Divergent effects of platelet-endothelial cell adhesion molecule-1 and beta 3 integrin blockade on leukocyte transmigration in vivo

A peptidic network antibody inhibits both angiogenesis and inflammatory response

Corneal neovascularization (CNV) is a global threat to human health. Traditional anti-angiogenesis agent may have therapy effect, while the inflammation in disease area remains unsolved. Herein, we reported two binding-induced fibrillogenesis (BIF) peptides as peptidic network antibodies for high-efficient and long-lasting anti-angiogenesis with reduced inflammatory response. BIF peptides could self-assemble into nanoparticles and further perform BIF behavior through binding Ca2+. In vitro, the migration of integrin αvβ3 highly expressed endothelial cells was inhibited by BIF peptides. In vivo, one BIF peptide (0.012 mg/Kg) exhibited higher anti-angiogenesis effect than monoclonal antibody bevacizumab (0.96 mg/Kg) in a CNV rabbit model on day 14, despite that the dose of BIF was only 1.3% of bevacizumab. Meanwhile, the inflammatory response, such as PI3 kinase/Akt pathway in CNV was successfully inhibited as well. The peptidic network antibody could block integrin αvβ3 via a long-term retention mode, which led to long-term therapeutic effect. The study provides BIF peptides as promising therapeutic agents for both anti-angiogenesis and reduced inflammatory response.

Identifying Immune-Specific Subtypes of Adrenocortical Carcinoma Based on Immunogenomic Profiling

BACKGROUND

The tumor immune microenvironment (TIME) of adrenocortical carcinoma (ACC) is heterogeneous. However, a classification of ACC based on the TIME remains unexplored.

METHODS

We hierarchically clustered ACC based on the enrichment levels of twenty-three immune signatures to identify its immune-specific subtypes. Furthermore, we comprehensively compared the clinical and molecular profiles between the subtypes.

RESULTS

We identified two immune-specific subtypes of ACC: Immunity-H and Immunity-L, which had high and low immune signature scores, respectively. We demonstrated that this subtyping method was stable and reproducible by analyzing five different ACC cohorts. Compared with Immunity-H, Immunity-L had lower levels of immune cell infiltration, worse overall and disease-free survival prognosis, and higher tumor stemness, genomic instability, proliferation potential, and intratumor heterogeneity. Furthermore, the ACC driver gene CTNNB1 was more frequently mutated in Immunity-L than in Immunity-H. Several proteins, such as mTOR, ERCC1, Akt, ACC1, Cyclin_E1, β-catenin, FASN, and GAPDH, were more highly expressed in Immunity-L than in Immunity-H. In contrast, p53, Syk, Lck, PREX1, and MAPK were more highly expressed in Immunity-H. Pathway and gene ontology analysis showed that the immune, stromal, and apoptosis pathways were highly enriched in Immunity-H, while the cell cycle, steroid biosynthesis, and DNA damage repair pathways were highly enriched in Immunity-L.

CONCLUSIONS

ACC can be classified into two stable immune-related subtypes, which have significantly different antitumor responses, molecular characteristics, and clinical outcomes. This subtyping may provide clinical implications for prognostic and immunotherapeutic stratification of ACC.

Perspectives on Vascular Regulation of Mechanisms Controlling Selective Immune Cell Function in the Tumor Immune Response

The vasculature plays a major role in regulating the tumor immune cell response although the underlying mechanisms explaining such effects remain poorly understood. This review discusses current knowledge on known vascular functions with a viewpoint on how they may yield distinct immune responses. The vasculature might directly influence selective immune cell infiltration into tumors by its cell surface expression of cell adhesion molecules, expression of cytokines, cell junction properties, focal adhesions, cytoskeleton and functional capacity. This will alter the tumor microenvironment and unleash a plethora of responses that will influence the tumor’s immune status. Despite our current knowledge of numerous mechanisms operating, the field is underexplored in that few functions providing a high degree of specificity have yet been provided in relation to the enormous divergence of responses apparent in human cancers. Further exploration of this field is much warranted.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

Integrated proteomic analysis of tumor necrosis factor α and interleukin 1β-induced endothelial inflammation

The vascular endothelium provides a unique interaction plane for plasma proteins and leukocytes in inflammation. The pro-inflammatory cytokines Tumor Necrosis Factor α (TNFα) and interleukin 1β (IL-1β) have a profound effect on endothelial cells, which includes increased levels of adhesion molecules and a disrupted barrier function. To assess the endothelial response to these cytokines at the protein level, we evaluated changes in the whole proteome, cell surface proteome and phosphoproteome after 24 h of cytokine treatment. The effects of TNFα and IL-1β on endothelial cells were strikingly similar and included changes in proteins not previously associated with endothelial inflammation. Temporal profiling revealed time-dependent proteomic changes, including a limited number of early responsive proteins such as adhesion receptors ICAM1 and SELE. In addition, this approach uncovered a greater number of late responsive proteins, including proteins related to self-antigen peptide presentation, and a transient increase in ferritin. Peptide-based cell surface proteomics revealed extensive changes at the cell surface, which were in agreement with the whole proteome. In addition, site-specific changes within ITGA5 and ICAM1 were detected. Combined, our integrated proteomic data provide detailed information on endothelial inflammation, emphasize the role of the extracellular matrix therein, and include potential targets for therapeutic intervention. SIGNIFICANCE: Pro-inflammatory cytokines induce the expression of cell adhesion molecules in vascular endothelial cells. These molecules mediate the adhesion and migration of immune cells across the vessel wall, which is a key process to resolve infections in the underlying tissue. Dysregulation of endothelial inflammation can contribute to vascular diseases and the vascular endothelium is therefore an attractive target to control inflammation. Current strategies targeting endothelial adhesion molecules, including PECAM, CD99, ICAM1 and VCAM1 do not completely prevent transmigration. To identify additional therapeutic targets, we mapped the endothelial proteome after pro-inflammatory cytokine treatment. In addition to the whole proteome, we assessed the surface proteome to focus on cell adhesion molecules, and the phosphoproteome to uncover protein activation states. Here, we present an integrated overview of affected processes which further improves our understanding of endothelial inflammation and may eventually aid in therapeutic intervention of imbalanced inflammation.

Involvement of TIMP-1 in PECAM-1-mediated tumor dissemination

Platelet endothelial cell adhesion molecule-1 (PECAM-1) is expressed on the vascular endothelium and has been implicated in the late progression of metastatic tumors. The activity of PECAM-1 appears to be mediated by modulation of the tumor microenvironment (TME) and promotion of tumor cell proliferation, rather than through the stimulation of tumor angiogenesis. The present study aimed to extend those initial findings by indicating that the presence of functional PECAM-1 on the endothelium promotes a proliferative tumor cell phenotype in vivo, as well as in tumor cell (B16-F10 melanoma and 4T1 breast cancer cell lines) co-culture assays with mouse endothelial cells (ECs) or a surrogate EC line (REN-MP). The pro-proliferative effects were mediated by soluble endothelial-derived factors that were dependent on PECAM-1 homophilic ligand interactions, but which were independent of PECAM-1-dependent signaling. Further analysis of the conditioned media obtained from tumor/EC and tumor/REN-MP co-cultures identified TIMP metallopeptidase inhibitor-1 (TIMP-1) as a PECAM-1-regulated factor, the targeting of which in the tumor cell/REN-MP system inhibited tumor cell proliferation. In addition, TIMP-1 expression was decreased in metastatic tumors from the lungs of PECAM-1-null mice, thus providing evidence of the in vivo significance of co-culture studies. Taken together, these studies indicated that endothelial PECAM-1, through PECAM-1-dependent homophilic binding interactions, may induce release of TIMP-1 from the endothelium into the TME, thus leading to increased tumor cell proliferation.

