Differential requirements for Core2 glucosaminyltransferase for endothelial L-selectin ligand function in vivo

L-selectin is a calcium-dependent lectin on leukocytes mediating leukocyte rolling in high endothelial venules and inflamed microvessels. Many selecti n ligands require modification of glycoproteins by leukocyte core2 beta1,6- N-acetylglucosaminyltransferase (Core2GlcNAcT-I). To test the role of Core2 GlcNAcT-I for L-selectin ligand biosynthesis, we investigated leukocyte rol ling in venules of untreated and TNF-alpha -treated cremaster muscles and i n Peyer's patch high endothelial venules (HEV) of Core2GlcNAcT-I null (core 2(-/-)) mice. In the presence of blocking mAbs against P- and E-selectin, L -selectin-mediated leukocyte rolling was almost completely abolished in cre master muscle venules of core2(-/-) mice, but not littermate control mice. By contrast, leukocyte rolling in Peyer's patch HEV was not significantly d ifferent between core2(-/-) and control mice. To probe L-selectin ligands m ore directly, we injected L-selectin-coated beads. These beads showed no ro lling in cremaster muscle venules of core2(-/-) mice, but significant rolli ng in controls. In Peyer's patch HEV, beads coated with a low concentration of L-selectin showed reduced rolling in core2(-/-) mice. Beads coated with a 10-fold higher concentration of L-selectin rolled equivalently in core2( -/-) and control mice. Our data show that endothelial L-selectin ligands re levant for rolling in inflamed microvessels of the cremaster muscle are com pletely Core2GlcNAcT-I dependent. In contrast, L-selectin ligands in Peyer' s patch HEV are only marginally affected by the absence of Core2GlcNAcT-1, but are sufficiently functional to support L-selectin-dependent leukocyte r olling in Core2GlcNAcT-I-deficient mice.