Interleukin 21 Ameliorates The Liver Inflammation By Enhancing The Immune-Suppressive Activity Of Myeloid-Derived Suppressor Cells In Chronic HBV Infection

BackgroundThe World Health Organization reported that the hepatitis B virus(HBV)chronically infected approximately 257 million people in 2015 and causes 887000 deaths every year worldwide.HBV DNA clearance is mainly mediated by innate and adaptive immune response.However,in chronic HBV infection,insufficient immune response is inadequate for HBV clearance but causes hepatocyte apoptosis and necrosis,which may subsequently develop into cirrhosis,liver failure,and even hepatocellular carcinoma(HCC).Myeloid-derived suppressor cells(MDSCs)have been studied in the context of acute liver inflammation and are usually associated with protective functions in this setting.In addition,MDSCs expanded in chronic HBV infection,downregulated immune responses through,for example,the production of Arginase I and indoleamine-2,3-dioxygenase(IDO),which were L-arginine and tryptophan degrading enzymes,respectively,that could deprive immune effectors of these amino acids.Based on the capacity of MDSCs to potently inhibit T cell responses,it is reasonable to speculate that MDSCs are a protective factor in tissue damage in chronic HBV infection.Interleukin(IL)-21 is a cytokine produced by activated CD4+T cells and NKT cells and has broad pleiotropic functions against various immune cells.Ample evidence suggests that aberrant IL-21 responses may be contributed to the liver injury during the pathogenesis of chronic HBV infection.Besides,in a previous study,we determined that MDSC,gMDSC,and mMDSC populations substantially increased in IL-21 receptor(IL-21R)-knock out(KO)mice compared with wild type(WT)mice.As a cytokine with various function in HBV infection,the effects of IL-21 acting on the expansion and immunosuppressive function of MDSCs have not been identified.ObjectiveIn this study,we aimed to examine the characteristics of MDSCs in peripheral blood and liver in chronic HBV infection and the relationship between MDSCs and hepatitis activity through a horizontal cohort of chronic HBV infection;investigate the role of IL-21 on the number and function of MDSCs with in vitro and animal experiments;and provide a basic theoretical basis for the prevention and treatment of chronic hepatitis with IL-21 in clinic.MethodsEighty treatment-naive patients with chronic HBV infection were recruited and classified into the immune tolerant carrier(IT;n=37),hepatitis B e antigen(HBeAg)-positive chronic hepatitis B(CHB;n=16),and inactive carrier(IC;n=27)groups according to the American Association for the Study of Liver Diseases guidelines.Another 33 healthy controls(HCs)were also recruited in this study.In addition,intrahepatic mononuclear cells(HMCs)and matched peripheral blood mononuclear cells(PBMCs)were obtained from 9 treatment-naive patients with HBV-related HCC who underwent curative hepatectomy.Flow cytometry was used to detect the frequencies of and the expression of phenotypes and suppressor markers in MDSC subsets.Correlation analysis was conducted to explore the relationship between MDSCs and HBV liver inflammation.An APAP induced liver injury mouse model was established to detect the frequencies of MDSC subsets;an HBV mouse model was also established to study the distribution of MDSCs in HBV infection and the role of IL-21 on MDSCs in vivo.RNA sequencing was conducted to define the transcriptional profiles of MDSCs after IL-21 stimulation.Serum levels of IL-21 were determined by enzyme-linked immunosorbent assay(ELISA).Results1.The characteristics of MDSCs in chronic HBV infection1.1 The frequency of circulating MDSCs of patients with chronic HBV infection was significantly higher than that of HC group and negatively correlated with ALT levels.1.2 Circulating MDSCs in patients with chronic HBV infection possessed immunosuppressive function.2.Liver inflammation accumulates gMDSCs into the liver in chronic HBV infection2.1 The frequency of intrahepatic MDSCs was significantly higher than that in peripheral blood in patients with chronic HBV infection.2.2 The frequency of intrahepatic MDSCs in HBV infected mouse model was significantly higher than that in peripheral blood and spleen.2.3.Liver inflammation recruited gMDSCs into the liver and expressed higher levels of Arginase I.3.The role of IL-21 on MDSCs in chronic HBV infection3.1 IL-21 altered the landscape of gene expression profiles and activates the transcriptional regulation pathway of MDSCs.3.2 IL-21 induced the differentiation of MDSCs into M2-like macrophages.3.3 IL-21 stimulation in vitro promoted the immunosuppressive function of MDSCs.4.IL-21 ameliorates the liver inflammation by enhancing the immune-suppressive activity of MDSCs in chronic HBV infection4.1 The frequencies of circulating MDSCs and gMDSCs were negatively correlated with the serum ALT levels in the IL-21 high group.4.2 IL-21 reduced intrahepatic inflammation in HBV mice.4.3 IL-21 increased the number of and promoted the expression of Arginase I in MDSCs in HBV mice.Conclusions1.MDSCs expanded and possessed immunosupressive activity in patients with chronic HBV infection.2.Liver inflammation recruited MDSCs into the liver and expressed higher levels of Arginase I.3.IL-21 ameliorated the liver inflammation by enhancing the immune-suppressive activity of myeloid-derived suppressor cells in chronic HBV infection.