How leukocytes cross the vascular endothelium

Immune responses depend on the ability of leukocytes to move from the circulation into tissue. This is enabled by mechanisms that guide leukocytes to the right exit sites and allow them to cross the barrier of the blood vessel wall. This process is regulated by a concerted action between endothelial cells and leukocytes, whereby endothelial cells activate leukocytes and direct them to extravasation sites, and leukocytes in turn instruct endothelial cells to open a path for transmigration. This Review focuses on recently described mechanisms that control and open exit routes for leukocytes through the endothelial barrier.

Sepsis lethality via exacerbated tissue infiltration and TLR-induced cytokine production by neutrophils is integrin α3β1-dependent

Integrin-mediated migration of neutrophils to infected tissue sites is vital for pathogen clearance and therefore host survival. Although β2 integrins have been shown to mediate neutrophil transendothelial migration during systemic and local inflammation, relatively little information is available regarding neutrophil migration in sepsis beyond the endothelial cell layer. In this study, we report that integrin α3β1 (VLA-3; CD49c/CD29) is dramatically upregulated on neutrophils isolated from both human septic patients and in mouse models of sepsis. Compared with the α3β1 (low) granulocytes, α3β1 (high) cells from septic animals displayed hyperinflammatory phenotypes. Administration of a α3β1 blocking peptide and conditional deletion of α3 in granulocytes significantly reduced the number of extravasating neutrophils and improved survival in septic mice. In addition, expression of α3β1 on neutrophils was associated with Toll-like receptor-induced inflammatory responses and cytokine productions. Thus, our results show that α3β1 is a novel marker of tissue homing and hyperresponsive neutrophil subtypes in sepsis, and blocking of α3β1 may represent a new therapeutic approach in sepsis treatment.

The Role of Platelet-Endothelial Cell Adhesion Molecule-1 in Atheroma Formation Varies Depending on the Site-Specific Hemodynamic Environment

Objective—

Polymorphisms in the platelet-endothelial cell adhesion molecule (PECAM-1)-1 gene are linked to increased risk of coronary artery disease. Because PECAM-1 has been demonstrated to form a mechanosensory complex that can modulate inflammatory responses in murine arterial endothelial cells, we hypothesized that PECAM-1 contributes to atherogenesis in a shear-dependent and site-specific manner.

Approach and Results—

ApoE –/– mice that were wild-type, heterozygous, or deficient in PECAM-1 were placed on a high-fat diet. Detailed analysis of the aorta at sites with differing hemodynamics revealed that PECAM-1–deficient mice had reduced disease in areas of disturbed flow, whereas plaque burden was increased in areas of steady, laminar flow. In concordance with these observations, bone marrow chimera experiments revealed that hematopoietic PECAM-1 resulted in accelerated atheroma formation in areas of laminar and disturbed flow, however endothelial PECAM-1 moderated disease progression in areas of high sheer stress. Moreover, using shear stress–modifying carotid cuffs, PECAM-1 was shown to promote macrophage recruitment into lesions developing in areas of low shear stress.

Conclusions—

PECAM-1 on bone marrow cells is proatherogenic irrespective of the hemodynamic environment, however endothelial cell PECAM-1 is antiatherogenic in high shear environments. Thus, targeting this pathway therapeutically would require a cell-type and context-specific strategy.

Delay of migrating leukocytes by the basement membrane deposited by endothelial cells in long-term culture

We investigated the migration of human leukocytes through endothelial cells (EC), and particularly their underlying basement membrane (BM). EC were cultured for 20 days on 3 μm-pore filters or collagen gels to form a distinct BM, and then treated with tumour necrosis factor-α, interleukin-1β or interferon-γ. Neutrophil migration through the cytokine-treated EC and BM was delayed for 20-day compared to 4-day cultures. The BM alone obstructed chemotaxis of neutrophils, and if fresh EC were briefly cultured on stripped BM, there was again a hold-up in migration. In studies with lymphocytes and monocytes, we could detect little hold-up of migration for 20-day versus 4-day cultures, in either the filter- or gel-based models. Direct microscopic observations showed that BM also held-up neutrophil migration under conditions of flow. Treatment of upper and/or lower compartments of filters with antibodies against integrins, showed that neutrophil migration through the endothelial monolayer was dependent on β₂-integrins, but not β1- or β₃-integrins. Migration from the subendothelial compartment was supported by β1- and β₂-integrins for all cultures, but blockade of β₃-integrin only inhibited migration effectively for 20-day cultures. Flow cytometry indicated that there was no net increase in expression of β1- or β3-integrins during neutrophil migration, and that their specific subendothelial function was likely dependent on turnover of integrins during migration. These studies show that BM is a distinct barrier to migration of human neutrophils, and that β₃-integrins are particularly important in crossing this barrier. The lesser effect of BM on lymphocytes and monocytes supports the concept that crossing the BM is a separate, leukocyte-specific, regulated step in migration.

Mast cell adhesion to bronchial smooth muscle in asthma specifically depends on CD51 and CD44 variant 6

BACKGROUND

Mast cells infiltrate the bronchial smooth muscle (BSM) in asthmatic patients, but the mechanism of mast cell adhesion is still unknown. The adhesion molecules CD44 (i.e. hyaluronate receptor) and CD51 (i.e. vitronectin receptor) are widely expressed and bind to many extracellular matrix (ECM) proteins. The aims of the study are (i) to identify the role of ECM in mast cell adhesion to BSM and (ii) to examine the role of CD51 and CD44 in this adhesion.

METHODS

Human lung mast cells, human mast cell line (HMC-1), and BSM cells from control donors or asthmatic patients were cultured in the presence/absence of various cytokines. Mast cell-BSM interaction was assessed using (3)H-thymidine-pulsed mast cells, confocal immunofluorescence, or electron microscopy. Adhesion molecules expression and collagen production on both cell types were evaluated by quantitative RT-PCR, western blot, and flow cytometry.

RESULTS

Mast cell adhesion to BSM cells mostly involved type I collagen of the ECM. Such an adhesion was increased in normal BSM cells under inflammatory condition, whereas it was maximal in asthmatic BSM cells. Blockade of either CD51 or CD44 significantly decreased mast cell adhesion to BSM. At the molecular level, protein and the transcriptional expression of type I collagen, CD51 or CD44 remained unchanged in asthmatic BSM cells or in mast cells/BSM cells under inflammatory conditions, whereas that of CD44 variant isoform 6 (v6) was increased.

CONCLUSIONS

Mast cell-BSM cell adhesion involved collagen, CD44, and CD51, particularly under inflammatory conditions. CD44v6 expression is increased in asthmatic BSM cells.

Methods for quantitation of leukocyte chemotaxis and fugetaxis

Chemoattraction and chemorepulsion are complex directional responses of a cell to external chemotactic stimuli. The decision of a cell to move towards or away from a chemokinetic source includes detection and quantitation of the gradient of the chemotactic agent, biochemical transmission of the stimulus, and translation into a directional migration. This chapter describes a number of in vitro and in vivo assays that can be used to generate and measure both chemoattraction and chemorepulsion of leucocytes. These tools may eventually allow the further characterisation of the mechanism of this complex and physiologically and pathologically important phenomenon.

Predictive value of C-reactive protein after drug-eluting stent implantation

During the last few decades, with the evolution of techniques and materials and the increasing experience of operators, percutaneous coronary interventions (PCI) have become an equally efficient alternative to coronary artery bypass grafts for the treatment of most coronary stenoses. Bare-metal stent implantation represented a major step forward, compared with plain old balloon angioplasty (POBA), by improving the immediate angiographic success. However, the incidence of in-stent restenosis (ISR) remained unacceptably high. Development of the drug-eluting stent (DES) significantly improved the outcome of PCI by dramatically abating the rate of ISR and reducing the incidence of target lesion revascularization. However, ISR has not been eliminated and the persistence of metal vessel scaffolding also raises concern regarding the occurrence of late or very late stent thrombosis. POBA and stent implantation have been shown to induce a local and systemic inflammatory response, whose magnitude is associated with worse clinical outcome, and they increase the risk of ISR. C-reactive protein, a marker of systemic inflammation, has been demonstrated to predict clinical and angiographic outcome after POBA or bare-metal stent implantation. However, conflicting data regarding the prognostic value of C-reactive protein following DES implantation are available. In this paper, we review the literature regarding the clinical and pathophysiological association between inflammation and prognosis after DES implantation and suggest some possible therapeutic approaches to reduce inflammatory burden with the aim to improve clinical and angiographic outcome after PCI.

