IL-17A (also referred to as IL-17) is a member of the family of IL-17 ligands which also includes IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. It is mainly produced by a subset of T cells called TH17. TH17 cells are driven to differentiate by TGF-β, IL-1 and IL-6, while IL-23 is required to expand and stabilize the cell population. IL-17A has also been detected in other cells such as neutrophils and macrophages. While IL-17A is linked to the pathogenesis of diverse autoimmune and inflammatory diseases, it also plays an essential role in host defense against extracellular bacteria and fungi...