Enhanced Pathogenicity of Th17 cells Generated in the Absence of Transforming Growth Factor- Signaling

CD4+ T cells that selectively produce interleukin (IL)-17, are critical for host defense and autoimmunity1-4. Crucial for T helper17 (Th17) cells in vivo5,6, IL-23 has been thought to be incapable of driving initial differentiation. Rather, IL-6 and transforming growth factor (TGF)-1 have been argued to be the factors responsible for initiating specification7-10. Herein, we show that Th17 differentiation occurs in the absence of TGF- signaling. Neither IL-6 nor IL-23 alone efficiently generated Th17 cells; however, these cytokines in combination with IL-1 effectively induced IL-17 production in nave precursors, independently of TGF-. Epigenetic modification of the Il17a/Il17f and Rorc promoters proceeded without TGF-1, allowing the generation of cells that co-expressed Rort and T-bet. T-bet+Rort+ Th17 cells are generated in vivo during experimental allergic encephalomyelitis (EAE), and adoptively transferred Th17 cells generated with IL-23 in the absence of TGF-1 were more pathogenic in this experimental disease. These data suggest a new model for Th17 differentiation. Consistent with genetic data linking the IL23R with autoimmunity, our findings re-emphasize the role of IL-23 and therefore have important implications for the development of new therapies.

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