Antigen-receptor complex stimulation triggers protein kinase C-dependent CD11a/CD18-cytoskeleton association in T lymphocytes.

Although it is well accepted that intercellular adhesion involving the CD11a/CD18 (LFA-1) complex is critical in a wide array of T cell-dependent processes, recent demonstrations of an LFA-1 high avidity state, induced by triggering the T cell receptor (TCR) complex, has raised questions about the intracellular signals generated and molecular events leading to effective cell coupling, as well as their orderly sequence. In this study, we assessed the effects of T cell activation on the actin-based cytoskeleton, and LFA-1, as well as their interaction. Crosslinking the TCR complex with anti-CD3 mAb resulted in actin polymerization and colocalization with LFA-1, as detected by fluorescence microscopy. This association was confirmed by immunoprecipitating LFA-1 from the detergent insoluble, cytoskeletal-associated membrane fraction after TCR crosslinking. These consequences were inhibited by the protein kinase C (PKC) inhibitor staurosporine or by PKC desensitization, as was a transient CD11a hyperphosphorylation, induced by monoclonal anti-CD3. Furthermore, a small percentage of beta 2-deficient T cells maintained the ability to rearrange the cytoskeleton in response to TCR complex activation, with F-actin-VLA4 colocalization. These results provide evidence that the important consequences of TCR-induced signal transduction include a PKC-dependent cytoskeletal rearrangement, involving an association between leukocyte integrins and F-actin. We discuss the implications of these findings with respect to effective T cell functions.

Lymphocyte adhesion-dependent calcium signaling in human endothelial cells.

Vascular endothelial cells (ECs) can undergo dramatic phenotypic and functional alterations in response to humoral and cellular stimuli. These changes promote endothelial participation in the inflammatory response through active recruitment of immune effector cells, increased vascular permeability, and alteration in vascular tone. In an attempt to define early events in lymphocyte-mediated EC signaling, we investigated cytosolic-free calcium (Ca2+) changes in single, Fluo-3-labeled human umbilical vein ECs (HUVECs), using an ACAS interactive laser cytometer. Of all lymphocyte subsets tested, allogeneic CD3-, CD56+ natural killer (NK) cells uniquely elicited oscillatory EC Ca2+ signals in cytokine (interleukin [IL]-1- or tumor necrosis factor [TNF])-treated ECs. The induction of these signals required avid intercellular adhesion, consisted of both Ca2+ mobilization and extracellular influx, and was associated with EC inositol phosphate (IP) generation. Simultaneous recording of NK and EC Ca2+ signals using two-color fluorescence detection revealed that, upon adhesion, NK cells flux prior to EC. Lymphocyte Ca2+ buffering with 1,2-bis-5-methyl-amino-phenoxylethane-N,N,N'-tetra-acetoxymethyl acetate (MAPTAM) demonstrated that lymphocyte fluxes are, in fact, prerequisites for the adhesion-dependent EC signals. mAb studies indicate that the beta 2 integrin-intercellular adhesion molecule (ICAM)-1 adhesion pathway is critically involved. However, ICAM-1 antisense oligonucleotide inhibition of IL-1-mediated ICAM-1 hyperinduction had no effect on EC Ca2+ signaling in lymphocyte-EC conjugates, indicating that additional cytokine-induced EC alteration is required. These experiments combine features of lymphocyte-endothelial interactions, intercellular adhesion, EC cytokine activation and transmembrane signaling. The results implicate the IP/Ca2+ second messenger pathway in EC outside-in signaling induced by cytotoxic lymphocytes, and suggest that these signals may play a role in EC alteration by lymphocyte adhesion.

Phenotypic and functional characterization of lymphocytes that bind human microvascular endothelial cells in vitro. Evidence for preferential binding of natural killer cells.

