Endothelial cells and immune cell migration

Leukocyte ingress into the synovium is a key process in the pathogenesis of rheumatoid arthritis and other inflammatory conditions. In this review, the role of endothelial cells in leukocyte extravasation will be discussed, including the role of the most relevant cellular adhesion molecules. These molecules play an important role in mediating leukocyte-endothelial interactions. It is likely that different adhesive pathways are involved in different steps of leukocyte adhesion to and migration through endothelia. Targeting of pathological endothelial function, including leukocyte-endothelial adhesion, may be useful for the future management of inflammatory arthritis.     

Chemokine-leukocyte interactions. The voodoo that they do so well

Leukocyte recruitment from the circulation into inflammatory tissues requires a series of soluble and cell-bound signals between the responding leukocyte and vascular endothelial barrier. Chemotactic factors are believed to be responsible for this selective adhesion and transmigration. A superfamily of small, soluble, structurally-related molecules called ‘chemokines’ have been identified and shown to selectively promote the rapid adhesion and chemotaxis of a variety of leukocyte subtypes both in vivo and in vitro. Chemokines are produced by almost every cell type in the body in response to a number of inflammatory signals, in particular those which activate leukocyteendothelial cell interactions. These molecules also appear to play important roles in hematopoesis, cellular activation, and leukocyte effector functions. In addition, chemokines have been found in the tissues of a variety of disease states characterized by distinct leukocytic infiltrates, including rheumatoid arthritis, sepsis, atherosclerosis, asthma, psoriasis, ischemia/reperfusion injury, HIV replication, and a variety of pulmonary disease states. This review will primarily focus on the role of chemokines in cell adhesion and trafficking as well as their role as effector molecules.     

Integrin activation by chemokines: relevance to inflammatory adhesion cascade during T cell migration

The adhesive function of integrins is regulated through cytoplasmic signaling induced by several stimuli, whose process is designated "inside-out signaling". A large number of leukocytes are rapidly recruited to the sites of inflammation where they form an essential component of the response to infection, injury, autoimmune disorders, allergy, tumor invasion, atherosclerosis and so on. The recruitment of leukocytes into tissue is regulated by a sequence of interactions between the circulating leukocytes and the endothelial cells. Leukocyte integrins play a pivotal role in leukocyte adhesion to endothelial cells. During the process, the activation of integrins by various chemoattractants, especially chemokines, is essential for integrin-mediated adhesion in which a signal transduced to the leukocyte converts the functionally inactive integrin to an active adhesive configuration. We have proposed that H-Ras-sensitive activation of phosphoinositide 3 (PI 3)-kinase and subsequent profilin-mediated actin polymerization, can be involved in chemokine-induced integrin-dependent adhesion of T cells. The present review documents the relevance of cytoplasmic signaling and cytoskeletal assembly to integrin-mediated adhesion induced by chemoattractants including chemokines during inflammatory processes. In contrast, various adhesion molecules are known to transduce extracellular information into cytoplasm, which leads to T cell activation and cytokine production from the cells, designated "outside-in signaling". Such a bi-directional "cross-talking" among adhesion molecules and cytokines is most relevant to inflammatory processes by augmenting immune cell migration from circulation into inflamed tissue such as rheumatoid arthritis, tumor invasion, Beh?et's disease and atherosclerosis.     

Human leukocyte subpopulations from inflamed gut bind to joint vasculature using distinct sets of adhesion molecules

Reactive arthritis can be triggered by inflammatory bowel diseases. We hypothesized that migration of mucosal immune cells from inflamed gut to joints could contribute to the development of reactive arthritis. Here we isolated gut-derived leukocytes from patients with Crohn's disease and ulcerative colitis. Using function-blocking mAbs and in vitro frozen section adhesion assays we studied whether these cells bind to synovial vessels and which molecules mediate the interaction. The results showed that mucosal leukocytes from inflammatory bowel diseased gut bind well to venules in synovial membrane. Small intestinal lymphocytes adhered to synovial vessels using multiple homing receptors and their corresponding endothelial ligands (CD18-ICAM-1, alpha(4)beta(7)/alpha(4)beta(1)-integrin-VCAM-1, L-selectin-peripheral lymph node addressins, and CD44). Of these, only ICAM-1 significantly supported binding of immunoblasts. In contrast, P-selectin glycoprotein ligand-1-P-selectin interaction accounted for practically all synovial adherence of mucosal macrophages. In addition, blocking of vascular adhesion protein-1 significantly inhibited binding of all these leukocyte subsets to joint vessels. We conclude that different leukocyte populations derived from inflamed gut bind avidly to synovial vessels using distinct repertoire of adhesion molecules, suggesting that their recirculation may contribute to the development of reactive arthritis in inflammatory bowel diseases.     

