Differentiation of a human monocytic cell line by 1,25-dihydroxyvitamin D3 (calcitriol): a morphologic, phenotypic, and functional analysis.

Several recent studies have suggested a role for 1,25-dihydroxyvitamin D3 (calcitriol) in myeloid differentiation. We have examined the effects of calcitriol on the U937 monoblast cell line and found that calcitriol, at near physiologic concentrations, is a potent inhibitor of U937 growth. Moreover, calcitriol induces differentiation to a monocyte-macrophage phenotype marked by enhanced alpha-naphthyl esterase staining. Morphologic changes were attended by de novo induction of the myeloid specific antigen detected by the monoclonal antibody AML-2-23, as well as dramatic increases in Fc receptors for IgG. In addition, calcitriol induced U937 cells to perform phagocytosis and antibody-dependent cellular cytotoxicity. These results indicate the potential activity of calcitriol in myeloid differentiation and additionally suggest a role for calcitriol in monocyte-macrophage activation.