IL17A and rheumatoid arthritis: T helper type 17 (TH17) cells are characterized by the production of interleukin-17A (IL-17A), IL-17F, and IL-22 and have emerged as a subset of effector CD4+ T cells with an important role in the control of specific pathogens as well as in the development of autoimmune diseases, including rheumatoid arthritis and multiple sclerosis1,2.