Human leukocyte transmigration across Galalpha(1,3)Gal-negative porcine endothelium is regulated by human CD18 and CD99

BACKGROUND

In pig-to-human xenotransplantation cross-species receptor interactions mediate cellular infiltration and rejection of porcine grafts. However, the mechanisms responsible for recruitment of human leukocyte subsets across porcine endothelial cells (EC) remain largely unknown. Here, we investigated the role of CD99, CD18, and Galalpha(1,3)Gal (Gal) in this process.

METHODS

Adhesion and transmigration of human peripheral blood mononuclear cell (PBMC) subsets on Gal and Gal porcine EC (pEC) and on human EC was analyzed using a two-compartment system separated by a permeable membrane. The mechanisms of human PBMC recruitment to pEC were investigated by blocking cell surface receptors and by differentially measuring adhesion and transendothelial migration (TEM).

RESULTS

Blocking of CD18, but not CD99, decreased human PBMC adhesion on pEC, whereas blocking of CD18 or CD99 strongly reduced the subsequent human PBMC TEM across pEC. The inhibitory effect of CD99 blockade was slightly stronger across pEC as compared with human EC. A critical role for Gal in TEM of human monocytes, B, natural killer (NK), NK/T, and T cells was excluded by evaluating TEM across pEC derived from Gal and Gal pigs.

CONCLUSIONS

CD99 and CD18, but not Gal, play a critical role in human monocyte and lymphocyte TEM across pEC, and their respective porcine ligands may serve as targets to specifically inhibit human leukocyte recruitment in pig-to-human xenotransplantation.

A multicenter, randomized, open-label, therapeutic, and exploratory trial to evaluate the tolerability and efficacy of platelet glycoprotein IIb/IIIa receptor blocker (Clotinab) in high-risk patients with percutaneous coronary intervention

PURPOSE

This study was designed as a multicenter, randomized, open-label study to evaluate the efficacy and tolerability of Clotinab. We expected to obtain same results as with ReoPro in improving ischemic cardiac complications in high-risk patients who were about to undergo percutaneous coronary intervention (PCI).

PATIENTS AND METHODS

Patients of 19-80 years of age with acute coronary syndrome (ACS) who were about to undergo PCI were enrolled. After screening and confirmation of eligibility, patients were randomly assigned to different groups. Clotinab was given to 84 patients (58.7+/-10.6 years, M:F=68:16)and ReoPro(59.0+/-10.5 years, M:F=30:10) was given to 40 patients before PCI. The primary efficacy endpoint was the onset of major adverse cardiac event (MACE) within 30 days from day 1. The tolerability endpoints were assessed based on bleeding, thrombocytopenia, change in Hb/Hct, human antichimetric antibody development, and adverse events.

RESULTS

The number of Clotinab patients experiencing MACE was 0 out of 76 per protocol (PP) patients. The MACE rate was 0%, and its 95% exact CI was [0.00-4.74%]. A major bleeding event developed in 3 patients in the ReoPro group. The probability of MACE onset in Clotinab was estimated to be less than 5%. There was no clinically significant result in tolerability variables.

CONCLUSION

Clotinab is an effective and safe medicine in preventing ischemic cardiac complications for high-risk patients who will receive PCI.

Src tyrosine kinases mediate activations of NF-kappaB and integrin signal during lipopolysaccharide-induced acute lung injury

Src tyrosine kinases (TKs) are signaling proteins involved in cell signaling pathways toward cytoskeletal, membrane and nuclear targets. In the present study, using a selective Src TK inhibitor, PP1, we investigated the roles of Src TKs in the key pulmonary responses, NF-kappaB activation, and integrin signaling during acute lung injury in BALB/C mice intratracheally treated with LPS. LPS resulted in c-Src phosphorylation in lung tissue and the phospho-c-Src was predominantly localized in recruited neutrophils and alveolar macrophages. PP1 inhibited LPS-induced increases in total protein content in bronchoalveolar lavage fluid, neutrophil recruitment, and increases in the production or activity of TNF-alpha and matrix metalloproteinase-9. PP1 also blocked LPS-induced NF-kappaB activation, and phosphorylation and degradation of IkappaB-alpha. The inhibition of NF-kappaB activation by PP1 correlated with a depression of LPS-induced integrin signaling, which included increases in the phosphorylations of integrin beta(3), and of the focal adhesion kinase (FAK) family members, FAK and Pyk2, in lung tissue, and reductions in the fibrinogen-binding activity of alveolar macrophages. Moreover, treatment with anti-alpha(v), anti-beta(3), or Arg-Gly-Asp-Ser (RGDS), inhibited LPS-induced NF-kappaB activation. Taken together, our findings suggest that Src TKs play a critical role in LPS-induced activations of NF-kappaB and integrin (alpha(v)beta(3)) signaling during acute lung injury. Therefore, Src TK inhibition may provide a potential means of ameliorating inflammatory cascade-associated lung injury.

The Role of Platelet/Endothelial Cell Adhesion Molecule–1 (CD31) and CD38 Antigens in Marrow Microenvironmental Retention of Acute Myelogenous Leukemia Cells

In acute myelogenous leukemia (AML), leukemic cell-microenvironment interactions within various niches (stromal/osteoblastic or sinusoidal endothelial cell niches) have a role in leukemia cell survival and drug resistance. The AML leukemic cells express platelet/endothelial cell adhesion molecule-1 (CD31) and CD38, two adhesion molecules that could interact with microenvironmental elements, i.e., CD31 on the surface of marrow endothelial cells (CD31/CD31 and CD38/CD31 interactions) and hyaluronate (CD38/hyaluronate interactions). We report a physical association of these two antigens on the plasma membrane of myeloid leukemic cells. In this context, in vitro experiments done using interaction-blocking anti-CD31 and anti-CD38 monoclonal antibodies (CLB-HEC75 and OKT10, respectively) indicate that an excess of CD31 on the cell membrane of leukemic cells (CD31/CD38 MFI ratio >1) promotes a homotypic interaction with marrow endothelial cells, resulting in higher transendothelial migration. Conversely, an excess of CD38 (CD31/CD38 MFI ratio <1) allows leukemic cells to be entrapped within the bone marrow microenvironment through hyaluronate adhesion. The results obtained in vitro using fluorescence resonance energy transfer, co-capping, and co-immunoprecipitation experiments, and hyaluronate adhesion and transendothelial migration assays, are supported by immunophenotypic characterization of marrow leukemic cells from 78 AML patients on which CD38 expression levels were found to be positively correlated with those of CD31. Importantly, the excess of CD31 in those samples was associated with a higher peripheral WBC count. These findings indicate that bone marrow retention of AML cells depends on CD31 and CD38 coexpression levels.

PECAM-1: a multi-functional molecule in inflammation and vascular biology

Platelet endothelial cell adhesion molecule-1 (PECAM-1 or CD31) is a molecule expressed on all cells within the vascular compartment, being expressed to different degrees on most leukocyte sub-types, platelets, and on endothelial cells where its expression is largely concentrated at junctions between adjacent cells. As well as exhibiting adhesive properties, PECAM-1 is an efficient signaling molecule and is now known to have diverse roles in vascular biology including roles in angiogenesis, platelet function, and thrombosis, mechanosensing of endothelial cell response to fluid shear stress, and regulation of multiple stages of leukocyte migration through venular walls. This review will focus on some new developments with respect to the role of PECAM-1 in inflammation and vascular biology, highlighting the emerging complexities associated with the functions of this unique molecule.

