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O Lider

Publications and source records attributed to O Lider.

At least 55 records · Page 3Linked to original sources
PubMed1997

Extracellular matrix-anchored serum amyloid A preferentially induces mast cell adhesion.

Mast cells are known to accumulate in various inflammatory processes, some of which are known to be associated with increased local and systemic levels of acute-phase reactants such as serum amyloid A (SAA) or with amyloid deposition. The mechanism(s) by which mast cells are recruited to these sites, however, has not been fully elucidated. It has recently been shown that SAA interacts with extracellular matrix (ECM) components and thereby acts as a chemoattractant and regulator of immune cell migration. On the basis of these observations, we examined the effect of SAA on mast cell adhesion to ECM, an essential step in cellular transmigration. We could first demonstrate strong specific binding of recombinant human SAA (rSAA) to murine mast cells using flow cytometry. Moreover, radiolabeled rSAA was found to bind, in a saturable manner, to mast cells, reaching a binding affinity of 10(-8) M. When immobilized by preincubation with ECM, SAA or its proteolytically degraded amyloid A fragment (amino acid residues 2-82), which contains RGD-related adhesion motif but not the COOH-terminal portion of SAA (amino acid residues 77-104), induced the adhesion of resting mast cells to ECM or laminin. SAA and AA, in soluble or immobilized forms, did not activate mast cells to release mediators. Mast cell adhesion to the immobilized ECM-SAA complex appeared to occur through an integrin recognition, inasmuch as adhesion was calcium dependent and could be blocked by an RGD-containing peptide or by anti-CD29 monoclonal antibody. Genistein also inhibited adhesion, indicating that tyrosine kinase activity was involved. These data suggest that SAA bound to ECM may serve as an important inducer of mast cell adhesion, thus regulating mast cell recruitment and accumulation at these sites, which in turn could potentiate further pathology.

Animals↗
PubMed1996

The cell-binding domain of intimin from enteropathogenic Escherichia coli binds to beta1 integrins.

Bacteria interact with mammalian cells surface molecules, such as integrins, to colonize tissues and evade immunological detection. Herein, the ability of intimin, an outer membrane protein from enteropathogenic Escherichia coli, to bind beta1 integrins was investigated. Solid-phase binding assays revealed binding of the carboxyl-terminal 280 amino acids of intimin (Int280) to alpha4beta1 and alpha5beta1 integrins. The binding required divalent ions (in particular, it was enhanced by Mn2+) and was inhibited by an RGD-containing peptide. Nonderivatized Int280, but not Int280CS (like Int280 but with Cys-937 replaced by Ser) blocked the binding of biotinylated Int280 to integrins. Int280 did not efficiently inhibit beta1 integrin binding of invasin from Yersinia pseudotuberculosis. Both intimin and invasin, immobilized on plastic surfaces, mediated adherence of resting or phorbol 12-myristate 13-acetate-activated human CD4(+) T cells, whereas fibronectin mediated the adherence of only activated T cells. T cell binding to intimin and invasin was integrin mediated because it was specifically blocked by an RGD-containing peptide and by antibodies directed against the integrin subunits beta1, alpha4, and alpha5. These results demonstrate a specific integrin binding activity for intimin that is related to, but distinct from, that of invasin.

Adhesins, Bacterial↗
PubMed1996

Serum amyloid A binds specific extracellular matrix glycoproteins and induces the adhesion of resting CD4+ T cells.

Serum amyloid A (SAA), a prototypic acute phase protein reactant, exists naturally in the serum of healthy individuals. However, the levels of SAA in serum and its presence in sites of inflammation increase during certain chronic diseases associated with a local elevation of cytokine concentrations. Although the chemical structure of SAA is defined, its putative immunologic role(s) is still obscure. Nevertheless, it has been shown that 1) SAA acts as a chemoattractant and regulator of the migration of monocytes, polymorphonuclear cells, and T lymphocytes through endothelial cell monolayers; and 2) SAA and its proteolytically degraded N-terminal amyloid A fragment contain an extracellular matrix (ECM)-related cell adhesion epitopes. Herein, we examined whether SAA can associate with specific ECM moieties, and whether immobilized SAA-ECM complexes affect T lymphocyte adhesion. Radiolabeled human rSAA ([125I]rSAA) interacted avidly (Kd = 10(-9) M) and transiently with intact ECM, laminin, and vitronectin, but not with fibronectin or collagen type II. The binding of [125I]rSAA to ECM and laminin was inhibited by unlabeled rSAA and by the AA fragment, but not by the C-terminal portion of SAA (amino acid residues 2-82 and 77-104, respectively). Upon interactions with SAA or amyloid A, immobilized ECM, laminin, and vitronectin induced the adhesion of resting human CD4+ T cells in an apparently beta 1-integrin-mediated manner. Thus, the ECM appears to serve as a temporary anchorage site for SAA and amyloid A, and these ECM-complexed molecules seem to be involved in regulating the recruitment and accumulation of immunocytes in extravascular inflammatory compartments.

