Fig. 2. Mammalian PDGF/PDGFR binding interactions. The ability of different homo- and heterodimeric PDGF ligands to bind the different receptor dimers in vitro is shown. Arrows between ligands and receptors indicate the ability of a given ligand dimer to bind to and activate the designated receptor. PDGF dimers are represented by the letters of their constituent subunits, for example, AA is a PDGFA homodimer, and AB is a heterodimer of PDGFA and PDGFB.