• Overview
• Leukocyte Transmigration
• JAMs
• Selectins
• Integrins
• VLA-4/VCAM-1
• LFA-1/ICAM-1

Adhesion Molecules of Leukocyte Trafficking

Prior to transmigration of leukocytes across the vascular endothelium into the subendoethelial space, certain cell adhesion events must take place. Two families of cell adhesion molecules are involved in promoting monocyte adhesion and trafficking: selectins and integrins. Selectins and integrins have different roles in monocyte trafficking. P selectin mediates the initial attachment of circulating monocytes to the endothelium. The shear flow of the bloodstream causes the captured monocyte to roll along the vascular wall in a continuous cycle of adhesion with receptor-ligand pair breakage on the upstream portion of the monocyte, followed by forward pushing of the cell, and finally the formation of new binding pairs on the downstream surface. This rolling process is mediated by the interactions of the P selectin/PSGL 1 complex and of the VLA 4/VCAM 1 complex. Following activation by chemokines, the leukocytes adhere firmly to the endothelial cell via integrin-mediated adhesion (e.g., VLA-4/VCAM-1 and LFA-1/ICAM-1). The tightly adherent cell subsequently migrates to the transendothelial junctions, where transmigration of the leukocytes takes place.