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The stimulator of IFN genes (STING) protein senses cyclic dinucleotides released in response to double-stranded DNA and functions as an adaptor molecule for type I IFN (IFNI) signaling by activating IFNI-stimulated genes (ISG). We found impaired T cell infiltration into the peritoneum in response to TNF-α in global and EC-specific STING-/- mice and discovered that T cell transendothelial migration (TEM) across mouse and human endothelial cells (EC) deficient in STING was strikingly reduced compared with control EC, whereas T cell adhesion was not impaired. STING-/- T cells showed no defect in TEM or adhesion to EC, or immobilized endothelial cell-expressed molecules ICAM1 and VCAM1, compared with WT T cells. Mechanistically, CXCL10, an ISG and a chemoattractant for T cells, was dramatically reduced in TNF-α-stimulated STING-/- EC, and genetic loss or pharmacologic antagonisms of IFNI receptor (IFNAR) pathway reduced T cell TEM. Our data demonstrate a central role for EC-STING during T cell TEM that is dependent on the ISG CXCL10 and on IFNI/IFNAR signaling.

Clinical studies reveal changes in blood eosinophil counts and eosinophil cationic proteins that may serve as risk factors for human coronary heart diseases. Here we report an increase of blood or heart eosinophil counts in humans and mice after myocardial infarction (MI), mostly in the infarct region. Genetic or inducible depletion of eosinophils exacerbates cardiac dysfunction, cell death, and fibrosis post-MI, with concurrent acute increase of heart and chronic increase of splenic neutrophils and monocytes. Mechanistic studies reveal roles of eosinophil IL4 and cationic protein mEar1 in blocking H 2 O 2 - and hypoxia-induced mouse and human cardiomyocyte death, TGF-β-induced cardiac fibroblast Smad2/3 activation, and TNF-α-induced neutrophil adhesion on the heart endothelial cell monolayer. In vitro-cultured eosinophils from WT mice or recombinant mEar1 protein, but not eosinophils from IL4-deficient mice, effectively correct exacerbated cardiac dysfunctions in eosinophil-deficient ∆dblGATA mice. This study establishes a cardioprotective role of eosinophils in post-MI hearts.

T follicular helper (Tfh) cell migration into germinal centers (GCs) is essential for the generation of GC B cells and antibody responses to T cell-dependent (TD) antigens. This process requires interactions between lymphocyte function-associated antigen 1 (LFA-1) on Tfh cells and ICAMs on B cells. The mechanisms underlying defective antibody responses to TD antigens in DOCK8 deficiency are incompletely understood. We show that mice selectively lacking DOCK8 in T cells had impaired IgG antibody responses to TD antigens, decreased GC size, and reduced numbers of GC B cells. However, they developed normal numbers of Tfh cells with intact capacity for driving B cell differentiation into a GC phenotype in vitro. Notably, migration of DOCK8-deficient T cells into GCs was defective. Following T cell receptor (TCR)/CD3 ligation, DOCK8-deficient T cells had impaired LFA-1 activation and reduced binding to ICAM-1. Our results therefore indicate that DOCK8 is important for LFA-1-dependent positioning of Tfh cells in GCs, and thereby the generation of GC B cells and IgG antibody responses to TD antigen.

Antibodies that bind CD47 on tumor cells and prevent interaction with SIRPα on phagocytes are active against multiple cancer types including T-cell lymphoma (TCL). Here we demonstrate that surface CD47 is heterogeneously expressed across primary TCLs, whereas major histocompatibility complex (MHC) class I, which can also suppress phagocytosis, is ubiquitous. Multiple monoclonal antibodies (mAbs) that block CD47-SIRPα interaction promoted phagocytosis of TCL cells, which was enhanced by cotreatment with antibodies targeting MHC class I. Expression levels of surface CD47 and genes that modulate CD47 pyroglutamation did not correlate with the extent of phagocytosis induced by CD47 blockade in TCL lines. In vivo treatment of multiple human TCL patient-derived xenografts or an immunocompetent murine TCL model with a short course of anti-CD47 mAb markedly reduced lymphoma burden and extended survival. Depletion of macrophages reduced efficacy in vivo, whereas depletion of neutrophils had no effect. F(ab')2-only fragments of anti-CD47 antibodies failed to induce phagocytosis by human macrophages, indicating a requirement for Fc-Fcγ receptor interactions. In contrast, F(ab')2-only fragments increased phagocytosis by murine macrophages independent of SLAMF7-Mac-1 interaction. Full-length anti-CD47 mAbs also induced phagocytosis by Fcγ receptor-deficient murine macrophages. An immunoglobulin G1 anti-CD47 mAb induced phagocytosis and natural killer cell-mediated cytotoxicity of TCL cells that was augmented by cotreatment with mogamulizumab, an anti-CCR4 mAb, or a mAb blocking MHC class I. These studies help explain the disparate activity of monotherapy with agents that block CD47 in murine models compared with patients. They also have direct translational implications for the deployment of anti-CD47 mAbs alone or in combination., (© 2019 by The American Society of Hematology.)

