab responses following antigen immunization and viral infections. However, the contribution of CD19 in the context of CNS infections has not been evaluated. This study demonstrates that antiviral protective ASC in the CNS are dependent on CD19 activation and peripheral GC formation, while accumulation of early-recruited IgD+ B cells is CD19 independent. This indicates that IgD+ B cells commonly found early in the CNS do not give rise to local ASC differentiation and that only antigen-primed, peripheral GC-derived ASC infiltrate the CNS, thereby limiting potentially harmful nonspecific Ab secretion. Expanding our understanding of activation signals driving CNS migration of distinct B cell subsets during neuroinflammatory insults is critical for preventing and managing acute encephalitic infections, as well as preempting reactivation of persistent viruses during immune-suppressive therapies targeting B cells in multiple sclerosis (MS), such as rituximab and ocrelizumab.
Vertical Transmission of Hepatitis C Virus: Variable Transmission Bottleneck and Evidence of Midgestation In Utero Infection J. Virol. (IF 4.663) Pub Date : 2017-12-01 Sébastien Fauteux-Daniel; Ariane Larouche; Virginie Calderon; Jonathan Boulais; Chanel Béland; Doris G. Ransy; Marc Boucher; Valérie Lamarre; Normand Lapointe; Isabelle Boucoiran; Armelle Le Campion; Hugo Soudeyns
Hepatitis C virus (HCV) can be transmitted from mother to child during pregnancy and childbirth. However, the timing and precise biological mechanisms that are involved in this process are incompletely understood, as are the determinants that influence transmission of particular HCV variants. Here we report results of a longitudinal assessment of HCV quasispecies diversity and composition in 5 cases of vertical HCV transmission, including 3 women coinfected with human immunodeficiency virus type 1 (HIV-1). The population structure of HCV variant spectra based on E2 envelope gene sequences (nucleotide positions 1491 to 1787), including hypervariable regions 1 and 2, was characterized using next-generation sequencing and median-joining network analysis. Compatible with a loose transmission bottleneck, larger numbers of shared HCV variants were observed in the presence of maternal coinfection. Coalescent Bayesian Markov chain Monte Carlo simulations revealed median times of transmission between 24.9 weeks and 36.1 weeks of gestation, with some confidence intervals ranging into the 1st trimester, considerably earlier than previously thought. Using recombinant autologous HCV pseudoparticles, differences were uncovered in HCV-specific antibody responses between coinfected mothers and mothers infected with HCV alone, in whom generalized absence of neutralization was observed. Finally, shifts in HCV quasispecies composition were seen in children around 1 year of age, compatible with the disappearance of passively transferred maternal immunoglobulins and/or the development of HCV-specific humoral immunity. Taken together, these results provide insights into the timing, dynamics, and biologic mechanisms involved in vertical HCV transmission and inform preventative strategies. IMPORTANCE Although it is well established that hepatitis C virus (HCV) can be transmitted from mother to child, the manner and the moment at which transmission operates have been the subject of conjecture. By carrying out a detailed examination of viral sequences, we showed that transmission could take place comparatively early in pregnancy. In addition, we showed that when the mother also carried human immunodeficiency virus type 1 (HIV-1), many more HCV variants were shared between her and her child, suggesting that the mechanism and/or the route of transmission of HCV differed in the presence of coinfection with HIV-1. These results could explain why cesarean section is ineffective in preventing vertical HCV transmission and guide the development of interventions to avert pediatric HCV infection.
Conformational Changes in the 5′ End of the HIV-1 Genome Dependent on the Debranching Enzyme DBR1 during Early Stages of Infection J. Virol. (IF 4.663) Pub Date : 2017-12-01 Alvaro E. Galvis; Hugh E. Fisher; Hung Fan; David Camerini
Previous studies in our laboratory showed that the RNA debranching enzyme (DBR1) is not required for early steps in HIV cDNA formation but is necessary for synthesis of intermediate and late cDNA products. To further characterize this effect, we evaluated the topology of the 5′ end of the HIV-1 RNA genome during early infection with and without inhibition of DBR1 synthesis. Cells were transfected with DBR1 short hairpin RNA (shRNA) followed 48 h later by infection with an HIV-1-derived vector containing an RNase H-deficient reverse transcriptase (RT). RNA was isolated at several times postinfection and treated with various RNA-modifying enzymes prior to rapid amplification of 5′ cDNA ends (5′ RACE) for HIV-1 RNA and quantitative reverse transcriptase PCR (qRT-PCR). In infected cells, DBR1 knockdown inhibited detection of free HIV-1 RNA 5′ ends at all time points. The difference in detection of free HIV-1 RNA 5′ ends in infected DBR1 knockdown versus control cells was eliminated by in vitro incubation of infected cell RNAs with yeast or human DBR1 enzyme prior to 5′ RACE and qRT-PCR. This was dependent on the 2′-5′ phosphatase activity of DBR1, since it did not occur when we used the catalytically inactive DBR1(N85A) mutant. Finally, HIV-1 RNA from infected DBR1 knockdown cells was resistant to RNase R that degrades linear RNAs but not RNAs in circular or lariat-like conformations. These results provide evidence for formation of a lariat-like structure involving the 5′ end of HIV-1 RNA during an early step in infection and the involvement of DBR1 in resolving it. IMPORTANCE Our findings support a new view of the early steps in HIV genome replication. We show that the HIV genomic RNA is rapidly decapped and forms a lariat-like structure after entering a cell. The lariat-like structure is subsequently resolved by the cellular enzyme DBR1, leaving a 5′ phosphate. This pathway is similar to the formation and resolution of pre-mRNA intron lariats and therefore suggests that similar mechanisms may be used by HIV. Our work therefore opens a new area of investigation in HIV replication and may ultimately uncover new targets for inhibiting HIV replication and for preventing the development of AIDS.