Anti-inflammatory effects of alphav integrin antagonism in acute kidney allograft rejection

Integrin-mediated cell adhesion and signaling is essential to vascular development and inflammatory processes. Elevated expression of integrin alpha(v)beta(3) has been detected in ischemia-reperfusion injury and rejecting heart allografts. We thus hypothesized that the inhibition of alpha(v)-associated integrins may have potent anti-inflammatory effects in acute kidney allograft rejection. We studied the effects of a peptidomimetic antagonist of alpha(v) integrins in two rat models of renal allotransplantation, differing in degree of major histocompatibility complex mismatch. Integrin alpha(v)beta(3) was up-regulated in rejecting renal allografts. Integrin antagonist reduced the histological signs of acute rejection, the intensity of the mononuclear cell infiltration, and cell proliferation in the grafted kidneys. This could be correlated to a reduced leukocyte-endothelial interaction and an improved peritubular microcirculation observed by intravital microscopy. In vitro under laminar flow conditions, the arrest of monocytes to interleukin-1beta-activated endothelium was decreased. Furthermore, in co-culture models the proliferation and transmigration of monocytes/macrophages, endothelium, and fibroblasts induced by renal tubular epithelia was efficiently inhibited by alpha(v) integrin antagonism. These data reveal an important role of this integrin subclass in leukocyte recruitment and development and maintenance of acute rejection; blockade of alpha(v) integrins may provide a new therapeutic strategy to attenuate acute allograft rejection.

The Neutrophil-specific Antigen CD177 Is a Counter-receptor for Platelet Endothelial Cell Adhesion Molecule-1 (CD31)

Human neutrophil-specific CD177 (NB1 and PRV-1) has been reported to be up-regulated in a number of inflammatory settings, including bacterial infection and granulocyte-colony-stimulating factor application. Little is known about its function. By flow cytometry and immunoprecipitation studies, we identified platelet endothelial cell adhesion molecule-1 (PECAM-1) as a binding partner of CD177. Real-time protein-protein analysis using surface plasmon resonance confirmed a cation-dependent, specific interaction between CD177 and the heterophilic domains of PECAM-1. Monoclonal antibodies against CD177 and against PECAM-1 domain 6 inhibited adhesion of U937 cells stably expressing CD177 to immobilized PECAM-1. Transendothelial migration of human neutrophils was also inhibited by these antibodies. Our findings provide direct evidence that neutrophil-specific CD177 is a heterophilic binding partner of PECAM-1. This interaction may constitute a new pathway that participates in neutrophil transmigration.

Integrin beta 3 genotype influences asthma and allergy phenotypes in the first 6 years of life

BACKGROUND

The integrin beta3 gene (ITGB3) encodes a subunit of the platelet and monocyte-specific fibrinogen receptor and the widely expressed vitronectin receptor, which have diverse roles in cell migration, adhesion, and signaling. Previous work from our laboratory reported associations between single nucleotide polymorphisms (SNPs) in ITGB3 and asthma and allergic sensitization in 4 populations.

OBJECTIVE

To examine whether SNPs in ITGB3 are associated with the development of asthma and allergic phenotypes in early life.

METHODS

We typed 13 SNPs in 206 children participating in a birth cohort study and tested for associations with asthma and allergy phenotypes in the first 6 years of life.

RESULTS

Our study revealed significant associations between SNPs in ITGB3 and asthma, wheezing, and IgE levels, suggesting an early role for this gene in the development of asthma and allergy. In particular, SNPs at the 3' end of the gene were significantly associated with IgE levels beginning at 1 year of age, whereas a SNP in intron 1 showed significant interaction effects with viral respiratory illness in infancy on asthma susceptibility.

CONCLUSION

Our results suggest that genetic variation in ITGB3 contributes to asthma susceptibility and allergic sensitization, and that the effects of this gene begin early in life. Similar to our earlier study, different SNPs in the gene are associated with asthma and IgE.

CLINICAL IMPLICATIONS

ITGB3 may play an important role in the development of asthma and allergy and may represent a potential therapeutic target for the treatment of these disorders.

Fibrinogen inhibits neurite outgrowth via beta 3 integrin-mediated phosphorylation of the EGF receptor

Changes in the molecular and cellular composition of the CNS after injury or disease result in the formation of an inhibitory environment that inhibits the regeneration of adult mammalian CNS neurons. Although a dramatic change in the CNS environment after traumatic injury or disease is hemorrhage because of vascular rupture or leakage of the blood-brain barrier, the potential role for blood proteins in repair processes remains unknown. Here we show that the blood protein fibrinogen is an inhibitor of neurite outgrowth that is massively deposited in the spinal cord after injury. We show that fibrinogen acts as a ligand for beta3 integrin and induces the transactivation of EGF receptor (EGFR) in neurons. Fibrinogen-mediated inhibition of neurite outgrowth is reversed by blocking either beta3 integrin or phoshorylation of EGFR. Inhibition of Src family kinases that mediate the cross-talk between integrin and growth factor receptors rescue the fibrinogen-induced phosphorylation of EGFR. These results identify fibrinogen as the first blood-derived inhibitor of neurite outgrowth and suggest fibrinogen-induced EGFR transactivation on neuronal cells as a molecular link between vascular and neuronal damage in the CNS after injury.

Beta 3 integrins regulate lymphocyte migration and cytokine responses in heart transplant rejection

Integrin alpha v beta 3 is important for cell survival, signaling and migration, particularly during angiogenesis and tumorigenesis, where it has been proposed as a therapeutic target. alpha v beta 3 is up-regulated following transplantation and beta 3 polymorphisms are associated with increased acute kidney rejection, suggesting that alpha v beta 3 may also play a role in transplant rejection. Here, using a model of allogeneic heart transplantation, we show that allograft survival is prolonged in beta 3 integrin-deficient (beta 3(-/-)) mice. This is associated with Th2-type immune responses and reduced T-cell infiltration into grafts and T cells from beta 3(-/-) mice show impaired adhesion and migration, consistent with a role for alpha v beta 3 in transmigration. These studies provide evidence that targeting beta 3 integrins impairs recruitment of effector cells and alters cytokine production, so prolonging graft survival. We also show that low doses of blocking antibodies against leukocyte function associated antigen-1 (LFA-1)/alpha L beta 2 and very late antigen-4 (VLA-4)/alpha 4 beta 1, when combined with deletion of beta 3, lead to long-term survival of allografts with no evidence of chronic rejection. Hence we provide strong mechanistic evidence supporting previous genetic studies, demonstrate the involvement of beta 3 integrins in both acute and chronic rejection and identify beta 3 as a new target for immunosuppressive therapy.

Randomized Early Versus Late Abciximab in Acute Myocardial Infarction Treated With Primary Coronary Intervention (RELAx-AMI Trial)

OBJECTIVES

This prospective randomized trial evaluates the impact of early abciximab administration on angiographic and left ventricular function parameters.

BACKGROUND

Glycoprotein IIb/IIIa inhibitors improve myocardial reperfusion in patients with acute myocardial infarction (AMI) undergoing primary percutaneous coronary intervention (PCI), but optimal timing of administration remains unclear.

METHODS

Two-hundred ten consecutive patients with first AMI undergoing primary PCI were randomized to abciximab administration either in the emergency room (early group: 105 patients) or in the catheterization laboratory, after coronary angiography (late group: 105 patients). Primary end points were initial Thrombolysis In Myocardial Infarction (TIMI) flow grade, corrected TIMI frame count (cTFC), and myocardial blush grade (MBG), as well as left ventricular function recovery as assessed by serial echocardiographic evaluations.

