HBsAg血清学转换是HBV感染临床治愈的标志，但发生率极低，因此探索此事件的免疫调节机制尤为重要。我们前期工作发现滤泡辅助性T（Tfh）细胞通过分泌IL21促进B细胞产生HBV相关抗体，且IL21R基因敲除小鼠建立的HBV模型HBsAg清除延迟，不能产生HBsAb，由此我们推测“Tfh细胞-IL21-B细胞”轴作为重要一环参与了HBsAg血清学转换。本项目拟通过慢性HBV感染横向和抗病毒治疗纵向队列，结合体外实验以及基因工程小鼠HBV模型，探讨Tfh细胞、IL21以及B细胞在HBsAg血清学转换过程中的免疫调节作用；同时为了阐明IFN-α抗病毒治疗较核苷（酸）类药获得更高HBsAg血清学转换率的潜在机制，我们将借助体内外实验研究IFN-α对“Tfh细胞-IL21-B细胞”轴的影响。本研究有助于揭示HBsAg血清学转换的免疫调节机制，对优化现有治疗策略和寻找乙肝治疗新靶点具有重要意义。

As a symbol for clinical cure of HBV infection, HBsAg seroconversion reflects recovery of host immunity against HBV. However, the immunological mechanisms involved in HBsAg seroconversion are still not fully understood. Our previous work has found that circulating follicular T helper (Tfh) cells have a significant role in facilitating production of antibodies against HBV in patients with chronic HBV infection by producing IL21, and HBV mouse model based on IL21 receptor knockout mice demonstrated a deferred clearance of HBsAg and an inability of HBsAb generation. Thus, we make a speculation that "Tfh cells-IL21-B cells" axis act as an important part involved in the process of HBsAg seroconversion. With the help of cross-sectional cohort with chronic HBV infection and longitudinal cohort with antiviral treatment, and in combination with in vitro experiments and HBV mouse model established on genetically engineered mice, we aim to investigate the potential role of Tfh cells, IL21, and B cells in the process of HBsAg seroconversion. In addition, we will assay the effect of IFN-α on the regulation of "Tfh cells-IL21-B cells" axis with the aim to clarify potential immunological mechanisms involved in conclusively clinical observation that IFN-α-based therapy induce higher rate of HBsAg seroconversion than nucleoside/nucleotide analogues in CHB patients. This study will help to provide clues to development of novel immunotherapeutic strategy for chronic HBV infection.