Sources of murine macrophage colony-stimulating factor that also contain growth factors for primitive macrophage progenitor cells.

A new growth factor (synergistic factor, SF) has recently been described, which, in combination with a macrophage CSF source, is able to stimulate the proliferation of primitive high-proliferative-potential macrophage-progenitor cells (HPP-CFC) in mouse bone marrow in culture. It has been found that the addition of supraoptimal amounts of the crude CSF sources, extracts of pregnant mouse uterus and embryo, media conditioned by L cells or the mouse mammary tumor cell line (EMT6), stimulated the proliferation of HPP-CFC in the absence of any added SF. These preparations thus appear to contain a factor with similar biological properties to those of SF. This conclusion is supported by the results obtained from Sephacryl S200 chromatography of these three CSF sources, which indicate that in all three cases fractions with apparent molecular weight (MW) greater than 68,000 contained the major portion of the CSF-1 activity, whereas fractions with MW less than 68,000 contained the SF-like activity, together with minor amounts of CSF-1 activity.