ABSTRACT
Interleukin -21 (IL -21)is a cytokine produced by activated CD4 + T cells and can affect the function of various lymphocytes. It should be noted that IL -21 - mediated cellular and humoral immune responses play an important role in determining the outcome of viral infec-tion. This article introduces the research advances in the important role of IL -21 in hepatitis B virus (HBV)infection. IL -21 secreted by vi-rus - specific CD4 + T cells plays key roles in sustaining CD8 + T lymphocyte response and promoting B - lymphocyte response,which is vital for effective viral control. However,as an inflammatory mediator,IL -21 is also involved in the development of hepatitis B - related liver cir-rhosis and aggravation of liver injury. Therefore,IL -21 is considered as an immunoregulatory cytokine in HBV infection. Immunotherapeutic strategies aim at optimizing the beneficial effects of IL -21 in HBV infection,which may be a serious challenge in the future.