Mouse peritoneal macrophages produce CFU-gm and CFU-meg growth-promoting factors

The effect of peritoneal macrophage-conditioned medium (macrophage CM) from lipopolysaccharide-injected mice on granulocyte-macrophage colony (CFU-gm) and megakaryocyte colony (CFU-meg) formation was examined using a plasma clot culture system. Macrophage CM stimulated mouse bone marrow cells to form CFU-gm and CFU-meg in the presence of pokeweed mitogen-stimulated spleen cell-conditioned medium, but it had no effect on colony formation in the absence of exogenous colony-stimulating factors (CSF). CFU-gm and CFU-meg colony formation was enhanced by low concentrations of exogenous GM-CSF or Meg-CSF alone. These data demonstrate that macrophage CM contains an activity that sensitized CFU-gm and CFU-meg to exogenous CSF.