Role of complement receptors in uptake of Mycobacterium avium by macrophages in vivo: evidence from studies using CD18-deficient mice.
(49/1480)
Mycobacterium avium is an intracellular pathogen that has been shown to invade macrophages by using complement receptors in vitro, but mycobacteria released from one cell can enter a second macrophage by using receptors different from complement receptors. Infection of CD18 (beta(2) integrin) knockout mice and the C57 BL/6 control mice led to comparable levels of tissue infection at 1 day, 2 days, 1 week, and 3 weeks following administration of bacteria. A histopathological study revealed similar granulomatous lesions in the two mouse strains, with comparable numbers of organisms. In addition, transmission electron microscopy of spleen tissues from both strains of mice showed bacteria inside macrophages. Our in vivo findings support the hypothesis that M. avium in the host is likely to use receptors other than CR3 and CR4 receptors to enter macrophages with increased efficiency. (+info)
Beta-glucan, a "specific" biologic response modifier that uses antibodies to target tumors for cytotoxic recognition by leukocyte complement receptor type 3 (CD11b/CD18).
(50/1480)
beta-Glucans were identified 36 years ago as a biologic response modifier that stimulated tumor rejection. In vitro studies have shown that beta-glucans bind to a lectin domain within complement receptor type 3 (CR3; known also as Mac-1, CD11b/CD18, or alphaMbeta2-integrin, that functions as an adhesion molecule and a receptor for factor I-cleaved C3b, i.e., iC3b) resulting in the priming of this iC3b receptor for cytotoxicity of iC3b-opsonized target cells. This investigation explored mechanisms of tumor therapy with soluble beta-glucan in mice. Normal mouse sera were shown to contain low levels of Abs reactive with syngeneic or allogeneic tumor lines that activated complement, depositing C3 onto tumors. Implanted tumors became coated with IgM, IgG, and C3, and the absent C3 deposition on tumors in SCID mice was reconstituted with IgM or IgG isolated from normal sera. Therapy of mice with glucan- or mannan-rich soluble polysaccharides exhibiting high affinity for CR3 caused a 57-90% reduction in tumor weight. In young mice with lower levels of tumor-reactive Abs, the effectiveness of beta-glucan was enhanced by administration of a tumor-specific mAb, and in SCID mice, an absent response to beta-glucan was reconstituted with normal IgM or IgG. The requirement for C3 on tumors and CR3 on leukocytes was highlighted by therapy failures in C3- or CR3-deficient mice. Thus, the tumoricidal function of CR3-binding polysaccharides such as beta-glucan in vivo is defined by natural and elicited Abs that direct iC3b deposition onto neoplastic cells, making them targets for circulating leukocytes bearing polysaccharide-primed CR3. Therapy fails when tumors lack iC3b, but can be restored by tumor-specific Abs that deposit iC3b onto the tumors. (+info)
Cytosolic phospholipase A2 activation is essential for beta 1 and beta 2 integrin-dependent adhesion of human eosinophils.
(51/1480)
We examined the role of cytosolic phospholipase A2 (cPLA2) during human eosinophil adherence to ICAM-1- or VCAM-1-coated plates. IL-5-stimulated eosinophils adhered to ICAM-1 through the beta 2 integrin CD11b/CD18, while nonstimulated eosinophils did not. By contrast, nonstimulated eosinophils adhered to VCAM-1 through the beta 1-integrin VLA-4/CD29. Both IL-5-induced adhesion to ICAM-1 and spontaneous adhesion to VCAM-1 corresponded temporally to cPLA2 phosphorylation, which accompanied enhanced catalytic activity of cPLA2. The structurally unrelated cPLA2 inhibitors, arachidonyl trifluoromethylketone and surfactin, significantly inhibited eosinophil adhesion to ICAM-1 and VCAM-1 in a concentration-dependent manner. Inhibition of secretory PLA2, 5-lipoxygenase, or cyclooxygenase did not affect eosinophil adhesion. Addition of arachidonic acid to eosinophils after cPLA2 inhibition with arachidonyl trifluoromethylketone or surfactin did not reverse the blockade of adhesion to ICAM-1 or VCAM-1. However, CV-6209, a receptor-specific antagonist of platelet-activating factor, inhibited all integrin-mediated adhesion. The activated conformation of CD11b as identified by the mAb, CBRM1/5, as well as quantitative surface CD11b expression were up-regulated after IL-5 stimulation. However, cPLA2 inhibition neither prevented CBRM1/5 expression nor blocked surface Mac-1 up-regulation caused by IL-5. Our data suggest that cPLA2 activation and its catalytic product platelet-activating factor play an essential role in regulating beta 1 and beta 2 integrin-dependent adhesion of eosinophils. This blockade occurs even in the presence of up-regulated eosinophil surface integrin. (+info)
Indomethacin induced gastropathy in CD18, intercellular adhesion molecule 1, or P-selectin deficient mice.