The Exonuclease Activity of Herpes Simplex Virus 1 UL12 Is Required for Production of Viral DNA That Can Be Packaged To Produce Infectious Virus J. Virol. (IF 4.663) Pub Date : 2017-12-01 Lorry M. Grady; Renata Szczepaniak; Ryan P. Murelli; Takeshi Masaoka; Stuart F. J. Le Grice; Dennis L. Wright; Sandra K. Weller
The herpes simplex virus (HSV) type I alkaline nuclease, UL12, has 5′-to-3′ exonuclease activity and shares homology with nucleases from other members of the Herpesviridae family. We previously reported that a UL12-null virus exhibits a severe defect in viral growth. To determine whether the growth defect was a result of loss of nuclease activity or another function of UL12, we introduced an exonuclease-inactivating mutation into the viral genome. The recombinant virus, UL12 D340E (the D340E mutant), behaved identically to the null virus (AN-1) in virus yield experiments, exhibiting a 4-log decrease in the production of infectious virus. Furthermore, both viruses were severely defective in cell-to-cell spread and produced fewer DNA-containing capsids and more empty capsids than wild-type virus. In addition, DNA packaged by the viral mutants was aberrant, as determined by infectivity assays and pulsed-field gel electrophoresis. We conclude that UL12 exonuclease activity is essential for the production of viral DNA that can be packaged to produce infectious virus. This conclusion was bolstered by experiments showing that a series of natural and synthetic α-hydroxytropolones recently reported to inhibit HSV replication also inhibit the nuclease activity of UL12. Taken together, our results demonstrate that the exonuclease activity of UL12 is essential for the production of infectious virus and may be considered a target for development of antiviral agents. IMPORTANCE Herpes simplex virus is a major pathogen, and although nucleoside analogs such as acyclovir are highly effective in controlling HSV-1 or -2 infections in immunocompetent individuals, their use in immunocompromised patients is complicated by the development of resistance. Identification of additional proteins essential for viral replication is necessary to develop improved therapies. In this communication, we confirm that the exonuclease activity of UL12 is essential for viral replication through the analysis of a nuclease-deficient viral mutant. We demonstrate that the exonuclease activity of UL12 is essential for the production of viral progeny and thus provides an attractive, druggable enzymatic target.
Vaccinia Virus Encodes a Novel Inhibitor of Apoptosis That Associates with the Apoptosome J. Virol. (IF 4.663) Pub Date : 2017-12-01 Melissa R. Ryerson; Monique M. Richards; Marc Kvansakul; Christine J. Hawkins; Joanna L. Shisler
Apoptosis is an important antiviral host defense mechanism. Here we report the identification of a novel apoptosis inhibitor encoded by the vaccinia virus (VACV) M1L gene. M1L is absent in the attenuated modified vaccinia virus Ankara (MVA) strain of VACV, a strain that stimulates apoptosis in several types of immune cells. M1 expression increased the viability of MVA-infected THP-1 and Jurkat cells and reduced several biochemical hallmarks of apoptosis, such as PARP-1 and procaspase-3 cleavage. Furthermore, ectopic M1L expression decreased staurosporine-induced (intrinsic) apoptosis in HeLa cells. We then identified the molecular basis for M1 inhibitory function. M1 allowed mitochondrial depolarization but blocked procaspase-9 processing, suggesting that M1 targeted the apoptosome. In support of this model, we found that M1 promoted survival in Saccharomyces cerevisiae overexpressing human Apaf-1 and procaspase-9, critical components of the apoptosome, or overexpressing only conformationally active caspase-9. In mammalian cells, M1 coimmunoprecipitated with Apaf-1–procaspase-9 complexes. The current model is that M1 associates with and allows the formation of the apoptosome but prevents apoptotic functions of the apoptosome. The M1 protein features 14 predicted ankyrin (ANK) repeat domains, and M1 is the first ANK-containing protein reported to use this inhibitory strategy. Since ANK-containing proteins are encoded by many large DNA viruses and found in all domains of life, studies of M1 may lead to a better understanding of the roles of ANK proteins in virus-host interactions. IMPORTANCE Apoptosis selectively eliminates dangerous cells such as virus-infected cells. Poxviruses express apoptosis antagonists to neutralize this antiviral host defense. The vaccinia virus (VACV) M1 ankyrin (ANK) protein, a protein with no previously ascribed function, inhibits apoptosis. M1 interacts with the apoptosome and prevents procaspase-9 processing as well as downstream procaspase-3 cleavage in several cell types and under multiple conditions. M1 is the first poxviral protein reported to associate with and prevent the function of the apoptosome, giving a more detailed picture of the threats VACV encounters during infection. Dysregulation of apoptosis is associated with several human diseases. One potential treatment of apoptosis-related diseases is through the use of designed ANK repeat proteins (DARPins), similar to M1, as caspase inhibitors. Thus, the study of the novel antiapoptosis effects of M1 via apoptosome association will be helpful for understanding how to control apoptosis using either natural or synthetic molecules.
