In vitro adhesion and migration of T lymphocytes across monolayers of human brain microvessel endothelial cells: Regulation by ICAM-1,VCAM-1, E-selectin and PECAM-1

Increased lymphocyte traffic across an altered blood-brain barrier (BBB) is a prominent and early event in inflammatory and immune-mediated CNS diseas es. The factors that control the entry of lymphocytes into the brain have n ot been fully elucidated. In this study, primary cultures of human brain mi crovessel endothelial cells (HBMEC) were used to investigate the role of en dothelial cell (EC) adhesion molecules in the adhesion and migration of per ipheral blood T lymphocytes across TNF-alpha treated and untreated monolaye rs. Adhesion of T cells to unstimulated HBMEC was minimal and few of the ad herent cells migrated across the monolayers. Treatment of HBMEC with TNF-al pha augmented adhesion by 5-fold. The binding to activated EC was significa ntly, but not completely, inhibited by monoclonal antibodies (mAbs) to ICAM -1 and VCAM-1, whereas adhesion to unstimulated EC was blocked by mAb to IC AM-1 but not VCAM-1. Transendothelial migration of lymphocytes increased by up to 30-fold following treatment of HBMEC with TNF-alpha. Migration acros s activated monolayers, but not across untreated EC, was almost completely blocked by Ab to ICAM-1 and significantly inhibited by Abs to PECAM-1 and E -selectin. VCAM-1 was not utilized during transendothelial migration. Ultra structurally, pseudopodia from lymphocytes contacted finger-like cytoplasmi c projections on EC and eventually penetrated the EC cytoplasm at focal poi nts along the apical surface. Migrating lymphocytes moved either through th e EC cytoplasm or between adjacent EC across intercellular contacts. The ov erlying monolayers showed no evidence of disruption and intercellular junct ions appeared intact over the migrated T cells. These studies indicate that adhesion and migration of T lymphocytes across the cerebral endothelial ba rrier are distinct processes that depend upon the activation state of EC an d are controlled by diverse receptor-ligand interactions.