Objective- Coronary artery thrombosis can occur in the absence of plaque rupture because of superficial erosion. Erosion-prone atheromata associate with more neutrophil extracellular traps (NETs) than lesions with stable or rupture-prone characteristics. The effects of NETs on endothelial cell (EC) inflammatory and thrombogenic properties remain unknown. We hypothesized that NETs alter EC functions related to erosion-associated thrombosis. Approach and Results- Exposure of human ECs to NETs increased VCAM-1 (vascular cell adhesion molecule 1) and ICAM-1 (intercellular adhesion molecule 1) mRNA and protein expression in a time- and concentration-dependent manner. THP-1 monocytoid cells and primary human monocytes bound more avidly to NET-treated human umbilical vein ECs than to unstimulated cells under flow. Treatment of human ECs with NETs augmented the expression of TF (tissue factor) mRNA, increased EC TF activity, and hastened clotting of recalcified plasma. Anti-TF-neutralizing antibody blocked NET-induced acceleration of clotting by ECs. NETs alone did not exhibit TF activity or acceleration of clotting in cell-free assays. Pretreatment of NETs with anti-interleukin (IL)-1α-neutralizing antibody or IL-1Ra (IL-1 receptor antagonist)-but not with anti-IL-1β-neutralizing antibody or control IgG-blocked NET-induced VCAM-1, ICAM-1, and TF expression. Inhibition of cathepsin G, a serine protease abundant in NETs, also limited the effect of NETs on EC activation. Cathepsin G potentiated the effect of IL-1α on ECs by cleaving the pro-IL-1α precursor and releasing the more potent mature IL-1α form. Conclusions- NETs promote EC activation and increased thrombogenicity through concerted action of IL-1α and cathepsin G. Thus, NETs may amplify and propagate EC dysfunction related to thrombosis because of superficial erosion.

CD47 is known to play an important role in CD4 + T cell homeostasis. We recently reported a reduction in mice deficient in the Cd47 gene (Cd47 -/- ) CD4 + T cell adhesion and transendothelial migration (TEM) in vivo and in vitro as a result of impaired expression of high-affinity forms of LFA-1 and VLA-4 integrins. A prior study concluded that Cd47 -/- mice were resistant to experimental autoimmune encephalomyelitis (EAE) as a result of complete failure in CD4 + T cell activation after myelin oligodendrocyte glycoprotein peptide 35-55 aa (MOG 35-55 ) immunization. As the prior EAE study was published before our report, authors could not have accounted for defects in T cell integrin function as a mechanism to protect Cd47 -/- in EAE. Thus, we hypothesized that failure of T cell activation involved defects in LFA-1 and VLA-4 integrins. We confirmed that Cd47 -/- mice were resistant to MOG 35-55 -induced EAE. Our data, however, supported a different mechanism that was not a result of failure of CD4 + T cell activation. Instead, we found that CD4 + T cells in MOG 35-55 -immunized Cd47 -/- mice were activated, but clonal expansion contracted within 72 h after immunization. We used TCR crosslinking and mitogen activation in vitro to investigate the underlying mechanism. We found that naïve Cd47 -/- CD4 + T cells exhibited a premature block in proliferation and survival because of impaired activation of LFA-1, despite effective TCR-induced activation. These results identify CD47 as an important regulator of LFA-1 and VLA-4 integrin-adhesive functions in T cell proliferation, as well as recruitment, and clarify the roles played by CD47 in MOG 35-55 -induced EAE., (© Society for Leukocyte Biology.)

