CSF-1R, also known as CD115 and M-CSFR, is a type I transmembrane protein belonging to the platelet-derived growth factor receptor family. The natural ligands for this c-fms (Fms) proto-oncogene product include M-CSF and IL-34. Structural studies of CD115 have described an immunoglobulin (Ig)-like extracellular domain, a transmembrane domain, an intracellular juxtamembrane domain, a split tyrosine kinase domain, and a C-terminal tail. Upon activation, the receptor not only undergoes phosphorylation and ubiquitination of its intracellular residues but also induces homodimerization. CD115 directly influences the differentiation and proliferation of tissue macrophages and osteoclasts. It is expressed on monocytes/macrophages, peritoneal exudate cells, plasma cells, conventional dendritic cells, and osteoclasts.
