High Endothelial Venules Endothelial Cells Research Articles

Endocytic stripping of ligands from migrant lymphocytes in high endothelial venules (HEV): implications for immunomodulation vs viral pathogenesis.

“Grooming ” of membrane detritis from lymphocyte surfaces by mononuclear phagocytes during migration through lymphatic tissues was proposed as a cause of differences in the potency of comparable populations of lymphocytes to produce the normal lymphocyte transfer reaction (LTR) when equivalent numbers of T cells from blood, afferent lymph, and efferent lymph were injected SC1. Three- to five-fold greater LTR activity was found with efferent lymph cells compared to blood or afferent lymph cells. It is possible that these differences in reactivity were due to anti-idiotypic antibodies or other “blocking factors ” occupying lymphocyte receptors. Isotypic, allotypic and idiotypic immunoregulation occurs in mice, rats, rabbits, and man2•5. The present studies employ light and electron microscopy, cytochemistry and immunochemistry to analyze the endocytic potential of Lewis Rat HEV endothelium toward both particulates and toward autologous lymphocytes whose surfaces have been modified by liganding. Results indicate that HEV endothelial cells nonspecifically remove receptor-blocking proteins during blood to tissue transit.KeywordsAlcian BlueHigh Endothelial VenuleMigrate LymphocyteLymphocyte SurfaceThoracic Duct LymphThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Scanning electron microscope studies of the rat mesenteric lymph node with special reference to high-endothelial venules and hitherto unknown lymphatic labyrinth.

Mesenteric lymph nodes of the rat were studied by scanning electron microscopy after arterial perfusion fixation. Observation was made mainly of the high endothelial venules (HEVs), inner cortex and medulla. The HEVs were distributed not only in the inner cortex, but also in the interfollicular areas in the outer cortex, extending to closely beneath the marginal sinus. Various surface structures of the HEV endothelial cells were recorded, from quite smooth to densely granular. Special attention was paid to endothelial cells with cytoplasmic ridges concentrated at the center of the cell apex. Lymphocytes were numerously attached to the luminal surface of the HEV. Many lymphocytes presumably under and after emigration through the HEV wall could be recognized. Hitherto unknown labyrinths densely filled with lymphocytes were demonstrated in the inner cortex. These tubular and saccular spaces lined by attenuated cells originated from beneath the germinal centers and from around the HEVs to pour into the medullary sinuses. The lymphatic labyrinths were differentiated from the sinuses by their lack of reticular cell trabeculae and by their containing almost exclusively small lymphocytes. It was proposed that lymphocytes in the blood in HEVs massively emigrate to the labyrinth, and via the medullary sinuses, enter the efferent lymphatics of the lymph node. In the medullary sinuses, some lymphocytes in association with a macrophage were found to extend wing-like processes, probably reflecting their activation. Large free cells extending laminar projections, but smooth in surface otherwise, were occasionally found. Their possible identity with the veiled cells (KELLY et al., 1978) was considered.

Differences in the migration of B and T lymphocytes: organ-selective localization in vivo and the role of lymphocyte-endothelial cell recognition.

The migration of B and T lymphocytes in the mouse has been studied by using 1) short-term in vivo homing studies, and 2) an in vitro assay of lymphocyte binding to specialized lymphoid organ venules (post-capillary, high endothelial venules (HEV)) in frozen sections of lymph nodes and Peyer's patches. The homing characteristics of B and T cell populations are largely independent of their organ of origin. B cells from any source distribute preferentially to Peyer's patches, whereas T cells home preferentially to peripheral lymph nodes. This organ specificity of migration appears to be determined at the site of lymphocyte exit from the blood by selective recognition of organ-specific determinants on the endothelial cells of HEV. In addition, the in vivo tendency of B cells to migrate preferentially to the spleen, and of T cells to localize better in lymph nodes is confirmed. The results indicate that, in a hypothetical situation in which an equal number of B and T lymphocytes localized in peripheral lymph nodes (or bound in vitro to peripheral node HEV), there would be about 2.5 B cells for every T cell in the mesenteric node, four to six B cells per T cell in Peyer's patches, and seven to nine B cells per T cell in the spleen. Comparison of these homing preferences with the distribution of B and T lymphocyte populations in situ suggests that selective lymphocyte migration may help determine the proportions of functionally distinct lymphocyte classes in particular lymphoid organs or sites of chronic inflammation, and thus may serve to influence the character of local immune responses.