TLR3 Agonists Attenuate Food Allergy In Mice Through The Induction Of Tregs

Background:Food allergy（FA）is an adverse reaction of the immune system of the intestine to certain food allergens.The clinical symptoms of FA vary from mild abdominal discomfort to life threatening anaphylactic shock.The etiology and immune mechanism of FA are still unclear,and there are no mature methods for the treatment of FA.It is generally believed that FA is the intolerance between the intestinal immune system and food antigens,resulting in the skewed Th2 polarization.Under normal circumstances,intestinal symbiotic flora tolerance,intestinal epithelial integrity,dendritic cells（DC）and regulatory T cells（Tregs）coordinate each other to maintain the balance between Th1 and Th2 immune responses.Tregs（CD4⁺CD25⁺Foxp3⁺T cells）play a negative regulatory role in the body’s immune system and play a key role in oral tolerance,and their dysfunction or decrease in number will break the intestinal tolerance.In mice and humans,Tregs express the forkhead box P3（Foxp3）or IL-10.The role of Foxp3-expressing Treg cells in maintaining immune tolerance has been confirmed.The mutation or less expression of Foxp3 gene may cause dysfunction of Tregs.Poly（I:C）is a TLR3 agonist,and studies have shown that TLR3 recognizes dsRNA（double-stranded RNA）to cause a non-specific inflammatory response,thereby enhancing the induction of peripheral Foxp3 and reducing the differentiation of effector T cells.Objective:In this study,Poly（I:C）was injected into mice to study the regulation of TLR3agonist（Poly（I:C））on Tregs and we established an animal model to see if it had immunomodulatory effects on FA,further clarify the mechanism of intestinal immune regulation and provide a basis for the treatment of allergic diseases.Methods:Eighteen 6-8-week-old BALB/C mice were randomly divided into Control,Model,and PolyI:C groups,with 6 rats in each group.The Model group was a FA model group;the PolyI:C group was a Poly（I:C）group,intraperitoneal injection of poly（I:C）200μɡ,continuous injection for 4 days.Then,like the Model group,sensitize and stimulate with OVA to establish a model of food allergy.Serum IgE,IgG₁ levels,intestinal tissue Th2 cytokine levels,spleen cell culture supernatant cytokine levels:IL-10 and TGF-βwere assessed.Flow cytometry were employed to assess the frequency of Tregs in spleen cells.Intestinal inflammation was observed by HE staining and toluidine blue staining.Tregs were detected by immunohistochemistry in intestinal frozen sections.Mice bone marrow cells were harvested and stimulated with different concentrations of Poly（I:C）to induce differentiation of bone marrow-derived dendritic cells（BMDC）to investigate the effect of Poly（I:C）on dendritic cells（DC）.Results:（1）Poly（I:C）can alleviate the symptoms of food allergic reaction in mice.Poly（I:C）reduces serum IgE and IgG₁ levels,and intestinal histopathological sections show that inflammatory cell infiltration is reduced in mice in Poly（I:C）group.The number of mast cells decreased,and the development of food allergy in mice was inhibited by Poly（I:C）.（2）Poly（I:C）increased the proportion of Tregs in mouse spleen cells and increased the number of Foxp3-positive cells in the intestine.Poly（I:C）induces Tregs and increases the expression of IL-10 and TGF-β.（3）Treatment of mouse BMDC with Poly（I:C）induces resistant DC production and increases the secretion of TGF-β.Conclusion:TLR3 agonists Poly（I:C）can be recognized by TLR3 on DC and transformed into a tolerant DC expressing TGF-βto regulate immune response;Poly（I:C）induce the production of Tregs in mice and increases the expression of IL-10 and TGF-β,thereby inhibiting food allergic reactions in mice.