Inhibition of endothelial cell retraction by ATP depletion.

To determine the relationship among endothelial cell (EC) retraction, cell adenosine triphosphate (ATP), and the status of cellular actin, ATP levels, F-actin content, and cytochemical redistribution in bovine pulmonary artery endothelial cells were assessed. EC monolayers 7 days after confluence were exposed to ethchlorvynol (ECV), histamine, or cytochalasin B (cyto B) for time intervals from 5-90 minutes. All 3 agents resulted in endothelial cell retraction without significant effect on cellular ATP content. Sixty-minute incubation of monolayers in glucose-free media containing antimycin A and 2-deoxyglucose depleted cellular ATP to less than 10% of control levels. ATP depleted monolayers failed to retract when incubated with ECV, histamine, or cyto B. ATP depletion resulted in loss of the prominent EC margins but only a rare gap between adjacent cells. When ATP levels were allowed to recover, the ability of EC monolayers to retract was restored. Actin filaments in control monolayers localized to a dense peripheral band of actin, a paranuclear complex, and bundles of microfilaments orientated parallel to the long axis of the cell. ECV induced complete loss of the dense peripheral band and other changes in the actin disposition. Monolayers exposed to histamine showed a retraction of the dense peripheral band of actin to a subcortical position. Cyto B caused loss of the dense peripheral band and the longitudinal microfilament bundles. Monolayers depleted of ATP lost their dense peripheral band and exhibited a disorganized, tangled web of microfilaments. Neither histamine nor ECV modified the actin distribution in ATP-depleted monolayers, whereas exposure to cyto B resulted in substantial change in actin with formation of a rim inside the cell membrane and considerable loss of actin filaments. ECV or histamine induced a small reduction in F-actin content while cyto B resulted in a 50% decline in 15 minutes. ATP depletion resulted in a 19% decrease in F-actin, with no further reduction on subsequent exposure to histamine or ECV. Cyto B treatment of ATP-depleted monolayers caused a drop in F-actin content equivalent to that observed in cells with normal ATP levels. These studies indicate that ATP is essential for changes in actin filament distribution and endothelial cell retraction produced by ECV, histamine or cyto B, and make it unlikely that any of these agents acts simply by depolymerization of actin filaments or modification of the dense peripheral band, although disruption of the dense peripheral band may facilitate retraction in the presence of adequate levels of cell ATP.     

Heterogeneous expression of cell adhesion molecules by endothelial cells in ARDS

ARDS (acute respiratory distress syndrome) can be associated with septic shock and multiple organ failure caused by an uncontrolled systemic inflammatory response to Gram-negative bacterial infection. While in animal models the key role of the endothelial adhesion molecules ICAM-1, E-selectin, and VCAM in ARDS has been extensively studied, there are scarcely any corresponding pathomorphological studies of human lung tissue. Hence, little is known about whether there is a comparable, or even heterogeneous, expression pattern of these molecules in the human pulmonary vasculature. This study was therefore undertaken to investigate the immunohistochemical expression of the constitutively expressed PECAM (CD31) and the inducible molecules ICAM-1, E-selectin, and VCAM in ARDS lungs from patients who had died in septic shock induced by Gram-negative bacteria. While in all specimens (ARDS and normal lungs) there was homogeneous strong expression of PECAM in all vessels, ICAM-1 was clearly up-regulated in ARDS lungs. E-selectin and VCAM were not expressed by endothelial cells (ECs) in normal lungs, but in ARDS lungs there was strong expression of both molecules in larger vessels, while in the capillaries there was only mosaic-like weak expression of a few ECs. This immunohistochemical investigation demonstrates the induction and up-regulation of adhesion molecules in human ARDS lungs, comparable to that described in animal models. There is also markedly heterogeneous expression of E-selectin and VCAM, indicating toporegional differences in the function of pulmonary ECs.     

Regulation of endothelial adhesion molecules by ligands binding to the scavenger receptor.

