The Studies On The Infection Mechanisms Of Influenza A Virus:Mast Cell And Regulatory T Cell

Influenza A virus cause acute respiratory infection in both humans and animals, the virus has become a public health threat due to its rapid epidemics develop, and high morbidity and mortality. Several studies suggest that virus-induced exaggerated inflammation response ("cytokine storm") is a major contributing factor of the high morbidity and mortality, however, the exact mechanism is not fully understood. In this thesis, we address the molecular mechanism of influenza A virus infection and immunity in mast cells and regulatory T cells.Here, we characterized that both avian-like (a-2,3-linked) and human-like (α-2,6-linked) sialic acid receptors were expressed on the surface of mouse mast cell line P815, mouse primary peritoneal and lung mast cells, rat primary peritoneal and lung mast cells and human primary lung mast cells. Basis on these, P815mast cells supported the productive replication of H1N1(A/WSN/33), H5N1(A/chicken/Henan/1/04) and H7N2(A/chicken/Hebei/2/02) in vitro. The replication efficiency of H1N1was the highest, H5N1was next only to H1N1, and H7N2was significant lower than H1N1and H5N1. Additionally, the observations of the H5N1infected mast cells in mouse nasal mucosa and lung and ferret lung in vivo provided further evidence. Following in vitro infection, TLR3and RIG-I signals were activated by all the three subtypes of viruses in P815mast cells, and the viruses caused P815cells to secrete various pro-inflammatory cytokines and chemokines, but not the antiviral ones. Furthermore, virus induced TLR3pathway activation and apoptosis were found to be beneficial to viral replications and promote the secretions of pro-inflammatory cytokines and chemokines. Collectively, our finding is the first to address the molecular mechanism of influenza A virus invasion and activation in mast cells.We found that immune effects and protective efficacy of formalin-inactivated H5N1virus immunization was suppressed during chronic heat stress, supporting by CHS1) increased the susceptibility of mice to the influenza, caused increased virus load and pathological injury in lung, and higher mortality rates,2) suppressed Thl and Th2immune responses to reduce antigen specific antibody titers,3) reduced CD8+T-cell proliferation and related cytokines. Furthermore, this suppression was found to be associated with the induced generation of CD4+CD25+Foxp3+Tregs and the increased secretions of IL-10and TGF-β in CD4+T cells. Adoptive transfer of the induced Tregs also suppressed the protective efficacy of formalin-inactivated H5N1virus immunization. Collectively, this study is the first to identify a novel mechanism of CHS immunosuppression mediated by regulating CD4+CD25+Foxp3+Tregs.