Calcitonin expression of high endothelial venules during lymphocyte migration in human pharyngeal tonsil

The migration routes of lymphocytes through high endothelial venules (HEVs) of control and hypertrophic pharyngeal tonsil (HPT) tissue sections were investigated by immunohistochemistry using the expression of a hormone [calcitonin (CT)] and two calcium-dependent endothelial adhesion molecules (E-selectin and P-selectin), as well as electron microscopy. A marked increase in CT-specific staining was observed in the endothelial cells of HEV in the HPT group compared to the control group. Expressions of E-selectin and P-selectin on HEVs of control group were faint, when compared to the strong expression of these selectins on HEVs of HPT. Electron microscopically, we demonstrated that lymphocytes transmigrated through HEV and observed the close membranous contact between endothelial cells and lymphocytes during this process. We speculate that increasing CT during inflammation may be important for lymphocyte migration through the HEVs via controlling the expression of E-selectin and P-selectin.     

Adhesion to high endothelial venules: a model for dissemination mechanisms in non-Hodgkin's lymphoma

The interaction of human lymphoma cells with high endothelial venules (HEVs) on sections of lymphatic tissues was studied in 44 cases of non- Hodgkin's lymphoma (NHL) with the in vitro HEV binding assay. The relative adherence ratio (RAR) of lymphoma cells to HEVs as related to that of reactive lymphocytes was 0.29 to 4.64 in 38 cases of B chronic lymphocytic leukemia (CLL), 1.15 and 1.54 in two cases of immunocytic NHL, 1.12 and 0.70 in two cases of centrocytic NHL, 1.98 in one case of a peripheral T-NHL, whereas plasma cell leukemia cells adhered very weakly (RAR 0.1). Among the patients suffering from CLL a pronounced HEV binding ability of tumor cells correlated significantly with the more unfavorable Binet stages B and C (median 1.32) as well as with a widespread lymphatic dissemination, which strongly indicates a hematogenous, HEV-mediated spread (median 1.34). In contrast, weak adherence to HEVs was associated with Binet stage A (median 0.85; P < .05) and with a lacking or only localized clinical involvement of lymph nodes (median 0.84; P < .01). Thus, specific HEV recognition processes even operate in lymphoid neoplasms and via this mechanism seem to influence the dissemination of tumors.     

Dendritic cells and high endothelial venules in the rheumatoid synovial membrane

Since dendritic cells are believed to play a crucial role in the pathogenesis of rheumatoid arthritis (RA) we studied the microenvironmental relationship of these cells with endothelial cells, lymphocytes and macrophages in the rheumatoid synovial membrane. With the monoclonal antibodies OKIa (MHC Class II determinants), RFD1 and L25 (both specific for "active" human dendritic cells) we identified large numbers of dendritic cells. With the monoclonal antibody HECA 452 [specific for a putative adhesion molecule notably present on high endothelial venules (HEV)], a subset of dendritic cells could be detected. HECA-452 positive dendritic cells were found in 2 basic patterns: (1) associated with small lymphoid cell clusters in the neighborhood of vessels with flat, HECA-452 negative endothelium, (2) at the periphery of dense organoid lymphoid infiltrates, surrounding HECA-452 positive HEV-like vessels. Our data suggest that the influx of HECA-452, L25, RFD1 and MHC Class II positive dendritic cells is an early event in the development of the inflammatory infiltrate found in the rheumatoid synovial membrane. The formation of organoid lymphoplasmacellular infiltrates with high endothelial venules would be secondary to this event.     

Antigen-induced changes on high endothelial venules in rat cervical lymph nodes

The effect of antigenic stimulation (paratyphoid vaccine) on high endothelial venules (HEVs) of rat cervical lymph nodes was studied using conventional histological and histometrical techniques. The sequential changes of some morphometric parameters (lymph node weight, HEV diameters) after the antigenic stimulation were studied in rat cervical lymph nodes over a period of five days with daily measurements. Measurements were made on the HEVs in the paracortex especially near the corticomedullary junction. HEVs diameters began to increase two days after the antigenic stimulation (p<0.001) and erythrocytes were increased in the lumen of the HEVs. On day four, most of the lymphocytes were detected between the endothelial cells of the HEVs (p<0.001). On day five, not only HEVs were increased in number but also endothelial cells were increased in height (p<0.001). The weight of the lymph nodes was also highest on this day. The changes of HEVs determined after antigenic stimulation suggest that these specialized vessels have an important regulatory role in the primary immune response.     

