Mice Lacking E- Selectin Show Normal Numbers of Rolling Leukocytes but Reduced Leukocyte Stable Arrest on Cytokine- Activated Microvascular Endothelium DAVID S. MILSTONE,* ,† DAI FUKUMURA, † RICHARD C. PADGETT,* ,‡ PETER E. O’DONNELL,* VANNESSA M. DAVIS,* OSCAR J. BENAVIDEZ,* WAYNE L. MONSKY, † ROBERT J. MELDER, † RAKESH K. JAIN, † AND MICHAEL A. GIMBRONE, JR.* *Vascular Research Division, Departments of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA † Steele Laboratory, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA ‡ Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, IA, USA ABSTRACT Objective: Previous work indicated that E-selectin mediates transient interac- tions between leukocytes and cytokine-activated endothelium in vitro. Here we examine the role of E-selectin in blood leukocyte interactions with microvascular endothelium in vivo. Methods: E-selectin-deficient (E -/- ) mice were produced by gene targeting. The effect of this null mutation on leukocyte–endothelial interactions was determined by intravital microscopy before and 4 to 5 hours after local administration of the proinflammatory cytokine tumor necrosis factor  (TNF) in dermal microvessels with low blood flow (dorsal skin-fold chambers, intact ear skin), and after endotoxin activation in exteriorized mesenteric microvessels with higher blood flow. Results: E -/- mice were viable, fertile with normal circulating leukocyte and platelet profiles. Approximately 60% of circulating leukocytes rolled in dermal microvessels of both normal (E +/+ ) and E -/- mice without inflammatory stimu- lation. After local administration of TNF, rolling increased modestly and equivalently in both genotypes. The main effect of TNF was a dramatic in- crease in leukocyte stable adhesion and, unlike rolling, this manifestation of endothelial activation was significantly reduced in E -/- animals. This reflected fewer dermal microvessels supporting higher adhesion densities in E -/- mice, and a similar trend was observed in mesenteric microvessels. Conclusions: E-selectin plays a previously unappreciated role in facilitating and/ or mediating stable adhesion of leukocytes to inflamed microvascular endothelium. KEY WORDS: E-selectin, inflammation, endothelium, leukocyte adhesion, tumor- necrosis factor , intravital microscopy Microcirculation (1998) 5, 153–171 © 1998 Stockton Press All rights reserved 1073-9688/98 $12.00 http:/ / www.stockton-press.co.uk