Platelet-Derived Growth Factor-AA (PDGF-AA) is one of five dimers (PDGF-AA, AB, BB, CC, and DD) formed by 4 different PDGF subunits. In chemical terms, platelet-derived growth factor is a dimeric glycoprotein composed of two A (-AA) or two B (-BB) chains or a combination of the two (-AB). The dimeric isoforms PDGF-AA, AB and BB are differentially expressed in various cell types, and their effects are mediated through two distinct receptors termed α and β. Differences exist in isoform binding to each receptor. Ingeneral, PDGF isoforms are potent mitogens for connective tissue cells including dermal fibroblasts, glial cells, arterial smooth muscle cells and some epithelial andendothelial cells. In addition to its activity as a mitogen, PDGF is chemotactic for fibroblasts, smooth muscle cells, neutrophils and mononuclear cells. PDGF-AA plays a significant role in blood vessel formation (angiogenesis).