Macrophage colony-stimulating factor (M-CSF) is a hematopoietic growth factor that regulates the proliferation, differentiation, and functional activation of monocytes. Normally detected in human serum, M-CSF plays an important role in enhancing the effector functions of mature monocytes and macrophages. M-CSF serum levels are increased in CB and further increased in the neonate. The role of M-CSF is not only restricted to the monocyte/macrophage cell lineage. By interacting with its membrane receptor (CSF1R or M-CSF-R encoded by the c-fms proto-oncogene), M-CSF also modulates the proliferation of earlier hematopoietic progenitors and influence numerous physiological processes involved in immunology, metabolism, fertility and pregnancy. 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.