Hydrocortisone promotes survival and proliferation of granulocyte-macrophage progenitors via monocytes/macrophages.

We have determined the mechanism by which hydrocortisone (Hc) promotes the survival and proliferation of normal human granulocyte-macrophage progenitors (granulocyte-macrophage colony-forming units, CFU-GM). Peripheral blood mononuclear cells were cultured in a liquid system with 0-10.0 microM Hc over 3 weeks. At 7-day intervals 50% of the culture media along with the cells (suspension cells) present in the media were removed and replaced with fresh media. No CFU-GM or very small numbers of CFU-GM were contained in the suspension cells of the 14- and 21-day-old liquid cultures without Hc; CFU-GM were present and increased with increasing concentrations of Hc. The CFU-GM content in suspension cells of 14- and 21-day-old liquid cultures with 1.0 microM Hc was at least threefold higher compared to liquid cultures without Hc. In a double-layer CFU-GM agar culture system, the suspension cells from liquid cultures with 1.0 microM Hc, but not from liquid cultures without Hc, supported CFU-GM proliferation from normal human bone marrow cells. The CFU-GM proliferation-inducing ability was confined to the monocytes/macrophages (Mo). CFU-GM colony inhibitory and stimulatory activities were detected in cell-free media recovered from liquid cultures without Hc, but only colony stimulatory activity was detected in the media from cultures with 1.0 microM Hc. These results indicate that greater than or equal to physiological concentrations of Hc (0.1-1.0 microM) are required for the persistence and proliferation of CFU-GM, and the effect of Hc is mediated through the Mo, probably by inhibiting the production of one or more of the CFU-GM colony inhibitory molecules.