Monocyte colony-stimulating factor (M-CSF, CSF-1) is a macrophage lineage-specific growth factor. Full length human M-CSF transcripts encode a 522 amino acid (aa) type I transmembrane (TM) protein with a 464 aa extracellular region, a 21 aa TM domain, and a 37 aa cytoplasmic tail that forms a 140 kDa covalent dimer. The first 223 aa of mature human M-CSF shares 88%, 86%, 81% and 74% aa identity with corresponding regions of dog, cow, mouse and rat M_x001E_CSF, respectively. M-CSF Induces vascular endothelial growth factor production and angiogenic activity from human monocytes. Whatmore, M-CSF and GM-CSF are mediators involved in regulating the numbers and function of macrophage lineage populations and have been shown to contribute to macrophage heterogeneity.