The Mechanism And Potential Application Of Flagellin In Regulating Intrahepatic T Cell Response

Liver is an important metabolic organ,and it is also an unique immune organ.To sustain liver homeostasis,it tends to induce immune tolerance due to persistently stimulated by food-derived antigens and bacterial products from gastrointestinal tract.The immune tolerance are modulated by parenchymal hepatocytes and nonparenchymal liver cells which have mutiple mechanisms to suppress the immune response.Hepatophilic pathogens such as parasites,hepatitis B virus(HBV)and hepatitis C virus(HCV),might utilize this hepatic immunosuppressive privilege to develop chronic infection.Antigen-specific CD8~+T cells are usually low in number and become tolerance during chronic infection.Some studies reported that the pathogen-associated molecular patterns(PAMPs),can promote the intrahepatic CD8~+T cell reponse to control the infection by modulating liver sinusoidal endothelial cells(LSECs)and Kupffer cells(KCs).Flagellin,a type of PAMPs from bacteria,can recognize and activate the extracellular TLR5 or the intracellular NLRC4 inflammasome pathway.We speculate that flagellin could recognize and stimulate the liver cells which express TLR5 or inflammasome receptor,.In this study,using the recombinant Salmonella flagellin(SF),we detected the influence of flagellin to the liver cells such as hepatocytes,LSECs and KCs,analyzed the potential modulation and mechanism of flagellin to the intrahepatic CD8~+T cells,and preliminarily investigated the potential antiviral effect of flagellin in a chronic HBV replicative mouse model.1.To analyze the modulation of SF to liver cells and CD8~+T cells in an in vitro liver cells and lymphocytes co-culture system.The immunosuppression of hepatocytes to T cells function rather than that of LSECs or KCs,was found to be alleviated by SF-stimulation in a dose-dependent manner.And this modulation was induced by activating the TLR5 not the NLRC4 signal pathway of hepatocytes.TLR5pathway activated hepatocytes can also promote the CD25,CD44,CD69 expression and the transcription factors T-bet and Eome expression of CD8~+T cells and elevate the production of its functional cytokines IFN-?and TNF-?.Furthermore TLR5-activated hepatocytes were found to directly modulate the activation and cytokines production of multiclonal activated CD8~+T cells,independent of the help of antigen presenting cells(APCs)or CD4~+T cells.And it has the same capacity to modulate the activation and function of antigen-specific CD8~+T cells.This part demonstrates that SF could modulate the immunoregulatory function of hepatocytes by activating its TLR5 signal pathway,and then promote the activation and function of CD8~+T cells.2.The modulation of SF to the importantly immunoregulatory live cells,intrahepatic CD8~+T cells and acute HBV replication were further investigated by SF-injection ways in vivoin mice.SF by multiple intraperitoneal injections could alleviate the immunosuppression of hepatocytes to T cells function,improve the expression of bioenergy metabolism-related proteins of intrahepatic CD8~+T cells but have low impact to the acute HBV replication and antigen-specific T cell response.Hydrodynamic injection(HDI)of SF changed the activation and function of intrahepatic CD8~+T cells at 5-7 days post-injection,And the enhancement of intrahepatic CD8~+T cell function is associated with SF-induced change in the immunoregulatory function of hepatocytes.Moreover,HDI of SF can transiently impair HBV DNA at a very early stage,and predominantly improves the intrahepatic but not systemic HBV-specific CD8~+T cell responses.These indicate that SF in-vivo injection can modulate the immunoregulatory function of hepatocytes and the activation and function of intrahepatic CD8~+T cells,and promoted the intrahepatic virus-specific CD8~+T cell response.3.The potential appliction of SF to the chronic HBV treatment was evaluated in a chronic HBV replicative mouse model.HDI of SF just transiently inhibited the HBV DNA at early days,but there is no influence on the whole kinetics of virus replication.Then transferring CD8~+T cells into chronic HBV replicative mice,we found:SF pre-treatment by multiple intraperitoneal injection can suppress the HBV replication and accelerate the HBV clearance;SF pre-treatment by HDI can also suppress the HBV replication and increase the percent of intrahepatic antigen-specific CD8~+T cells,but have no impact to the HBV clearance.These indicate that SF can promote the function of intrahepatic antigen-specific CD8~+T cells to control chronic virus infection by modulating intrahepatic immune response which is beneficial to control the viruse infection.However,the method of administration,the dose and the coordation with immune response need to be further optimized.In summary,this study demonstrates that flagellin can modulate the intrahepatic CD8~+T cells response by modulating the immunoregulatoty capability of hepatocytes in vitro and in vivo,and promote the function of CD8~+T cells to treat chronic HBV infection.And this study prelimitarily illuminates the effect and the cellular and molecular mechanism of flagellin to modulate the intrahepatic CD8~+T cells response,which has an potential application value for the treatment of chronic HBV infection.