Background：Interleukin 21 （IL-21） is a potent immunomodulatory cytokine mainly produced by NKT and CD4+ T-cells, particularly the inflammatory Th17 subset, and has pleiotropic effects on both innate and adaptive immune responses. These actions include positive effects such as enhancing proliferation of NK cells and cytotoxic T cells, and inhibitory effects on the antigen-presenting function of dendritic cells. It can also be proapoptotic for B cells and NK cells. Studies have shown that IL-21 is also an autocrine cytokine that potently induces Th17 differentiation, suppresses Foxp3 expression, and serves as a target for treating inflammatory diseases.
