TH-17 cells in the circle of immunity and autoimmunity

CD4(+) effector T cells have been categorized into two subsets: T helper type 1 ( T(H)1) and T(H)2. Another subset of T cells that produce interleukin 17 ( IL-17; 'T-H-17 cells') has been identified that is highly proinflammatory and induces severe autoimmunity. Whereas IL-23 serves to expand previously differentiated T-H-17 cell populations, IL-6 and transforming growth factor-beta ( TGF-beta) induce the differentiation of T-H-17 cells from naive precursors. These data suggest a dichotomy between CD4(+) regulatory T cells positive for the transcription factor Foxp3 and T-H-17 cells: TGF-beta induces Foxp3 and generates induced regulatory T cells, whereas IL-6 inhibits TGF-beta-driven Foxp3 expression and together with TGF-beta induces TH-17 cells. Emerging data regarding T-H-17 cells suggest a very important function for this T cell subset in immunity and disease.