Genome-Wide Mutagenesis of Dengue Virus Reveals Plasticity of the NS1 Protein and Enables Generation of Infectious Tagged Reporter Viruses J. Virol. (IF 4.663) Pub Date : 2017-12-01 Nicholas S. Eyre; Stephen M. Johnson; Auda A. Eltahla; Maria Aloi; Amanda L. Aloia; Christopher A. McDevitt; Rowena A. Bull; Michael R. Beard
Dengue virus (DENV) is a major global pathogen that causes significant morbidity and mortality in tropical and subtropical areas worldwide. An improved understanding of the regions within the DENV genome and its encoded proteins that are required for the virus replication cycle will expedite the development of urgently required therapeutics and vaccines. We subjected an infectious DENV genome to unbiased insertional mutagenesis and used next-generation sequencing to identify sites that tolerate 15-nucleotide insertions during the virus replication cycle in hepatic cell culture. This revealed that the regions within capsid, NS1, and the 3′ untranslated region were the most tolerant of insertions. In contrast, prM- and NS2A-encoding regions were largely intolerant of insertions. Notably, the multifunctional NS1 protein readily tolerated insertions in regions within the Wing, connector, and β-ladder domains with minimal effects on viral RNA replication and infectious virus production. Using this information, we generated infectious reporter viruses, including a variant encoding the APEX2 electron microscopy tag in NS1 that uniquely enabled high-resolution imaging of its localization to the surface and interior of viral replication vesicles. In addition, we generated a tagged virus bearing an mScarlet fluorescent protein insertion in NS1 that, despite an impact on fitness, enabled live cell imaging of NS1 localization and traffic in infected cells. Overall, this genome-wide profile of DENV genome flexibility may be further dissected and exploited in reporter virus generation and antiviral strategies. IMPORTANCE Regions of genetic flexibility in viral genomes can be exploited in the generation of reporter virus tools and should arguably be avoided in antiviral drug and vaccine design. Here, we subjected the DENV genome to high-throughput insertional mutagenesis to identify regions of genetic flexibility and enable tagged reporter virus generation. In particular, the viral NS1 protein displayed remarkable tolerance of small insertions. This genetic flexibility enabled generation of several novel NS1-tagged reporter viruses, including an APEX2-tagged virus that we used in high-resolution imaging of NS1 localization in infected cells by electron microscopy. For the first time, this analysis revealed the localization of NS1 within viral replication factories known as “vesicle packets” (VPs), in addition to its acknowledged localization to the luminal surface of these VPs. Together, this genetic profile of DENV may be further refined and exploited in the identification of antiviral targets and the generation of reporter virus tools.
Exploring the Human-Nipah Virus Protein-Protein Interactome J. Virol. (IF 4.663) Pub Date : 2017-12-01 Luis Martinez-Gil; Natalia M. Vera-Velasco; Ismael Mingarro
Nipah virus is an emerging, highly pathogenic, zoonotic virus of the Paramyxoviridae family. Human transmission occurs by close contact with infected animals, the consumption of contaminated food, or, occasionally, via other infected individuals. Currently, we lack therapeutic or prophylactic treatments for Nipah virus. To develop these agents we must now improve our understanding of the host-virus interactions that underpin a productive infection. This aim led us to perform the present work, in which we identified 101 human-Nipah virus protein-protein interactions (PPIs), most of which (88) are novel. This data set provides a comprehensive view of the host complexes that are manipulated by viral proteins. Host targets include the PRP19 complex and the microRNA (miRNA) processing machinery. Furthermore, we explored the biologic consequences of the interaction with the PRP19 complex and found that the Nipah virus W protein is capable of altering p53 control and gene expression. We anticipate that these data will help in guiding the development of novel interventional strategies to counter this emerging viral threat. IMPORTANCE Nipah virus is a recently discovered virus that infects a wide range of mammals, including humans. Since its discovery there have been yearly outbreaks, and in some of them the mortality rate has reached 100% of the confirmed cases. However, the study of Nipah virus has been largely neglected, and currently we lack treatments for this infection. To develop these agents we must now improve our understanding of the host-virus interactions that underpin a productive infection. In the present work, we identified 101 human-Nipah virus protein-protein interactions using an affinity purification approach coupled with mass spectrometry. Additionally, we explored the cellular consequences of some of these interactions. Globally, this data set offers a comprehensive and detailed view of the host machinery's contribution to the Nipah virus's life cycle. Furthermore, our data present a large number of putative drug targets that could be exploited for the treatment of this infection.
