IL17A and rheumatoid arthritis: Further classifying CD4+ T cells according to their combined expression of IL-17 and IFNγ revealed significantly greater suppressive effects of 1,25(OH)2D3 on Th17 (IL-17+IFNγ-) and Th17.1 (IL-17+IFNγ+) T cells in RA blood relative to SF, whilst Th1 (IL-17-IFNγ+) frequencies were not affected by 1,25(OH)2D3 in blood or SF (Fig. 1C).