The deposition of immune complexes (IC) in tissues induces a "type III hypersensitivity" that results in tissue damage and underlies the pathogenesis of many autoimmune diseases. The neutrophil is the first immune cell recruited into sites of IC deposition and plays a critical role in shaping the overall tissue response. However, the mechanism by which IC initiate and propagate neutrophil infiltration into tissue is not known. Here, using intravital multiphoton joint imaging of IC-induced arthritis in live mice, we found that the complement C5a receptor (C5aR) was the key initiator of neutrophil adhesion on joint endothelium. C5a presented on joint endothelium induced β2 integrin-dependent neutrophil arrest, facilitating neutrophil spreading and transition to crawling, and subsequent leukotriene B 4 receptor (BLT1)-mediated extravasation of the first neutrophils. The chemokine receptor CCR1 promoted neutrophil crawling on the joint endothelium while CXCR2 amplified late neutrophil recruitment and survival once in the joint. Thus, imaging arthritis has defined a new paradigm for type III hypersensitivity where C5a directly initiates neutrophil adhesion on the joint endothelium igniting inflammation., Competing Interests: Competing interests: The authors declare no competing financial interests.

Endomucin is a membrane-bound glycoprotein expressed luminally by endothelial cells that line postcapillary venules, a primary site of leukocyte recruitment during inflammation. Here we show that endomucin abrogation on quiescent endothelial cells enables neutrophils to adhere firmly, via LFA-1-mediated binding to ICAM-1 constitutively expressed by endothelial cells. Moreover, TNF-α stimulation downregulates cell surface expression of endomucin concurrent with increased expression of adhesion molecules. Adenovirus-mediated expression of endomucin under inflammatory conditions prevents neutrophil adhesion in vitro and reduces the infiltration of CD45(+) and NIMP-R14(+) cells in vivo. These results indicate that endomucin prevents leukocyte contact with adhesion molecules in non-inflamed tissues and that downregulation of endomucin is critical to facilitate adhesion of leukocytes into inflamed tissues.

The mechanisms driving T cell homing to lymph nodes and migration to tissue are well described but little is known about factors that affect T cell egress from tissues. Here, we generate mice with a T cell-specific deletion of the scaffold protein A kinase anchoring protein 9 (AKAP9) and use models of inflammatory disease to demonstrate that AKAP9 is dispensable for T cell priming and migration into tissues and lymph nodes, but is required for T cell retention in tissues. AKAP9 deficiency results in increased T cell egress to draining lymph nodes, which is associated with impaired T cell re-activation in tissues and protection from organ damage. AKAP9-deficient T cells exhibit reduced microtubule-dependent recycling of TCRs back to the cell surface and this affects antigen-dependent activation, primarily by non-classical antigen-presenting cells. Thus, AKAP9-dependent TCR trafficking drives efficient T cell re-activation and extends their retention at sites of inflammation with implications for disease pathogenesis.

This issue of Tissue Barriers contains the inaugural special issue devoted to recent advances in barrier function of endothelial and epithelial cells. We used this opportunity to invite experts in vascular endothelial cell biology and epithelial cell biology to comment on critical questions and problems in permeability of organ and tissue barriers, and to provide insight into common areas in these fields, namely how these cells maintain homeostasis and response to injury and infection. To complement these reviews, this issue also contains four research articles that explore specific questions related respiratory and intestinal epithelial cell function.

CD47 plays an important but incompletely understood role in the innate and adaptive immune responses. CD47, also called integrin-associated protein, has been demonstrated to associate in cis with β1 and β3 integrins. Here we test the hypothesis that CD47 regulates adhesive functions of T-cell α4β1 (VLA-4) and αLβ2 (LFA-1) in in vivo and in vitro models of inflammation. Intravital microscopy studies reveal that CD47(-/-) Th1 cells exhibit reduced interactions with wild-type (WT) inflamed cremaster muscle microvessels. Similarly, murine CD47(-/-) Th1 cells, as compared with WT, showed defects in adhesion and transmigration across tumor necrosis factor-α (TNF-α)-activated murine endothelium and in adhesion to immobilized intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion protein 1 (VCAM-1) under flow conditions. Human Jurkat T-cells lacking CD47 also showed reduced adhesion to TNF-α-activated endothelium and ICAM-1 and VCAM-1. In cis interactions between Jurkat T-cell β2 integrins and CD47 were detected by fluorescence lifetime imaging microscopy. Unexpectedly, Jurkat CD47 null cells exhibited a striking defect in β1 and β2 integrin activation in response to Mn(2+) or Mg(2+)/ethylene glycol tetraacetic acid treatment. Our results demonstrate that CD47 associates with β2 integrins and is necessary to induce high-affinity conformations of LFA-1 and VLA-4 that recognize their endothelial cell ligands and support leukocyte adhesion and transendothelial migration.

