Platelet-derived growth factor is a potent mitogen for cells of mesenchymal origin. Binding of this growth factor to its affinity receptor elicits a variety of cellular responses. It is released by platelets upon wounding and plays an important role in stimulating adjacent cells to grow and thereby heal the wound. [SUBUNIT] Antiparallel disulfide-linked dimer of nonidentical (A and B) chains. Homodimers of A and B chains are implicated in transformation processes. A-A and B-B, as well as A-B, dimers can bind to the PDGF receptor. Belongs to the PDGF/VEGF growth factor family.