Distinct Phenotype of E-Selectin–Deficient Mice: E-Selectin Is Required for Slow Leukocyte Rolling In Vivo

Abstract

Leukocyte capture and rolling are mediated by calcium-dependent lectins expressed on most leukocytes (L-selectin) and the vascular endothelium (P- and E-selectin). To study the role of the selectins during inflammation, we have investigated leukocyte rolling in venules of tumor necrosis factor-α (TNF-α)–treated mouse cremaster muscles in wild-type mice and gene-targeted mice with homozygous deficiency for L-, P-, or E-selectin (L−/−, P−/−, or E−/−, respectively). TNF-α treatment induces expression of E-selectin and increases expression of P-selectin on endothelial cells. Consistent with previous reports of redundant P- and E-selectin function, a combination of monoclonal antibodies (mAbs) against P- and E-selectin (RB40.34 and 9A9, respectively) was necessary to block rolling in wild-type mice. The rolling leukocyte flux fraction (percent rolling cells) in L−/− mice was similar to that in wild-type mice, but rolling in these mice was blocked by a P-selectin mAb. The velocity of rolling leukocytes in TNF-α–treated wild-type, P−/−, or L−/− mice was 5 to 10 times slower (3 to 7 μm/s) than during trauma-induced rolling (20 to 50 μm/s). In contrast, leukocytes in venules of TNF-α–treated E−/− mice rolled significantly faster (12 to 20 μm/s); the rolling leukocyte flux fraction was more than doubled compared with wild-type, L−/−, or P−/− mice; and the number of adherent leukocytes was reduced. Addition of an E-selectin mAb, but not a P-selectin mAb, increased rolling flux fraction and rolling velocity in wild-type mice. Histological analysis revealed that 90% to 95% of all leukocytes interacting (rolling and adherent) with the venular endothelium in TNF-α–treated wild-type, L−/−, P−/−, and E−/− mice were granulocytes. These results identify a previously unrecognized phenotype of E−/− mice by establishing that at the site densities prevailing in vivo, E-selectin is responsible for slow (≈5 μm/s) granulocyte rolling. E-selectin–dependent slow rolling drastically increases the transit time of leukocytes rolling through an inflamed tissue and thus aids in targeting leukocytes activated by chemoattractants to the inflammatory microenvironment.