Objective: Although endothelial CD47, a member of the immunoglobulin superfamily, has been implicated in leukocyte diapedesis, its capacity for intracellular signaling and physical localization during this process has not been addressed in detail. This study examined endothelial CD47 spatiotemporal behavior and signaling pathways involved in regulating T-cell transendothelial migration., Approach and Results: By biochemical methods, transmigration assays, and live-cell microscopy techniques, we show that endothelial CD47 engagement results in intracellular calcium mobilization, increased permeability, and activation of Src and AKT1/phosphoinositide 3-kinase in brain microvascular endothelial cells. These signaling pathways converge to induce cytoskeleton remodeling and vascular endothelial cadherin phosphorylation, which are necessary steps during T-cell transendothelial migration. In addition, during T-cell migration, transmigratory cups and podo-prints enriched in CD47 appear on the surface of the endothelium, indicating that the spatial distribution of CD47 changes after its engagement. Consistent with previous findings of intercellular adhesion molecule 1, blockade of CD47 results in decreased T-cell transmigration across microvascular endothelium. The overlapping effect of intercellular adhesion molecule 1 and CD47 suggests their involvement in different steps of the diapedesis process., Conclusions: These data reveal a novel role for CD47-mediated signaling in the control of the molecular network governing endothelial-dependent T-cell diapedesis.

Vascular endothelium is a dynamic cellular interface that displays a unique phenotypic plasticity. This plasticity is critical for vascular function and when dysregulated is pathogenic in several diseases. Human genotype-phenotype studies of endothelium are limited by the unavailability of patient-specific endothelial cells. To establish a cellular platform for studying endothelial biology, we have generated vascular endothelium from human induced pluripotent stem cells (iPSCs) exhibiting the rich functional phenotypic plasticity of mature primary vascular endothelium. These endothelial cells respond to diverse proinflammatory stimuli, adopting an activated phenotype including leukocyte adhesion molecule expression, cytokine production, and support for leukocyte transmigration. They maintain dynamic barrier properties responsive to multiple vascular permeability factors. Importantly, biomechanical or pharmacological stimuli can induce pathophysiologically relevant atheroprotective or atheroprone phenotypes. Our results demonstrate that iPSC-derived endothelium possesses a repertoire of functional phenotypic plasticity and is amenable to cell-based assays probing endothelial contributions to inflammatory and cardiovascular diseases.

Aims: Activation of vascular endothelial cells (ECs) contributes importantly to inflammation and atherogenesis. We previously reported that apolipoprotein CIII (apoCIII), found abundantly on circulating triglyceride-rich lipoproteins, enhances adhesion of human monocytes to ECs in vitro. Statins may exert lipid-independent anti-inflammatory effects. The present study examined whether statins suppress apoCIII-induced EC activation in vitro and in vivo., Methods and Results: Physiologically relevant concentrations of purified human apoCIII enhanced attachment of the monocyte-like cell line THP-1 to human saphenous vein ECs (HSVECs) or human coronary artery ECs (HCAECs) under both static and laminar shear stress conditions. This process mainly depends on vascular cell adhesion molecule-1 (VCAM-1), as a blocking VCAM-1 antibody abolished apoCIII-induced monocyte adhesion. ApoCIII significantly increased VCAM-1 expression in HSVECs and HCAECs. Pre-treatment with statins suppressed apoCIII-induced VCAM-1 expression and monocyte adhesion, with two lipophilic statins (pitavastatin and atorvastatin) exhibiting inhibitory effects at lower concentration than those of hydrophilic pravastatin. Nuclear factor κB (NF-κB) mediated apoCIII-induced VCAM-1 expression, as demonstrated via loss-of-function experiments, and pitavastatin treatment suppressed NF-κB activation. Furthermore, in the aorta of hypercholesterolaemic Ldlr(-/-) mice, pitavastatin administration in vivo suppressed VCAM-1 mRNA and protein, induced by apoCIII bolus injection. Similarly, in a subcutaneous dorsal air pouch mouse model of leucocyte recruitment, apoCIII injection induced F4/80+ monocyte and macrophage accumulation, whereas pitavastatin administration reduced this effect., Conclusions: These findings further establish the direct role of apoCIII in atherogenesis and suggest that anti-inflammatory effects of statins could improve vascular disease in the population with elevated plasma apoCIII.