RESULTS

Angiographic pre-PCI analysis showed a significantly better initial TIMI flow grade 3 (24% vs. 10%; p = 0.01), cTFC (78 +/- 30 frames vs. 92 +/- 21 frames; p = 0.001), and MBG 2 or 3 (15% vs. 6%; p = 0.02) favoring the early group. Consistently, post-PCI tissue perfusion parameters were significantly improved in the early group, as assessed by 60-min ST-segment reduction > or =70% (50% vs. 35%; p = 0.03) and MBG 2 or 3 (79% vs. 58%; p = 0.001). Left ventricular function recovery at 1 month was significantly greater in the early group (mean gain ejection fraction 8 +/- 7% vs. 6 +/- 7%, p = 0.02; mean gain wall motion score index 0.4 +/- 0.3 vs. 0.3 +/- 0.3, p = 0.03).

CONCLUSIONS

In patients with AMI treated with primary PCI, early abciximab administration improves pre-PCI angiographic findings, post-PCI tissue perfusion, and 1-month left ventricular function recovery, possibly by starting early recanalization of the infarct-related artery.

The role of JAM-A and PECAM-1 in modulating leukocyte infiltration in inflamed and ischemic tissues

Innate and adaptive immunological responses are accompanied by leukocyte adhesion to the blood-vessel wall and their subsequent infiltration into the underlying tissues. In the majority of the cases, leukocytes cross the endothelium by squeezing through the border of apposed endothelial cells, a process that is known as diapedesis. Many data suggest that proteins at endothelial junctions establish homophilic interactions with identical proteins, which are present on leukocytes. These interactions might then direct the passage of leukocytes through the endothelial border. In this review, we focus on two endothelial junctional proteins [junctional adhesion molecule-A (JAM-A) and PECAM], which play an important role in leukocyte diapedesis. In vivo data with blocking antibodies or inactivation of JAM-A and PECAM genes indicate that the role of these two proteins depends on the stimulus and the experimental model used.

PECAM-1 isoform-specific activation of MAPK/ERKs and small GTPases: implications in inflammation and angiogenesis

Platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) is expressed on the surface of endothelial cells (EC) and leukocytes. PECAM-1 plays an important role in endothelial-leukocyte and endothelial-endothelial cell-cell interactions. The anti-PECAM-1 antibody-mediated blockade of these interactions inhibits transendothelial migration (TEM) of leukocytes and angiogenesis. PECAM-1 may accommodate these processes through the regulation of cell adhesive and migratory mechanisms. How PECAM-1 regulates these dynamic processes remain unknown. Here we show that PECAM-1 transduces outside-in signals, which activate MAPK/ERKs and small GTPases. This occurs through PECAM-1-mediated formation of intracellular-signaling complexes, Shc/Grb2/SOS1 and/or Crkl/C3G, which is initiated by PECAM-1 engagement on the surface of leukocytes and/or EC. Src, SHP2, and alternative PECAM-1 pre-mRNA splicing play a regulatory role in these signaling events. Our findings reveal that PECAM-1 engagement on the cell surface can transduce "outside-in" signals and activate MAPK/ERKs and small GTPases, impacting both cadherin-mediated cell-cell and integrin-mediated cell-matrix interactions. Thus, we propose PECAM-1 is an important mediator of vascular barrier and regulator of leukocyte and EC adhesion and migration.

Abciximab and angiographic restenosis after coronary stent placement. Analysis of the angiographic substudy of ISAR-REACT--a double-blind, placebo-controlled, randomized trial evaluating abciximab in patients undergoing elective percutaneous coronary interventions after pretreatment with a high loading dose of clopidogrel

BACKGROUND

ISAR-REACT was a trial designed to evaluate whether the glycoprotein IIb/IIIa inhibitor abciximab is beneficial in patients undergoing elective percutaneous coronary intervention (PCI) with stent placement after pretreatment with a 600 mg loading dose of clopidogrel. Objective for the angiographic substudy was to determine the impact of abciximab on angiographic restenosis after coronary stent placement. Previous analyses have suggested a reduction in the incidence of restenosis after the administration of abciximab.

METHODS

The angiographic substudy comprises 1885 of 2159 patients enrolled in ISAR-REACT: 994 patients were randomly assigned to abciximab and 941 patients to placebo. All patients were scheduled for a routine angiographic follow-up after 6 months (performed in 80% of eligible patients). End points for the angiographic substudy were the rates of angiographic restenosis (> or = 50% diameter stenosis) and target lesion revascularization.

RESULTS

The incidence of angiographic restenosis was 27% in the abciximab group and 29% in the placebo group (relative risk 0.92, 95% CI 0.79-1.06, P = .27). Late angiographic lumen loss was 0.95 +/- 0.68 and 0.99 +/- 0.70 mm, respectively (P = .25). Similar results were obtained in a subgroup analysis focusing on high-risk subsets. The rate of target lesion revascularization procedures was 22% in the abciximab group and 23% in the placebo group (relative risk 0.94, 95% CI 0.79-1.12, P = .52).

CONCLUSIONS

In low- to intermediate-risk patients who undergo elective PCI after pretreatment with a high loading dose of clopidogrel >2 hours before PCI, the additional administration of the glycoprotein IIb/IIIa inhibitor abciximab is not associated with a significant reduction in angiographic restenosis.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Neutrophil chemorepulsion in defined interleukin-8 gradients in vitro and in vivo

We report for the first time that primary human neutrophils can undergo persistent, directionally biased movement away from a chemokine in vitro and in vivo, termed chemorepulsion or fugetaxis. Robust neutrophil chemorepulsion in microfluidic gradients of interleukin-8 (IL-8; CXC chemokine ligand 8) was dependent on the absolute concentration of chemokine, CXC chemokine receptor 2 (CXCR2), and was associated with polarization of cytoskeletal elements and signaling molecules involved in chemotaxis and leading edge formation. Like chemoattraction, chemorepulsion was pertussis toxin-sensitive and dependent on phosphoinositide-3 kinase, RhoGTPases, and associated proteins. Perturbation of neutrophil intracytoplasmic cyclic adenosine monophosphate concentrations and the activity of protein kinase C isoforms modulated directional bias and persistence of motility and could convert a chemorepellent to a chemoattractant response. Neutrophil chemorepulsion to an IL-8 ortholog was also demonstrated and quantified in a rat model of inflammation. The finding that neutrophils undergo chemorepulsion in response to continuous chemokine gradients expands the paradigm by which neutrophil migration is understood and may reveal a novel approach to our understanding of the homeostatic regulation of inflammation.

Therapeutic Effect of Anti–TNF-α Antibodies in an Experimental Model of Anti-Neutrophil Cytoplasm Antibody–Associated Systemic Vasculitis

The therapeutic options for anti-neutrophil cytoplasm antibody (ANCA)-associated systemic vasculitis (AASV) remain limited and hampered by adverse effects. One potential novel therapeutic avenue involves inhibition of TNF-alpha, with encouraging uncontrolled data in humans with one agent (infliximab) but disappointing controlled data from another (etanercept). For investigating the potential role of TNF-alpha as a therapeutic target in AASV, the effect of an anti-rat TNF-alpha mAb (CNTO 1081) in a rat model of AASV was investigated. For testing the effect of TNF-alpha blockade in this model, starting on day 28 after immunization (a point when glomerulonephritis is established), animals were randomized to treatment with CNTO 1081 or control mouse IgG. Treatment with CNTO 1081 significantly reduced albuminuria (mean 1.1 +/- 0.3 mg/24 h CNTO 1081 versus 8.0 +/- 1.9 controls; P < 0.05) and crescent formation (0% CNTO 1081 versus 60% controls; P < 0.05). Lung hemorrhage was also reduced (CNTO 1081: median score 0, range 0 to 2; controls: 2, range 1 to 3; P < 0.05). When analyzed by intravital microscopy, there was a 43% inhibition of leukocyte transmigration in mesenteric venules in response to topical CXCL1 (a neutrophil chemoattractant) in the CNTO 1081 group compared with controls (P < 0.001). Anti-myeloperoxidase antibody titers were similar in both groups throughout the study. In conclusion, these findings indicate that TNF-alpha plays an important role in the pathogenesis of experimental autoimmune vasculitis and suggest that blockade of this cytokine with an mAb is effective in treating established vasculitis. The therapeutic action of anti-TNF-alpha reagents may be mediated, in part, by suppression of the enhanced leukocyte-endothelial interactions in this disorder.

