Differential regulation of transendothelial migration of THP-1 cells by ICAM-1/LFA-1 and VCAM-1/VLA-4.

The adhesion molecules intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) expressed in atherogenic lesions are thought to regulate monocyte diapedesis. To better understand their specific roles we used function-blocking antibodies and examined in a culture model the morphology, motility, and diapedesis of THP-1 cells interacting with human coronary artery endothelial cells. The number of motile THP-1 cells was reduced only when VCAM-1 or both ICAM-1 and VCAM-1 were blocked. Blockade of ICAM-1 and VCAM-1, either separately or together, reduced to the same degree the distance that THP-1 cells traveled. Diapedesis was reduced only during the simultaneous blockade of both adhesion molecules. Blockade of either ICAM-1 or VCAM-1 inhibited pseudopodia formation, but ICAM-1 blockade induced the formation of filopodia. We suggest that the interactions of endothelial ICAM-1 and VCAM-1 with their ligands differentially regulate distinct steps of diapedesis by modulating the ratio of active and inactive forms of small GTPases such as Rho, Rac, and Cdc42.