The IL-17-secreting CD4+ T cells have been defined as Th17 cells, and constitute ~1% of CD4+ T cells in the peripheral blood of healthy donors.857 Through the secretion of IL-17, IL-17F, and IL-22, Th17 cells play key roles in many human diseases including inflammation, autoimmune diseases, and cancer. The gene discussed is CD4; the disease is autoimmune disease.