Action of the colony-stimulating factor, CSF-1.

Colony-stimulating factor 1 (CSF-1) is a glycoprotein growth factor that specifically regulates the survival, proliferation and differentiation of mononuclear phagocytes and their precursors via a cell surface receptor selectively expressed on these cell types. The purified receptor is a single glycosylated polypeptide, Mr 165 000, which exhibits CSF-1-dependent autophosphorylation in tyrosine. CSF-1 alone regulates cells of the mononuclear phagocytic series (CSF-1-dependent colony-forming unit [CFU-C]----monoblast----promonocyte----monocyte----macrophage). However, the presence of a multipotent haemopoietic cell growth factor, haemopoietin-1, permits CSF-1 to stimulate precursors of CFU-C to proliferate and differentiate to macrophages. Precursors of CFU-C possess low levels of the CSF-1 receptor but there is an increase in receptor levels on CFU-C just before their differentiation to adherent, proliferating mononuclear phagocytes. As the timing of this developmentally associated increase in receptor expression coincides with the acquisition of responsiveness to CSF-1 alone, it is an early indicator of determination to the mononuclear phagocytic lineage.