The microvascular endothelium has been postulated to be a critical target in the rejection of vascularized allografts. This study was undertaken to examine the ability of human sheep erythrocyte rosette forming lymphocytes (E-RFC) to form stable conjugates with microvascular endothelial cells (EC), and to assess whether a receptor-ligand interaction mediates this event. Human foreskin microvascular EC monolayers were used as targets of chromium-51-labeled E-RFC in a quantitative adherence assay. Binding was saturable, displaceable by unlabeled E-RFC, augmented by recombinant interleukin 1 (rIL-1) and inhibited by anti-LFA1 antibody. The Leu-11+ lymphocyte subset, known to be enriched for natural killer (NK) cells, bound preferentially. Only the EC-adherent lymphocyte fraction contained NK effectors, which lysed EC and classical NK targets. Thus, NK cells adhere to microvascular EC via a specific receptor-ligand interaction. The possibility exists that such binding occurs in recipients of vascularized allografts, representing the initial stage of graft rejection.

Effects of 17beta-estradiol on cytokine-induced endothelial cell adhesion molecule expression.

One of the earliest events in atherosclerosis is interaction of circulating mononuclear leukocytes and the endothelium. Endothelial cell (EC) activation by cytokines results in expression of adhesion molecules and production of chemotactic factors, augmenting leukocyte adhesion and recruitment, respectively. The incidence of atherosclerosis in premenopausal women is significantly less than that observed in age-matched males with similar risk profiles. Because estrogen has gene regulatory effects, we investigated whether 17beta-estradiol (E2) can inhibit cytokine-mediated EC adhesion molecule transcriptional activation. Cultured human umbilical vein EC (estrogen receptor-positive) were propagated in gonadal hormone-free medium and were E2-pretreated for 48 h before IL-1 activation. Detected by FACS analysis, E2 strongly (60-80%) inhibited IL-1-mediated membrane E-selectin and vascular cell adhesion molecule-1 induction, and intercellular adhesion molecule-1 hyperinduction. 17alpha-estradiol (an inactive E2 stereoisomer) had no effect. This inhibition correlated with similar reductions in steady state-induced E-selectin mRNA levels, and was abrogated by the E2 antagonist ICI 164,384, demonstrating a specific, estrogen receptor-mediated effect. Nuclear run-offs confirmed suppression at the transcriptional level. The implications of these results for the cardiovascular protective role of estrogen are discussed.

Integrin-dependent induction of functional urokinase receptors in primary T lymphocytes.

In order to reach the sites of inflammation, lymphocytes leave the bloodstream and migrate into peripheral tissues, in a process involving integrin-mediated adhesion to the vascular endothelium, followed by transmigration across the endothelial barrier and through the underlying interstitial matrix. We have investigated the role of the plasminogen activator/plasmin system in normal T cell migration. Receptors for urokinase plasminogen activator (uPAR) were not expressed in resting T lymphocytes, but could be efficiently induced at the mRNA and protein level by coclustering of the antigen receptor complex and beta1 or beta2 integrins, through a signalling pathway involving both protein kinase C activation and an increase in intracellular cyclic AMP. Catalytic activation of plasminogen by uPAR-expressing T cells promoted their migration through an extracellular matrix in vitro. Plasmin-induced invasion was inhibited by plasmin-and urokinase inhibitors and by anti-uPAR antibodies. Finally, cytofluorimetric and immunohistochemical analysis of primary human tumor specimens showed the presence of uPAR positive infiltrating T cells in vivo. Collectively, these findings suggest that plasminogen activation may play a role in lymphocyte migration in vivo, and that integrin-dependent expression of membrane-associated endopeptidases could represent an additional step in the regulated process of leukocyte transmigration.

Minireview: estrogen receptor-mediated rapid signaling.