High endothelial venules as traffic control points maintaining lymphocyte population homeostasis in lymph nodes

Millions of lymphocytes enter and exit mammal lymph nodes (LNs) each day, accessing the parenchyma via high endothelial venules (HEVs) and egressing via lymphatics. Despite this high rate of cellular flux and the many entry and exit sites within a given LN, the number of lymphocytes present in a resting LN is extraordinary stable over time, raising the question of how this steady-state is maintained. Here we have examined the anatomic details of lymphocyte movement in HEVs, finding that HEVs create pockets within which lymphocytes reside for several minutes before entering the LN proper. The function of these pockets was revealed in experiments performed under conditions in which lymphocyte egress from the LN was compromised by any of several approaches. Under such conditions, the HEVs pockets behaved as "waiting areas" in which lymphocytes were held until space was made available to them for entry into the parenchyma. Thus, rather than being simple entry ports, HEVs act as gatekeepers able to stack, hold and grant lymphocytes access to LN parenchyma in proportion to the rate of lymphocyte egress from the LN, enabling the LN to maintain a constant steady-state cellularity while supporting the extensive cellular trafficking necessary for repertoire scanning.     

CXCL13 is an arrest chemokine for B cells in high endothelial venules

Chemokine receptor signaling is critical for lymphocyte trafficking across high endothelial venules (HEVs), but the exact mode of action of individual chemokines expressed in the HEVs is unclear. Here we report that CXCL13, expressed in a substantial proportion of HEVs in both lymph nodes (LNs) and Peyer patches (PPs), serves as an arrest chemokine for B cells. Whole-mount analysis of mesenteric LNs (MLNs) showed that, unlike T cells, B cellsa dhere poorly to the HEVs of CXCL13-/- mice and that B-cell adhesion is substantially restored in CXCL13-/- HEVs when CXCL13 is added to the MLNs by superfusion, as we have previously observed in PP HEVs by intravital microscopy. In vitro, CXCL13 activated the small guanosine triphosphatase (GTPase) Rap1 in B cells, and corroborating this observation, a deficiency of RAPL, the Rap1 effector molecule, caused a significant reduction in shear-resistant B-cell adhesion to intercellular adhesion molecule 1 (ICAM-1). In addition, CXCL13 induced B-cell adhesion to mucosal addressin cell adhesion molecule 1 (MAdCAM-1) by activating alpha4 integrin. These data identify CXCL13 as an arrest chemokine for B cells in HEVs and show that CXCL13 plays an important role in B-cell entry into not only PPs but also MLNs.     

LYVE-1 expression on high endothelial venules (HEVs) of lymph nodes

LYVE-1 (lymphatic endothelium hyaluronan receptor) has been identified as a powerful marker for lymphatic endothelium. Apart from lymphatic endothelium, LYVE-1 is expressed in normal liver blood sinusoids, spleen endothelium and activated tissue macrophages. LYVE-1 has not been detected in blood vascular endothelium with the exception of blood vessels in the lung. High endothelial venules (HEVs) belong to the vascular compartment of lymph nodes. They are the major site of entry for circulating lymphocytes into the node. HEVs are characterized by cuboidal endothelial cells, the existence of discontinuous junctions between these endothelial cells, and the presence of large numbers of lymphocytes within their walls. 40 paraffin-embedded lymph node biopsy specimens from newly diagnosed patients with non-Hodgkin lymphoma were evaluated as well as 10 lymph node biopsy specimens from adult patients with reactive lymphadenitis, and 10 normal, non-metastatic lymph nodes obtained from adult patients during cancer surgery served as controls. Samples were fixed in 10% buffered formalin, paraffin embedded, and stained with hematoxylin and eosin for histopathological evaluation. Sections were also evaluated with mouse monoclonal antibodies against LYVE-1 and CD34, and expression of both LYVE-1 and CD34 was demonstrated in HEVs. LYVE-1 expression was also found on the endothelial cells of the lymphatic sinus and in reticular cells in the lymph nodes.     

Adhesion of rheumatoid peripheral blood and synovial fluid mononuclear cells to high endothelial venules of gut mucosa.

Mononuclear cells isolated from paired blood and synovial fluid of seven patients with rheumatoid arthritis showed cytoadherence to porcine Peyer's patch high endothelial venules using the Stamper-Woodruff method. A significantly greater proportion of binding was found among the synovial fluid lymphocytes. These would appear to be a population of cells that share adherence characteristics with cells known to be of gut mucosal origin, suggesting that in rheumatoid arthritis some lymphocytes derived from mucosa migrate to joints.     

