IL17A and autoimmune disease: Among various CD4+ T helper (Th) cell subsets, pro-inflammatory interleukin (IL)-17-producing Th17 cells play critical roles in the pathogenesis of inflammatory and autoimmune diseases as well as host defense and maintenance of mucosal barrier functions by secreting inflammatory cytokines such as IL-17A, IL-22, and granulocyte macrophage colony-stimulating factor (GM-CSF)1,2.