In addition to nuclear-initiated (genomic) responses, estrogen receptors (ERs) have the ability to facilitate rapid, membrane-initiated, estrogen-triggered signaling cascades via a plasma membrane-associated form of the receptor. These rapid responses are dependent on assembly of membrane ER-centered multimolecular complexes, which can transduce ligand-activated signals to affect a variety of enzymatic pathways, often occurring in a cell-type-specific fashion with tissue-specific physiological outcomes. In some instances, cross-talk occurs between these membrane-initiated and nuclear responses, ultimately regulating transcriptional activation. The role of splice variants in membrane-initiated estrogen responses has been described, notably those within the vascular endothelium. In this review, we describe the evidence for membrane ERs, the molecular components of the aforementioned signaling complexes and pathways, the relevance of ER splice variants, and ER-mediated responses in specific tissues. Our growing understanding of ER-mediated actions at a molecular level will provide insight into the controversies surrounding hormone replacement therapy in postmenopausal women.

Membrane estrogen receptor engagement activates endothelial nitric oxide synthase via the PI3-kinase-Akt pathway in human endothelial cells.

17beta-Estradiol (E(2)) is a rapid activator of endothelial nitric oxide synthase (eNOS). The product of this activation event, NO, is a fundamental determinant of cardiovascular homeostasis. We previously demonstrated that E(2)-stimulated endothelial NO release can occur without an increase in cytosolic Ca(2+). Here we demonstrate for the first time, to our knowledge, that E(2) rapidly induces phosphorylation and activation of eNOS through the phosphatidylinositol 3 (PI3)-kinase-Akt pathway. E(2) treatment (10 ng/mL) of the human endothelial cell line, EA.hy926, resulted in increased NO production, which was abrogated by the PI3-kinase inhibitor, LY294002, and the estrogen receptor antagonist ICI 182, 780. E(2) stimulated rapid Akt phosphorylation on serine 473. As has been shown for vascular endothelial growth factor, eNOS is an E(2)-activated Akt substrate, demonstrated by rapid eNOS phosphorylation on serine 1177, a critical residue for eNOS activation and enhanced sensitivity to resting cellular Ca(2+) levels. Adenoviral-mediated EA.hy926 transduction confirmed functional involvement of Akt, because a kinase-deficient, dominant-negative Akt abolished E(2)-stimulated NO release. The membrane-impermeant E(2)BSA conjugate, shown to bind endothelial cell membrane sites, also induced rapid Akt and consequent eNOS phosphorylation. Thus, engagement of membrane estrogen receptors results in rapid endothelial NO release through a PI3-kinase-Akt-dependent pathway. This explains, in part, the reduced requirement for cytosolic Ca(2+) fluxes and describes an important pathway relevant to cardiovascular pathophysiology.

Tumor necrosis factor alpha-induced vascular leakage involves PECAM1 phosphorylation.

Herein we show that exposure of human umbilical vein endothelial cells to tumor necrosis factor alpha (TNFalpha) led to platelet endothelial cell adhesion molecule-1 (PECAM1) surface redistribution, disruption of cytoskeleton connections, and increased PECAM1 phosphorylation, accompanied by increased permeability to macromolecules. The in vitro use of inhibitors of tyrosine or serine-threonine kinases could prevent both PECAM1 surface redistribution and the increase in permeability induced by the cytokine. In vivo administration of lavendustin A, a natural tyrosine kinase inhibitor, protected endothelial cells from TNFalpha-dependent vascular leakage in mouse liver. We propose that the involvement of PECAM1 in TNFalpha-mediated effects on vascular permeability may depend on a dynamically regulated cytoskeletal association, related to the degree of PECAM1 phosphorylation.

Modulation of circulating cellular adhesion molecules in postmenopausal women with coronary artery disease.

