PDGF-A and PDGF-B are platelet-derived growth factors that can form disulfide-linked homodimers or heterodimers with each other. These proteins regulate diverse cellular functions by binding to and inducing the homo- or hetero-dimerization of PDGF R alpha and R beta. PDGF-AB binds to alpha receptor homodimers as well as the heterodimeric receptor. PDGF-AA and -AB promote cell proliferation, cell survival, cytoskeletal rearrangement, cell migration and extracellular matrix production. They are important for the development of oligodendrocytes, testicular Leydig cells, alveolar smooth muscle cells, hair follicles, and intestinal villus.