Correction for Avey et al., “Discovery of a Coregulatory Interaction between Kaposi's Sarcoma-Associated Herpesvirus ORF45 and the Viral Protein Kinase ORF36” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Denis Avey; Sarah Tepper; Benjamin Pifer; Amritpal Bahga; Hunter Williams; Joseph Gillen; Wenwei Li; Sarah Ogden; Fanxiu Zhu
Volume 90, no. 13, p. 5953–5964, 2016, https://doi.org/10.1128/JVI.00516-16. Page 5959, Fig. 5B: The 32P image for FLAG-Rb in the upper right panel was a duplicate of that for GST-K8 in the bottom right panel. The upper right panel of Fig. 5B should appear as shown below. This correction does not affect the interpretation of the figure.
Correction for Ansari et al., “Constitutive Interferon-Inducible Protein 16-Inflammasome Activation during Epstein-Barr Virus Latency I, II, and III in B and Epithelial Cells” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Mairaj Ahmed Ansari; Vivek Vikram Singh; Sujoy Dutta; Mohanan Valiya Veettil; Dipanjan Dutta; Leela Chikoti; Jie Lu; David Everly; Bala Chandran
Volume 87, no. 15, p. 8606–8623, 2013, https://doi.org/10.1128/JVI.00805-13. Page 8609, line 3: The following should be inserted before “(A)”: “Lanes 1 and 3 belong to the same experiment and same blot.” Page 8610, Fig. 2D: Due to an error during figure assembly, Nuclear Tubulin lanes (lanes 3 and 4) were inadvertent duplicates of Cyto TBP lanes (lanes 1 and 2). The Nuclear Tubulin lanes in Fig. 2D should appear as shown below. Page 8614, Fig. 5B: Due to an error during figure assembly, NLRP3 and AIM2 lanes (lanes 1 and 2) were inadvertent duplicates of the NLRP3 and AIM2 lanes (lanes 1 and 2) in Fig. 3B. The NLRP3 and AIM2 lanes in Fig. 5B should appear as shown below. These corrections do not alter any of the conclusions made in our paper.
Correction for Wang et al., “Mitogen-Activated Protein Kinase Kinase 2, a Novel E2-Interacting Protein, Promotes the Growth of Classical Swine Fever Virus via Attenuation of the JAK-STAT Signaling Pathway” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Jinghan Wang; Shucheng Chen; Yajin Liao; Enyu Zhang; Shuo Feng; Shaoxiong Yu; Lian-Feng Li; Wen-Rui He; Yongfeng Li; Yuzi Luo; Yuan Sun; Mo Zhou; Xiao Wang; Muhammad Munir; Su Li; Hua-Ji Qiu
Volume 90, no. 22, p. 10271–10283, 2016, https://doi.org/10.1128/JVI.01407-16. Page 10277, Fig. 4: The panel for 0.25 to 1 hpi was an inadvertent duplicate of that for 3 to 12 hpi in both the Npro and E2 rows. The corrected images for the Npro and E2 rows of Fig. 4 at 0.25 to 1 hpi, obtained from original data, should appear as shown below. The changes do not affect the interpretation of the data or the conclusions of the study.
Correction for Perez et al., “A Short cis-Acting Motif in the M112-113 Promoter Region Is Essential for IE3 To Activate M112-113 Gene Expression and Is Important for Murine Cytomegalovirus Replication” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Kareni J. Perez; Francisco Puerta Martínez; Ruth Cosme-Cruz; Neysa M. Perez-Crespo; Qiyi Tang
Volume 87, no. 5, p. 2639–2647, 2013, https://doi.org/10.1128/JVI.03171-12. Page 2644, Fig. 3C: Due to an error in preparing the figure, the Western blot data for IE3 in the right panel was inadvertently duplicated from the TBP protein data. The IE3 lane in the right panel of Fig. 3C should appear as shown below. Correction of this error does not affect the original data, data interpretation, or conclusions of the study.
Correction for Yoon et al., “p53-Derived Host Restriction of HIV-1 Replication by Protein Kinase R-Mediated Tat Phosphorylation and Inactivation” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Cheol-Hee Yoon; Sang-Yoon Kim; Se Eun Byeon; Yideul Jeong; Jinjoo Lee; Kwang Pyo Kim; Jinseu Park; Yong-Soo Bae
Volume 89, no. 8, p. 4262–4280, 2015, https://doi.org/10.1128/JVI.03087-14. Page 4271, Fig. 5: The Flag-Tat and β-actin Western blots in the lower portion of Fig. 5C were inadvertent duplicates of those in Fig. 5B. Corrected images have been constructed by using the Western blot images from our original data. The corrected image demonstrates the normalization between the samples. The lower portion of Fig. 5C should appear as shown below.
