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Original Article

^a The Center for Blood Research, Department of Pathology,
^b Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115
^c Department of Medicine, Mount Sinai School of Medicine, New York, New York 10029
^d Institute of Cell Biology, Zentrum für die Molekularbiologie der Entzündung,
^e Department of Anaesthesiology and Intensive Care Medicine, University of Münster, D-48149 Münster, Germany
Mount Sinai School of Medicine, Department of Medicine, One Gustave L. Levy Pl., Box 1079, New York, NY 10029.212-849-2574212-659-9693

paul.frenette{at}mssm.edu

The platelet plays a pivotal role in maintaining vascular integrity. In a manner similar to leukocytes, platelets interact with selectins expressed on activated endothelium. P-selectin glycoprotein ligand 1 (PSGL-1) is the main P-selectin ligand expressed on leukocytes. Searching for platelet ligand(s), we used a P-selectin–immunoglobulin G (IgG) chimera to affinity purify surface-biotinylated proteins from platelet lysates. P-selectin–bound ligands were eluted with ethylenediaminetetraacetic acid. An 210-kD biotinylated protein was isolated from both human neutrophil and platelet preparations. A band of the same size was also immunopurified from human platelets using a monoclonal anti–human PSGL-1 antibody and could be blotted with P-selectin–IgG. Under reducing conditions, both the predicted PSGL-1 210-kD dimer and the 120-kD monomer were isolated from platelets. Comparative immunoelectron microscopy and Western blotting experiments suggested that platelet PSGL-1 expression is 25–100-fold lower than that of leukocytes. However, patients with chronic idiopathic thrombocytopenic purpura who harbor predominantly young platelets displayed greater expression, indicating that PSGL-1 expression may be decreased during platelet aging. By flow cytometry, thrombin-activated platelets from normal individuals exhibited greater expression than those unstimulated. An inhibitory anti–PSGL-1 antibody significantly reduced platelet rolling in mesenteric venules, as observed by intravital microscopy. Our results indicate that functional PSGL-1 is expressed on platelets, and suggest an additional mechanism by which selectins and their ligands participate in inflammatory and/or hemostatic responses.

Key Words: P-selectin • endothelium • hemostasis • inflammation • adhesion

Abbreviations used in this paper: ACD, acid citrate dextrose; FucT, fucosyltransferase; GPIb, glycoprotein Ib; HRP, horseradish peroxidase; ITP, idiopathic thrombocytopenic purpura; PBS/BSA, PBS containing 1% BSA; PGE1, prostaglandin E1; PRP, platelet-rich plasma; PSGL-1, P-selectin glycoprotein ligand 1; RT, room temperature; V_crit, critical velocity; vWf, von Willebrand factor.

© 2000 The Rockefeller University Press

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