Production of erythroid potentiating factor(s) by a human monocytic cell line

U-937 is a human monocytic cell line that has been shown to elaborate factors that affect normal human hematopoiesis in vitro. Studies on the effects of these factors demonstrated an erythroid potentiating factor (EPF) and a potent inhibitor of granulocyte-macrophage (CFU-GM) colony growth. The EPF was present in both serum-containing and serum-free U-937 conditioned media, had a dose-dependent effect on erythroid colony formation and was remarkably heat stable. The CFU-GM inhibitory activity was also detected in serum-free conditioned medium, was dose-dependent, heat labile and its effect was reversed by indomethacin. Indomethacin (Sigma, St. Louis, Mo.) did not alter the erythroid effects of the U-937 conditioned medium. No colony stimulating factor (CSF) or erythropoietin (Ep) could be detected in this medium. The existence of a human cell line capable of producing EPF without simultaneous CSF production will permit further studies on the biochemical and biologic nature of these factors.