Amino Acid Sequence↗
PubMed1996

Inhibition of experimentally-induced liver cirrhosis in rats by a nonpeptidic mimetic of the extracellular matrix-associated Arg-Gly-Asp epitope.

AIMS/METHODS: In the present study, we examined whether a nonpeptidic mimetic of Arg-Gly-Asp (RGD), which specifically inhibits RGD-dependent adhesion of CD4+ T lymphocytes or fibroblasts to fibronectin, can prevent thioacetamide-induced liver cirrhosis in rats. The nonpeptidic RGD mimetic, rather than the RGD peptide was utilized, since the peptide is rapidly degraded, and therefore, relatively ineffective for in vivo use. RESULTS: We now report that rats treated with thioacetamide and the RGD analogue SF-6,5 for 12 weeks had lower histopathologic scores than those treated with thioacetamide alone. Further improvement in liver histology was observed after another 8 weeks of treatment with the analogue SF-6,5. Quantitative microscopic analysis by computerized imaging morphometry of liver biopsies from the three groups and controls confirmed the semi-quantitative histopathologic scores (p < 0.001). After 3 months of treatment, the spleen weights in the SF-6,5-treated rats were 30% less than those of rats that received only thioacetamide, which indicated that the analogue-treated rats were less portal hypertensive. CONCLUSIONS: The observed inhibition of the progression of cirrhosis in rats by the nonpeptidic RGD analogue suggests that RGD mimetics may be useful therapeutically in inhibiting pathological processes that involve RGD recognition.

Amino Acid Sequence↗
PubMed1996

Keratinocytes-associated chemokines and enzymatically quiescent heparanase induce the binding of resting CD4+ T cells.

Whether the chemokines macrophage inflammatory protein-1 beta (MIP-1 beta) and regulated on activation normal T expressed and secreted (RANTES), which interact specifically with glycosaminoglycans and thus mediate the recruitment, attachment, and migration of leukocytes to vascular endothelia and extracellular matrix, are also involved in interactions between CD4+ murine T lymphocytes and keratinocytes was examined. We have previously observed that depending on the local pH, a mammalian extracellular matrix-degrading enzyme, endo-beta-D glucuronidase (heparanase), which cleaves heparin sulfate proteoglycans, can function wither as an enzyme or as an adhesion molecule for CD4+ T lymphocytes. Herein, the involvement of heparanase in T cell-keratinocyte interactions was also probed. At 37 degree C and pH 7.2, radioactively labeled MIP-1 beta, RANTES, and heparanase bound to confluent layers of resting keratinocytes in a saturable and an heparan sulfate- or heparin-dependent manner, and thereby induced the adhesion of resting CD4+ T cells to keratinocytes. At a relatively acidic pH characteristic of inflammatory milieu, enzymatically active heparanase did not bind to the keratinocytes but, rather, inhibited the binding of MIP-1beta, RANTES, and the enzymatically quiescent heparanase to keratinocytes. These results suggest that certain chemokines and heparanase may function to restrict passing leukocytes, notable T lymphocytes, in the cutaneous micro-environment, a site which is continuously challenged with antigens. These keratinocyte-bound lymphocytes can serve as a reservoir of immediate responders to immunological stimuli.

Animals↗
PubMed1995

A disaccharide that inhibits tumor necrosis factor alpha is formed from the extracellular matrix by the enzyme heparanase.

