CD4 and Autoimmunity: Although these studies indicate that 1,25(OH)2D3 modulates Th1 cells under certain circumstances, given their relatively small role in autoimmune pathogenesis and the low expression of VDR compared to other CD4+ T cell subsets, it is unlikely that they play an important role in the suppression of autoimmunity by 1,25(OH)2D3 (110, 112).