DBP limits the bioavailability of 25(OH)D
and inhibits vitamin D-induced gene expression in T cells. Relative CD38 cell surface expression (n = 6) (A) and mRNA expression (n = 4) (B), CTLA-4 expression (n = 4) (C), PLC-γ1 expression (n = 4) (D), IL-13 production (n = 3) (E) and mRNA expression (n = 4) (F), IFN-γ production (n = 4) (G) and mRNA expression (n = 4) (H), and 1,25(OH)2D3 in the medium (n = 6) (I) of T cells activated for 3 days in X-VIVO 15 (medium), or X-VIVO 15 supplemented with either 100 nM 25(OH)D3 (25D3), 1 μM DBP (DBP) or the combination of 25(OH)D3 and DBP (25D3/DBP). The mean concentration of IL-13 and IFN-γ in the supernatants of cells activated in X-VIVO 15 (medium) was 246 pg/ml and 26 ng/ml, respectively. (A-I) Mean + SEM from the numbers of independent experiments indicated by n in the legend above.