OBJECTIVES: The present study examined the association of estrogen (E2) and the inflammatory response of endothelium in coronary artery disease (CAD) by measuring circulating cellular adhesion molecules (cCAMs) in subjects with atherosclerosis. BACKGROUND: Atherosclerotic plaque demonstrates features similar to inflammation. Endothelial cell activation by inflammatory cytokines induces expression of cellular adhesion molecules (CAMs), thereby perhaps augmenting leukocyte adhesion and recruitment and subsequent development of atherosclerosis. The incidence of CAD is lower in women; this may be due to the cardioprotective effects of E2. METHODS: Consecutive eligible subjects with CAD admitted for cardiac catheterization were studied. The groups evaluated were men, postmenopausal women receiving E2 replacement therapy (ERT), postmenopausal women not receiving ERT and premenopausal women. Control groups included men and women without CAD. Preprocedural blood samples were drawn from all groups. Measurements of cCAMs, E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 were performed by enzyme-linked immunoabsorbant assay. E2 levels were assessed by radioimmunoassay. RESULTS: We observed a statistically significant increase in all cCAMs in men with CAD and postmenopausal women with CAD not receiving ERT compared with postmenopausal women with CAD receiving ERT. Premenopausal women with CAD and postmenopausal women with CAD receiving ERT had a significant increase in VCAM-1 alone compared with the female control group. CONCLUSIONS: A possible mechanism by which E2 exerts one of its cardioprotective effects is by limiting the inflammatory response to injury by modulating the expression of CAMs from the endothelium.

Initiation of cardiac allograft rejection New developments in cellular and molecular mechanisms.

Although cardiac transplantation has become a viable therapeutic option for end-stage heart disease, long-term success is limited by rejection and medical complications of immunosuppression. Earliest events in rejection revolve around T-lymphocyte recognition of foreign antigen through a panel of specialized cell surface proteins. This is followed by a cascade of signaling events, transcription of multiple genes, and cytokine production. The central importance of these events, collectively known as T-cell activation, to the rejection process is underscored by the clinical utility of cyclosporine, which prevents T-cell activation. The specific site of action of cyclosporine within the T cell has recently been elucidated at the molecular level, revealing important details of T-cell biology. Once the immune response has been initiated, localization of inflammatory cells to the graft requires alteration in the functional state of the vascular endothelium, which can then express adhesive ligands for immune effector cells. Recent evidence suggests that host natural killer lymphocytes may play a role in this process. Understanding the molecular details of these and other early events in rejection will facilitate the development of more specific and effective immunosuppressive therapies.

Evidence that cytotoxic lymphocytes alter and traverse allogeneic endothelial cell monolayers.

In an attempt to study the effects of allogeneic lymphocytes on endothelial cells (EC) and analyze the mechanism whereby such lymphocytes traverse an EC barrier, we have established human microvascular EC monolayers, in vitro, and analyzed the effects of lymphocyte subpopulations on such monolayers. Previous studies have shown that CD16+ (natural killer) and CD8+ (cytotoxic) lymphocytes but not CD4+ (helper) cells bind and induce the appearance of class II major histocompatibility complex antigens on allogeneic EC. The current findings indicate that these same lymphocyte subsets induce marked swirling and elongation of allogeneic EC, and traverse intact EC monolayers. In contrast, none of the functional consequences of the initial lymphocyte-EC adhesion were observed using autologous combinations, despite the presence of significant intercellular binding. Scanning and electron micrographs demonstrate extensive areas of lymphocyte-EC surface contact and EC-coated pit formation, whereas a panel of recombinant cytokines known to alter the surface phenotype of EC fail to induce the same morphologic changes whether used singly or in combination. We postulate that the cellular interactions observed here, in vitro, may represent the initial steps in the rejection of vascularized allografts in vivo.

Human natural killer lymphocytes directly recognize evolutionarily conserved oligosaccharide ligands expressed by xenogeneic tissues.