Monocyte adherence to the endothelium, their penetration to the subendothelial space and excessive lipid accumulation (foam cell formation) are the initial events in atherogenesis. Scavenger receptors have been reported to play an important role in foam cell formation, since modified low density lipoproteins can be taken up via scavenger receptors in a non-down-regulated fashion. In this study we demonstrate that stimulation of scavenger receptors in endothelial cells induces the expression of endothelial adhesion molecules. Polyinosinic acid (poly I), a known scavenger receptor ligand, significantly induced the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on human umbilical vein endothelial cells when compared with polycytidylic acid (poly C), a structurally related compound to poly I, which does not bind to the scavenger receptor. The effect of scavenger receptor ligands on the endothelial cell line EA hy. 926 was also tested. Poly I up-regulated ICAM-1 expression also on EA hy. 926 cells, while it had no effect on IL-1 beta or tumour necrosis factor-alpha (TNF-alpha) production on the same cell line. Poly I-induced ICAM-1 expression on EA hy. 926 cells could be inhibited by H7, a protein kinase C inhibitor, while HA 1004, a preferential protein kinase A inhibitor, had no effect on ICAM-1 expression. The role of protein kinase C in scavenger receptor-mediated adhesion molecule upregulation was confirmed by the ability of poly I to directly activate protein kinase C, when measured with 3H-phorbol dibutyrate binding to EA hy. 926 cells, while poly C again was ineffective.     

T-T cell interactions are mediated by adhesion molecules.

The mechanism by which T cells signal other T cells is not well defined. This was investigated by studying the ability of circulating T cells to induce the proliferation of autologous T cell clones. Peripheral blood T cells activated by cross-linking of the CD3/T cell receptor complex, which increased the expression of cell adhesion molecules LFA-1, LFA-3 and ICAM-1, induced the proliferation of autologous T cell clones. Irradiated antigen-activated peripheral blood T cells could also induce the proliferation of T cell clones which could not recognize that antigen. T-T cell activation required cell contact, was not major histocompatibility complex (MHC) restricted and was blocked by monoclonal antibodies directed against adhesion molecules CD2 and LFA-3 but was not blocked by antibody to class II MHC determinants. As CD2 is the natural ligand for LFA-3, increased expression of T cell surface adhesion molecules LFA-1, ICAM-1 and particularly LFA-3 during an inflammatory response may rapidly recruit T cells that are activated through the CD2 pathway. These results allow a simplified model to explain how relatively few antigen/MHC-specific T cells can recruit large numbers of non-antigen-specific T cells in the generation of an inflammatory response and postulates a novel role of the CD2 molecule in T cell immune function.     

Morphine attenuates endothelial cell adhesion molecules induced by the supernatant of LPS-stimulated colon cancer cells

A large reservoir of bacterial lipopolysaccharide (LPS) is available in the colon and this could promote colon cancer metastasis by enhancing tumor cell adhesion, intravasation, and extravasation. Furthermore, adhesion molecules like ICAM-1, VCAM-1, and E-selectin play important roles in the adhesion of tumor cells to endothelium. This study was designed to determine whether morphine can attenuate the expressions of adhesion molecules up-regulated by the supernatant of LPS-stimulated HCT 116 colon cancer cells (LPS-Sup). In this study, we divided to three groups by cell-growth medium of human umbilical vascular endothelial cells (HUVECs): the control group was incubated in growth factor-free endothelial medium, the Sup group was incubated in the supernatant of HCT 116 cells (Sup), and the LPS-Sup group was incubated in LPS-Sup. To observe effect of morphine to the adhesion molecules expressions in the LPS-Sup group, we co-treated morphine with LPS or added it to LPS-Sup. Adhesion molecule expressions on HUVECs in all three groups were measured during incubation period. Consquentially, ICAM-1, VCAM-1, and E-selectin expressions on HUVECs were significantly lower when morphine was co-treated with LPS than not co-treated. Thus, we suggest that morphine affects the expressions of adhesion molecules primarily by attenuating LPS stimuli on tumor cells.     

Cyclic-strain-induced endothelial cell expression of adhesion molecules and their roles in monocyte-endothelial interaction.

