IL-21 in the pathogenesis and treatment of skin diseases.

Interleukin-21 (IL-21) is a potent immunomodulatory cytokine, with pleiotropic effects on both innate and adaptive immune responses. These actions include positive effects, such as enhanced proliferation of lymphoid cells, increased cytotoxicity of CD8(+) T cells and natural killer cells, and differentiation of B cells into plasma cells. IL-21 is also produced by Th17 cells and is a critical regulator of Th17 development. IL-21 has potent antitumor activity, but is also associated with the development of autoimmune disease. Many of these activities are critically involved in the pathogenesis of several skin diseases such as psoriasis, atopic dermatitis, lupus erythematosus, and melanoma. Here we review recent advancements on the understanding of the role of IL-21 in skin diseases and how this knowledge can be translated into innovative therapeutic approaches.