Endogenous inhibitors of human granulocyte/macrophage colony forming cells in vitro are inactivated by free radical scavengers.

Granulocyte/macrophage colony forming cells (GM-CFC) require colony stimulating factors (CSF) for growth in vitro. Crude preparations of CSF also contain inhibitors. To investigate whether this inhibition involves free radicals, the following scavenging agents were tested on human GM-CFC grown in agar: cysteine, reduced glutathione, dithiothreitol, sodium selenite, alpha-tocopherol, superoxide dismutase, catalase and ascorbic acid. All except ascorbic acid and catalase had enhancing and stabilising effects on colony formation. The colonies also contained more cells but no changes in cell composition were detected. Cysteine, the most extensively tested substance, was active at concentrations present in body fluids and enhanced colony formation without an exogenous source of CSF. Our results are consistent with an imbalance between the production and removal of free radicals generated in the human GM-CFC assay in vitro. This hampers investigation of regulators of granulopoiesis and results in underestimation of GM-CFC, but can be alleviated by the addition of free radical scavengers.