Background & Aims: Signaling lymphocyte activation molecule (Slamf)1 is a co-stimulatory receptor on T cells and regulates cytokine production by macrophages and dendritic cells. Slamf1 regulates microbicidal mechanisms in macrophages, therefore we investigated whether the receptor affects development of colitis in mice., Methods: We transferred CD45RB(hi) CD4(+) T cells into Rag(-/-) or Slamf1(-/-)Rag(-/-) mice to induce colitis. We also induced colitis by injecting mice with an antibody that activates CD40. We determined the severity of enterocolitis based on disease activity index, histology scores, and levels of cytokine production, and assessed the effects of antibodies against Slamf1 on colitis induction. We quantified migration of monocytes and macrophage to inflamed tissues upon induction of colitis or thioglycollate-induced peritonitis and in response to tumor necrosis factor-α in an air-pouch model of leukocyte migration., Results: Colitis was reduced in Slamf1(-/-)Rag(-/-) mice, compared with Rag(-/-) mice, after transfer of CD45RB(hi) CD4(+) T cells or administration of the CD40 agonist. The numbers of monocytes and macrophages were reduced in inflamed tissues of Slamf1(-/-)Rag(-/-) mice, compared with Rag(-/-) mice, after induction of colitis and other inflammatory disorders. An antibody that inhibited Slamf1 reduced the level of enterocolitis in Rag(-/-) mice., Conclusions: Slamf1 contributes to the development of colitis in mice. It appears to indirectly regulate the appearance of monocytes and macrophages in inflamed intestinal tissues. Antibodies that inhibit Slamf1 reduce colitis in mice, so human SLAMF1 might be a therapeutic target for inflammatory bowel disease., (Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Vascular endothelial-cadherin (VE-cad) is localized to adherens junctions at endothelial cell borders and forms a complex with alpha-, beta-, gamma-, and p120-catenins (p120). We previously showed that the VE-cad complex disassociates to form short-lived "gaps" during leukocyte transendothelial migration (TEM); however, whether these gaps are required for leukocyte TEM is not clear. Recently p120 has been shown to control VE-cad surface expression through endocytosis. We hypothesized that p120 regulates VE-cad surface expression, which would in turn have functional consequences for leukocyte transmigration. Here we show that endothelial cells transduced with an adenovirus expressing p120GFP fusion protein significantly increase VE-cad expression. Moreover, endothelial junctions with high p120GFP expression largely prevent VE-cad gap formation and neutrophil leukocyte TEM; if TEM occurs, the length of time required is prolonged. We find no evidence that VE-cad endocytosis plays a role in VE-cad gap formation and instead show that this process is regulated by changes in VE-cad phosphorylation. In fact, a nonphosphorylatable VE-cad mutant prevented TEM. In summary, our studies provide compelling evidence that VE-cad gap formation is required for leukocyte transmigration and identify p120 as a critical intracellular mediator of this process through its regulation of VE-cad expression at junctions.

Leukocyte transendothelial migration (TEM) is a critical event during inflammation. CD47 has been implicated in myeloid cell migration across endothelium and epithelium. CD47 binds to signal regulatory protein (SIRP), SIRPalpha and SIRPgamma. So far, little is known about the role of endothelial CD47 in T-cell TEM in vivo or under flow conditions in vitro. Fluorescence-activated cell sorting and biochemical analysis show that CD3(+) T cells express SIRPgamma but not SIRPalpha, and fluorescence microscopy showed that CD47 was enriched at endothelial junctions. These expression patterns suggested that CD47 plays a role in T-cell TEM through binding interactions with SIRPgamma. We tested, therefore, whether CD47-SIRPgamma interactions affect T-cell transmigration using blocking mAb against CD47 or SIRPgamma in an in vitro flow model. These antibodies inhibited T-cell TEM by 70% plus or minus 6% and 82% plus or minus 1%, respectively, but had no effect on adhesion. In agreement with human mAb studies, transmigration of murine wild-type T helper type 1 cells across TNF-alpha-activated murine CD47(-/-) endothelium was reduced by 75% plus or minus 2% even though murine T cells appear to lack SIRPgamma. Nonetheless, these findings suggest endothelial cell CD47 interacting with T-cell ligands, such as SIRPgamma, play an important role in T-cell transendothelial migration.