Classic Spotlight, 2012 and 2013: Articles of Significant Interest Selected from the Journal of Virology Archives by the Editors J. Virol. (IF 4.663) Pub Date : 2017-12-01
Dengue virus (DENV), a single-strand positive-sense RNA virus, is transmitted by mosquitos and can cause severe disease. DENV has four closely related antigenically distinct serotypes, DENV-1 to DENV-4, which differ by 25 to 40% at the amino acid level. Thai et al. (K. T. D. Thai et al., J Virol 86:835–843, 2012, https://doi.org/10.1128/JVI.05985-11) investigated intrahost DENV variation to determine the extent and pattern of genetic diversity. Sequence data in domain III of the envelope gene was obtained from serial plasma samples (n = 49) taken from 17 patients infected with DENV-1, totaling some 8,458 clones. Nucleotide sequence diversities of viral populations were very low, with conservative estimates of the average levels of genetic diversity ranging from 0 to 0.0013. However, there was clear evidence for mixed infection, with the presence of multiple phylogenetically distinct lineages present within the same host. However, no relationship was observed between the extent and pattern of DENV-1 genetic diversity and disease severity, immune status, or level of viremia.
Correction for Cousins et al., “Human Herpesvirus 8 Viral Interleukin-6 Signaling through gp130 Promotes Virus Replication in Primary Effusion Lymphoma and Endothelial Cells” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Emily Cousins; Yang Gao; Gordon Sandford; John Nicholas
Volume 88, no. 20, p. 12167–12172, 2014, https://doi.org/10.1128/JVI.01751-14. Page 12168, Fig. 1D, bottom right: “2 days + Dox” should read “1 day + Dox.” Page 12168, legend to Fig. 1C and D, line 5 from bottom: The following should be added before “(E)”: “The data for panels C and D were from the same experiment, so the NS data sets are the same for both panels.”
Vaccination with Recombinant Parainfluenza Virus 5 Expressing Neuraminidase Protects against Homologous and Heterologous Influenza Virus Challenge J. Virol. (IF 4.663) Pub Date : 2017-12-01 Alaina J. Mooney; Jon D. Gabbard; Zhuo Li; Daniel A. Dlugolenski; Scott K. Johnson; Ralph A. Tripp; Biao He; S. Mark Tompkins
Seasonal human influenza virus continues to cause morbidity and mortality annually, and highly pathogenic avian influenza (HPAI) viruses along with other emerging influenza viruses continue to pose pandemic threats. Vaccination is considered the most effective measure for controlling influenza; however, current strategies rely on a precise vaccine match with currently circulating virus strains for efficacy, requiring constant surveillance and regular development of matched vaccines. Current vaccines focus on eliciting specific antibody responses against the hemagglutinin (HA) surface glycoprotein; however, the diversity of HAs across species and antigenic drift of circulating strains enable the evasion of virus-inhibiting antibody responses, resulting in vaccine failure. The neuraminidase (NA) surface glycoprotein, while diverse, has a conserved enzymatic site and presents an appealing target for priming broadly effective antibody responses. Here we show that vaccination with parainfluenza virus 5 (PIV5), a promising live viral vector expressing NA from avian (H5N1) or pandemic (H1N1) influenza virus, elicited NA-specific antibody and T cell responses, which conferred protection against homologous and heterologous influenza virus challenges. Vaccination with PIV5-N1 NA provided cross-protection against challenge with a heterosubtypic (H3N2) virus. Experiments using antibody transfer indicate that antibodies to NA have an important role in protection. These findings indicate that PIV5 expressing NA may be effective as a broadly protective vaccine against seasonal influenza and emerging pandemic threats. IMPORTANCE Seasonal influenza viruses cause considerable morbidity and mortality annually, while emerging viruses pose potential pandemic threats. Currently licensed influenza virus vaccines rely on the antigenic match of hemagglutinin (HA) for vaccine strain selection, and most vaccines rely on HA inhibition titers to determine efficacy, despite the growing awareness of the contribution of neuraminidase (NA) to influenza virus vaccine efficacy. Although NA is immunologically subdominant to HA, and clinical studies have shown variable NA responses to vaccination, in this study, we show that vaccination with a parainfluenza virus 5 recombinant vaccine candidate expressing NA (PIV5-NA) from a pandemic influenza (pdmH1N1) virus or highly pathogenic avian influenza (H5N1) virus elicits robust, cross-reactive protection from influenza virus infection in two animal models. New vaccination strategies incorporating NA, including PIV5-NA, could improve seasonal influenza virus vaccine efficacy and provide protection against emerging influenza viruses.
