Synthesis in vitro of 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 by interferon-gamma-stimulated normal human bone marrow and alveolar macrophages.

Cultured human macrophages from normal donors were examined for their capability to metabolize 25-hydroxyvitamin D3 (25-(OH)D3). Upon exposure to recombinant human interferon-gamma (IFN-gamma) both bone marrow-derived macrophages (BMM) and pulmonary alveolar macrophages (PAM) produced a polar 25-(OH)D3 metabolite which was purified from conditioned media and unequivocally identified as 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) by UV-absorbance spectrophotometry and mass spectrometry. The BMM and PAM also synthesized a second 25-(OH)D3 metabolite which was structurally identified as 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3). The time course of 25-(OH)D3 metabolism by macrophages suggested that the production of 24,25-(OH)2D3 was stimulated by high intracellular levels of 1,25-(OH)2D3 and not by IFN-gamma. The 1,25-(OH)2D3 obtained from BMM and PAM promoted macrophage-like differentiation of promyelocytic HL-60 leukemia cells and inhibited IFN-gamma production by normal human lymphocytes. Our data suggest that locally high levels of 1,25-(OH)2D3 in the microenvironment of IFN-gamma-stimulated BMM and PAM may modulate the function of hormone-responsive cells.