The Metabolite la , 25 - Dihydroxyvitamin D 3 Enhances Lymphokine - Mediated Activation of the Oxidative Metabolism of the U 937 Cell Line and Phosphorylation of a 48 - kD Respiratory Burst - Associated Protein

U937 cells respond to a variety of stimuli with increased differentiation as manifested by reduced growth. increased adherence. increased expression of several surface receptors. and increased capacity for phagocytosis and formation of reactive oxygen intermediates. In the present study the effects of lymphocyte conditioned media. recombinant interferon-’y (lFNy). and la.25-dihydroxyvitamin D3 (1 .25(OH)2D3) on the ability to form reactive oxygen intermediates by U937 cells were measured by using the luminol-dependent luminescence (LDL) assay. Neither 1 .25(OH)2D3 alone nor IFN-’y alone enhanced competence for phorbol mynistate acetate-stimulated LDL. Cells were capable of moderate LDL after exposure to lymphocyte conditioned media. and this was enhanced by 1 .25(OH)2D3 (10’ mol/L) and other vitamin D metabolites at higher