CD47, also known as Integrin-Associated Protein (IAP) and OA3, is a ubiquitous transmembrane protein that binds to SIRP family members on macrophages, neutrophils, and T cells. These interactions prevent macrophage-mediated clearance of healthy CD47-expressing cells and promote immune cell transmigration across the vascular endothelium. CD47 associates in cis with Fas on T cells and enhances Fas-mediated apoptosis; its ligation promotes T cell anergy and dampens Th1 immune responses. CD47 also associates in cis with several Integrins which can positively or negatively modulate Integrin-mediated function. CD47 binding by Thrombospondin-1 inhibits the angiogenic and vasorelaxant effects of nitric oxide. On dendritic cells and myeloma cells, CD47 ligation by TSP-1 induces giant cell formation and osteoclast differentiation.