Stimulation of in vitro granulocyte--macrophage colony formation by mouse heart conditioned medium.

Medium conditioned by mouse heart tissue was found to contain colony-stimulating factor(s) (CSF) which produced in vitro colonies of granulocytes and/or macrophages with bone marrow cells of CBA mice. The action of this CSF type (CSFMHCM) was compared with that of post-endotoxin mouse serum (CSFES on colony formation by density subpopulations of colony-forming cells (CFU-c), separated by isopycnic centrifugation in a continous albumin density gradient. The number, size and morphology of colonies were examined. Mouse heart conditioned medium produced slightly more colonies and of larger size than endotoxin serum but the density distribution of their CFU-c were similar. Low density CFU-c produced predominately pure granulocytic colonies and high density ones predominately pure macrophage colonies with both types of CSF. There was no apparent relationship between colony size and CFU-c density.