Cytokine-activated human endothelial monolayers support enhanced neutrophil transmigration via a mechanism involving both endothelial-leukocyte adhesion molecule-1 and intercellular adhesion molecule-1

rIL-1β treatment of cultured human endothelial cells (HEC) promotes polymorphonuclear leukocyte (PMN) adhesion and transmigration. Using in vitro quantitative monolayer adhesion and videomicroscopic transmigration assays, we have examined the contributions of endothelial-leukocyte adhesion molecule-1 (ELAM-1), intercellular adhesion molecule-1 (ICAM-1), and the leukocyte adhesion complex, CD11/CD18, to these processes. Maximal enhancement of PMN adhesion and transmigration were observed after 4 h of rIL-1β treatment, when surface expression of ELAM-1 had peaked and ICAM-1 was modestly increased. Blocking mAb directed to either ELAM-1 or ICAM-1 inhibited >90% of the up-regulated PMN transmigration. Blocking mAb directed to either CD11a/CD18 (LFA-1, a ICAM-1 counter-receptor), CD11b/CD18 (Mo-1), or CD18 (common β₂-integrin) also blocked >90% of PMN transmigration. At later time points (24 or 48 h), ELAM-1 surface expression was markedly decreased, whereas ICAM-1 expression was increased cver the 4-h level; PMN adhesion remained elevated (~50 to 60% of 4 h level), but transmigration returned to levels seen with unactivated HEC. These data indicate that PMN interaction with at least two distinct HEC adhesion molecules is necessary for transendothelial migration and suggests that PMN adhesion and transmigration, although interrelated, are mechanistically distinct processes.