A role for the macrophage in normal hemopoiesis. I. Functional capacity of bone-marrow-derived macrophages to release hemopoietic growth factors.

Almost pure macrophage populations were obtained when mouse bone marrow cells were cultured under low-oxygen tension on hydrophobic Teflon foils. Macrophage content was determined using nonspecific esterase staining and binding of the mouse, macrophage-specific monoclonal antibody directed against the F4/80 antigen. Using both these techniques, the macrophage content present after 14 days in culture was approximately 98%. This represented an approximate two- to fourfold increase over the initial macrophage content present in primary bone marrow cell suspensions. Granulocytes and erythroblasts were found to be the contaminating cell types. No T-lymphocytes were present at 14 days of culture. The activities of three hemopoietic growth factors (erythropoietin, colony-stimulating factor, and a factor enhancing early erythroid progenitor cells [BFU-E] and stimulating in vitro multipotential stem cells) present in the supernatant were shown to increase in parallel with macrophage content. The results demonstrate that bone-marrow-derived macrophage populations are functionally capable of producing and secreting hemopoietic growth factors. These results form the basis of a hypothesis in which the macrophage is perceived as a regulator cell for hemopoiesis.