Four distinct colony-stimulating factors (CSFs) that promote survival, proliferation and differentiation of bone marrow precursor cells have been well characterized: granulocyte macrophage CSF (GMCSF), granulocyte CSF (GCSF), macrophage CSF (MCSF), and Interleukin-3 (IL-3, Multi CSF). Both GMCSF and IL-3 are multipotential growth factors, stimulating proliferation of progenitor cells from more than one hematopoietic lineage. In contrast, GCSF and MCSF are lineage restricted hematopoietic growth factors, stimulating final mitotic divisions and the terminal cellular maturation of the partially differentiated hematopoietic progenitors.

Macrophage CSF, also known as CSF1, is produced by monocytes, fibroblasts and endothelial cells. It stimulates the formation of macrophage colonies, enhances antibody-dependent, cell-mediated cytotoxicity by monocytes and macrophages, and inhibits bone resorption by osetoclasts. Natural human MCSF is a dimeric glycoprotein of 70-90 kD molecular weight, existing in multiple glycosylation forms. It binds to a 165 kD glycoprotein of the receptor tyrosine kinase subclass III, a family that includes the receptors for platelet derived growth factor (PDGF) and stem cell factor (SCF).