Polymorphonuclear leukocyte transverse migration induces rapid alterations in endothelial focal contacts

Abstract: Transmigrated polymorphonuclear leu-kocytes (PMNs) usually undergo subendothelial transverse migration before penetrating into inner tissue layers. Whether or how endothelial cells (ECs) respond to the PMN migrating underneath them is unknown. A tissue flow chamber was used to establish a fMLP gradient and to observe PMN transverse mi-gration along with its associated endothelial responses in culture (on a collagen gel) or in vascular tissues. Our results indicated that transversely migrating PMNs were in direct contact with the basal side of ECs. Contrasting to focal adhesion kinase (FAK) or proteins with phosphorylated tyrosine, paxillin disap-peared rapidly (<1 min) from endothelial focal con-tacts after encountering the leukocyte’s leading edge and soon rejoined them after the PMN had left. In addition, FAK moved away or became dephosphory-lated when PMNs remained at the same subendothe-lial location for longer than 10 min, leaving actin filaments apparently unaltered. Unlike PMN transen-dothelial migration, PMN transverse migration did not induce any detectable endothelial calcium signal-ing. Taken together, our findings indicated that PMN transverse migration interrupted endothelial-matrix interactions and induced rapid alterations in endo-thelial focal contact composition. J. Leukoc. Biol