Differential movements of VE-cadherin and PECAM-1 during transmigration of polymorphonuclear leukocytes through human umbilical vein endothelium

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Abstract
Most existing evidence regarding junction protein movements during transendothelial migration of leukocytes comes from taking postfixation snap shots of the transendothelial migration process that happens on a cultured endothelial monolayer. In this study, we used junction protein–specific antibodies that did not interfere with the transendothelial migration to examine the real-time movements of vascular endothelial–cadherin (VE-cadherin) and platelet/endothelial cell adhesion molecule-1 (PECAM-1) during transmigration of polymorphonuclear leukocytes (PMNs) either through a cultured endothelial monolayer or through the endothelium of dissected human umbilical vein tissue. In either experimental model system, both junction proteins showed relative movements, not transient disappearance, at the PMN transmigration sites. VE-cadherin moved away to different ends of the transmigration site, whereas PECAM-1 opened to surround the periphery of a transmigrating PMN. Junction proteins usually moved back to their original positions when the PMN transmigration process was completed in less than 2 minutes. The relative positions of some junction proteins might rearrange to form a new interendothelial contour after PMNs had transmigrated through multicellular corners. Although transmigrated PMNs maintained good mobility, they only moved laterally underneath the vascular endothelium instead of deeply into the vascular tissue. In conclusion, our results obtained from using either cultured cells or vascular tissues showed that VE-cadherin–containing adherent junctions were relocated aside, not opened or disrupted, whereas PECAM-1–containing junctions were opened during PMN transendothelial migration.