Vascular involvement in rheumatic diseases: 'vascular rheumatology'

The vasculature plays a crucial role in inflammation, angiogenesis, and atherosclerosis associated with the pathogenesis of inflammatory rheumatic diseases, hence the term 'vascular rheumatology'. The endothelium lining the blood vessels becomes activated during the inflammatory process, resulting in the production of several mediators, the expression of endothelial adhesion molecules, and increased vascular permeability (leakage). All of this enables the extravasation of inflammatory cells into the interstitial matrix. The endothelial adhesion and transendothelial migration of leukocytes is a well-regulated sequence of events that involves many adhesion molecules and chemokines. Primarily selectins, integrins, and members of the immunoglobulin family of adhesion receptors are involved in leukocyte 'tethering', 'rolling', activation, and transmigration. There is a perpetuation of angiogenesis, the formation of new capillaries from pre-existing vessels, as well as that of vasculogenesis, the generation of new blood vessels in arthritis and connective tissue diseases. Several soluble and cell-bound angiogenic mediators produced mainly by monocytes/macrophages and endothelial cells stimulate neovascularization. On the other hand, endogenous angiogenesis inhibitors and exogenously administered angiostatic compounds may downregulate the process of capillary formation. Rheumatoid arthritis as well as systemic lupus erythematosus, scleroderma, the antiphospholipid syndrome, and systemic vasculitides have been associated with accelerated atherosclerosis and high cardiovascular risk leading to increased mortality. Apart from traditional risk factors such as smoking, obesity, hypertension, dyslipidemia, and diabetes, inflammatory risk factors, including C-reactive protein, homocysteine, folate deficiency, lipoprotein (a), anti-phospholipid antibodies, antibodies to oxidized low-density lipoprotein, and heat shock proteins, are all involved in atherosclerosis underlying inflammatory rheumatic diseases. Targeting of adhesion molecules, chemokines, and angiogenesis by administering nonspecific immunosuppressive drugs as well as monoclonal antibodies or small molecular compounds inhibiting the action of a single mediator may control inflammation and prevent tissue destruction. Vasoprotective agents may help to prevent premature atherosclerosis and cardiovascular disease.     

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis.

1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner.
2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis.
3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-α. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis.
4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

     

Isolation and characterization of human esophageal microvascular endothelial cells: mechanisms of inflammatory activation

Gastroesophageal reflux disease is the most common malady of the esophagus, affecting 7% of the United States population. Histological assessment demonstrates classic inflammatory mechanisms including selective leukocyte recruitment and hemorrhage, suggesting a prominent role for the microvasculature. We isolated and characterized human esophageal microvascular endothelial cells (EC) (HEMEC), examined inflammatory activation in response to cytokines, LPS, and acidic pH exposure, and identified signaling pathways that underlie activation. HEMEC displayed characteristic morphological and phenotypic features including acetylated LDL uptake. TNF-alpha/LPS activation of HEMEC resulted in upregulation of the cell adhesion molecules (CAM) ICAM-1, VCAM-1, E-selectin, and mucosal addressin CAM-1 (MAdCAM-1), increased IL-8 production, and enhanced leukocyte binding. Both acid and TNF-alpha/LPS activation lead to activation of SAPK/JNK in HEMEC that was linked to VCAM-1 expression and U-937 leukocyte adhesion. Expression of constitutive inducible nitric oxide synthase in HEMEC was in marked contrast to intestinal microvascular endothelial cells. In this study, we demonstrate that HEMECs are phenotypically and functionally distinct from lower gut-derived endothelial cells and will facilitate understanding of inflammatory mechanisms in esophageal inflammation.     