Vascular endothelial cells (ECs) are constantly subjected to hemodynamic forces that may regulate monocyte-endothelial interaction in vivo. To examine the effects of cyclic strain on endothelial expression of monocyte adhesion molecules, E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) ECs were exposed to physiologically relevant levels of cyclic strain. When ECs were under 25% maximal strain at 30 cycles/min for 24 h, the expression of E-selectin significantly (p<0.05) increased, by 83%, compared to control ECs under static conditions. Similarly, monocyte adhesion to ECs under strain (maximum of 15 or 25% at 30 and 60 cycles/min for 24 h) also significantly (p<0.05) increased, by >82%. This cyclic-strain-induced monocyte adhesion was substantially inhibited (83.5%) by anti-E-selectin antibody. ICAM-1 expression also significantly increased, by 62%, when ECs were under 25% maximal strain at 30 cycles/min for 3 h whereas VCAM-1 expression by ECs under strain (for 0.5, 3, and 24 h) did not change compared to static ECs. When ECs were treated with anti-ICAM-1 antibody and monocytes with anti-VLA-4 antibody, an increase in monocyte adhesion to ECs under cyclic strain was reduced significantly. These results demonstrate that cyclic strain can induce EC expression of monocyte adhesion molecules E-selectin, ICAM-1, and VCAM-1 in a time-dependent manner and thus can mediate monocyte adhesion.     

Expression of cellular adhesion molecules in Langerhans cell histiocytosis and normal Langerhans cells.

Langerhans cell histiocytosis (LCH) is characterized by lesions with an accumulation and/or proliferation of Langerhans cells (LCs). Little is known of the etiology and pathogenesis of LCH. Although the relation between the LCH cell and normal LCs is currently uncertain, the localizations of the LCH cells is considered aberrant when compared with normal LCs. Cellular adhesion molecules (CAMs) are known to play an important role in a variety of cell functions such as migration, antigen presentation, and activation. Aberrant migration of LCs may play a role in the pathogenesis of LCH. We investigated CAMs in 27 tissue specimens of 20 patients with LCH retrieved from our files during the last 15 years. LCH cells showed strong expression of CAMs such as CD54, CD58, and the beta 1-integrin alpha 4 that are upregulated during activation of normal LCs. In contrast, CAMs not found on normal LCs could be demonstrated in a number of cases on LCH cells like CD2, CD11a, and CD11b. Also CD62L, normally expressed only by epidermal LCs, could be detected on LCH cells. The integrins alpha 5 and alpha 6, not or only weakly found on epidermal LCs and highly expressed by activated LCs, could not be demonstrated on LCH cells. Our data suggest abnormal expression of CAMs on LCH cells that may contribute to abnormal migration of LCs in LCH. The aberrant phenotype of LCH cells has characteristics of both epidermal LCs and activated LCs and may be indicative of an arrested state of activation and/or differentiation of LCs.     

Cellular signaling by neural cell adhesion molecules of the immunoglobulin superfamily.

Neural cell adhesion molecules (CAMs) of the immunoglobulin superfamily nucleate and maintain groups of cells at key sites during early development and in the adult. In addition to their adhesive properties, binding of CAMs can affect intracellular signaling. Their ability to influence developmental events, including cell migration, proliferation, and differentiation can therefore result both from their adhesive as well as their signaling properties. This review focuses on the two CAMs for which the most information is known, the neural CAM, N-CAM, and L1. N-CAM was the first CAM to be characterized and, therefore, has been studied extensively. The binding of N-CAM to cells leads to a number of signaling events, some of which result in changes in gene expression. Interest in L1 derives from the fact that mutations in its gene lead to human genetic diseases including mental retardation. Much is known about modifications of the L1 cytoplasmic domain and its interaction with cytoskeletal molecules. The study of CAM signaling mechanisms has been assay-dependent rather than molecule-dependent, with particular emphasis on assays of neurite outgrowth and gene expression, an emphasis that is maintained throughout the review. The signals generated following CAM binding that lead to alterations in cell morphology and gene expression have been linked directly in only a few cases. We also review information on other CAMs, giving special consideration to those that are anchored in the membrane by a phospholipid anchor. These proteins, including a form of N-CAM, are presumed to be localized in lipid rafts, membrane substructures that include distinctive subsets of cytoplasmic signaling molecules such as members of the src-family of nonreceptor protein tyrosine kinases. In the end, these studies may reveal that what CAMs do after they bind cells together may have as profound consequences for the cells as the adhesive interactions themselves. This area will therefore remain a rich ground for future studies.     

