Dexamethasone enhances macrophage colony stimulating factor- and granulocyte macrophage colony stimulating factor-stimulated proliferation of bone marrow-derived macrophages.

Glucocorticoids are effective repressors of the immune system. We have examined the effect of glucocorticoids on the proliferation of murine macrophages. Dexamethasone by itself did not affect proliferation of differentiated or undifferentiated bone marrow-derived macrophages (BMM) and elicited peritoneal macrophages. However, dexamethasone enhanced the proliferation induced by macrophage colony stimulating factor (M-CSF) of these cells. The effect of dexamethasone was not restricted to M-CSF-dependent proliferation. Similarly, dexamethasone enhanced granulocyte macrophage colony stimulating factor (GM-CSF)-dependent proliferation of BMM. In agreement, macrophages transfected with the glucocorticoid receptor showed an enhancement of M-CSF-dependent proliferation. The enhancement of proliferation by dexamethasone or the glucocorticoid receptor was abolished by RU 486, an antagonist of the glucocorticoid receptor. Moreover, the addition of antibodies against M-CSF inhibits the effect of dexamethasone, suggesting that dexamethasone increases the autocrine production of M-CSF. This only occurs when M-CSF or GM-CSF, which induce M-CSF, are present in the media. In tissues, dexamethasone may enhance macrophage proliferation and contribute to the resolution of the inflammatory states.