Cyclosporine A enhances leukocyte binding by human intestinal microvascular endothelial cells through inhibition of p38 MAPK and iNOS. Paradoxical proinflammatory effect on the microvascular endothelium

The calcineurin inhibitor cyclosporine A (CsA) modulates leukocyte cytokine production but may also effect nonimmune cells, including microvascular endothelial cells, which regulate the inflammatory process through leukocyte recruitment. We hypothesized that CsA would promote a proinflammatory phenotype in human intestinal microvascular endothelial cells (HIMEC), by inhibiting inducible nitric-oxide synthase (iNOS, NOS2)-derived NO, normally an important mechanism in limiting endothelial activation and leukocyte adhesion. Primary cultures of HIMEC were used to assess CsA effects on endothelial activation, leukocyte interaction, and the expression of iNOS as well as cell adhesion molecules. CsA significantly increased leukocyte binding to activated HIMEC, but paradoxically decreased endothelial expression of cell adhesion molecules (E-selectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule-1). In contrast, CsA completely inhibited the expression of iNOS in tumor necrosis factor-alpha/lipopolysaccharide-activated HIMEC. CsA blocked p38 MAPK phosphorylation in activated HIMEC, a key pathway in iNOS expression, but failed to inhibit NFkappaB activation. These studies demonstrate that CsA exerts a proinflammatory effect on HIMEC by blocking iNOS expression. CsA exerts a proinflammatory effect on the microvascular endothelium, and this drug-induced endothelial dysfunction may help explain its lack of efficacy in the long-term treatment of chronically active inflammatory bowel disease.     

Rho-GTPase signaling in leukocyte extravasation

Leukocyte transendothelial migration (TEM) is one of the crucial steps during inflammation. A better understanding of the key molecules that regulate leukocyte extravasation aids to the development of novel therapeutics for treatment of inflammation-based diseases, such as atherosclerosis and rheumatoid arthritis. The adhesion molecules ICAM-1 and VCAM-1 are known as central mediators of TEM. Clustering of these molecules by their leukocytic integrins initiates the activation of several signaling pathways within the endothelium, including a rise in intracellular Ca²⁺, activation of several kinase cascades, and the activation of Rho-GTPases. Activation of Rho-GTPases has been shown to control adhesion molecule clustering and the formation of apical membrane protrusions that embrace adherent leukocytes during TEM. Here, we discuss the potential regulatory mechanisms of leukocyte extravasation from an endothelial point of view, with specific focus on the role of the Rho-GTPases.     

Down-regulation of cell adhesion molecules LFA-1 and ICAM-1 after in vitro treatment with the anti-TNF-alpha agent thalidomide.

The tumor necrosis factor-alpha (TNF-alpha) inhibitor thalidomide is known to be a potent modulator of host immunity, a potential treatment for autoimmune disorders such as rheumatoid arthritis (RA) and a treatment for complications of HIV-1 infection. RA is an autoimmune disease of the joints that has been associated with hyperactivity of lymphocytes and other leukocytes, over-expression of pro-inflammatory cytokines (TNF-alpha and IL-1) and chronic debilitating inflammation. Thalidomide may play a role in RA treatment by altering leukocyte function through down-modulation of cell adhesion molecules necessary for leukocyte migration to inflammatory sites. The present study investigates down-regulation of cell adhesion molecules (ICAM-1 and LFA-1) and decreases in cell-cell contacts between human T leukemic (CEM) cells and human umbilical vein endothelial cells (HUVEC) after thalidomide exposure. CEM cells were cultured in RPMI 1640 medium with 0, 10 or 50 microg/ml thalidomide, stained with fluorescent monoclonal antibodies specific to ICAM-1 and LFA-1 and expression was measured with flow cytometry. For cell-cell adhesion measurements, monolayers of HUVEC cultured in Kaign's F-12 medium were incubated with thalidomide treated CEM cells stained with calcein AM. Specific cell adhesion between the two cell types was visualized with fluorescence microscopy. Thalidomide treatment significantly reduced cell adhesion molecule expression in a dose-dependent fashion and inhibited HUVEC/CEM cell adhesion. These data support the hypothesis that thalidomide has modulatory actions on leukocyte functions through expression of cell adhesion molecules.     

Rho-GTPase signaling in leukocyte extravasation: An endothelial point of view

Leukocyte transendothelial migration (TEM) is one of the crucial steps during inflammation. A better understanding of the key molecules that regulate leukocyte extravasation aids to the development of novel therapeutics for treatment of inflammation-based diseases, such as atherosclerosis and rheumatoid arthritis. The adhesion molecules ICAM-1 and VCAM-1 are known as central mediators of TEM. Clustering of these molecules by their leukocytic integrins initiates the activation of several signaling pathways within the endothelium, including a rise in intracellular Ca²⁺, activation of several kinase cascades, and the activation of Rho-GTPases. Activation of Rho-GTPases has been shown to control adhesion molecule clustering and the formation of apical membrane protrusions that embrace adherent leukocytes during TEM. Here, we discuss the potential regulatory mechanisms of leukocyte extravasation from an endothelial point of view, with specific focus on the role of the Rho-GTPases.     

