On the regulation of differentiation and function of rat macrophages by 1,25-dihydroxyvitamin D3 and dexamethasone.

Abstract

Rat bone marrow macrophage progenitor cells develop in vitro in the presence of rat embryo fibroblast conditioned medium into colonies and clusters. 1 alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3) (0.12-12 nM) was found to enhance the formation of macrophage colonies and the proliferation of mononuclear phagocytes in liquid cultures of bone marrow cells (ED50 0.12-1.0 nM). Fractionation of bone marrow cells by centrifugal elutriation showed that: a) macrophage progenitors are heterogeneous in size; b) the progenitors eluted at early fractions have a lower proliferative capacity (form mainly small clusters) than those eluting at later fractions (higher counterflow velocities) which develop into macrophage colonies and c) that 1,25(OH)2D3 (at 12 nM) augments the expression of colony forming cells enriched in late eluting fractions while having a suppressive effect on expression of low proliferative potential cluster forming cells enriched in early eluting fractions. Dexamethasone was found to suppress the clonal growth of macrophage progenitor cells as well as their proliferation in liquid cultures (ED50 about 1 nM). Both dexamethasone and 1,25(OH)2D3 induced in mononuclear phagocytes of 4 d cultures an increased phagocytic capability. The data suggest a regulatory role for 1,25(OH)2D3 and glucocorticosteroids in myelopoietic processes in the rat. Furthermore, when compared with our recent findings with mouse bone marrow cells, the effects, their magnitude and concentration dependence imply genuine species differences in the responses of mice and rats to these hormones.