Factors regulating macrophage production and growth. Purification and some properties of the colony stimulating factor from medium conditioned by mouse L cells.

Study of the control of growth and differentiation of macrophages has been greatly facilitated in recent years by the development of assays for granulocyte-macrophage progenitor cells (1, 2) and for factors regulating in vitro growth and production of macrophages. Two factors whose properties and action on mouse cells have been described in some detail are macrophage growth factor (MGF) ~ (3-5), which stimulates the proliferation of peritoneal macrophages, and colony-stimulating factor (CSF) (6-8), which stimulates the differentiation of individual progenitor cells from bone marrow, spleen, and blood to colonies of granulocytes and macrophages. Both factors have similar properties, have been found in similar sources, and require the presence of serum for their in vitro effects. However, there are marked differences in the assay systems for MGF and CSF. In the MGF assay, adherent peritoneal cells from mice intraperitoneally injected with soluble starch 4 days previously are cultured on glass in liquid medium. In the presence of MGF, a proportion of these cells (up to 95%) incorporate 3Hthymidine and divide. The MGF activity is determined from autoradiographs and expressed as percent of total cells labeled (3). In the CSF assay, normal mouse bone marrow cells are