CD13 is a novel mediator of monocytic/endothelial cell adhesion

During inflammation, cell surface adhesion molecules guide the adhesion and migration of circulating leukocytes across the endothelial cells lining the blood vessels to access the site of injury. The transmembrane molecule CD13 is expressed on monocytes and endothelial cells and has been shown to mediate homotypic cell adhesion, which may imply a role for CD13 in inflammatory monocyte trafficking. Here, we show that ligation and clustering of CD13 by mAb or viral ligands potently induce myeloid cell/endothelial adhesion in a signal transduction-dependent manner involving monocytic cytoskeletal rearrangement and filopodia formation. Treatment with soluble recombinant (r)CD13 blocks this CD13-dependent adhesion, and CD13 molecules from monocytic and endothelial cells are present in the same immunocomplex, suggesting a direct participation of CD13 in the adhesive interaction. This concept is strengthened by the fact that activated monocytic cells adhere to immobilized recombinant CD13. Furthermore, treatment with anti-CD13 antibodies in a murine model of peritonitis results in a decrease in leukocyte infiltration into the peritoneum, suggesting a potential role for CD13 in leukocyte trafficking in vivo. Therefore, this work supports a new direction for CD13 biology, where these cell surface molecules act as true molecular interfaces that induce and participate in critical inflammatory cell interactions.     

Down-regulation of focal adhesion kinase, pp125FAK , in endothelial cell retraction during tumor cell invasion

Although endothelial cell retraction is required before tumor cell invasion, its molecular mechanism still remains obscure. We previously demonstrated that conditioned medium (CM) derived from a human pan-creatic cancer cell line, PSN-1, induced endothelial cell retraction and facilitated tumor cell invasion. To investigate the molecular change of events in the transduction of extracellular signals during endothelial cell retraction, we examined the effect of the CM derived from PSN-1 cells on the tyrosine phosphorylation in endothelial cells. Immunoblot analyses revealed that the PSN-1 CM decreased tyrosine phosphorylation of a 120-130 kD protein, and induced the concomitant down-regulation of focal adhesion kinase, pp125^FAK , dur-ing endothelial cell retraction in time- and dose-dependent fashions. These changes preceded endothelial cell retraction and were reversible after removal of the CM. Further quantitative densitometric analyses demon-strated that the extent of decrea se in tyrosine phosphorylated 120-130 kD protein during the endothelial cell retraction was likely to be proportional to that of the down-regulation of pp125^FAK . A tyrosine phosphory-lated 120-130 kD protein immunoprecipitated by anti-phosphotyrosine antibody immunoreacted with anti-pp125^FAK antibody. These results suggested that decreased amount of a tyrosine phosphorylated 120-130 kD protein probably due to the down-regulation of pp125^FAK might be associated with the signal transduction pathway in the endothelial cells during their retraction. Furthermore, these findings were also observed in the CM from another four human cancer cell lines, suggesting the down-regulation of pp125^FAK in endothelial cells during tumor cell invasion. © Rapid Science 1998     

Expression of adhesion molecules by endothelial cells of early human decidua

The expression of adhesion molecules by endothelial cells (EC) of early human decidua was studied with monoclonal antibodies and the immunoperoxidase technique. Although E-selectin, INCAM-110 and VCAM-1 were poorly detected on decidual EC, ICAM-1, P-selectin and DR antigens were highly expressed by these cells, some of which showed high endothelial venule-like morphology. Our results suggest that decidual EC are activated, and are probably involved in the active recruitment of leucocytes.     

T cell adhesion to extracellular matrix molecules secreted by endothelial cells cultured on a substrate of type IV collagen

T cell emigrating from the bloodstream into lymphoid organs or sites of inflammation in the connective tissue must adhere to, and traverse, the subendothelial basement membrane (BM). The goal of the current investigation was to develop a method to study the adhesion of T cells to endothelial cell (EC)-derived extracellular matrix (ECM) as a model for the interaction of T cells with the subendothelial BM in vivo. To be certain that we were truly measuring T cell adhesion to ECM molecules secreted by the EC, it was necessary to culture the EC on a substrate to which T cells could not attach. Non-tissue culture-treated microtiter plate wells which had been coated with type IV collagen (tIVC), a major constituent of BM in vivo, were found to be suitable for this purpose since EC, but very few T cells, adhered to such wells. After incubating the EC on a substrate of tIVC in non-treated wells for a period of 48 h, the EC were gently removed from their underlying ECM and T cell adhesion to that ECM was examined. Using this system, it was observed that approximately 15-40% of human peripheral blood T cells specifically adhered to ECM molecules produced by the EC. This method should be useful as a model for the interactions of T cells and other leukocytes with the vascular BM in vivo.     