The activation of T cells by antigens or mitogens leads to the secretion of cytokines and enzymes that shape the inflammatory response. Among these molecular mediators of inflammation is a heparanase enzyme that degrades the heparan sulfate scaffold of the extracellular matrix (ECM). Activated T cells use heparanase to penetrate the ECM and gain access to the tissues. We now report that among the breakdown products of the ECM generated by heparanase is a trisulfated disaccharide that can inhibit delayed-type hypersensitivity (DTH) in mice. This inhibition of T-cell mediated inflammation in vivo was associated with an inhibitory effect of the disaccharide on the production of biologically active tumor necrosis factor alpha (TNF-alpha) by activated T cells in vitro; the trisulfated disaccharide did not affect T-cell viability or responsiveness generally. Both the in vivo and in vitro effects of the disaccharide manifested a bell-shaped dose-response curve. The inhibitory effects of the trisulfated disaccharide were lost if the sulfate groups were removed. Thus, the disaccharide, which may be a natural product of inflammation, can regulate the functional nature of the response by the T cell to activation. Such a feedback control mechanism could enable the T cell to assess the extent of tissue degradation and adjust its behavior accordingly.

Animals↗
PubMed1995

Molecular behavior adapts to context: heparanase functions as an extracellular matrix-degrading enzyme or as a T cell adhesion molecule, depending on the local pH.

Migration of lymphocytes into inflammatory sites requires their adhesion to the vascular endothelium and subendothelial extracellular matrix (ECM). The ensuing penetration of the ECM is associated with the expression of ECM-degrading enzymes, such as endo-beta-D glucuronidase (heparanase), which cleaves heparan sulfate (HS) proteoglycans. We now report that, depending on the local pH, a mammalian heparanase can function either as an enzyme or as an adhesion molecule. At relatively acidified pH conditions, heparanase performs as an enzyme, degrading HS. In contrast, at the hydrogen ion concentration of a quiescent tissue, heparanase binds specifically to HS molecules without degrading them, and thereby anchors CD4+ human T lymphocytes. Thus, the local state of a tissue can regulate the activities of heparanase and can determine whether the molecule will function as an enzyme or as a proadhesive molecule.

CD4-Positive T-Lymphocytes↗
PubMed1995

Characterization of biologically active antineutrophil cytoplasmic antibodies induced in mice. Pathogenetic role in experimental vasculitis.

OBJECTIVE: To investigate the pathogenetic role of antineutrophil cytoplasmic antibodies (ANCA) in Wegener's granulomatosis (WG). METHODS: BALB/c mice were immunized with human IgG ANCA from a patient with WG. Control mice were immunized with normal human IgG. Levels of mouse ANCA and other autoantibodies were determined. Mouse ANCA were tested for their ability to induce adhesion and respiratory burst of neutrophils. The mouse lungs and kidneys were examined for the development of vasculitis. RESULTS: Mice immunized with human ANCA developed anti-human ANCA and anti-anti-human ANCA (mouse ANCA), while the controls did not develop these antibodies. Mouse ANCA were capable of inducing adhesion of neutrophils to fibronectin and activating the respiratory burst in neutrophils. Moreover, the mice that were immunized with human ANCA developed perivascular mononuclear cell infiltrates in the lungs, suggesting vasculitis. CONCLUSION: The results suggest a pathogenic role of ANCA in WG, and may imply that activation of neutrophils is the initiating event in the development of vasculitis in WG.

Animals↗
PubMed1995

Differential effects of polysulfated polysaccharide on experimental encephalomyelitis, proliferation of autoimmune T cells, and inhibition of heparanase activity.

The extravasation of activated T lymphocytes through blood vessel walls and their migration to inflammatory loci are associated with secretion of extracellular matrix (ECM)-degrading enzymes, such as heparanase, which degrades heparan sulfate (HS) moieties of the ECM. The HS-degrading activity of heparanase was found to be inhibited by HS and heparin. Since induction of experimental autoimmune encephalomyelitis (EAE) requires extravasation and migration of autoimmune T cells, degradation of ECM by heparanase is expected to be involved in induction of the disease. Herein, we examined whether laminarin sulfate, a polysulfated polysaccharide (PSS) isolated from the cell walls of seaweeds and subjected to chemical sulfation, could inhibit ECM degradation by mammalian heparanase, and could prevent EAE. PSS was a more potent inhibitor of heparanase-mediated degradation of ECM than heparin. In-vivo, PSS, injected once a week, inhibited the severity of actively-induced EAE in rats. However, inhibition of EAE was not due to an overall suppression of autoimmune T cells, since PSS enhanced the proliferation of myelin basic protein (MBP)-specific, encephalitogenic T cells. PSS-activated autoimmune T cells, but not MBP-activated cells, failed to induce EAE in recipient rats. Moreover, rats injected with PSS-activated T cells were resistant to induction of EAE by anti-MBP CD4+ T cells. Thus, PSS may have potential clinical applications in the treatment of autoimmune diseases.

