Impaired macrophage activation in vitamin D₃ deficiency: Differential in vitro effects of 1,25-dihydroxyvitamin D₃ on mouse peritoneal macrophage functions

1,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) is known to interact in vitro with mononuclear phagocytes. The purpose of this study was to determine the role of the steroid in macrophage activation in vivo. Peritoneal macrophages from normal and vitamin D₃-deficient mice were obtained after i.p. injection of activating or eliciting agents. Cells obtained from vitamin D₃-deficient mice exhibited defected capabilities to perform anti-tumor activities (cytostasis and cytolysis) and to form oxygen reduction products (H₂O₂ and O₂^-). On the other hand, the level of the lysosomal enzyme acid phosphatase was unaffected by vitamin D₃ deficiency. In vitro, incubation of macrophages with 1,25(OH)₂D₃ enhanced their anti-tumor activities, but did not affect the cells' capacity to produce H₂O₂ and O₂^-, or acid phosphatase. Our results suggest that 1,25(OH)₂D₃ is essential for macrophage activation in vivo. However, in vitro, the hormone is only partially capable of affecting the macrophage funtions, probably because of the maturation state of the cells.