Lymphocyte transcellular migration occurs through recruitment of endothelial ICAM-1 to caveola- and F-actin-rich domains.

During inflammation, leukocytes bind to the adhesion receptors ICAM-1 and VCAM-1 on the endothelial surface before undergoing transendothelial migration, also called diapedesis. ICAM-1 is also involved in transendothelial migration, independently of its role in adhesion, but the molecular basis of this function is poorly understood. Here we demonstrate that, following clustering, apical ICAM-1 translocated to caveolin-rich membrane domains close to the ends of actin stress fibres. In these F-actin-rich areas, ICAM-1 was internalized and transcytosed to the basal plasma membrane through caveolae. Human T-lymphocytes extended pseudopodia into endothelial cells in caveolin- and F-actin-enriched areas, induced local translocation of ICAM-1 and caveolin-1 to the endothelial basal membrane and transmigrated through transcellular passages formed by a ring of F-actin and caveolae. Reduction of caveolin-1 levels using RNA interference (RNAi) specifically decreased lymphocyte transcellular transmigration. We propose that the translocation of ICAM-1 to caveola- and F-actin-rich domains links the sequential steps of lymphocyte adhesion and transendothelial migration and facilitates lymphocyte migration through endothelial cells from capillaries into surrounding tissue.