Interaction between lymphocytes and cultured high endothelial cells: an in vitro model of lymphocyte migration across high endothelial venule endothelium.

The interaction between lymphocytes and cultured high endothelial venule endothelium has been studied using light and electron microscopy. High endothelial cells (HEC) in monolayer culture bound lymphocytes 15-200-fold more efficiently than aortic endothelium, aortic fibroblasts or serum-coated glass. Light microscopy of lymphocytes bound to HEC showed two populations. Type I lymphocytes were phase-light, round and revealed no intracellular detail. Type II lymphocytes were phase-dark and flattened. The nucleus and cytoplasm of type II cells were clearly visible under high power light microscopy. The relative positions of these two populations were determined by electron microscopy. Type I lymphocytes were attached to the surface of HEC and type II lymphocytes were flattened underneath. The transition from type I to type II was accompanied by a loss of surface microvilli and a redistribution of intracellular organelles. This suggested that lymphocytes actively migrated across the HEC layer in this assay. The relationship between migrated lymphocytes and total adherent cells was determined by analysis of surface phenotype. Lymphocytes did not adhere randomly from the cell population plated. After 60 min there was an enrichment for B over T lymphocytes and the adherent T cell population was itself enriched for CD8+ cells over CD4+ cells. Migrated cells were, however, a random subpopulation of lymphocytes which adhered to HEC. This is clear evidence that migration was preceded by specific binding to HEC. Lymphocyte adhesion was independent of viable HEC showing that it was a passive event on the part of the endothelium. Lymphocyte migration was, however, completely dependent on viable high endothelium. We conclude that cultured HEC provide a biologically relevant, 3-dimensional matrix which supports the specific adhesion of lymphocytes and actively promotes lymphocyte migration. These observations suggest to us that cultured high endothelium provides a novel in vitro model for the study of lymphocyte migration into lymph nodes from the blood.