The Role of IL-21 in Chronic Inflammatory Skin Diseases

Interleukin (IL)-21 is a type I cytokine involved in both innate and adaptive immunity. In structure, due to the common γ-chain, it shares significant homology with IL-2, IL-4, and IL-15 but binds to a unique receptor chain, IL-21R, activating the Jak/STAT pathway. Like most cytokines, IL-21 exhibits a plethora of actions, modulating both humoral and cell-mediated immune responses. Summing, it has effect on lineages, such as CD4 and CD8 T cells, regulatory T cells, B cells, natural killer cells, and dendritic cells, as well as on nonimmune cells. The variety of effects that IL-21 has on the immunity explains its critical role in the initiation and progression of several inflammatory and autoimmune diseases. Several studies support its involvement in the pathogenesis of inflammatory bowel disease, celiac disease, rheumatoid arthritis, type I diabetes, and some inflammatory skin disorders, even if the exact mechanism is not fully understood. We will summarize recent discoveries on the role of IL-21 in inflammatory skin diseases. © 2012 Springer Science+Business Media New York.