Competition between erythropoietin and colony-stimulating factor for target cells in mouse marrow.

We have assessed the effects of erythropoietin (ape) and colony-stimulating factor (CSF) on mouse bone marrow cells in vitro. When pure human urinary epo, at a dose that maximally stimulated erythroid burst formation. was added to cultures along with increasing amounts of CSF. two types of competitive effect were evident. Epo caused suppression of the number of granulocyte-macrophage (G-M) colonies formed because of low concentrations of CSF; at higher CSF levels. as the number of G-M colonies increased, erythroid burst formation was suppressed . Increasing amounts of CSF caused dose-dependent suppression of epo-induced hemoglobin synthesis . Complete suppression was found at a concentration of CSF that was within the linear portion of the log-doselog-response curve for CSF-dependent G-M colony formation using the same pool of marrow cells. Competition was found only in cultures at relatively high cell densities. Epo caused suppression of CSFinduced G-M colonies, and CSF caused suppression of 8-day hemoglobin synthesis. when there were more than 1 X 1 O marrow cells per milliliter. Relatively high cell concentrations may be required so that mechanisms important in regulating hemopoietic differentiation can be studied in vitro.