Transendothelial migration of lymphocytes across high endothelial venules into lymph nodes is affected by metalloproteinases

The migration of lymphocytes from the bloodstream into lymph nodes (LNs) via high endothelial venules (HEVs) is a prerequisite for the detection of processed antigen on mature dendritic cells and the initiation of immune responses. The capture and arrest of lymphocytes from flowing blood is mediated by the multistep adhesion cascade, but the mechanisms that lymphocytes use to penetrate the endothelial lining and the basement membrane of HEVs are poorly understood. Matrix metalloproteinases (MMPs) control the metastatic spread of tumor cells by regulating the penetration blood vessel basement membranes. In this study, synthetic and natural inhibitors were used to determine the role of MMPs and MMP-related enzymes in regulating lymphocyte extravasation in mice. Mice were treated systemically with the hydroxamate-based MMP inhibitor Ro 31-9790 and plasma monitored for effective levels of Ro 31-9790, which block shedding of L-selectin. The total numbers of lymphocytes recruited into LNs were not altered, but L-selectin levels were higher in mice treated with Ro 31-9790. A reduced number of lymphocytes completed diapedesis and there was an increase in the number of lymphocytes in the endothelial cell lining, rather than the lumen or the basement membrane of HEVs. Lymphocyte migration and L-selectin expression in the spleen were not altered by Ro 31-9790 treatment. Two MMP inhibitors, TIMP1 and Ro 32-1541, did not block L-selectin shedding and had no effect on lymphocyte migration across HEVs. These results suggest that metalloproteinase activity is required for lymphocyte transmigration across HEVs into LNs and provide evidence for the concept that metalloproteinases are important players in some forms of transendothelial migration. (Blood. 2001;98:688-695)     

Interferon-gamma regulates an antigen specific for endothelial cells involved in lymphocyte traffic.

One of the most striking examples of localized vascular differentiation is exhibited by specialized lymphoid organ venules that mediate the extravasation of circulating lymphocytes from the blood. These vessels are characterized by cuboidal or "high" endothelial cell morphology and are unique in their functional capacity to interact with migrating lymphocytes, regulating both the rate and specificity of lymphocyte traffic through particular regions of the body. We describe here a monoclonal antibody, MECA-325, that defines an endothelial cell differentiation antigen selectively expressed on high endothelium in the mouse. Thus an antigen defining a specific functional subset of endothelial cells has been found. Furthermore, we demonstrate that the MECA-325 antigen can be induced in mouse lung or bone marrow-derived endothelial cell lines in vitro by interferon-gamma but not by interferon-beta, interleukin-1, or endothelial cell mitogens. The results define a unique marker associated with differentiated endothelial cells mediating lymphocyte traffic from the blood, and they provide evidence that the specialized phenotype of these high endothelial cells may be induced and controlled by local factors associated with immune activity.     

Preferential binding of leukocytes to the endothelial junction region in venules in situ

OBJECTIVE: To determine whether leukocytes show a preference to firmly adhere to the endothelium near the endothelial cell (EC) junction in their native environment, i.e., blood-perfused venules in situ. METHODS: Intravital confocal microscopy was used to determine the positions of firmly adherent leukocytes with respect to EC junctions in cremaster muscle venules in anesthetized mice. EC area and EC junction locations were identified using immunofluorescent labeling of platelet-endothelial cell adhesion molecule-1 (PECAM-1), an endothelial junction protein. Leukocytes were identified using transillumination through the same optical path. RESULTS: Seventy-five percent of firmly adherent leukocytes overlapped an EC junction (the average distance to the nearest EC junction was 2.4 +/- 0.1 micro m, n = 263). This distance was less in smaller diameter venules, hence the percentage of adherent leukocytes that overlapped an endothelial junction was larger. EC shape and size varied with venular diameter: in smaller venules (30-49 micro m diameter), ECs had significantly less area (316 +/- 19 micro m(2)) and were narrower (12.5 +/- 0.4 micro m) than in larger (70-89 micro m diameter) venules, which had 614 +/- 28 micro m(2) area and 17.8 +/- 0.5 micro m width, respectively (p < .001). Furthermore, the majority (73.0%) of firmly adherent leukocytes crawled an average distance of 29.4 +/- 2.8 micro m at a mean intralumenal migration velocity of 7.6 +/- 0.4 micro m/min before undergoing transmigration or detaching and reentering the free fluid stream. CONCLUSIONS: Most adherent leukocytes in blood-perfused venules are located at or near EC junctions. This is primarily due to the size and shape of venular ECs. Further, most leukocytes that appear to be adherent are in fact motile, and migrate a significant distance along the lumenal wall. The authors speculate that this reflects movement to those EC junctional regions that support transendothelial migration.     

