Abstract
The phagocytosis of apoptotic cells within an organism is a critical terminal physiological process in programmed cell death. Evidence suggests that apoptotic cell engulfment and removal by macrophages is facilitated by phosphatidylserine (PS) displayed at the exofacial surface of the plasma membrane; however, neither the macrophage receptors responsible for PS recognition, nor characterization of the PS molecular species potentially involved, have been clearly defined. We show that the class B scavenger receptor CD36 plays an essential role in macrophage clearance of apoptotic cells in vivo. Further, macrophage recognition of apoptotic cells via CD36 is shown to occur via interactions with membrane-associated oxidized PS (oxPS) and, to a lesser extent, oxidized phosphatidylcholine, but not nonoxidized PS molecular species. Mass spectrometry analyses of oxPS species identify structures of candidate ligands for CD36 in apoptotic membranes that may facilitate macrophage recognition. Collectively, these results identify oxPS-CD36 interactions on macrophages as potential participants in a broad range of physiologic processes where macrophage-mediated engulfment of apoptotic cells is involved.