Platelet-derived growth factor-B (PDGF-B) is a cytokine that can form disulfide-linked homodimers or heterodimers with PDGF-A. 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 and the heterodimeric receptor, while PDGF-BB additionally binds to beta receptor homodimers. 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.