Monocyte recruitment from the vasculature involves sequential engagement of multiple receptors, culminating in transendothelial migration and extravasation. Junctional adhesion molecule-C (JAM-C) is localized at endothelial intercellular junctions and plays a role in monocyte transmigration. Here, we show that blockade of JAM-B/-C interaction reduced monocyte numbers in the extravascular compartment through increased reverse transmigration rather than by reduced transmigration. This was confirmed in vivo, showing that an anti-JAM-C antibody reduced the number of monocytes in inflammatory tissue and increased the number of monocytes with a reverse-transmigratory phenotype in the peripheral blood. All together, our results suggest a novel mechanism of reducing accumulation of monocytes at inflammation sites by disruption of JAM-C-mediated monocyte retention.

The inflammatory response is a critical component of host defense. An important goal of our group has been to understand the endothelial-dependent mechanisms that mediate leukocyte recruitment during an inflammatory response. In this chapter, we present a detailed method for the isolation and in vitro culture of murine vascular endothelial cells from the lung and heart. The endothelial cells are of high purity (85-99%) and retain certain of their functional differences, including constitutive and cytokine inducible adhesion molecule expression and chemokine production. Such endothelial cells, therefore, can be used for various in vitro models including leukocyte adhesion assay or in depth biochemical analyses.

In vivo, leukocyte transendothelial migration (TEM) occurs at endothelial cell junctions (paracellular) and nonjunctional (transcellular) locations, whereas in vitro models report that TEM is mostly paracellular. The mechanisms that control the route of leukocyte TEM remain unknown. Here we tested the hypothesis that elevated intercellular adhesion molecule-1 (ICAM-1) expression regulates the location of polymorphonuclear leukocyte (PMN) TEM. We used an in vitro flow model of tumor necrosis factor-alpha (TNF-alpha)-activated human umbilical vein endothelium cells (HUVECs) or an HUVEC cell line transfected with ICAM-1GFP (green fluorescent protein) and live-cell fluorescence microscopy to quantify the location of PMN adhesion and TEM. We observed robust transcellular TEM with TNF-alpha-activated HUVECs and ICAM-1GFP immortalized HUVECS (iHUVECs). In contrast, primary CD3+ T lymphocytes exclusively used a paracellular route. Endothelial ICAM-1 was identified as essential for both paracellular and transcellular PMN transmigration, and interfering with ICAM-1 cytoplasmic tail function preferentially reduced transcellular TEM. We also found that ICAM-1 surface density and distribution as well as endothelial cell shape contributed to transcellular TEM. In summary, ICAM-1 promotes junctional and nonjunctional TEM across inflamed vascular endothelium via distinct cytoplasmic tail associations.

Endothelial cell-cell junctional proteins and cortical actin are of central importance for regulating vascular permeability. Rap1, a member of the Ras family of GTPases, is enriched at endothelial cell-cell contacts and activated by cyclic AMP (cAMP) through a PKA-independent pathway. Activation of a cAMP-inducible guanine-exchange factor for Rap, Epac, results in markedly enhanced basal endothelial barrier function by increasing cortical actin and subsequent redistribution of adherens and tight junctional molecules to cell-cell contacts. Activation of Epac also counteracts thrombin-induced hyperpermeability through down-regulation of Rho GTPase activation, suggesting cross-talk between Rap and Rho GT-Pases. Thus, Epac/Rap activation represents a new pathway for regulating endothelial cell barrier function.

The most prominent cell-surface integrin alpha4beta1 partner, a 70-kDa protein, was isolated from MOLT-4 T leukemia cells, using anti-alpha4beta1 integrin antibody-coated beads. By mass spectrometry, this protein was identified as EWI-2, a previously described cell-surface partner for tetraspanin proteins CD9 and CD81. Wild-type EWI-2 overexpression had no effect on MOLT-4 cell tethering and adhesion strengthening on the alpha4beta1 ligand, vascular cell adhesion molecule-1 (VCAM-1), in shear flow assays. However, EWI-2 markedly impaired spreading and ruffling on VCAM-1. In contrast, a mutant EWI-2 molecule, with a different cytoplasmic tail, neither impaired cell spreading nor associated with alpha4beta1 and CD81. The endogenous wild-type EWI-2-CD81-alpha4beta1 complex was fully soluble, and highly specific as seen by the absence of other MOLT-4 cell-surface proteins. Also, it was relatively small in size (0.5 x 10(6) Da to 4 x 10(6) Da), as estimated by size exclusion chromatography. Overexpression of EWI-2 in MOLT-4 cells caused reorganization of cell-surface CD81, increased the extent of CD81-CD81, CD81-alpha4beta1, and alpha4beta1-alpha4beta1 associations, and increased the apparent size of CD81-alpha4beta1 complexes. We suggest that EWI-2-dependent reorganization of alpha4beta1-CD81 complexes on the cell surface is responsible for EWI-2 effects on integrin-dependent morphology and motility functions.