Animals↗
PubMed1995

Treatment of immune cell-mediated liver damage by nonpeptidic mimetics of the extracellular matrix-associated Arg-Gly-Asp epitope.

The etiology of T-cell-mediated liver injury involves the migration of immune cells, notably CD4+ T lymphocytes, into liver tissues. This process is mediated primarily by integrin-recognition of the sub-endothelium basement membranes and the extracellular matrix. The Arg-Gly-Asp-containing peptide, a major cell-adhesive ligand of extracellular matrix, is present in various plasma- and matrix-glycoproteins, such as fibronectin. Recently, we have described the design and usage of nonpeptide mimetics of Arg-Gly-Asp which bind specifically to integrins, and thereby, inhibit T cell immunity in vivo. We examined the efficacy of Arg-Gly-Asp-mimetics as potential therapeutic compounds for the treatment of experimental T-cell-mediated liver injury induced in mice by injection of Concanavalin-A. We now report that the Arg-Gly-Asp-mimetics specifically inhibited the binding of murine T cells to fibronectin, but did not affect the proliferative response of these cells in vitro. Intraperitoneal or oral administration of the Arg-Gly-Asp-mimetics but not the Arg-Gly-Asp-containing peptide, inhibited liver damage in mice if given before their inoculation with Con-A, as manifested by a lesser elevation in their serum levels of hepatic enzymes. The inhibitory effect of the Arg-Gly-Asp-mimetics was dose-dependent, the ED50 of the tested molecules being in the range of 100 micrograms per mouse and reaching maximal effect, e.g. approximately 95% inhibition, at 500 micrograms per mice. Thus, the Arg-Gly-Asp-mimetics described here may be used therapeutically to prevent immune-cell-mediated acute or chronic pathological reactions in the liver.

Animals↗
PubMed1995

Interactions of migrating T lymphocytes, inflammatory mediators, and the extracellular matrix.

Leukocytes are mobile units of the immune system. The process of leukocytes migration from blood vessels to inflamed tissues involves two major steps: (1) extravasation through the vessel wall and (2) movement through the underlying basement membrane and extracellular matrix (ECM). The ECM is a complex macromolecular mesh composed of proteoglycans and adhesive glycoproteins, such as collagen, laminin, and fibronectin, and serves as a supportive structure surrounding cells and can also provide co-stimulatory signals to immune cells. Hence, the basement membrane and the ECM play important roles as contexts in which biological processes take place, and therefore these moieties should be considered as microenvironment milieu in which extravasating cells function, communicate, and signal their messages; the outcome of which can result in the immunological eradication of hazardous elements. During migration, leukocytes continuously exchange information with the surrounding microenvironment. This cross-talk, which is also influenced by cytokines and chemokines, determines the type and the strength of the resulting immune response to foreign determinants. As suggested in the present article, these signals determine the response to a specific antigen and enable the migrating leukocytes to recognize any insult in their vicinity and to rapidly modify their activities.

Cell Communication↗
PubMed1995

Tumour necrosis factor-alpha interacts with laminin and functions as a pro-adhesive cytokine.

Certain cytokines, chemokines and growth factors interact with components of the extracellular matrix (ECM) and, in particular, sulphated polysaccharides and proteoglycans. Recently, we demonstrated that tumour necrosis factor-alpha (TNF-alpha), an inflammatory cytokine, can bind fibronectin (FN), a cell-adhesive glycoprotein of the ECM, and that TNF-alpha bound to FN enhances the binding of T cells to the glycoprotein. In the present study, we studied the interactions of TNF-alpha and laminin (LN), another glycoprotein present in basement membranes and extracellular matrices. 125I-labelled TNF-alpha was found to bind to immobilized LN, and more avidly to the E1 and P1 fragments of LN, which contain its integrin- and non-integrin-dependent cell-adhesive sites, suggesting that cryptic TNF-alpha-binding sites are exposed upon proteolytic fragmentation of LN by enzymes such as elastase or pepsin. The bound cytokine did not dissociate from the LN and its fragments during a 24-hr period, indicating that in vivo LN can serve to restrict TNF-alpha adjacent to inflammatory sites. The LN-associated TNF-alpha retained at least some of its biological activities, since both diffusible and, to a greater extent, LN-bound TNF-alpha elevated the beta 1-integrin-dependent adhesion to LN of phorbol ester-activated human CD4+ T cells. Thus, LN and TNF-alpha may act in concert to transmit synergistic activating signals to infiltrating leucocytes, and thereby regulate immune cell reactions in extravascular inflammatory tissue.

