IL21 and autoimmune disease: It is currently believed that AA is an autoimmune disease associated with Th1 (IL-2, IFN-γ, TNF, IL-12, and IL-18), Th2 (IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-17E, IL-31, and IL-33), Th17 (IL-17, dysregulation of IL-17F, IL-21, IL-22, IL-23, and TGF-β), and Treg (IL-35) type cytokines.