(52/1480)
BACKGROUND: Neutrophil-endothelial cell interactions are thought to play a critical role in the pathophysiology of non-steroidal anti-inflammatory drug (NSAID) induced gastropathy. AIMS: To optimise a mouse model of NSAID induced gastropathy and to evaluate the importance of adhesion molecules using adhesion molecule deficient mice. METHODS: Gastropathy was induced in C57BL/6 mice or their adhesion molecule deficient counterparts via oral administration of indomethacin (20 mg/kg). Lesion scores, mucosal permeability, and histopathology were used to assess gastric mucosal injury. RESULTS: Intragastric administration of indomethacin induced linear haemorrhagic mucosal lesions, primarily in the corpus of the stomach that were first observed at six hours. These lesions continued to develop over the next six hours with maximal lesion scores and mucosal permeabilities at 12 hours. When indomethacin was administered to mice deficient in CD18, intercellular adhesion molecule 1 (ICAM-1), or P-selectin, there were significant decreases in lesion scores compared with their C57BL/6 controls. In addition, mucosal permeabilities were found to be significantly lower in CD18 or ICAM-1 deficient mice observed at 12 hours. CONCLUSION: Certain leucocyte and endothelial cell adhesion molecules are important determinants for full expression of indomethacin induced gastropathy. It is proposed that this modification of the mouse model may be useful for the investigation of other pathophysiological mechanisms of NSAID induced gastropathy. (+info)
A tyrosine-based sorting signal in the beta2 integrin cytoplasmic domain mediates its recycling to the plasma membrane and is required for ligand-supported migration.
(53/1480)
Integrins play pivotal roles in supporting shear- and mechanical-stress-resistant cell adhesion and migration. These functions require the integrity of the short beta subunit cytoplasmic domains, which contain multiple, highly conserved tyrosine-based endocytic signals, typically found in receptors undergoing regulated, clathrin-dependent endocytosis. We hypothesized that these sequences may control surface integrin dynamics in statically adherent and/or locomoting cells via regulated internalization and polarized recycling of the receptors. By using site-directed mutagenesis and ectopic expression of the alphaL/beta2 integrin in Chinese hamster ovary cells, we found that Y735 in the membrane-proximal YRRF sequence is selectively required for recycling of spontaneously internalized receptors to the cell surface and to growth factor-induced membrane ruffles. Disruption of this motif by non-conservative substitutions has no effect on the receptor's adhesive function, but diverts internalized integrins from a recycling compartment into a degradative pathway. Conversely, the non-conservative F754A substitution in the membrane-proximal NPLF sequence abrogates ligand-dependent adhesion and spreading without affecting receptor recycling. Both of these mutants display a severe impairment in ligand-supported migration, suggesting the existence in integrin cytoplasmic domains of independent signals regulating apparently unrelated functions that are required to sustain cell migration over specific ligands. (+info)
Short exposure of intestinal epithelial cells to TNF-alpha and histamine induces Mac-1-mediated neutrophil adhesion independent of protein synthesis.
