1,25-Dihydroxyvitamin D3 and the regulation of the differentiation and function of macrophages and granulocytes.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) exerts a differential inhibitory effect on the formation of granulocyte, granulocyte/macrophage, and macrophage colonies grown from mouse bone marrow precursor cells; 50% inhibition was attained at 1.1, 2.3, and 23 nM 1,25(OH)2D3, respectively. The inhibition of colony formation, as well as phagocyte proliferation in liquid cultures, requires the presence of 1,25(OH)2D3 in the early stages of culture (up to 72 h after culture initiation). 1,25(OH)2D3 induces a dose- and time-dependent augmentation of the phagocytic capability of mononuclear phagocytes (up to 100%) towards both heat-killed yeast cells and IgG-coated sheep red blood cells. The augmentation of the phagocytic capability of the mononuclear phagocytes depends critically on when 1,25(OH)2D3 is added. It is effective when added up to 72 h after culture initiation, while at later stages (greater than or equal to 96 h) the cells are no longer induced to express enhanced phagocytic capability. We suggest that these phenomena may be relevant to hemopoietic processes.