Correction for Dixit et al., “FUSE Binding Protein 1 Facilitates Persistent Hepatitis C Virus Replication in Hepatoma Cells by Regulating Tumor Suppressor p53” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Updesh Dixit; Ashutosh K. Pandey; Zhihe Liu; Sushil Kumar; Matthew B. Neiditch; Kenneth M. Klein; Virendra N. Pandey
Volume 89, no. 15, p. 7905–7921, 2015, https://doi.org/10.1128/JVI.00729-15. Page 7911, Fig. 4: Due to an error in figure assembly, the Western blot for p53 in Fig. 4B was an inadvertent duplicate of the Western blot for p21 in Fig. 4C. The p53 blot in Fig. 4B should appear as shown below. We apologize for this mix-up. The correction to Fig. 4B does not affect the scientific results and conclusions.
Correction for Gutierrez et al., “Ets-1 Is Required for the Activation of VEGFR3 during Latent Kaposi's Sarcoma-Associated Herpesvirus Infection of Endothelial Cells” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Kimberley D. Gutierrez; Valerie A. Morris; David Wu; Serge Barcy; Michael Lagunoff
Volume 87, no. 12, p. 6758–6768, 2013, https://doi.org/10.1128/JVI.03241-12. Page 6761, Fig. 1: Due to errors in preparing the figure, panels H, I, and J were inadvertently shifted and are therefore incorrectly labeled. Panel J should have been panel H in the Ets1 column. Panel H should have been panel I in the Orf73 column and labeled 40× magnification. Panel I should have been panel J and labeled 63×. The bottom portion of Fig. 1 should appear as shown below. Correction of the shifted panels in no way alters the interpretation or conclusions of the immunohistochemistry staining, this figure, or the paper as a whole. We apologize for any confusion the errors may have caused.
Correction for Gjyshi et al., “Activated Nrf2 Interacts with Kaposi's Sarcoma-Associated Herpesvirus Latency Protein LANA-1 and Host Protein KAP1 To Mediate Global Lytic Gene Repression” J. Virol. (IF 4.663) Pub Date : 2017-12-01 Olsi Gjyshi; Arunava Roy; Sujoy Dutta; Mohanan Valiya Veettil; Dipanjan Dutta; Bala Chandran
Volume 89, no. 15, p. 7874–7892, 2015, https://doi.org/10.1128/JVI.00895-15. Page 7879, Fig. 2A: The Tubulin band in Fig. 2A was an inadvertent duplicate of the Actin band (lanes 1 to 4) in Fig. 1B. The Fig. 2A Tubulin blot should appear as shown below. This correction does not alter any of the conclusions made in our paper.
Articles of Significant Interest Selected from This Issue by the Editors J. Virol. (IF 4.663) Pub Date : 2017-12-01
A failed HIV vaccine trial suggested that CD4+ T helper cell activation can abrogate protective vaccine effects because these cells, albeit required for an immune response, constitute ideal targets for HIV. Comparing two similar vaccination protocols, Sauermann et al. (e01120-17) showed that acquisition of challenge virus is significantly delayed only in the group with low levels of vaccine-specific CD4+ T cells and high levels of activated CD8+ T cells. Both the vaccine vector and the route of immunization affected the level of CD4+ T-cell responses. Activated T helper cells thus represent a major hurdle for HIV vaccine development. Number of challenge virus exposures correlated with vaccine-induced virus-specific CD4+ T-cell responses and activated CD8+ T-cell levels.
