REGULATION OF TNF-ALPHA RELEASE FROM BONE-MARROW-DERIVED MACROPHAGES BY VITAMIN-D

The calcium-regulating hormone 1,25-dihydroxyvitam in D-3[1,25(OH)(2)D-3] is recognized as an immuno-modulator affecting the activities of macrophages and lymphocytes. We have shown that macrophages harvested from vitamin D-deficient mice (-D MPs) exhibit impaired phagocytic and tumoricidal activities as compared with control cells (+D MPs), and that bone marrow-derived macrophage (BMDM) differentiation is modulated by 1,25(OH)(2)D-3. The release of tumor necrosis factor-alpha (TNF-alpha) by macrophages is considered a major mechanism by which these cells exert their tumoricidal function. This cytokine was also implicated in modulation of bone resorption. In the present study we examine the role of 1,25(OH)(2)D-3 in TNF-alpha: synthesis and release. BMDMs were harvested from +D and -D mice, cultured in vitro, and their conditioned media were analyzed for the presence of TNF-alpha. BMDMs did not release measurable amounts of TNF-alpha without stimulation. Addition of endotoxin (LPS) to the cultures resulted in a marked stimulation of TNF-alpha release. 1,25(OH)(2)D-3 increased the stimulatory action of LPS, but failed to elicit a stimulatory effect in the absence of LPS. The use of another macrophage activator, interferon-gamma (IFN-gamma), yielded essentially similar results. +D and -D mice were injected with LPS and TNF-alpha levels in the serum were measured. A marked reduction (similar to fourfold) in the TNF-alpha levels was observed in the serum of -D mice as compared with +D mice. Western blot and immunoprecipitation analyses suggested that the main effect of 1,25(OH)(2)D-3 is on TNF-alpha synthesis. Our findings suggest that,25(OH)(2)D-3 plays a role in the regulation of TNF-alpha secretion by mononuclear phagocytes. (C) 1994 Wiley-Liss, Inc.