BACKGROUND: In discordant xenogeneic species combinations, vascularized transplants are hyperacutely rejected, due to binding of xenoreactive natural antibodies (XNA) to selected tissues of the graft, followed by activation of the complement and coagulation cascades. A major epitope recognized by human XNA is the terminal disaccharide Gal alpha(1,3)Gal. Poorly defined, early cell-mediated events also contribute to recognition and rejection of discordant xenografts, and we have suggested a role of natural killer (NK) lymphocytes in this process. METHODS: Human NK cells were used as effectors in functional assays of adhesion to and lysis of xenogeneic discordant endothelial cells in vitro. Adhesion and lysis inhibition experiments were performed using a large panel of carbohydrates, as well as F(ab')2 fragments of human XNA. COS cells transduced with the porcine alpha-galactosyltransferase were also used as targets for NK cell adhesion. RESULTS: We demonstrate that XNA-reactive carbohydrate epitopes expressed by xenogeneic cells, including Gal alpha(1,3)Gal, are also directly recognized by human NK cells. First, selected carbohydrates in solution displace with comparable efficiency both XNA and NK cell binding to xenogeneic endothelium; second, XNA F(ab')2 fragments selectively inhibit human NK cell adhesion to porcine endothelium, but not to human endothelium; third, unstimulated NK lymphocytes adhere selectively to COS-7 cells expressing the porcine glycosyltransferase that encodes the Gal alpha(1,3)Gal epitope. CONCLUSIONS: Collectively, our findings suggest that humoral and cellular components of the natural immune response against heterologous species independently evolved recognition patterns directed against overlapping carbohydrate determinants.

Inhibition of interferon-gamma-mediated microvascular endothelial cell major histocompatibility complex class II gene activation by HMG-CoA reductase inhibitors.

BACKGROUND: Graft vascular disease, a major cause of late graft failure in cardiac transplant patients, is associated with the presence of class II major histocompatibility complex molecules on the endothelium. 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, e.g., simvastatin, have been shown to reduce the incidence of graft vascular disease. We studied the effect of simvastatin on interferon (IFN)-gamma-induced human leukocyte antigen (HLA)-DR expression in human microvascular endothelial cells (MVECs). METHODS AND RESULTS: Simvastatin pretreatment inhibited MVEC HILA-DR induction by IFN-gamma, as detected by flow cytometry. Simvastatin's inhibitory effect was reversed by the cholesterol synthesis pathway intermediates mevalonate and geranylgeranyl pyrophosphate but not squalene, indicating the involvement of protein prenylation in this process. Reverse transcription-polymerase chain reaction analysis demonstrated that induction of class II transactivator (CIITA), and consequently, HLA-DRalpha mRNA, is abrogated by simvastatin. Although signal transducer and activator of transcription (STAT)-1 is a critical CIITA gene transactivator, immunofluorescence studies, Western blotting, and electrophoretic mobility shift assays demonstrated that IFN-gamma-induced STAT-1 phosphorylation, nuclear translocation, and DNA binding are not affected by simvastatin. However, simvastatin inhibited IFN-gamma-induced transactivation of a CIITA promoter IV reporter construct, indicating the involvement of this promoter in the inhibitory effect of simvastatin. CONCLUSIONS: Simvastatin pretreatment inhibits CIITA and consequent HLA-DR induction by IFN-gamma in MVECs through interference with protein prenylation. This inhibitory effect occurs at the level of transcription and is directed, at least in part, at the CIITA promoter IV. These results explain some of the beneficial effects of HMG-CoA reductase inhibitors in cardiac transplantation.

Monoclonal antibodies reactive with subsets of mouse and human thymic epithelial cells.

We describe monoclonal antibodies (MAB) reactive with subsets of mouse and human thymic epithelial cells. Rat MAb CDR1 reacts with mouse but not human cortical epithelial cells. Immunologic staining of thymic nurse cells in suspension indicates the CDR1 antigen is located on the cell surface. Mouse MAb CDR2 reacts with human but not mouse cortical thymic epithelial cells. Rat MAb MD1 and MD2 detect different determinants expressed by most medullary epithelial cells in mouse thymus but fewer such cells in human thymus. In addition, MD1 detects flattened subcapsular cells rarely in mouse thymus but frequently in human thymus. Two-color stains using an anti-keratin antiserum demonstrate the epithelial nature of the cells reactive with these antibodies. The antigens detected by CDR1 and MD1 first appear during the neonatal period, achieving adult distribution by postnatal days 14 and 4, respectively. The extra-thymic staining of these MAb is described. On the basis of their intra- and extra-thymic reactivities, these MAb differ from those previously reported and may permit dissection of the thymic microenvironment.