Antineutrophil cytoplasm antibodies directed against myeloperoxidase augment leukocyte-microvascular interactions in vivo

Systemic small vessel vasculitis is associated with antineutrophil cytoplasm antibodies (ANCAs). While there is mounting in vitro evidence to suggest that ANCAs are capable of enhancing leukocyte-endothelial interactions, no in vivo evidence for this has been provided. In this study a novel rat model of ANCA-associated experimental autoimmune vasculitis (EAV), induced by immunization with human myeloperoxidase (MPO), was used to analyze directly the potential effect of ANCAs on leukocyte-venular wall interactions in vivo as observed by intravital microscopy. These rats developed anti-MPO antibodies directed against rat leukocytes, showed pathologic evidence of small vessel vasculitis, and had enhanced leukocyte adhesion and transmigration in response to the chemokine Groα (CXCL1 [CXC ligand 1]). Passive transfer of immunoglobulin from rats with EAV to naive rats conferred enhanced adhesion and transmigration responses in the recipients. Furthermore, rats with EAV and recipients of ANCA-positive immunoglobulin developed extensive microvascular injury, as manifested by mesenteric hemorrhage, in response to CXCL1. This study provides the first direct in vivo evidence for the ability of ANCAs to enhance leukocyteendothelial interactions and cause microvascular hemorrhage, thereby providing a mechanism by which ANCAs could exert pathogenic effects in systemic vasculitis. (Blood. 2005;106:2050-2058)

Rho GTPases and leucocyte-induced endothelial remodelling

Leucocytes in the bloodstream respond rapidly to inflammatory signals by crossing the blood vessel wall and entering the tissues. This process involves adhesion to, and subsequent transmigration across, the endothelium, mediated by a cascade of interactions between adhesion molecules and stimulation of intracellular signalling pathways in both leucocytes and endothelial cells. This leads to changes in endothelial cell morphology that assist leucocyte extravasation, including endothelial cell contraction, intercellular junction disruption, increased permeability, remodelling of the endothelial apical surface and alterations in vesicle trafficking. Rho GTPases play a central role in many of the endothelial responses to leucocyte interaction. In this review, we discuss recent findings on leucocyte-induced alterations to endothelial cells, and the roles of Rho GTPases in these responses.

Variation in ITGB3 is associated with asthma and sensitization to mold allergen in four populations

RATIONALE

Recent genetic studies have implicated integrins in asthma and atopy susceptibility. We therefore evaluated the integrin-beta3 gene (ITGB3), an integrin gene within an asthma linkage peak on chromosome 17, as a candidate for susceptibility to asthma- and atopy-related phenotypes.

METHODS AND MEASUREMENTS

We genotyped and performed association tests on 19 single nucleotide polymorphisms in ITGB3 in the Hutterites, a founder population, and in three outbred replication populations.

MAIN RESULTS

Variation in ITGB3 was strongly associated with susceptibility to bronchial hyperresponsiveness and protection from allergic sensitization to mold allergens in this population. Three independent case-control populations representing Caucasians and African Americans were used to replicate this finding, also revealing ITGB3 alleles that are associated with asthma susceptibility and protection from mold allergen sensitization.

CONCLUSIONS

This study provides evidence that ITGB3 plays a role in the pathogenesis of asthma and sensitization to mold allergens.

Bovine respiratory syncytial virus infection influences the impact of alpha- and beta-integrin-mediated adhesion of peripheral blood neutrophils

Neutrophil migration into the airways and pulmonary tissue is a common finding in bovine respiratory syncytial virus (BRSV) infections. Although neutrophil trans-endothelial migration in general depends on beta2-integrins, alternative integrins such as the alpha4-integrins have been implicated. In this study, rolling and firm adhesion of peripheral blood neutrophils isolated from healthy and BRSV-infected calves to tumour necrosis factor (TNF)-alpha activated pulmonary endothelium was investigated under flow conditions in vitro. For neutrophils obtained from healthy animals, inhibition of the beta2-integrin reduced firm adhesion to 63% and inhibition of alpha4-integrin to 73% compared with untreated controls. Inhibition of both integrins reduced firm adhesion to 25%. Rolling velocity, which is used as a parameter for integrin involvement in neutrophil rolling, increased 1.7-fold by blocking beta2-integrin and was significantly augmented to 2.5-fold by blocking both alpha4- and beta2-integrins. For neutrophils obtained from BRSV-infected animals, however, rolling velocities at 10 days after infection (p.i.) were not influenced by blocking adhesion of alpha4- and beta2-integrins, indicating that these integrins did not support neutrophil rolling. In addition, the inhibition of firm adhesion by blocking both alpha4- and beta2-integrins was reduced significantly 9 days post-infection, resulting in a residual 68% neutrophil binding at 9 days p.i. Non-blocked firm adherence was not reduced, indicating that binding was achieved by other mechanisms than through alpha4- and beta2-integrins. These results demonstrate an important function for alpha4- and beta2-integrins in rolling and firm adherence of bovine neutrophils, to TNF-alpha-activated endothelium and show the dynamic use of these integrins for adhesion and migration by neutrophils in the course of BRSV infection.

Differences in platelet endothelial cell adhesion molecule-1 expression between peripheral circulation and pancreatic microcirculation in cerulein-induced acute edematous pancreatitis

AIM: To investigate the changes of platelet endothelial cell adhesion molecule-1 (PECAM-1) expression on polymorphonuclear leukocytes (PMNs) in peripheral circulation and pancreatic microcirculation in cerulein-induced acute edematous pancreatitis (AEP).

METHODS: Fifty Wistar rats were randomly divided into control group (n = 10) and AEP group (n = 40). A model of AEP was established by subcutaneous injection of cerulein 5.5 and 7.5 μg/kg at 0 and 1 h after the beginning of experiment respectively. PECAM-1 expression on PMNs from splenic vein and inferior vena cava was determined by RT-PCR at mRNA level and determined by flow cytometry at protein level.

RESULTS: In experimental rats, an increased PECAM-1 mRNA expression was seen from 4 to 8 h of AEP in peripheral circulation (0.77±0.25%, 0.76±0.28%, 0.89±0.30%, 1.00±0.21%), while in pancreatic microcirculation, expression decreased from 2 h and reached the lowest level at 6 h of AEP (0.78±0.29%, 0.75±0.26%, 0.62±0.28%, 0.66±0.20%). There were significant differences at 8-h time point of AEP between peripheral circulation and pancreatic microcirculation (1.00±0.21% vs 0.66±0.20%, P<0.05). Meanwhile, the difference at protein level was also found.

CONCLUSION: A reverse expression of PECAM-1 on PMNs was found between peripheral circulation and pancreatic microcirculation, suggesting that inhibition of PECAM-1 expression may improve the pathological change of AEP.

Identification of a novel transcript of human PECAM-1 and its role in the transendothelial migration of monocytes and Ca2+ mobilization

Platelet-endothelial cell adhesion molecule-1 (PECAM-1) is an integral component of endothelial cells and has been implicated in the transendothelial migration (TEM) of circulating leukocytes mediated by its 1st and 2nd extracellular immunoglobulin (Ig)-like domains and regulation of intracellular Ca(2+) homeostasis with its 6th domain. Up-to-date, little is known about the role of the 5th extracellular (Ig)-like domain. We have discovered a novel human PECAM-1 transcript missing the entire 7th exon, which encodes the 5th extracellular (Ig)-like domain of PECAM-1. A synthetic peptide with sequence homology to the 5th domain of PECAM-1 (JHS-7 peptide) and a corresponding polyclonal antibody (JHS-7 Ab) were prepared and their potential role in transendothelial migration and Ca(2+) influx was measured. The JHS-7 peptide and the antibody exerted a dose dependent decrease (50-80%) in the transendothelial migration of freshly isolated human monocytes and a promonocytic cell line (U-937) in resting HUVECs and HUVECs activated with tumor necrosis factor-alpha. This was accompanied by an increase in Ca(2+) influx and decrease in refilling of the intracellular Ca(2+) stores in HUVECs. In summary, we have identified a novel PECAM-1 transcript (Deltaexon 7) and shown that the 5th (Ig)-like domain of PECAM-1 plays a role in monocyte TEM and Ca(2+) homeostasis.

