Interleukin (IL)-

A new class of inflammatory CD4؉ T cells that produce interleukin-17 (IL-17) (termed Th17) has been identified, which plays a critical role in numerous inflammatory conditions and autoimmune diseases. Interleukin-17A (IL-17A)-producing T cells are a subset of CD4 ϩ T cell lineage, termed Th17, distinct from Th1, Th2, and T regulatory (T reg ) subsets (52). IL-17 is involved in the pathogenesis of autoimmune inflammation and has been implicated in numerous autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis (MS) (10,21,26,41). IL-17 mRNA and protein levels in patients with MS have been shown to be increased in mononuclear cells isolated from blood, in cerebrospinal fluid, and in brain lesions (39,41). IL-17 is also increased in lymphocytes derived from mice with experimental autoimmune encephalomyelitis (EAE; mouse model for multiple sclerosis) (33). In IL-17A knockout (KO) mice, EAE is markedly suppressed, indicating that IL-17 contributes to the development of EAE (33). Although it has been reported that the transcription factors nuclear factor for activated T cells (NFAT), retinoid orphan nuclear receptor ␥t (ROR␥t), and Runt-related transcription factor 1 (Runx1) are important for the T cell receptor (TCR)-mediated transcriptional regulation of IL-17A (24, 29, 38, 74), knowledge of the factors involved in the cellular and molecular regulation of IL-17A remains limited.The principle function of the active form of vitamin D,, is the maintenance of calcium and phosphate homeostasis (13). However, vitamin D has numerous other functions, including downregulation of autoimmunity (7,8,25,55). 1,25(OH) 2 D 3 has been reported to at least partially protect against a number of experimental autoimmune diseases, including EAE (7,8,11,35,40,53). In addition, numerous epidemiological studies have indicated a negative correlation between increased sun exposure, which would result in a higher vitamin D synthetic rate, and diets rich in vitamin D and MS prevalence (34,55,70

The biological activities of the inflammatory cytokine interleukin (IL)-17 have been widely studied. However, comparatively little is known about how IL-17 expression is controlled. Here, we examined the basis for transcriptional regulation of the human IL-17 gene. IL-17 secretion was induced in peripheral blood mononuclear cells following anti-CD3 cross-linking to activate the T cell receptor (TCR), and costimulatory signaling through CD28 strongly enhanced CD3-induced IL-17 production. To define cis-acting elements important for IL-17 gene regulation, we cloned 1.25 kb of genomic sequence upstream of the transcriptional start site. This putative promoter was active in Jurkat T cells following CD3 and CD28 cross-linking, and its activity was inhibited by cyclosporin A and MAPK inhibitors. The promoter was also active in Hut102 T cells, which we have shown to secrete IL-17 constitutively. Overexpression of nuclear factor of activated T cells (NFAT) or Ras enhanced IL-17 promoter activity, and studies in Jurkat lines deficient in specific TCR signaling pathways provided supporting evidence for a role for NFAT. To delineate the IL-17 minimal promoter, we created a series of 5 truncations and identified a region between ؊232 and ؊159 that was sufficient for inducible promoter activity. Interestingly, two NFAT sites were located within this region, which bound to NFATc1 and NFATc2 in nuclear extracts from Hut102 and Jurkat cells. Moreover, mutations of these sites dramatically reduced both specific DNA binding and reporter gene activity, and chromatin immunoprecipitation assays showed occupancy of NFAT at this region in vivo. Together, these data show that NFAT is the crucial sensor of TCR signaling in the IL-17 promoter.