Abstract
Interleukin-21 (IL-21) is a cytokine mainly secreted by activated CD4+ T cells and natural killer T cells and has multiple effects. It is involved in innate and adaptive immune responses. Recent studies have shown that IL-21 can promote functional activation of various immune cells in the process of hepatitis B virus (HBV) infection, and the gene polymorphisms of IL-21 is associated with the susceptibility to HBV. In addition, the expression of IL-21 is closely associated with HV genotype, HBV clearance, HBeAg seroconversion, HBV-related liver cirrhosis, liver failure, liver cancer, and autoimmune disease. This article reviews the research advances in clinical trials with reference to the aspects above.