The Effect And Mechanism Of Flagellin In The Modulation Of CD4~+ T Cell Response

Vaccination is the most effective strategy to prevent infectious diseases.Most pathogens infect human body through mucosal surfaces.Therefore,the best strategy to prevent pathogen invasion is to establish an effective mucosal immune response in advance.Vaccines inoculated through mucosal routes can induce both systemic and mucosal immune responses.By activating innate immunity,adjuvants enhance vaccine antigen specific adaptive immune response and improve the protective effect of vaccine.Therefore,adjuvant is an important part of vaccination especially for subunit vaccination.Flagellin,the primary structural protein of bacterial flagellar filaments,is a unique pathogen-associated molecular pattern(PAMP)capable of activating Toll-like receptor 5(TLR5)and NLRC4 signaling pathways.Our previous studies have demonstrated that flagellin is a efficient nasal mucosal adjuvant to enhance antigen-specific immune responses and vaccine efficacy.Objective:This study employs a cell transfer model,a mouse intranasal immunization model,and an in vitro cell model to investigate the regulatory effect of flagellin on CD4~+T cell responses and explore the mechanism of flagellin modulated CD4~+T cell responses through regulating DC function.Methods:Initially,na?ve CD4~+T cells from OTII mice were adoptively transferred into WT and TLR5 knockout mice,followed by intranasal immunization with either OVA alone or OVA plus SF.The impact of flagellin protein on CD4~+T cell responses was then analyzed.To further investigate the effect of SF on antigen-specific immune responses,HIV-1 core antigen P24 was used as a model antigen for intranasal immunization.The difference in antibody and CD4~+T cell responses between P24alone and the fusion protein SF-P24 was analyzed.Using in vivo nasal immunization and in vitro somatic cell co culture model,we explored the regulatory effect of flagellin on DC from migration,activation and induction of CD4~+T cell response.And the mechanism of flagellin modulated CD4~+T cell response was studied using an in vitro cell co-culture model.The efficiency of flagellin protein to stimulate nasal epithelial cells(NECs)in regulating dendritic cells(DCs)and mediating Th17response was observed and analyzed.Result:In summary,this study has demonstrated the regulatory role of flagellin in CD4~+T cell response using an in vivo animal model.The results demonstrated that flagellin induces a Th17-biased CD4~+T cell response in a TLR5-dependent manner.The study also shed some light on the mechanism of flagellin modulated Th17 cell responses.Specifically,the study shows that flagellin promotes DC migration to draining lymph nodes and activates them,enabling them to induce Th17 response.Based on our previous studies,our study suggests that the modulation of flagellin on DC is indirect and occurs through the pre-activation of NEC secretion of soluble cytokines.The findings of this study not only provide a foundation for the development of novel mucosal adjuvants and vaccines based on flagellin,but also help to elucidate the unique mechanisms of respiratory mucosal immune responses.