MOBILIZING LIPOCORTIN-1 IN ADHERENT HUMAN-LEUKOCYTES DOWN-REGULATES THEIR TRANSMIGRATION

Polymorphonuclear leukocyte (PMN) migration into sites of inflammation is fundamental to the host defense response. Activation of endothelia l cells and PMNs increases the expression or activation of adhesion mo lecules, culminating in rolling and subsequent adherence of these cell s to the vascular wall(1,2). Further activation of adherent PMNs, poss ibly by endothelial cell ligands, leads, within a few minutes, to extr avasation itself. This process is not clearly understood, but adhesion molecules' or related proteins(4), as well as endogenous chemokines(5 ), may play an important role. The anti-inflammatory glucocorticoids d elay extravasation(6), which implies that an inhibitory regulatory sys tem exists. Resting PMNs contain abundant cytoplasmic lipocortin 1 (LC 1, also called annexin I)(7), and the activity profile of this protein (8-10) suggests that it could reduce PMN responsiveness. To investigat e this we have assessed neutrophil transmigration both in vivo and in vitro and examined the content and subcellular distribution of LC1 in PMNs by fluorescence-activated cell-sorting (FAGS) analysis, western b lotting and confocal microscopy. We report that LC1 is mobilized and e xternalized following PMN adhesion to endothelial monolayers in vitro or to venular endothelium in vivo and that the end point of this proce ss is a negative regulation of PMN transendothelial passage.