The PDGF family is comprised of five different disulphide-linked dimers of four different polypeptide chains: A, B, C and D (PDGF-AA, PDGF-BB, PDGF-AB, PDGF-CC and PDGF-DD). Synthesized mainly by megakaryocytes, PDGFs are stored in the alpha granules of platelets from which they are released following platelet activation. Functioning as an autocrine and paracrine growth factor, PDGFs are involved in a number of biological processes that include but not limited to hyperplasia, chemotaxis, embryonic neuron development, wound healing and respiratory tubule epithelial cell development. Aberrant expression of PDGFs is observed with vascular proliferative diseases such as atherosclerosis. PDGFs regulate the synthesis of their own receptor and also influence the expression of membrane receptors for IL1, EGF, 5-Hydroxytryptamine, LDL and transferrin. Recombinant human PDGFB is a disulfide-linked homodimer of two B chains.