Interactions between leukocytes and endothelial cells in gout: lessons from a self-limiting inflammatory response

Interactions with endothelium are necessary for leukocytes to pass from the blood into extravascular tissues, and such interactions are facilitated in inflammation by the coordinated expression of endothelial adhesion molecules and chemoattractants. Although the general mechanisms and intracellular pathways of endothelial activation are now fairly well characterised in vitro, relatively little detailed information exists on how endothelial activation changes during the course of inflammatory responses and how such change influences the amount of leukocyte recruitment and the types of leukocytes recruited. Having developed a radiolabelled-antibody-uptake technique for quantifying the expression of endothelial adhesion molecules in relation to leukocyte trafficking, we have analysed the acute, self-limiting inflammatory response to injection of monosodium urate (MSU) crystals. Our studies have supported the view that endothelial activation is closely paralleled by leukocyte recruitment at the onset of the response and have highlighted separate vascular and extravascular stages of downregulation. More recent studies addressing the extravascular contribution to downregulation point to an important role for monocyte-macrophage differentiation in limiting further endothelial activation as a consequence of phagocytosis of MSU crystals.     

Leukocyte and endothelial adhesion molecules in patients with hypercholesterolemia: the effect of atorvastatin treatment

Atherogenesis involves the migration of leukocytes into vascular subendothelial space, a process mediated by endothelial and leukocyte cell adhesion molecules. Endothelial molecules are assessed indirectly via serum levels, but leukocyte molecules can be assessed directly. We have therefore hypothesized that leukocyte adhesion molecules are altered to a greater degree in hypercholesterolemia than serum endothelial adhesion molecules. We examined 29 subjects with hypercholesterolemia and 27 controls at baseline and after 12 weeks of atorvastatin treatment (20 mg/day). Expression of leukocyte integrins CD11a, CD11b, CD18, and CD49d and of L-selectin was measured by flow cytometry. Serum ICAM-1, E-selectin and von Willebrand factor were measured by ELISA. Expression of leukocyte adhesion molecules was significantly higher in patients at baseline than in the controls, except for CD11a. Expression significantly decreased after atorvastatin in most adhesion molecules except for CD11b. In contrast, there was no effect of hypercholesterolemia and/or atorvastatin on the serum endothelial molecules. Leukocyte but not endothelial adhesion molecules were influenced by hypercholesterolemia and by lipid lowering treatment. Leukocyte molecules may therefore be a more sensitive marker of atherogenesis than endothelial molecules. Our results support the role of increased leukocyte adhesiveness in atherogenesis.     

Manifestations of inflammatory arthritis are critically dependent on LFA-1

Leukocyte infiltration of synovial fluid and tissues is the hallmark of inflammatory arthritis. Selectins and beta2 integrins have been implicated in the multistep process of leukocyte adhesion to vascular endothelium. However, previous work has revealed disparate requirements for leukocyte recruitments to specific anatomic locales. Moreover, the mechanisms regulating recruitment of leukocytes to the joint in inflammatory arthritis models are not fully understood. We hypothesized that beta2 integrins, expressed on leukocytes, might play a pathogenic role in synovial inflammation. Using mice deficient in all beta2 integrins (CD18 null mice), we demonstrate that expression of these heterodimeric adhesion molecules is critical for arthritis induction in the K/B x N serum transfer model. Using null-allele mice and blocking mAbs, we demonstrate specifically that CD11a/CD18 (LFA-1) is absolutely required for the development of arthritis in this model. Blocking mAbs further revealed an ongoing requirement for LFA-1 I-domain adhesive function in disease perpetuation. These findings suggest that the LFA-1 I-domain forms an attractive target for treatment of human inflammatory arthritis.     