Biosynthesis of core2 O-glycans on T cell surface glycoproteins is essential for their interactions with selectins expressed by activated endothelium, and may also regulate susceptibility to apoptosis. Beta-galactoside alpha2,3-sialyltransferase-I (ST3Gal-I) is a major inhibitor of core2 O-glycan formation on CD43 and CD45 in naive T cells. Here we show that ST3Gal-I mRNA is extensively expressed during Th2, but not Th1 differentiation. Consistent with this, developing Th1 cells display the non-sialylated core1 galactose (Gal1-3GalNAc-Ser/Thr) and strongly react with peanut agglutinin, while Th2 cells do not. These Th subset differences are also associated with greater expression of the high molecular glycoform of CD43 on the surface of Th1 cells compared with Th2 cells, and similar differences in surface expression of sialyl Lewis-X. We suggest that lack of ST3Gal-I expression in Th1 cells allows the formation of surface core2 O-glycans and supports their interactions with endothelial selectins.

An essential function of the inflammatory response is selective targeting of appropriate leukocyte types to a site of infection or injury. The past decade has witnessed an explosion in the level of detail concerning the identification and deciphering of the molecular mechanisms that capture leukocytes from flowing blood and promote leukocyte arrest on the vessel wall. In contrast, less information is known about the migration of adherent blood leukocytes through endothelial cell-to-cell borders (transendothelial migration, TEM) and into the underlying tissues. This article reviews the endothelial-dependent mechanisms that coordinate TEM in peripheral vasculature and highlights the role of certain lateral junctional proteins and protein complexes.

Mast cells (MCs) are central to asthma and other allergic diseases, and for responses to infection and tissue injuries. MCs arise from committed progenitors (PrMCs) that migrate from the circulation to tissues by incompletely characterized mechanisms, and differentiate in situ in perivascular connective tissues of multiple organs. PrMCs derived in vitro from human cord blood were examined for adhesion molecule expression and their ability to adhere to human umbilical vein endothelial cells (HUVECs) under conditions that mimic physiologic shear flow. The PrMCs expressed alpha(4)beta(1), low levels of beta7, and the beta2-integrins alphaLbeta2 and alphaMbeta2. The PrMCs also expressed PSGL-1, but not L-selectin. At low (0.5 dynes/cm(2)-1.0 dynes/cm(2)) shear stress, PrMCs attached and rolled on recombinant E-selectin and P-selectin and VCAM-1. An anti-PSGL-1 monoclonal antibody (mAb) blocked essentially all adhesion to P-selectin but reduced adhesion to E-selectin by only 40%, suggesting PrMCs express other ligands for E-selectin. PrMCs adhered strongly to tumor necrosis factor-alpha (TNF-alpha)-activated HUVECs, whereas adhesion to interleukin 4 (IL-4)-activated HUVECs was lower. PrMC adhesion to IL-4-activated HUVECs was totally alpha4-integrin- and VCAM-1-dependent. Adhesion to TNF-alpha-activated HUVECs was blocked by 50% by mAbs against alpha4-integrin, vascular cell adhesion molecule-1 (VCAM-1), E-selectin, or PSGL-1, whereas combinations of mAbs to alpha4-integrin plus PSGL-1, or VCAM-1 plus E-selectin, blocked adhesion by greater than 70%. Thus, PrMCs derived in vitro predominantly use alpha4-integrin, VCAM-1, PSGL-1, and other ligands that bind E-selectin for adhesion to cytokine-activated HUVEC monolayers. These observations may explain the abundance of MCs at sites of mucosal inflammation, where VCAM-1 and E-selectin are important inducible receptors.