蜂胶水提物对血管内皮细胞黏附分子表达的影响

目的:采用TNF-α诱导体外培养的人脐静脉内皮细胞(HUCECs)活化,观察蜂胶水提物(WEP)对血管内皮细胞黏附分子表达的影响,从而探讨蜂胶抗动脉粥样硬化的作用及其机制。方法:用50μg/L TNF-α诱导体外培养HUVECs损伤,用50 mg/L、100 mg/L、200 mg/L WEP分别进行干预6 h、12 h、24 h,利用流式细胞仪检测HUVEC表面ICAM-1和VCAM-1表达。结果:与对照组比较,模型组ICAM-1和VCAM-1荧光强度明显升高(P0.01)。与模型组比较,100 mg/L WEP组和200 mg/L WEP组ICAM-1和VCAM-1荧光强度明显降低(P0.01)。不同浓度WEP组ICAM-1和VCAM-1荧光强度随WEP浓度的增加下调。析因分析结果显示,用200 mg/L WEP和氟伐他汀钠(FS)联合预处理组与单一药物预处理组比较,ICAM-1和VCAM-1活性明显降低(P0.01)。结论:WEP能够减少ICAM-1和VCAM-1的表达,且在一定的范围内,有随WEP浓度升高和作用时间延长效应增强的趋势。WEP与FS联合用药,对抑制ICAM-1和VCAM-1表达有协同作用。     

Hypoxic tumor cell death and modulation of endothelial adhesion molecules in the regression of granulocyte colony-stimulating factor-transduced tumors.

C-26 colon adenocarcinoma cells transduced with the granulocyte colony-stimulating factor (G-CSF) gene form large tumors when injected into sublethally irradiated mice. These tumors regress when leukocyte function is reconstituted. Electron microscopy and immunocytochemical analysis of regressing C-26/G-CSF nodules indicates that tumor destruction is due mainly to hypoxia resulting from the functional loss of tumor vasculature and is only marginally due to direct cytolysis. Desegregation of basal lamina, cell swelling, and loss of junctions characterized the vessels within regressing tumors. Tumor cells were necrotic or filled with lipid vacuoles regardless of the distance from nearby vessels. Damage of tumor vasculature was dependent on the infiltrating leukocytes and the cytotoxic cytokines they produced. Locally produced interleukin-1 and tumor necrosis factor-alpha (TNF-alpha) induced vascular cellular adhesion molecule-1 (VCAM-1) and E-selectin on tumor vessels. Treatment with monoclonal antibodies to interferon-gamma (IFN-gamma) or TNF-alpha blocked tumor regression by inhibiting VCAM-1 and E-selectin expression on tumor-associated endothelial cells resulting in a reduced number of infiltrating leukocytes. Thus, C-26/G-CSF tumor regression presents features typical of hemorrhagic necrosis that occurs through the cytokines produced by infiltrating leukocytes in response to G-CSF.     

Subcellular organization of GABAergic synapses: role of ankyrins and L1 cell adhesion molecules

In vertebrate nervous systems, different classes of synaptic inputs are often segregated into restricted compartments of target neurons. For example, distinct types of GABAergic interneurons preferentially innervate subcellular domains and have been implicated in the precise temporal regulation of integration within neurons and activity within networks. Recent studies suggest that the subcellular segregation of different classes of GABAergic synapses is largely genetically determined. The localization and signaling of L1 family immunoglobulin proteins recruited by ankyrin-based membrane adaptors might serve as compartmental labels, which contribute to subcellular synapse organization in cerebellar Purkinje neurons.     