Glass fiber manufacturing and fiber safety: the producer's perspective.

Historically, the potential health effects of airborne fibers have been associated with the dose, dimension, and durability. Increasing focus is being placed on the latter category. Concern about airborne fiber safety could be reduced by manufacturing fibers that are not respirable; however, due to performance and manufacturing constraints on glasswool insulations, this is not possible today. These products are an important part of today's economy and as a major manufacturer, Owens-Corning is committed to producing and marketing materials that are both safe and effective in their intended use. To this end, manufacturing technology seeks to produce materials that generate low concentrations of airborne fibers, thus minimizing exposure and irritation. The range of fiber diameters is controlled to assure effective product performance and, as far as possible, to minimize respirability. Glass compositions are designed to allow effective fiber forming and ultimate product function. Fiber dissolution is primarily a function of composition; this too, can be controlled within certain constraints. Coupled with these broad parameters is an extensive product stewardship program to assure the safety of these materials. This article will discuss the factors that influence glasswool insulation production, use, and safety.

Development of an evaluation model for computer foodservice management systems.

Business evaluation practices were used to develop a model for postimplementation of a computer system in a foodservice. Four levels of success with a corresponding indicator for evaluation were identified as: I. Management Action--management implements data and reports; II. Management Change--management initiates use of system to find solutions to problems; III. Management Uses Analytical Approach--management uses system as a routine part of problem-solving; and IV. Management Change in Task-management's role changes as a result of the computer system. Five computer functions were identified for evaluation: integrity, performance, use, efficiency, and effectiveness. Criteria, measurements, standards, and actual sections were then developed for each function. An instrument was developed on the basis of the evaluation, including forms, questionnaires, learning experiences, and scenarios. The instrument was then applied to two computer foodservice management systems--a custom-designed system and a packaged software system. The instrument was applied to software systems by the scenario method. Five criteria with key indicators were developed to determine successful application of the instrument. The evaluation model and the final instrument developed and applied in this study should be useful to dietitians evaluating a computer system 6 to 12 months after implementation in their foodservice.

Vascular cell adhesion molecule-1-targeted detection of endothelial activation in human microvasculature.

The hallmark of endothelial activation, an early and critical step in many alloimmune and inflammatory responses, is the transcriptional induction and expression of endothelial adhesion molecules (eg, vascular cell adhesion molecule-1 [VCAM-1]). We assessed the feasibility of VCAM-1-targeted in vivo detection of endothelial activation using I-125-labeled-F(ab')2 fragments of E1/6, a monoclonal antibody against human but not murine VCAM-1. The Kd and Bmax, determined by saturation binding in tumor necrosis factor (TNF)-activated human endothelial cells (ECs), were 3.2 +/- 0.6 nmol/L and 5600 +/- 300 binding sites per EC, respectively. Biodistribution and in vivo binding characteristics of I-125-E1/6 F(ab')2 were assessed in a novel chimeric human/mouse model, in which human skin (as a source of human microvasculature) is grafted onto SCID/beige mice. I-125-E1/6 F(ab')2 localized to TNF-activated human skin grafts as detected by autoradiography and gamma well-counting. Relative uptakes (uptake in human skin graft/uptake in the surrounding mouse skin) were, respectively, 2.6 +/- 0.8 (n = 14) and 1.6 +/- 0.3 (n = 12) for E1/6 and MOPC-21, an isotype-matched control antibody (P < .01). The preferential uptake in human skin graft was not due to differences in tissue vascularity assessed by Tc-99m-labeled murine red blood cells. In conclusion, the chimeric human/mouse model is a novel experimental tool for in vivo evaluation of human endothelial cell-specific radiopharmaceuticals. Although I-125-E1/6 F(ab')2 localized to human skin grafts, the limited number of VCAM-1 molecules/endothelial cell adversely affects its suitability as a target for in vivo imaging of endothelial activation.