Transgenic LacZ under control of Hec-6st regulatory sequences recapitulates endogenous gene expression on high endothelial venules

Hec-6st is a highly specific high endothelial venule (HEV) gene that is crucial for regulating lymphocyte homing to lymph nodes (LN). The enzyme is also expressed in HEV-like vessels in tertiary lymphoid organs that form in chronic inflammation in autoimmunity, graft rejection, and microbial infection. Understanding the molecular nature of Hec-6st regulation is crucial for elucidating its function in development and disease. However, studies of HEV are limited because of the difficulties in isolating and maintaining the unique characteristics of these vessels in vitro. The novel pClasper yeast homologous recombination technique was used to isolate from a BAC clone a 60-kb DNA fragment that included the Hec-6st (Chst4) gene with flanking sequences. Transgenic mice were generated with the beta-galactosidase (LacZ) reporter gene inserted in-frame in the exon II of Hec-6st within the isolated BAC DNA fragment. LacZ was expressed specifically on HEV in LN, as indicated by its colocalization with peripheral node vascular addressin. LacZ was increased in nasal-associated lymphoid tissue during development and was reduced in LN and nasal-associated lymphoid tissue by LTbetaR-Ig (lymphotoxin-beta receptor human Ig fusion protein) treatment in a manner identical to the endogenous gene. The transgene was expressed at high levels in lymphoid accumulations with characteristics of tertiary lymphoid organs in the salivary glands of aged mice. Thus, the Hec-6s-LacZ construct faithfully reproduces Hec-6st tissue-specific expression and can be used in further studies to drive expression of reporter or effector genes, which could visualize or inhibit HEV in autoimmunity.     

A chemokine expressed in lymphoid high endothelial venules promotes the adhesion and chemotaxis of naive T lymphocytes

Preferential homing of naive lymphocytes to secondary lymphoid organs is thought to involve the action of chemokines, yet no chemokine has been shown to have either the expression pattern or the activities required to mediate this process. Here we show that a chemokine represented in the EST database, secondary lymphoid-tissue chemokine (SLC), is expressed in the high endothelial venules of lymph nodes and Peyer’s patches, in the T cell areas of spleen, lymph nodes, and Peyer’s patches, and in the lymphatic endothelium of multiple organs. SLC is a highly efficacious chemoattractant for lymphocytes with preferential activity toward naive T cells. Moreover, SLC induces firm adhesion of naive T lymphocytes via β2 integrin binding to the counter receptor, intercellular adhesion molecule-1, a necessary step for lymphocyte recruitment. SLC is the first chemokine demonstrated to have the characteristics required to mediate homing of lymphocytes to secondary lymphoid organs. In addition, the expression of SLC in lymphatic endothelium suggests that the migration of lymphocytes from tissues into efferent lymphatics may be an active process mediated by this molecule.     

Ribophorin I regulates substrate delivery to the oligosaccharyltransferase core

Protein N-glycosylation is widespread among biological systems, and the fundamental process of transferring a lipid-linked glycan to suitable asparagine residues of newly synthesized proteins occurs in both prokaryotes and eukaryotes. The core reaction is mediated by Stt3p family members, and in many organisms this component alone is sufficient to constitute the so called oligosaccharyltransferase (OST). However, eukaryotes typically have a more elaborate OST with several additional subunits of poorly defined function. In the mammalian OST complex one such subunit, ribophorin I, is proposed to facilitate the N-glycosylation of certain precursors during their biogenesis at the endoplasmic reticulum. Here, we use cell culture models to show that ribophorin I depletion results in substrate-specific defects in N-glycosylation, clearly establishing a defined physiological role for ribophorin I. To address the molecular mechanism of ribophorin I function, a cross-linking approach was used to explore the environment of nascent glycoproteins during the N-glycosylation reaction. We show for the first time that ribophorin I can regulate the delivery of precursor proteins to the OST complex by capturing substrates and presenting them to the catalytic core.     