Cell Adhesion Molecules: Potential Therapeutic &; Diagnostic Implications

The role of cell adhesion molecules (CAM) and extracellular matrix proteins (ECM) in various pathological processes including angiogenesis, thrombosis, apoptosis, cell migration & proliferation are well documented. These processes can lead to both acute and chronic disease states such as ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling, and neurodegenerative disorders. A key success in this field is evident from the potential role of the platelet GPIIb/IIIa integrin in the prevention and diagnosis of various thromboembolic disorders. Additionally, the use of soluble adhesion molecules as potential diagnostic markers for acute and chronic leukocyte, platelet, and endothelial cellular insult are increasingly utilized. The development of various therapeutic and diagnostic candidates based on the key role of CAM, with special emphasis on integrins in various diseases as well as the structure-function aspects of cell adhesion and signaling of the different CAM and ECM are highlighted.     

Endothelial cell phenotypes in the rheumatoid synovium: activated,angiogenic, apoptotic and leaky

Endothelial cells are active participants in chronic inflammatory diseases. These cells undergo phenotypic changes that can be characterised as activated, angiogenic, apoptotic and leaky. In the present review, these phenotypes are described in the context of human rheumatoid arthritis as the disease example. Endothelial cells become activated in rheumatoid arthritis pathophysiology, expressing adhesion molecules and presenting chemokines, leading to leukocyte migration from the blood into the tissue. Endothelial cell permeability increases, leading to oedema formation and swelling of the joints. These cells proliferate as part of the angiogenic response and there is also a net increase in the turnover of endothelial cells since the number of apoptotic endothelial cells increases. The endothelium expresses various cytokines, cytokine receptors and proteases that are involved in angiogenesis, proliferation and tissue degradation. Associated with these mechanisms is a change in the spectrum of genes expressed, some of which are relatively endothelial specific and others are widely expressed by other cells in the synovium. Better knowledge of molecular and functional changes occurring in endothelial cells during chronic inflammation may lead to the development of endothelium-targeted therapies for rheumatoid arthritis and other chronic inflammatory diseases.     

Pitavastatin prevents NMDA-induced retinal ganglion cell death by suppressing leukocyte recruitment

Excitotoxicity is a major cause of retinal ganglion cell (RGC) death during ischemic diseases such as vessel occlusion and diabetic retinopathy. However, the underlying mechanisms are not well understood. Statins, inhibitors of the HMG-CoA reductase, have neuroprotective effects in addition to their original role in lowering cholesterol. We hypothesize that pitavastatin, a recently introduced potent statin, is protective against N-methyl-d-aspartic acid (NMDA)-induced RGC death. Pitavastatin, administered by gavage, abolished NMDA-induced loss of RGCs. To elucidate the mechanisms underlying the neuroprotective effect of pitavastatin, we investigated its impact on inflammation. NMDA increased the expression of interleukin-1beta and TNF-alpha, and endothelial adhesion molecules, including ICAM-1, and induced leukocyte accumulation in the retinal vessels. Pitavastatin significantly reduced NMDA-induced leukocyte accumulation and up-regulation of endothelial adhesion molecules, whereas cytokine expression was unaffected. Systemic blockade of ICAM-1 in wild-type mice or absence of CD18 in gene-deficient (CD18(-/-)) mice significantly suppressed NMDA-induced leukocyte accumulation and RGC death. These findings suggest a novel and causative role for inflammatory leukocyte recruitment in NMDA-induced excitotoxicity. Furthermore, we show the novel neuroprotective effect of statins against excitotoxicity-induced RGC death. Statins or other anti-inflammatory agents may thus have therapeutic benefits in excitotoxicity-associated neuronal diseases through blockade of leukocyte recruitment.     

Platelet-mediated adhesion facilitates leukocyte sequestration in hypoxia-reoxygenated microvessels

Leukocyte transendothelial migration and sequestration are two distinct outcomes following leukocyte adhesion to endothelium during ischemia-reperfusion injury, in which platelets may play a pivotal role. In the present study, we established an in vitro hypoxia-reoxygenation model to mimic ischemia-reperfusion injury and found platelet pre-incubation significantly increased leukocyte adhesion to endothelial cells after hyoxia-reoxygenation (over 67%). Blockade of endothelial-cell-expressed adhesion molecules inhibited leukocyte direct adhesion to endothelial cells, while platelet-mediated leukocyte adhesion was suppressed by blockade of platelet-expressed adhesion molecules. Further experiments revealed platelets acted as a bridge to mediate leukocyte adhesion, and platelet-mediated adhesion was the predominant pattern in the presence of platelets. However, platelet pre-incubation significantly suppressed leukocyte transendothelial migration after hypoxia-reoxygenation (over 31%), which could be aggravated by blockade of endothelial-cell-expressed adhesion molecules, but alleviated by blockade of platelet- expressed adhesion molecules. This would indicate that platelet-mediated adhesion disrupted leukocyte transendothelial migration. An in vivo mesenteric ischemia-reperfusion model demonstrated leukocyte transfusion alone caused mild leukocyte adhesion to reperfused vessels and subsequent leukocyte infiltration, while simultaneous leukocyte and platelet transfusion led to massive leukocyte adhesion and sequestration within reperfused microvessels. Our studies revealed platelets enhanced leukocyte adhesion to endothelial cells, but suppressed leukocyte transendothelial migration. Overall, this leads to leukocyte sequestration in hypoxia-reoxygenated microvessels.     

