Chinese yam polysaccharides PLGA-stabilized Pickering emulsion as an adjuvant system for PCV- 2 vaccine to enhance immune response
Introduction
Porcine circovirus type 2 (PCV-2), a highly infectious pathogen in swine-producing countries, is the main pathogenic factor of porcine circovirus disease (PCVD) [1], [2]. PCV-2 can lead to post-weaning multisystemic wasting syndrome (PMWS) and other PCV-2 related diseases. It mainly impacts swine aged 2–4 months with a prevalence of 5–30 % and causes huge economic damage [3], [4]. Vaccination is the most effective strategy to prevent and control PCV-2 infection [5], [6]. Although various PCV-2 vaccines have been confirmed to help reduce clinical symptoms caused by PCV-2 infection, they have failed to entirely prevent the spread and infection of PCV-2 [7]. Given the enormous damage caused by PCV-2 infection to the swine industry, it is imperative to design an effective adjuvant to enhance vaccine immunity and prevent PCV-2 infection.
Polysaccharide-based adjuvants have received widespread attention due to the modulation and stimulation activities of herbal polysaccharides in the immune response [8], [9], [10]. Chinese yam polysaccharides (CYP) is a biologically active substance derived from Chinese yam and consists of α-1-galactose, α-1,6-galactose, β-1,3-glucose with 16,619 Da [11]. CYP has received increasing attention due to its immunomodulatory activity. Numerous studies have found that CYP could promote the splenic lymphocyte proliferation and T lymphocyte differentiation, as well as increase macrophages activation and phagocytosis [12], [13]. Additionally, it can regulate the secretion of cytokines (IL-4, IFN-γ, TNF-α) [14] and the level of antibodies [15], [16]. However, the immunomodulatory activity of Chinese yam polysaccharides is limited in clinical application due to the short biological half-life and unfocused scope of action [17], [18].
Due to the excellent stability, good biocompatibility, and high loading capacity, solid particles stabilized emulsions (Pickering emulsions) have been widely applied in biomedical applications [19]. Pickering emulsions have been reported for their potential in drug encapsulation, topical drug delivery, and oral drug delivery [20], [21]. Poly (D, L-lactic-co-glycolic acid) (PLGA), one of the most attractive biodegradable polymers, was employed as the stabilizer for Pickering emulsion [22], [23]. Pickering emulsions exhibited mobility and flexibility, which provide the efficient delivery platform for antigens and immunomodulators to improve the immune response [24], [25]. The particle adsorption gap in Pickering emulsion has a large specific surface area, which contributes to the identification of target molecules and receptors by antigen-presenting cells. Meanwhile, particle-stabilized Pickering emulsion showed pliability, which could adhere to the cell membrane to increase the cell contact area [24].
The success of the PCV-2 vaccine is supported by the activation of efficient humoral and cellular immunity in resistance to PCV-2 infection [26]. The commonly applied aluminum salt adjuvants and oil emulsion adjuvants may cause local inflammation or systemic side effects, while lacking the ability to induce a strong cell-mediated immune response [27], [28]. Thus, designing a potential particle-stabilized Pickering emulsion as the adjuvant system to enhance humoral and cellular immunity is very promising. Vaccine-mediated antigen-specific cytotoxic T lymphocyte (CTL) responses are regarded as essential for the clearance of viral and intracellular infections [29], [30]. Our previous study has revealed that Chinese yam polysaccharides PLGA-stabilized Pickering emulsion (CYP-PPAS) was the efficient adjuvant system for inducing a robust humoral immune response after vaccination of OVA [31]. However, there have been few reports on the potential of CYP-PPAS adjuvant to induce the robust cellular immune response and the cytotoxic T lymphocyte response against PCV-2 infection.
In this study, we hypothesized that CYP-PPAS would function as an efficient adjuvant system for PCV-2 vaccines to enhance macrophage phagocytosis and induce strong humoral and cellular immunities after immunization with PCV-2 vaccine. The characterization of CYP-PPAS was accessed and the effect of antigen uptake capacity by macrophages with CYP-PPAS was examined in vitro. In addition, dendritic cells activation in draining lymph nodes, the proliferation and differentiation of splenic T lymphocytes, and the cytotoxic T lymphocytes response was followed investigated. Moreover, the levels of PCV-2 specific antibodies and cytokines in serum were determined to access the adjuvant activity of CYP-PPAS in vivo.
Section snippets
Materials
Chinese yam polysaccharides (CYP, 97.3 %, CY200623, Ciyuan Biological Technology Co., Ltd). PLGA (75:25, 15 kDa, Jinan Daigang Biomaterial Co., Ltd). Pluronic F68 (Yuanye Biomaterial Co., Ltd). Squalene (Macklin Biomaterial Co., Ltd). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) (Sigma-Aldrich Co. Ltd). Alum adjuvant (Thermo Biomaterial Co., Ltd). CD11C-PE/Cyanine 7, CD80-FITC, CD86(B7–2)-PE (Biolegend, USA). Anti-CD3e-FITC, Anti-CD8a-PE, Anti-CD4-APC, Anti-CD8a-FITC,
FT-IR spectra of Chinese yam polysaccharides
To investigate the main functional groups of plant polysaccharides, the FT-IR spectra of CYP was measured (Fig. 1). The stretching vibration of O
H was observed at 3381.72 cm−1, which is related to the glycosidic linkages of polysaccharides [37]. The small band at 2929.49 cm−1 was attributed to the CH stretching vibration of CH2 groups [38]. The characteristic stretching vibration at 1645.47 cm−1 was due to the C
O bond [39]. The absorption peak at 1368.93 cm−1 is the CH bond stretching
Discussion
Vaccination is the important strategy to avoid infectious diseases. Designing adjuvants with high safety profile, rapid assembly antigen, and enhanced humoral and cellular immune responses to increase vaccine efficacy are essential for fighting infections. It was reported that solid particles absorbed at the interface possessed high energy, which made Pickering emulsion efficient loaded with antigen and immunomodulators [42], [43]. Our previous study demonstrated the Chinese yam polysaccharides
Conclusion
CYP-PPAS was an efficient vaccine delivery system to enhance macrophages uptake in vitro. In addition, CYP-PPAS induced robust PCV-2 specific IgG and elicited a mixed Th1/Th2 immune response and enhanced the cytotoxic T lymphocyte response after immunization with the PCV-2 vaccine in mice. Thus, CYP-PPAS has a promising prospect as an adjuvant to improve humoral and cellular responses against PCV-2 infection.
CRediT authorship contribution statement
Yue Zhang: Data curation, Formal analysis, Investigation, Methodology, Project administration, Supervision, Resources, Validation, Software, Writing – original draft, Writing – review & editing.
Pengfei Gu: Formal analysis, Methodology, Project administration, Software, Writing – review & editing.
Lina Jiao: Formal analysis, Investigation, Project administration.
Jin He: Project administration, Software, Project administration.
Lin Yu: Software, Project administration.
Zhenguang Liu: Writing –
Acknowledgements
The project was supported by the National Natural Science Foundation of China (Grant No. 32072905, 31872509), the Fundamental Research Funds for the Central Universities (Grant No. KYZ201844), A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and Postgraduate Research & Practice Innovation Program of Jiangsu Province (Grant No. KYCX21_0642). We are grateful to all of the other staff members at the Institute of Traditional Chinese
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