The IL-17 family is a subset of cytokines composed of IL-17A-F, a hallmark of the newly defined T helper 17 (TH17) cell subset, plays an important role in protecting the host against extracellular pathogens, and promotes inflammatory pathology in autoimmune diseases, while IL-17F is mainly involved in mucosal host defence mechanisms. Here, IL17A is linked to autoimmune disease.