The role of endothelial cell adhesion molecules P-selectin, E-selectin and intercellular adhesion molecule-1 in leucocyte recruitment induced by exogenous methylglyoxal

Methylglyoxal (MG) is a reactive dicarbonyl metabolite formed during glucose, protein and fatty acid metabolism. In hyperglycaemic conditions, increased MG level has been linked to the development of diabetes and its vascular complications at the macrovascular and microvascular levels where inflammation plays a role. To study the mechanism of MG‐induced inflammation in vivo, we applied MG locally to healthy mice and used intravital microscopy to investigate the role of endothelial cell adhesion molecules in MG‐induced leucocyte recruitment in cremasteric microvasculature. Administration of MG (25 and 50 mg/kg) to the tissue dose‐dependently induced leucocyte recruitment at 4·0–5·5 hr, with 84–92% recruited cells being neutrophils. Such MG treatment up‐regulated the expression of endothelial cell adhesion molecules P‐selectin, E‐selectin, intercellular adhesion molecule‐1, but not vascular cell adhesion molecule‐1. Activation of the nuclear factor‐κB signalling pathway contributed to MG‐induced up‐regulation of these adhesion molecules and leucocyte recruitment. The role of the up‐regulated endothelial cell adhesion molecules in MG‐induced leucocyte recruitment was determined by applying specific functional blocking antibodies to MG‐treated animals and observing changes in leucocyte recruitment parameters. Our data demonstrate that the up‐regulation of P‐selectin, E‐selectin and intercellular adhesion molecule‐1 contributes to the increased leucocyte rolling flux, reduced leucocyte rolling velocity, and increased leucocyte adhesion, respectively. Our results reveal the role of endothelial cell adhesion molecules in MG‐induced leucocyte recruitment in microvasculature, an inflammatory condition related to diabetic vascular complications.     

Oxidized forms of fibrinogen induce expression of cell adhesion molecules by cultured endothelial cells from human blood vessels

Oxidized forms of fibrinogen similarly to initial non-oxidized fibrinogen induced expression of P-selectin and ICAM-1 cell adhesion molecules in the cultured endothelial cells derived from human umbilical vein. The effect of oxidized fibrinogen on the expression of adhesion molecules was more pronounced. These data attest to more active participation of oxidized forms of fibrinogen into inflammation in the vascular wall, the first stage of atherogenesis. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 9, pp. 277–281, September, 2006     

Expression of endothelial adhesion molecules in vivo. Increased endothelial ICAM-2 expression in lymphoid malignancies.

The authors have compared the reactivity of monoclonal antibodies (MAb) directed against endothelial adhesion molecules (ICAM-1, ICAM-2, VCAM-1, ELAM-1) in hyperplastic, nonmalignant, and malignant lymph nodes. The authors demonstrate that the reactivity with ICAM-1 MAb is stronger in the high endothelial venules (HEV) and other smaller vessels (SV) in lymphomas compared with hyperplastic lymph nodes. Similarly, the reactivity of an ICAM-2 MAb (6D5) was shown to be higher in malignant lymph nodes compared with nonmalignant ones. ICAM-2 MAb stained both the HEV and SV. VCAM-1 MAb reacted strongly with germinal centers and its endothelial reactivity was higher in the lymphoma nodes. ELAM-1 MAb stained only faintly some endothelial cells in malignant tissue. These data suggest that besides the known regulatable endothelial adhesion molecules ICAM-1 and VCAM-1, the expression of ICAM-2 can be modified.     

Direct cell/cell contact with stimulated T lymphocytes induces the expression of cell adhesion molecules and cytokines by human brain microvascular endothelial cells

Upon inflammation, stimulated, but not resting T lymphocytes cross the blood-brain barrier and migrate into the central nervous system. This study shows that direct contact between stimulated T lymphocytes and human brain microvascular endothelial cells (HB-MVEC) induces phenotypic and functional changes on the latter cells. Plasma membranes isolated from stimulated T lymphocytes (S-PM) up-regulated the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin on isolated HB-MVEC. In addition, HB-MVEC activated by S-PM secreted interleukin (IL)-6 and IL-8. The levels of ICAM-1, E-selectin, IL-6, and IL-8 expressed in S-PM-activated HB-MVEC were similar to those observed with 1000 U/ml tumor necrosis factor (TNF). In contrast, VCAM-1 expression was 15% of that induced by TNF. Inhibitors of TNF diminished (≤ 45 %), but did not abolish the expression of cell adhesion molecules and IL-6 induced by S-PM, IL-8 production being insignificantly affected (≤ 10 %). This suggests that membrane-associated TNF was partially involved in HB-MVEC activation. The present study demonstrates that stimulated T lymphocytes are able to activate HB-MVEC upon direct cell contact. This novel mechanism of inducing the expression of cell adhesion molecules may prompt the initial adhesion of stimulated T lymphocytes to brain endothelium.