IMPORTANT CONTRIBUTIONS OF P-SELECTIN GLYCOPROTEIN LIGAND-1-MEDIATED SECONDARY CAPTURE TO HUMAN MONOCYTE ADHESION TO P-SELECTIN, E-SELECTIN, AND TNF-ALPHA-ACTIVATED ENDOTHELIUM UNDER FLOW IN-VITRO

In this study, an in vitro how model and a blocking mAb to P-selectin glycoprotein ligand-1 (PSGL-1) were used to define the role of PSGL-1 in monocyte attachment and rolling on E- and P-selectin and in attachm ent and accumulation on 6-h TNF-alpha-activated HUVEC, KPL1, an adhesi on-blocking mAb directed against the tyrosine sulfate motif of PSGL-1, abolished monocyte-adhesive interactions with P-selectin, but only pa rtially blocked monocyte interaction with E-selectin, Further analysis showed that on E-selectin, KPL1 blocked only secondary (i.e., monocyt e/monocyte) interactions, but did not block primary (i.e., monocyte/E- selectin) interactions, with secondary adhesion accounting for 90% of the total adhesive interactions on either E- or P-selectin. On cytokin e-activated HUVEC, monocytes initially attached and formed linear stri ngs of adherent cells, which involved both primary and secondary adhes ion. PSGL-1 or L-selectin mAb reduced string formation, and the combin ation of PSGL-1 and L-selectin mAb prevented monocyte strings and inhi bited 86% of accumulation, Monocyte attachment and rolling on purified adherent monocytes were also critically dependent on PSGL-1 on;the ad herent monocytes, These studies document that secondary interactions b etween monocytes, mediated by PSGL-1, are crucial for monocyte initial attachment, rolling, and accumulation on activated endothelium under laminar shear flow.