IL21 and autoimmune disease: IL‐21, which act on both nonlymphoid and lymphoid cells and have a role in the humoral immune responses’ regulation, is essential in the alterations to the T‐helper cells such as B cell subsets (such as naive B, memory B, and antibody‐secreting cells), Tfh, and regulatory T cells, and Th17, whose pathogenesis has also been clarified in several autoimmune disorders and linked with the elevated IL‐21 or IL‐21R expressions.21