Extracellular signal-regulated kinase (ERK)-dependent gene expression contributes to L1 cell adhesion molecule-dependent motility and invasion

The cell adhesion molecule L1 has been implicated in a variety of motile processes, including neurite extension, cerebellar cell migration, extravasation, and metastasis. Homophilic or heterophilic L1 binding and concomitant signaling have been shown to promote cell motility in the short term. In this report, L1 is also shown to induce and maintain a motile and invasive phenotype by promoting gene transcription. In the presence of serum or platelet-derived growth factor, L1 promotes heightened and sustained activation of the extracellular signal-regulated kinase pathway. Activation of this pathway then induces the expression of motility- and invasion-associated gene products, including the beta(3)-integrin subunit, small GTPases, and the cysteine proteases cathepsin-L and -B. Induction of integrin alpha(v)beta(3) and rac-1 is shown to contribute directly to L1-dependent haptotaxis, whereas induction of cathepsins-L and -B promotes matrix invasion. This study provides a novel translational mechanism to account for the association between L1 expression and motile processes involved in metastasis and development.

Role for platelet-endothelial cell adhesion molecule-1 in macrophage Fcgamma receptor function

Platelet-endothelial cell adhesion molecule-1 (PECAM-1) (CD31), a 130-kD transmembrane glycoprotein that functions in adhesion and signaling, is thought to play a role in some forms of leukocyte transmigration. In the lung, PECAM-1 is highly expressed, yet there have been few studies examining its role in pulmonary pathology. We therefore examined the inflammatory response (measured by bronchoalveolar lavage cell counts and protein content) after several types of lung injury in wild-type and PECAM-1 knockout mice. Consistent with studies in other organs, instillation of an endothelial stimulant (interleukin-1) was PECAM-1-dependent. In contrast, we noted that three other forms of acute lung injury (acid aspiration, adenoviral instillation, and tumor necrosis factor instillation) were completely PECAM-1-independent. Interestingly, in situ immune complex deposition injury, another complex lung disease, was also PECAM-1-dependent. This surprising finding was investigated in more detail and found to be due to a defect in macrophage activation, and not to a blockade of leukocyte transmigration. Experiments in bone marrow chimeric mice as well as ex vivo data demonstrated that Fcgamma receptor-dependent phagocytosis and tumor necrosis factor release were significantly reduced in macrophages derived from PECAM-1 knockout mice. Although PECAM-1 may not be required for transmigration of leukocytes into the alveolar space in many forms of complex lung inflammation, it is important in the function of Fcgamma receptors on alveolar macrophages.

Signaling in leukocyte transendothelial migration

Under a variety of (patho) physiological conditions, leukocytes will leave the bloodstream by crossing the endothelial monolayer that lines the vessels and migrate into the underlying tissues. It is now clear that the process of extravasation involves a range of adhesion molecules on both leukocytes and endothelial cells, as well as extensive intracellular signaling that drives adhesion and chemotaxis on the one hand and controls a transient modulation of endothelial integrity on the other. We review here the current knowledge of the intracellular signaling pathways that are activated in the context of transendothelial migration in leukocytes and in endothelial cells. In leukocytes, polarization of receptors and of the signaling machinery is of key importance to drive adhesion and directional migration. Subsequent adhesion-induced signaling in endothelial cells, mediated by Rho-like GTPases and reactive oxygen species, induces a transient and focal loss of endothelial cell-cell adhesion to allow transmigration of the leukocyte. This review underscores the notion that we have likely just scratched the surface in revealing the complexity of the signaling that controls leukocyte transendothelial migration.

Inflammation as a therapeutic target: a unique role for abciximab

Vascular inflammation is a central pathogenic mechanism for both acute coronary syndromes and the vascular response to injury after percutaneous coronary intervention. The magnitude of vascular inflammation has been correlated with adverse late clinical outcomes (death, myocardial infarction, recurrent ischemia, restenosis). Vascular inflammation is also increased in patients with diabetes mellitus. Many adjunctive pharmacotherapies used in the treatment of acute coronary syndromes or during percutaneous coronary intervention have anti-inflammatory effects, which are distinct from their perceived primary mechanism of action. Data in support of the anti-inflammatory effects of abciximab are presented and the role that these effects may play in modulating atherosclerotic plaque stability and late clinical outcomes is discussed. Vascular inflammation represents the "final common pathway" for many disease processes and thus represents the "ultimate therapeutic target" for pharmacologic intervention.

Agonist-induced capping of adhesion proteins and microparticle shedding in cultures of human renal microvascular endothelial cells

Capping and release of membranous, small (< 1.5 microm) endothelial microparticles were quantified by immunofluorescence microscopy and flow cytometry after treatment of cultures of human renal microvascular endothelial cells with agonists tumor necrosis factor-alpha (TNF-alpha) or mitomycin C. For constitutive marker CD31, both agonist-treated attached, monolayer, and detached, free endothelial cells formed caps and released microparticles. TNF-alpha and mitomycin C induced dissimilar appearing CD31-containing caps after 3 h, followed by endothelial microparticle release after 6 h. The degree of capping correlated with increasing counts of released microparticles. For lymphokine-inducible CD54, TNF-alpha also induced CD54-containing caps and microparticle release, but mitomycin C failed to induce the expression of either entity. Neither capping nor microparticle release caused by TNF-alpha was part of an apoptotic pathway that involved caspase 3. Mitomycin C treatment of endothelial cells caused capping and microparticle release with a time course similar to TNF-alpha induction for 15 to 24 h, but assays for caspase 3 were positive, confirming the apoptotic action of mitomycin C. Membrane capping and microparticle release from endothelial cells are a convenient experimental model for studying protein movement, release of microparticles, and their possible biological significance.

PECAM-1-dependent neutrophil transmigration is independent of monolayer PECAM-1 signaling or localization

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), a tyrosine phosphoprotein highly expressed on endothelial cells and leukocytes, is an important component in the regulation of neutrophil transendothelial migration. Engagement of endothelial PECAM-1 activates tyrosine phosphorylation events and evokes prolonged calcium transients, while homophilic engagement of neutrophil PECAM-1 activates leukocyte beta-integrins. Although PECAM-1 modulates polymorphoneutrophil transmigration via homophilic PECAM-1-PECAM-1 interaction, the mechanisms underlying endothelial PECAM-1 function are unknown. Proposed mechanisms include (1) formation of a haptotactic gradient that "guides" neutrophils to the cell-cell border, (2) service as a "passive ligand" for neutrophil PECAM-1, ultimately mediating activation of neutrophil beta integrins, (3) regulation of endothelial calcium influx, and (4) mediation of SH2 protein association, and/or (5) catenin and non-SH2 protein interaction. Utilizing PECAM-1-null "model" endothelial cells (REN cells), we developed a neutrophil transmigration system to study PECAM-1 mutations that specifically disrupt PECAM-1-dependent signaling and/or PECAM-1 cell localization. We report that interleukin-1 beta (IL-1 beta) elicits PECAM-1-dependent transmigration that requires homophilic PECAM-PECAM-1 engagement, but not heterophilic neutrophil PECAM-1 interactions, and is intercellular adhesion molecule-1 dependent. Conversely, whereas IL-8 and leukotriene-B(4)-mediated transmigration is PECAM-1-independent, PECAM-1 and IL-8-dependent transmigration represent separable and additive components of cytokine-induced transmigration. Surprisingly, neither monolayer PECAM-1-regulated calcium signaling, cell border localization, nor the PECAM-1 cytoplasmic domain was required for monolayer PECAM-1 regulation of neutrophil transmigration. We conclude that monolayer (endothelial cell) PECAM-1 functions as a passive homophilic ligand for neutrophil PECAM-1, which after engagement leads to neutrophil signal transduction, integrin activation, and ultimately transmigration in a stimulus-specific manner.

