Platelet-derived growth factors (PDGFs) are homo- or heterodimers of four polypeptides, known as A, B, C and D chains.? PDGF was initially discovered as a major mitogenic factor present in serum but absent from plasma. ?Five PDGF isoforms (AA, BB, AB, CC and DD) have been identified.? The dimeric isoforms of PDGFs are differentially expressed in various cell types and their effects are mediated through distinct dimeric receptors made up of two structurally similar protein-tyrosine kinase receptor subunits (αα-, αβ-, or ββ-PDGFR). ?PDGF-AA, AB, and BB dimers are processed intracellularly and secreted as active dimers that readily activate PDGF receptors. ?PDGF-CC and DD are secreted as full-length, latent dimers, and the proteolytic removal of a CUB domain is required for the growth factor domain of PDGF-CC or DD to activate the PDGF receptors. ?PDGFs are potent mitogens for connective tissue cells, including dermal fibroblasts, glial cells, arterial smooth muscle cells and some epithelial and endothelial cells. ?PDGFs usually act primarily in paracrine manner and may be engaged in autocrine loops in tumors.? In addition to its activity as a mitogen, PDGF is chemotactic for fibroblasts, smooth muscle cells, neutrophils and mononuclear cells. ? Marketing note: Growth factor that plays an essential role in the regulation of embryonic development, cell proliferation, cell migration, survival and chemotaxis.