Dust mite-derived Enterobacterial fimbriae H protein enforces the allergen specific immunotherapy in asthma mice

Abstract

Background

The mite alimentary canal contains plenty of microbiota. It is accepted that some of the microbial products function as adjuvants to speed up immune responses.

Objectives

We identified five bacterial proteins from dust mite, and Enterobacterial fimbriae H (FimH) was one of them. This study aims to test a hypothesis that the FimH protein enforces immunotherapy in asthmatic mice.

Methods

Asthmatic mice were treated by allergen specific immunotherapy (ASIT) with rDer f1/f2 or rDer f1/f2 plus FimH. Changes in inflammatory cell infiltration, airway hyperreactivity, frequency of Tregs, splenic CD4⁺IFN-γ⁺ cells, and serum levels of TGF-β, IL-10, IL-13 and IL-17A of asthmatic mice were checked.

Results

ASIT with rDer f1/f2 plus FimH reduced inflammatory cell infiltration, airway hyperreactivity (AHR), and levels of IgE and IgG1 compared to ASIT with rDer f1/f2 alone, but the levels of IgG2a increased. Asthmatic mice that underwent ASIT with rDer f1/f2 plus FimH showed increased frequency of Tregs, splenic CD4⁺IFN-γ⁺ cells, serum levels of TGF-β and IL-10; and deceased splenic CD4⁺IL-4⁺ cells, and serum levels of IL-13 and IL-17A. In vitro study showed FimH triggered IL-10 expression in a concentration dependent manner and facilitated the differentiation of Tregs.

Conclusion

Used as an adjuvant, FimH enforces the effect of ASIT in asthmatic mice via augmenting Tregs.

Introduction

Allergic asthma is an IgE-mediated chronic inflammatory disease with the characteristics of pulmonary eosinophilic granulocyte infiltration and airway hyperreactivity.1, 2 Its prevalence has increased rapidly in recent decades and is still on the rise worldwide. According to statistics, the treatment cost of allergic asthma reaches a billion euros in the European Union every year.³ Allergic asthma is the most common allergic disease in China⁴; the number of patients has reached about 30 million and children involved in asthma reached at least 10 million.5, 6 Thus, asthma represents a major socio-economic and health burden worldwide.

Allergen specific immunotherapy (ASIT) is where the patient is treated with regular small amounts of the allergen of interest with the intention of achieving a tolerogenic response.⁷ Currently, the two administration techniques for allergic asthma involve subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) but the techniques are developing with new approaches involving application of extracts to the skin with patches, injection into inguinal lymph nodes, and alterations to the allergen molecules by chemical treatment or recombinant technology.⁸ As the only effective approach to cure allergic asthma; ASIT is recommended by the World Health Organization (WHO) as a specific therapy for asthma.9, 10, 11 ASIT for asthmatic patients induced by dust mite is administered by vaccination using extracts from whole house dust mite (HDM) or using purified recombinant allergenic proteins. Whole HDM extracts contain the major HDM allergens, such as Dermatophagoides farinae (Der f) 1 and Der f2 and numerous irrelevant proteins. The latter may induce new allergic responses, which is a drawback of ASIT with HDM extracts as vaccines.¹² Recombinant allergenic protein vaccines have defined antigenic components which are easily standardized, and cause fewer side effects during vaccination.13, 14 However, it was reported that the therapeutic efficacy of an allergenic extract vaccine was better than recombinant allergenic protein vaccines,¹⁵ and the reason behind this phenomenon is unclear; it cannot be explained by the differences between dosage and the types of allergens.

Our previous studies primarily confirmed the abundant presence of microbiota in the guts of HDM; with the Enterobacter species the predominant genus.¹⁶ Enterobacterial fimbriae H (FimH) is the adhesion portion of type 1 fimbriae produced by most Enterobacteriaceae, which is a ligand of Toll like receptor 4 (TLR4).17, 18 Current evidence suggests that TLR ligands are important immune adjuvants for vaccine development.19, 20 TLR ligands activate the host immune system through TLRs present in various antigen-presenting cells such as monocytes, macrophages, and dendritic cells. As such, one TLR4 agonist adjuvant, monophosphoryl lipid A, has been approved by the Food and Drug Administration.²¹ Adjuvants can be used in ASTI to induce a quicker, more potent, and longer-lasting immune response.⁷ In this way, the use of a TLR4 ligand to enhance vaccine-specific responses is likely to beneficial for ASIT.

Therefore, we hypothesize that the products of microbiota in dust mites, in particular FimH, play an immune adjuvant role in ASIT. To test this hypothesis, we examined the ability of FimH to enforce the therapeutic effect of the dust mite vaccine-based ASIT in an asthmatic mouse model.