Polymorphonuclear leukocyte transverse migration induces rapid alterations in endothelial focal contacts.

Transmigrated polymorphonuclear leukocytes (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 migration 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 disappeared rapidly (<1 min) from endothelial focal contacts after encountering the leukocyte's leading edge and soon rejoined them after the PMN had left. In addition, FAK moved away or became dephosphorylated when PMNs remained at the same subendothelial location for longer than 10 min, leaving actin filaments apparently unaltered. Unlike PMN transendothelial migration, PMN transverse migration did not induce any detectable endothelial calcium signaling. Taken together, our findings indicated that PMN transverse migration interrupted endothelial-matrix interactions and induced rapid alterations in endothelial focal contact composition.