In vitro analysis of the homing properties of human lymphocytes: developmental regulation of functional receptors for high endothelial venules

Circulating lymphocytes leave the blood by binding to specialized high endothelial cells lining postcapillary venules in lymphoid organs or sites of chronic inflammations, migrating through the vessel wall into the surrounding tissue. The capacity of lymphocytes to recognize and bind to high endothelial venules (HEVs) is thus central to the overall process of lymphocyte traffic and recirculation. We show that viable human lymphocytes bind selectively to HEVs in frozen sections of normal human lymph nodes, thus defining a simple in vitro model for the study of human lymphocyte homing properties. Optimal conditions for the quantitative analysis of lymphocyte-HEV interaction are described. Furthermore, by using this assay, we demonstrate that the ability of human lymphocyte populations to bind to HEVs parallels their presumed migratory status in vivo. Thus, thymocytes and bone marrow cells, which are sessile in vivo, bind poorly to HEVs in comparison with mature circulating lymphocytes in peripheral blood or in peripheral lymphoid tissues. These results indicate that HEV-binding ability is a regulated property of mature lymphocytes and, as demonstrated previously in animal models, probably plays a fundamental role in controlling lymphocyte traffic in humans. The in vitro model of lymphocyte-HEV interaction thus provides a unique means to assay the migratory properties of normal and neoplastic human lymphocyte subsets, to analyze the role of lymphocyte traffic mechanisms in normal and pathologic inflammatory reactions, and to define some of the molecular mechanisms responsible for the control of lymphocyte migration and positioning in humans.     

Magnetofection potentiates gene delivery to cultured endothelial cells

Modification of cellular functions by overexpression of genes is increasingly practised for research of signalling pathways, but restricted by limitations of low efficiency. We investigated whether the novel technique of magnetofection (MF) could enhance gene transfer to cultured primary endothelial cells. MF of human umbilical vein endothelial cells (HUVEC) increased transfection efficiency of a luciferase reporter gene up to 360-fold compared to various conventional transfection systems. In contrast, there was only an up to 1.6-fold increase in toxicity caused by MF suggesting that the advantages of MF outbalanced the increase in toxicity. MF efficiently increased transfection efficiency using several commercially available cationic lipid transfection reagents and polyethyleneimine (PEI). Using PEI, even confluent HUVEC could be efficiently transfected to express luciferase activity. Using a green fluorescent protein vector maximum percentages of transfected cells amounted up to 38.7% while PEI without MF resulted in only 1.3% transfected cells. Likewise, in porcine aortic endothelial cells MF increased expression of a luciferase or a beta-galactosidase reporter, reaching an efficiency of 37.5% of cells. MF is an effective tool for pDNA transfection of endothelial cells allowing high efficiencies. It may be of great use for investigating protein function in cell culture experiments.     

Disparate lymphoid chemokine expression in mice and men: no evidence of CCL21 synthesis by human high endothelial venules

T-cell homing to secondary lymphoid tissues generally depends on chemokine-induced firm adhesion in high endothelial venules (HEVs) and is primarily mediated through the CC chemokine receptor 7 (CCR7) on lymphocytes. The CCR7 ligand designated CCL21 is considered the most important trigger because it appears constitutively expressed by murine HEVs. Surprisingly, when we analyzed human tissues, no CCL21 mRNA could be detected in HEVs. In fact, CCL21 mRNA was only expressed in extravascular T-zone cells and lymphatics, whereas immunostaining revealed CCL21 protein within HEVs. This suggests that T-cell recruitment to human lymphoid tissues depends on the transcytosis of lymphoid chemokines through HEV cells because there is at present no evidence of alternative chemokine production in these cells that could explain the attraction of naive T lymphocytes.     

A developmental switch in lymphocyte homing receptor and endothelial vascular addressin expression regulates lymphocyte homing and permits CD4+ CD3- cells to colonize lymph nodes.

IN adult mice, the dominant adhesion molecules involved in homing to lymph nodes are L-selectin homing receptors on lymphocytes and the peripheral lymph node addressins on specialized high endothelial venules. Here we show that, from fetal life through the first 24 hr of life, the dominant adhesion molecules are the mucosal addressin MAdCAM-1 on lymph node high endothelial venules and its counterreceptor, the Peyer's patch homing receptor, integrin alpha 4 beta 7 on circulating cells. Before birth, 40-70% of peripheral blood leukocytes are L-selectin-positive, while only 1-2% expresses alpha 4 beta 7. However, the fetal lymph nodes preferentially attract alpha 4 beta 7-expressing cells, and this can be blocked by fetal administration of anti-MAdCAM-1 antibodies. During fetal and early neonatal life, when only MAdCAM-1 is expressed on high endothelial venules, an unusual subset of CD4 + CD3- cells, exclusively expressing alpha 4 beta 7 as homing receptors, enters the lymph nodes. Beginning 24 hr after birth a developmental switch occurs, and the peripheral node addressins are upregulated on high endothelial venules in peripheral and mesenteric lymph nodes. This switch in addressin expression facilitates tissue-selective lymphocyte migration and mediates a sequential entry of different cell populations into the lymph nodes.