INHIBITION OF VITAMIN-D-3-INDUCED CELL-DIFFERENTIATION BY INTERFERON-GAMMA IN HL-60 CELLS DETERMINED BY A NITROBLUE TETRAZOLIUM REDUCTION TEST

The combined effects of 1 alpha,25-dihydroxyvitamin D-3 [1,25(OH)(2)D- 3] and interferon-gamma (IFN-gamma) or tumor necrosis factor alpha (TN F-alpha) on cell differentiation in HL-60 human promyelocytic leukemia cells were examined by a nitroblue tetrazolium (NET) reduction test, 1,25(OH)(2)D-3 at the concentrations of 7-70 nM induced NBT-positive c ells, which was used as a criterion of cell differentiation, IFN-gamma itself showed little effect on induction of NET-positive cells or on cell growth at a concentration up to 1000 U/ml. However, in a combinat ion of 1,25(OH)(2)D-3 with IFN-gamma (100 and 300 U/ml), cell differen tiation was strongly inhibited and was accompanied by growth inhibitio n, Treatment with a combination of 1,25(OH)(2)D-3 and TNF-alpha or IFN -alpha and TNF-alpha showed an additive effect on cell differentiation , IFN-gamma seems to act as a specific inhibitor for 1,25(OH)(2)D-3-in duced cell differentiation, To elucidate the cause of the inhibition o f cell differentiation by IFN-gamma, the ability of the cells to produ ce superoxide (O-2(-)) was examined after culture for 5 days in the pr esence of 1,25(OH)(2)D-3 and IFN-gamma. The results indicated that the inhibition of IFN-gamma was caused by a reduction in the ability of t he cells to produce O-2(-) in response to stimulation by 12-O-tetradec anoylphorbol-13-acetate (TPA).