CD47 plays a critical role in T-cell recruitment by regulation of LFA-1 and VLA-4 integrin adhesive functions

CD47 plays an important but incompletely understood role in the innate and adaptive immune responses. CD47, also called integrin-associated protein, has been demonstrated to associate in cis with beta 1 and beta 3 integrins. Here we test the hypothesis that CD47 regulates adhesive functions of T-cell alpha 4 beta 1 (VLA-4) and alpha L beta 2 (LFA-1) in in vivo and in vitro models of inflammation. Intravital microscopy studies reveal that CD47(-/-) Th1 cells exhibit reduced interactions with wild-type (WT) inflamed cremaster muscle microvessels. Similarly, murine CD47(-/-) Th1 cells, as compared with WT, showed defects in adhesion and transmigration across tumor necrosis factor-alpha (TNF-alpha)-activated murine endothelium and in adhesion to immobilized intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion protein 1 (VCAM-1) under flow conditions. Human Jurkat T-cells lacking CD47 also showed reduced adhesion to TNF-alpha-activated endothelium and ICAM-1 and VCAM-1. In cis interactions between Jurkat T-cell beta 2 integrins and CD47 were detected by fluorescence lifetime imaging microscopy. Unexpectedly, Jurkat CD47 null cells exhibited a striking defect in beta 1 and beta 2 integrin activation in response to Mn2+ or Mg2+/ethylene glycol tetraacetic acid treatment. Our results demonstrate that CD47 associates with beta 2 integrins and is necessary to induce high-affinity conformations of LFA-1 and VLA-4 that recognize their endothelial cell ligands and support leukocyte adhesion and transendothelial migration.