IL-17 was initially associated with a Th1-type pro-inflammatory response and pathogenesis of Th1-type autoimmune diseases, but the realization that IL-23p19- and IL-12p40-deficient mice showed distinct phenotypes in terms of susceptibility to autoimmune diseases helped to establish Th17 as a unique helper T cell subset distinct from Th1 and Th2 cells [5,6]. The gene discussed is IL17A; the disease is autoimmune disease.