(54/1480)
Neutrophils play an important role in intestinal inflammation by interacting with intestinal epithelial cells. In this study, we evaluated neutrophil adhesion to intestinal epithelial cells using intestinal epithelial cell line HT29 stimulated with tumor necrosis factor alpha (TNF-alpha) and histamine for a short time (30 min). The TNF-alpha and histamine stimulation markedly increased neutrophil adhesion. The increased adhesion was inhibited by anti-CD11b and anti-CD18 monoclonal antibodies (mAbs), but not by anti-CD11a and anti-CD54 (ICAM-1) mAbs. It is interesting that flow cytometric analysis revealed that ICAM-1 expression on HT29 cells was not changed by TNF-alpha and histamine stimulation. Moreover, the increased adhesion was inhibited by proteinase K treatment but not cycloheximide treatment of HT29 cells. Together these observations suggest that short exposure of HT29 cells to TNF-alpha and histamine induces CD11b/CD18 (Mac-1)-dependent but CD11a/CD18 (LFA-1)-independent neutrophil adhesion to intestinal epithelial cells, and ICAM-1 is not likely to be involved in the interactions. Furthermore, epithelial cell ligand(s) for neutrophils is likely protein molecule(s) that is expressed on the cell by stimulation independent protein synthesis. However, it is also possible that neutrophil activating factor(s), which stimulates neutrophils to bind with epithelial ligands via Mac-1, is expressed by epithelial cells during stimulation. (+info)
A role for beta(2) integrins (CD11/CD18) in the regulation of cytokine gene expression of polymorphonuclear neutrophils during the inflammatory response.
(55/1480)
Growing evidence supports the idea that adhesion via beta(2) integrins not only allows cellular targeting, but also induces intracellular signaling, which in turn activates functional responses of adherent cells. This study investigates whether beta(2) integrin-mediated adhesion of human polymorphonuclear neutrophils (PMN) has a functional impact on cytokine production. Aggregation of the beta(2) integrin Mac-1 (CD11b/CD18) by antibody cross-linking was found to induce substantial de novo synthesis of IL-8 mRNA as measured by semiquantitative RT-PCR and Northern blotting technique, respectively. Induction of IL-8 mRNA was also observed upon adhesion of PMN to immobilized fibrinogen, a functional equivalent of its clotting product fibrin that serves as a native ligand of Mac-1. Results were confirmed using PMN derived from CD18-deficient mice, which were unable to produce MIP-2 mRNA, a homologue of human IL-8, in the presence of immobilized fibrinogen. In contrast, a substantial increase of MIP-2 mRNA was observed when wild-type PMN were incubated on immobilized fibrinogen. In human PMN, ELISA technique showed that the gene activation that required tyrosine kinase activity resulted in a substantial production and secretion of biologically active IL-8 and IL-1beta. In contrast, no TNF-alpha or IL-6 production was found, revealing that beta(2) integrins mediate differential expression of proinflammatory cytokines. The biological relevance of the present findings was confirmed in an in vivo model of acute inflammation. Altogether, the present findings provide evidence for a functional link between clotting and inflammatory responses that may contribute to the recruitment and/or activation of PMN and other cells at sites of lesion. (+info)
Cytokine-activated endothelial cells delay neutrophil apoptosis in vitro and in vivo. A role for granulocyte/macrophage colony-stimulating factor.
(56/1480)
The activation of endothelium is important in recruiting neutrophils to sites of inflammation and in modulating their function. We demonstrate that conditioned medium from cultured, activated endothelial cells acts to significantly delay the constitutive apoptosis of neutrophils, resulting in their enhanced survival and increased phagocytic function. The antiapoptotic activity is, in part, attributable to granulocyte/macrophage colony-stimulating factor (GM-CSF) secreted by activated endothelial cells. The in vivo relevance of these findings was investigated in a cytokine-induced model of acute meningitis in mice. Peripheral blood neutrophils (PBNs) from mice with meningitis exhibited a delay in apoptosis compared with untreated mice. Furthermore, neutrophils recovered from the inflamed cerebrospinal fluid (CSF) exhibited enhanced survival compared with neutrophils isolated from the peripheral blood of the same animals. In unchallenged GM-CSF-deficient mice, the apoptosis of circulating PBNs was similar to wild-type animals; however, after cytokine-induced meningitis, the delay in neutrophil apoptosis typically observed in wild-type mice was attenuated. In contrast, the apoptosis of neutrophils recovered from the CSF of mice of both genotypes was comparable. Taken together, these studies suggest that neutrophil apoptosis is regulated during an inflammatory response, in both intravascular and extravascular compartments. GM-CSF released by activated endothelium can act to increase neutrophil survival and function in the peripheral blood, whereas other factor(s) appear to perform this function in the extravascular space. (+info)