HLA-B*14:02-Restricted Env-Specific CD8+ T-Cell Activity Has Highly Potent Antiviral Efficacy Associated with Immune Control of HIV Infection J. Virol. (IF 4.663) Pub Date : 2017-11-15 Ellen M. Leitman; Christian B. Willberg; Ming-Han Tsai; Huabiao Chen; Søren Buus; Fabian Chen; Lynn Riddell; David Haas; Jacques Fellay; James J. Goedert; Alicja Piechocka-Trocha; Bruce D. Walker; Jeffrey Martin; Steven Deeks; Steven M. Wolinsky; Jeremy Martinson; Maureen Martin; Ying Qi; Asier Sáez-Cirión; Otto O. Yang; Philippa C. Matthews; Mary Carrington; Philip J. R. Goulder
Immune control of human immunodeficiency virus type 1 (HIV) infection is typically associated with effective Gag-specific CD8+ T-cell responses. We here focus on HLA-B*14, which protects against HIV disease progression, but the immunodominant HLA-B*14-restricted anti-HIV response is Env specific (ERYLKDQQL, HLA-B*14-EL9). A subdominant HLA-B*14-restricted response targets Gag (DRYFKTLRA, HLA-B*14-DA9). Using HLA-B*14/peptide-saporin-conjugated tetramers, we show that HLA-B*14-EL9 is substantially more potent at inhibiting viral replication than HLA-B*14-DA9. HLA-B*14-EL9 also has significantly higher functional avidity (P < 0.0001) and drives stronger selection pressure on the virus than HLA-B*14-DA9. However, these differences were HLA-B*14 subtype specific, applying only to HLA-B*14:02 and not to HLA-B*14:01. Furthermore, the HLA-B*14-associated protection against HIV disease progression is significantly greater for HLA-B*14:02 than for HLA-B*14:01, consistent with the superior antiviral efficacy of the HLA-B*14-EL9 response. Thus, although Gag-specific CD8+ T-cell responses may usually have greater anti-HIV efficacy, factors independent of protein specificity, including functional avidity of individual responses, are also critically important to immune control of HIV. IMPORTANCE In HIV infection, although cytotoxic T lymphocytes (CTL) play a potentially critical role in eradication of viral reservoirs, the features that constitute an effective response remain poorly defined. We focus on HLA-B*14, unique among HLAs associated with control of HIV in that the dominant CTL response is Env specific, not Gag specific. We demonstrate that Env-specific HLA-B*14-restricted activity is substantially more efficacious than the subdominant HLA-B*14-restricted Gag response. Env immunodominance over Gag and strong Env-mediated selection pressure on HIV are observed only in subjects expressing HLA-B*14:02, and not HLA-B*14:01. This reflects the increased functional avidity of the Env response over Gag, substantially more marked for HLA-B*14:02. Finally, we show that HLA-B*14:02 is significantly more strongly associated with viremic control than HLA-B*14:01. These findings indicate that, although Gag-specific CTL may usually have greater anti-HIV efficacy than Env responses, factors independent of protein specificity, including functional avidity, may carry greater weight in mediating effective control of HIV.
Minocycline Has Anti-inflammatory Effects and Reduces Cytotoxicity in an Ex Vivo Spinal Cord Slice Culture Model of West Nile Virus Infection J. Virol. (IF 4.663) Pub Date : 2017-11-15 Eamon D. Quick; Scott Seitz; Penny Clarke; Kenneth L. Tyler
West Nile virus (WNV) is a neurotropic flavivirus that can cause significant neurological disease. Mouse models of WNV infection demonstrate that a proinflammatory environment is induced within the central nervous system (CNS) after WNV infection, leading to entry of activated peripheral immune cells. We utilized ex vivo spinal cord slice cultures (SCSC) to demonstrate that anti-inflammatory mechanisms may also play a role in WNV-induced pathology and/or recovery. Microglia are a type of macrophage that function as resident CNS immune cells. Similar to mouse models, infection of SCSC with WNV induces the upregulation of proinflammatory genes and proteins that are associated with microglial activation, including the microglial activation marker Iba1 and CC motif chemokines CCL2, CCL3, and CCL5. This suggests that microglia assume a proinflammatory phenotype in response to WNV infection similar to the proinflammatory (M1) activation that can be displayed by other macrophages. We now show that the WNV-induced expression of these and other proinflammatory genes was significantly decreased in the presence of minocycline, which has antineuroinflammatory properties, including the ability to inhibit proinflammatory microglial responses. Minocycline also caused a significant increase in the expression of anti-inflammatory genes associated with alternative anti-inflammatory (M2) macrophage activation, including interleukin 4 (IL-4), IL-13, and FIZZ1. Minocycline-dependent alterations to M1/M2 gene expression were associated with a significant increase in survival of neurons, microglia, and astrocytes in WNV-infected slices and markedly decreased levels of inducible nitric oxide synthase (iNOS). These results demonstrate that an anti-inflammatory environment induced by minocycline reduces viral cytotoxicity during WNV infection in ex vivo CNS tissue. IMPORTANCE West Nile virus (WNV) causes substantial morbidity and mortality, with no specific therapeutic treatments available. Antiviral inflammatory responses are a crucial component of WNV pathology, and understanding how they are regulated is important for tailoring effective treatments. Proinflammatory responses during WNV infection have been extensively studied, but anti-inflammatory responses (and their potential protective and reparative capabilities) following WNV infection have not been investigated. Minocycline induced the expression of genes associated with the anti-inflammatory (M2) activation of CNS macrophages (microglia) in WNV-infected SCSC while inhibiting the expression of genes associated with proinflammatory (M1) macrophage activation and was protective for multiple CNS cell types, indicating its potential use as a therapeutic reagent. This ex vivo culture system can uniquely address the ability of CNS parenchymal cells (neurons, astrocytes, and microglia) to respond to minocycline and to modulate the inflammatory environment and cytotoxicity in response to WNV infection without peripheral immune cell involvement.
