Leukocyte transendothelial migration (TEM) is a critical event during inflammation. CD47 has been implicated in myeloid cell migration across endothelium and epithelium. CD47 binds to signal regulatory protein (SIRP), SIRPalpha and SIRPgamma. So far, little is known about the role of endothelial CD47 in T-cell TEM in vivo or under flow conditions in vitro. Fluorescence-activated cell sorting and biochemical analysis show that CD3(+) T cells express SIRPgamma but not SIRPalpha, and fluorescence microscopy showed that CD47 was enriched at endothelial junctions. These expression patterns suggested that CD47 plays a role in T-cell TEM through binding interactions with SIRPgamma. We tested, therefore, whether CD47-SIRPgamma interactions affect T-cell transmigration using blocking mAb against CD47 or SIRPgamma in an in vitro flow model. These antibodies inhibited T-cell TEM by 70% plus or minus 6% and 82% plus or minus 1%, respectively, but had no effect on adhesion. In agreement with human mAb studies, transmigration of murine wild-type T helper type 1 cells across TNF-alpha-activated murine CD47(-/-) endothelium was reduced by 75% plus or minus 2% even though murine T cells appear to lack SIRPgamma. Nonetheless, these findings suggest endothelial cell CD47 interacting with T-cell ligands, such as SIRPgamma, play an important role in T-cell transendothelial migration.
