Th17 cells were first recognized when assessing the role of IL-23 in various mouse models of chronic inflammation and autoimmunity, including inflammatory bowel diseases (IBDs), collagen-induced arthritis (CIA), or experimental autoimmune encephalomyelitis (EAE, a murine model of multiple sclerosis) [2, 16, 17]. The gene discussed is IL23A; the disease is multiple sclerosis.