Zika Virus Infects Human Sertoli Cells and Modulates the Integrity of the In Vitro Blood-Testis Barrier Model J. Virol. (IF 4.663) Pub Date : 2017-11-15 David N. Siemann; Daniel P. Strange; Payal N. Maharaj; Pei-Yong Shi; Saguna Verma
Confirmed reports of Zika virus (ZIKV) in human seminal fluid for months after the clearance of viremia suggest the ability of ZIKV to establish persistent infection in the seminiferous tubules, an immune-privileged site in the testis protected by the blood-testis barrier, also called the Sertoli cell (SC) barrier (SCB). However, cellular targets of ZIKV in human testis and mechanisms by which the virus enters seminiferous tubules remain unclear. We demonstrate that primary human SCs were highly susceptible to ZIKV compared to the closely related dengue virus and induced the expression of alpha interferon (IFN-α), key cytokines, and cell adhesion molecules (vascular cell adhesion molecule 1 [VCAM-1] and intracellular adhesion molecule 1 [ICAM-1]). Furthermore, using an in vitro SCB model, we show that ZIKV was released on the adluminal side of the SCB model with a higher efficiency than in the blood-brain barrier model. ZIKV-infected SCs exhibited enhanced adhesion of leukocytes that correlated with decreases in SCB integrity. ZIKV infection did not affect the expression of tight and adherens junction proteins such as ZO-1, claudin, and JAM-A; however, exposure of SCs to inflammatory mediators derived from ZIKV-infected macrophages led to the degradation of the ZO-1 protein, which correlated with increased SCB permeability. Taken together, our data suggest that infection of SCs may be one of the crucial steps by which ZIKV gains access to the site of spermatozoon development and identify SCs as a therapeutic target to clear testicular infections. The SCB model opens up opportunities to assess interactions of SCs with other testicular cells and to test the ability of anti-ZIKV drugs to cross the barrier. IMPORTANCE Recent outbreaks of ZIKV, a neglected mosquito-borne flavivirus, have identified sexual transmission as a new route of disease spread, which has not been reported for other flaviviruses. To be able to sexually transmit for months after the clearance of viremia, ZIKV must establish infection in the seminiferous tubules, the site of spermatozoon development. However, little is known about the cell types that support ZIKV infection in the human testis. Currently, there are no models to study mechanisms of virus persistence in the seminiferous tubules. We provide evidence that ZIKV infection of human Sertoli cells, which are an important component of the seminiferous tubules, is robust and induces a strong antiviral response. The use of an in vitro Sertoli cell barrier to describe how ZIKV or inflammatory mediators derived from ZIKV-infected macrophages compromise barrier integrity will enable studies to explore the interactions of other testicular cells with Sertoli cells and to test novel antivirals for clearing testicular ZIKV infection.
Human Cytomegalovirus Particles Treated with Specific Antibodies Induce Intrinsic and Adaptive but Not Innate Immune Responses J. Virol. (IF 4.663) Pub Date : 2017-11-15 Zeguang Wu; Ruifang Qin; Li Wang; Matteo Bosso; Myriam Scherer; Thomas Stamminger; Dominik Hotter; Thomas Mertens; Giada Frascaroli
Human cytomegalovirus (HCMV) persistently infects 40% to 100% of the human population worldwide. Experimental and clinical evidence indicates that humoral immunity to HCMV plays an important role in restricting virus dissemination and protecting the infected host from disease. Specific immunoglobulin preparations from pooled plasma of adults selected for high titers of HCMV antibodies have been used for the prevention of CMV disease in transplant recipients and pregnant women. Even though incubation of HCMV particles with these preparations leads to the neutralization of viral infectivity, it is still unclear whether the antibody-treated HCMV particles (referred to here as HCMV-Ab) enter the cells and modulate antiviral immune responses. Here we demonstrate that HCMV-Ab did enter macrophages. HCMV-Ab did not initiate the expression of immediate early antigens (IEAs) in macrophages, but they induced an antiviral state and rendered the cells less susceptible to HCMV infection upon challenge. Resistance to HCMV infection seemed to be due to the activation of intrinsic restriction factors and was independent of interferons. In contrast to actively infected cells, autologous NK cells did not degranulate against HCMV-Ab-treated macrophages, suggesting that these cells may not be eliminated by innate effector cells. Interestingly, HCMV-Ab-treated macrophages stimulated the proliferation of autologous adaptive CD4+ and CD8+ T cells. Our findings not only expand the current knowledge on virus-antibody immunity but may also be relevant for future vaccination strategies. IMPORTANCE Human cytomegalovirus (HCMV), a common herpesvirus, establishes benign but persistent infections in immunocompetent hosts. However, in subjects with an immature or dysfunctional immune system, HCMV is a major cause of morbidity and mortality. Passive immunization has been used in different clinical settings with variable clinical results. Intravenous hyperimmune globulin preparations (IVIg) are obtained from pooled adult human plasma selected for high anti-CMV antibody titers. While HCMV neutralization can be shown in vitro using different systems, data are lacking regarding the cross-influence of IVIg administration on the cellular immune responses. The aim of this study was to evaluate the effects of IVIg on distinct components of the immune response against HCMV, including antigen presentation by macrophages, degranulation of innate natural killer cells, and proliferation of adaptive CD4+ and CD8+ T cells.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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