CD4-Positive T-Lymphocytes↗
PubMed1994

Regulation of adhesion of CD4+ T lymphocytes to intact or heparinase-treated subendothelial extracellular matrix by diffusible or anchored RANTES and MIP-1 beta.

Chemokines, a superfamily of 8- to 11-kDa mediators of inflammation, affect the attachment of immune cells to vascular endothelia by binding to cell surface glycosaminoglycans. We analyzed whether chemokines are also involved in interactions between CD4+ T lymphocytes and the subendothelial extracellular matrix (ECM). Soluble mediators, such as MIP-1 beta and RANTES, induced the binding of resting human CD4+ T cells to ECM in an integrin-dependent manner. Both MIP-1 beta and RANTES bound to intact ECM and retained their adhesive properties, and moreover, ECM-bound RANTES and MIP-1 beta prolonged the time course of interactions between the CD4+ T cells and the ECM. Because the adhesive effect of these chemokines was restricted by an inhibitor of GTP-binding proteins, the adhesive effect of ECM-bound RANTES and MIP-1 beta, which requires an intact cytoskeleton, seems to involve activation of a G protein-linked receptor. MIP-1 beta and RANTES exert their pro-adhesive effects through interactions with glycosaminoglycans, because heparinase-treated ECM did not bound chemokines and because the chemokines ability to induce T cell adhesion was abrogated if: 1) either of the chemokines is pretreaed with heparin or heparan-sulfate (HS), 2) HS is removed from intact ECM by heparinase, an HS-specific endoglycosidase, or 3) the ECM-bound chemokines are released by pretreatment with heparinase. Hence, the adhesive effects of immobilized chemokines is not restricted to T cells interacting with endothelial cells, but also affects the migration of immune cells which reside and function in the context of ECM.

CD4-Positive T-Lymphocytes↗
PubMed1994

TNF-alpha associated with fibronectin enhances phorbol myristate acetate- or antigen-mediated integrin-dependent adhesion of CD4+ T cells via protein tyrosine phosphorylation.

The effects of cytokines on immune cells may be influenced by their milieu, such as the extracellular matrix (ECM), in the vicinities of which cytokines and inflammatory cells interact and function. Previously, we demonstrated that TNF-alpha bound to fibronectin (FN) and augments the level of adhesion of activated CD4+ cells. Herein, we examined the mechanisms of this pro-adhesive activity of TNF-alpha and its putative physiologic consequences using human or rat CD4+ cells. A brief exposure of CD4+ cells to low dosages of soluble TNF-alpha or of FN- or laminin-bound TNF-alpha synergized with PMA to enhance the integrin-mediated binding of CD4+ cells to these immobilized ECM moieties. TNF-alpha-enhanced adhesion of CD4+ cells did not delay or inhibit the subsequent detachment of the cells from the substrate, and adhesion was increased provided the cells were treated with TNF-alpha immediately after their exposure to PMA. This indicates that the enhancing effect of TNF-alpha requires a previous activation of the cells. When TNF-alpha was immobilized on FN, less TNF-alpha was required to induce CD4+ cell binding to FN. Soluble, and to a greater extent FN-bound, TNF-alpha synergizes with PMA to intensify protein tyrosine phosphorylation in FN-bound CD4+ cells, and this effect of TNF-alpha was inhibited by inhibitors of tyrosine kinase. That FN-bound or soluble TNF-alpha also amplified the binding of an Ag-specific autoimmune rat T cell line to immobilized FN, emphasizes the physiologic relevance of our findings. Thus, the signal transduction and cell adhesive properties of ECM glycoproteins may be modulated upon their association with TNF-alpha, and matrix-linked TNF-alpha may recruit and direct immune cells to inflammatory sites.

Animals↗