Deficiency of P-selectin or P-selectin glycoprotein ligand-1 leads to accelerated development of glomerulonephritis and increased expression of CC chemokine ligand 2 in lupus-prone mice

The selectins and their ligands mediate leukocyte rolling on endothelial cells, the initial step in the emigration cascade leading to leukocyte infiltration of tissue. These adhesion molecules have been shown to be key promoters of acute leukocyte emigration events; however, their roles in the development of long-term inflammatory responses, including those that occur during chronic inflammatory diseases such as systemic lupus erythematosus, are unclear. To assess participation of P-selectin in such disorders, we studied the progression of systemic lupus erythematosus-like disease in P-selectin-deficient and control MRL/MpJ-Fas(lpr) (Fas(lpr)) mice. Surprisingly, we found that P-selectin deficiency resulted in significantly earlier mortality, characterized by a more rapid development of glomerulonephritis and dermatitis. Expression of CCL2 (MCP-1) was increased in the kidneys of P-selectin mutant mice and in supernatants of LPS-stimulated primary renal endothelial cell cultures from these mice. A closely similar phenotype, including elevated renal expression of CCL2, was also observed in Fas(lpr) mice deficient in the major P-selectin ligand, P-selectin glycoprotein ligand-1. These results indicate that P-selectin and P-selectin glycoprotein ligand-1 are not required for leukocyte infiltration and the development of autoimmune disease in Fas(lpr) mice, but rather expression of these adhesion molecules is important for modulating the progression of glomerulonephritis, possibly through down-regulation of endothelial CCL2 expression.     

Relative contribution of the leukocyte molecules Mo1, LFA-1, and p150,95 (LeuM5) in adhesion of granulocytes and monocytes to vascular endothelium is tissue- and stimulus-specific

Adhesion of human monocytes and granulocytes to vascular endothelium plays an important role in migration of these cells to inflammatory sites in tissues. A family of three human leukocyte heterodimeric surface molecules named Mo1, LFA-1, and p150,95 (LeuM5) has been shown to mediate leukocyte adhesion to confluent monolayers of human umbilical vein endothelial cells (HUVE). The relative contribution of each of the three molecules in leukocyte endothelial adhesion was studied using a variety of stimuli. Purified human granulocytes and monocytes were radiolabelled and incubated with HUVE for 45 minutes in a 37 degrees C humidified 5% CO2 incubator in the presence or absence of subunit-specific monoclonal antibodies (MAbs). Adhesion was assessed by quantitation of endothelial cell-associated radioactivity and confirmed by microscopic evaluation. MAbs directed against the alpha subunit of LFA-1 as well as to the beta subunit common to all three antigens significantly inhibited unstimulated monocyte adhesion to HUVE. Small but significant inhibiton was also observed using MAbs directed against Mo1a and p150. Phorbol myristate acetate (PMA)-induced grranulocyte adhesion to HUVE was significantly inhibited by anti-Mo1a and anti-beta, but not by anti-LFA-1a or anti-p150. When HUVE were prestimulated by recombinant IL-1, a different pattern of antigen utilization by granulocytes was observed. MAbs directed against each of the three alpha subunits as well as the common beta subunit all inhibited granulocyte adhesion to HUVE. Furthermore the effect of the three anti-alpha subunit MAbs on granulocyte-HUVE adhesion was additive. These studies show that relative contribution of Mo1, LFA-1, and p150,95 to leukocyte endothelial adhesion varies depending on the cell type and the stimulus used. These studies also reveal a novel role for p150,95 in promoting monocyte and granulocyte adhesion to HUVE.