Platelet endothelial cell adhesion molecule-1 in neutrophil emigration during acute bacterial pneumonia in mice and rats

Platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31) is an adhesion molecule believed to mediate transendothelial migration of neutrophils and other leukocytes after CD11/CD18-mediated adhesion. Our study evaluated the role of PECAM-1 in neutrophil emigration across the pulmonary capillaries and the bronchial microvasculature using blocking anti-PECAM-1 antibodies in mice and rats. Neutrophil emigration was induced by Escherichia coli, a stimulus eliciting CD11/CD18-dependent emigration, or Streptococcus pneumoniae, a stimulus inducing CD11/CD18-independent emigration. Although anti-PECAM-1 antibodies partially inhibited glycogen-induced neutrophil emigration into the peritoneum, neutrophil emigration across either the pulmonary capillaries or the bronchial microvasculature in response to either E. coli or S. pneumoniae was not prevented when the function of PECAM-1 was inhibited in either mice or rats. There was also no increase in the number of intravascular neutrophils within the bronchial vessels after treatment with anti-PECAM-1 antibody. These studies indicate that either CD11/CD18-dependent or -independent adhesion pathways may lead to PECAM-1-independent transendothelial migration through the pulmonary or the bronchial endothelium.

Platelet glycoprotein IIb/IIIa receptor blockade and coronary resistance in unstable angina

OBJECTIVES

We designed a study to explore the effect of glycoprotein (GP) IIb/IIIa blockade on the atherosclerotic plaque and distal coronary vasculature.

BACKGROUND

Platelet GP IIb/IIIa blockers have been proven to be beneficial in acute ischemic syndromes. This effect has also been attributed to the prevention of microvascular obstruction, although the underlying mechanisms have not been fully defined.

METHODS

Eighteen patients with unstable refractory angina pectoris underwent cardiac catheterization and angioplasty. Trans-stenotic and microvascular resistances to flow were measured at baseline, during hyperventilation, and after intracoronary adenosine. Measurements were repeated early after abciximab administration and after successful percutaneous transluminal coronary angioplasty.

RESULTS

Hyperventilation induced an ischemic attack in 12 of 18 patients and increased epicardial (12.8 +/- 16.9 vs. 6.1 +/- 6.1 mm Hg/ml per min, p < 0.05) and microvascular (9.9 +/- 7.5 vs. 6.8 +/- 5.8 mm Hg/ml per min, p < 0.05) coronary resistance. Abciximab had no significant effect on epicardial resistance, although it significantly reduced distal coronary resistance under all study conditions, including baseline (4.8 +/- 4.8 mm Hg/ml per min, p < 0.01), hyperventilation (5.1 +/- 5.4 mm Hg/ml per min, p < 0.01), and intracoronary adenosine (2.7 +/- 3.0 vs. 4.3 +/- 4.3 mm Hg/ml per min, p < 0.05). The hyperventilation test became negative in all patients after abciximab administration.

CONCLUSIONS

These observations confirm the immediate beneficial effects of platelet GP IIb/IIIa blockade with abciximab in acute ischemic syndromes and suggest that improvement of microvascular function may play a central role in the mechanism of action of this drug.

Neutrophil migration in the lung, general and bovine-specific aspects

Lung inflammation is often associated with sustained neutrophil migration into the lung tissue, causing undesired side effects, i.e. substantial damage of lung tissue and fibrin deposition, which hamper complete recovery. The need for additional anti-inflammatory treatment strategies focused attention on the function of cellular adhesion molecules (CAMs) on the leukocyte membrane, which guide migration of leukocytes across the endothelium to the site of inflammation. Recent data indicate that neutrophil migration in the lung is mediated by unique pathways, involving different CAM as compared to other organs. These pulmonary characteristics of neutrophil migration enable specific targeting of CAM for anti-inflammatory treatment of pneumonia. In addition, the recent interest in intracellular signaling revealed that most CAM not only function in adhesion, but also play an important role in initiation of intracellular signal transduction and vice versa may be modulated by intracellular signaling molecules (ISMs). In this review, the mechanisms of neutrophil migration in the lung and the role of ISM with respect to CAM function are described in the context of potential anti-inflammatory intervention strategies.

The GP IIb/IIIa inhibitor abciximab (c7E3) inhibits the binding of various ligands to the leukocyte integrin Mac-1 (CD11b/CD18, alphaMbeta2)

Cross-reactivity with integrins other than glycoprotein IIb/IIIa (GP IIb/IIIa) is discussed as a potential reason for the overall clinical benefits of the GP IIb/IIIa-blocking antibody-fragment abciximab. We evaluated whether abciximab binds to the leukocyte integrin Mac-1, whether it inhibits binding of the distinct ligands and thereby may modulate inflammation, cell proliferation and coagulation. Binding of fluorescence-labelled abciximab to phorbolmyristate acetate-stimulated monocytes and to a monocytic cell line (THP-1) could be detected in flow cytometry. The binding of fibrinogen, the inactivated complement factor 3b (iC3b), and the coagulation factor X to Mac-1 could be inhibited by abciximab (10 microg/ml) in vitro. As a functional consequence, the conversion of factor X to factor Xa mediated by Mac-1, as detected by the chromogenic substrate SZ-2222, was impaired by abciximab. Adhesion of THP-1 cells to immobilized intercellular adhesion molecule 1 (ICAM-1) and to fibrinogen was reduced significantly by abciximab. Fibrinogen-mediated cell aggregation was also impaired. In conclusion, we describe binding of abciximab to Mac-1 on stimulated monocytes. Thereby, abciximab inhibits binding of the ligands fibrinogen, ICAM-1, iC3b and factor X. Furthermore, we demonstrated that Mac-1-dependent conversion from factor X to factor Xa is impaired by abciximab, arguing for the direct modulation of the coagulation cascade by abciximab. Overall, the inhibition of Mac-1 could provide additional clinical benefits of abciximab beyond the well-described blockade of GP IIb/IIIa.

Multi-year follow-up of abciximab therapy in three randomized, placebo-controlled trials of percutaneous coronary revascularization

There is considerable evidence supporting the use of platelet glycoprotein IIb/IIIa inhibitors to reduce ischemic complications of percutaneous coronary revascularization. However, long-term follow-up has been limited. In three large-scale randomized trials that tested abciximab at a uniform bolus dose and 12-hour infusion against placebo, in a double-blind fashion, a total of 5799 patients had their long-term follow-up vital status determined at a minimum of 7 years (EPIC), 4.5 years (EPILOG), or 3 years (EPISTENT) after randomization (median, 4.8 years). The prespecified primary endpoint was all-cause mortality by intention-to-treat analysis at 3 years in patients randomly assigned to a common intervention. Follow-up for 5603 of the 5799 patients was 96.6% complete at 3 years; 320 deaths had occurred by that time. After 3 years of follow-up, mortality was 6.4% in the placebo groups and 5.0% in the abciximab groups (hazard ratio [HR] = 0.78; 95% confidence interval [CI]: 0.63 to 0.98; P = 0.03). A similar reduction in mortality was observed on an intention-to-treat basis when all follow-up information was utilized after a median of 4.8 years of follow-up (n = 652 deaths): 12.6% in the placebo groups and 10.2% in the abciximab groups (HR = 0.82; 95% CI: 0.70 to 0.96; P = 0.01).Abciximab treatment reduced all-cause mortality by about 20% during long-term follow-up after percutaneous coronary intervention. The findings were similar in magnitude and consistent in direction for each of the three trials, and the absolute survival benefit appeared to increase over time. Brief intervention with this monoclonal antibody during percutaneous coronary revascularization is associated with significant improvement of long-term survival.