Lactobacillus GG treatment ameliorates alcohol-induced intestinal oxidative stress, gut leakiness, and liver injury in a rat model of alcoholic steatohepatitis

Because only 30% of alcoholics develop alcoholic liver disease (ALD), a factor other than heavy alcohol consumption must be involved in the development of alcohol-induced liver injury. Animal and human studies suggest that bacterial products, such as endotoxins, are the second key co-factors, and oxidant-mediated gut leakiness is one of the sources of endotoxemia. Probiotics have been used to prevent and treat diseases associated with gut-derived bacterial products and disorders associated with gut leakiness. Indeed, "probiotic"Lactobacillus rhamnosus has been successfully used to treat alcohol-induced liver injury in rats. However, the mechanism of action involved in the potential beneficial effects of L. rhamnosus in alcohol liver injury is not known. We hypothesized that probiotics could preserve normal barrier function in an animal model of ALD by preventing alcohol-induced oxidative stress and thus prevent the development of hyperpermeability and subsequent alcoholic steatohepatitis (ASH). Male Sprague-Dawley rats were gavaged with alcohol twice daily (8 gm/kg) for 10 weeks. In addition, alcoholic rats were also treated with once daily gavage of either 2.5 x 10(7) live L. rhamnosus Gorbach-Goldin (LGG) or vehicle (V). Intestinal permeability (baseline and at 10 weeks) was determined using a sugar bolus and GC analysis of urinary sugars. Intestinal and liver tissues were analyzed for markers of oxidative stress and inflammation. In addition, livers were assessed histologically for severity of ASH and total fat (steatosis). Alcohol+LGG (ALC+LGG)-fed rats had significantly (P< or =.05) less severe ASH than ALC+V-fed rats. L. rhamnosus Gorbach-Goldin also reduced alcohol-induced gut leakiness and significantly blunted alcohol-induced oxidative stress and inflammation in both intestine and the liver. L. rhamnosus Gorbach-Goldin probiotic gavage significantly ameliorated ASH in rats. This improvement was associated with reduced markers of intestinal and liver oxidative stress and inflammation and preserved gut barrier function. Our study provides a scientific rationale to test probiotics for treatment and/or prevention of alcoholic liver disease in man.

Basic fibroblast growth factor accelerates matrix degradation via a neuro-endocrine pathway in human adult articular chondrocytes

Pain-related neuropeptides released from synovial fibroblasts, such as substance P, have been implicated in joint destruction. Substance P-induced inflammatory processes are mediated via signaling through a G-protein-coupled receptor, that is, neurokinin-1 tachykinin receptor (NK(1)-R). We determined the pathophysiological link between substance P and its receptor in human adult articular cartilage homeostasis. We further examined if catabolic growth factors such as basic fibroblast growth factor (bFGF or FGF-2) or IL-1beta accelerate matrix degradation via a neural pathway upregulation of substance P and NK(1)-R. We show here that substance P stimulates the production of cartilage-degrading enzymes, such as matrix metalloproteinase-13 (MMP-13), and suppresses proteoglycan deposition in human adult articular chondrocytes via NK(1)-R. Furthermore, we have demonstrated that substance P negates proteoglycan stimulation promoted by bone morphogenetic protein-7, suggesting the dual role of substance P as both a pro-catabolic and anti-anabolic mediator of cartilage homeostasis. We report that bFGF-mediated stimulation of substance P and its receptor NK(1)-R is, in part, through an IL-1beta-dependent pathway.

Effect of alcohol on miR-212 expression in intestinal epithelial cells and its potential role in alcoholic liver disease

BACKGROUND AND AIMS

Alcohol-induced gut leakiness is a key factor in alcoholic liver disease (ALD); it allows endotoxin to enter the circulation and initiate liver damage. Zonula occludens 1 (ZO-1) protein is a major component of tight junctions that regulates intestinal permeability. microRNAs (miRNAs) are recently discovered regulatory molecules that inhibit expression of their target genes.

THE AIMS OF OUR STUDY WERE

(i) to investigate the effect of alcohol on miRNA-212 (miR-212) and on expression of its predicted target gene, ZO-1, (ii) to study the potential role of miR-212 in the pathophysiology of ALD in man.

METHODS

Using a TaqMan miRNA assay system, we measured miR-212 expression levels in colon biopsy samples from patients with ALD and in Caco-2 cells (a human intestinal epithelial cell line) treated with or without EtOH. We measured ZO-1 protein levels using western blots. ZO-1 mRNA was assayed using real-time PCR. Intestinal barrier integrity was measured using fluorescein sulfonic acid clearance and immunofluorescent staining for ZO-1.

RESULTS

Ethanol increased miR-212 expression, decreased ZO-1 protein levels, disrupted tight junctions, and increased the permeability of monolayers of Caco-2 cells. An miR-212 over-expression is correlated with hyperpermeability of the monolayer barrier. miR-212 levels were higher in colon biopsy samples in patients with ALD than in healthy controls; ZO-1 protein levels were lower.

CONCLUSION

These data suggest a novel mechanism for alcohol-induced gut leakiness, one in which EtOH induces miR-212 over-expression which causes gut leakiness by down-regulating ZO-1 translation. This mechanism is a potential therapeutic target for leaky gut in patients with or at risk for ALD.

NF-kappaB activation as a key mechanism in ethanol-induced disruption of the F-actin cytoskeleton and monolayer barrier integrity in intestinal epithelium

Intestinal barrier disruption has been implicated in several intestinal and systemic disorders including alcoholic liver disease (ALD). Using monolayers of intestinal (Caco-2) cells, we showed that ethanol (EtOH) disrupts the barrier integrity via destabilization of the cytoskeleton. Because proinflammatory conditions are associated with activation of NF-kappa B (NF-kappaB), we hypothesized that EtOH induces disruption of cytoskeletal assembly and barrier integrity by activating NF-kappaB. Parental cells were pretreated with pharmacological modulators of NF-kappaB. Other cells were stably transfected with a dominant negative mutant for the NF-kappaB inhibitor, I-kappaBalpha. Monolayers of each cell type were exposed to EtOH and we then monitored monolayer barrier integrity (permeability); cytoskeletal stability and molecular dynamics (confocal microscopy and immunoblotting); intracellular levels of the I-kappaBalpha (immunoblotting); subcellular distribution and activity of NF-kappaB (immunoblotting and sensitive ELISA); and intracellular alterations in the 43kDa protein of the actin cytoskeleton, polymerized F-actin, and monomeric G-actin (SDS-PAGE fractionation). EtOH caused destabilizing alterations, including I-kappaBalpha degradation, NF-kappaB nuclear translocation, NF-kappaB subunit (p50 and p65) activation, actin disassembly (upward arrow G-, downward arrow F-), actin cytoskeleton instability, and barrier disruption. Inhibitors of NF-kappaB and stabilizers of I-kappaBalpha (e.g., MG-132, lactacystin, etc) prevented NF-kappaB activation while protecting against EtOH-induced injury. In transfected I-kappaBalpha mutant clones, stabilization of I-kappaBalpha to inactivate NF-kappaB protected against all measures of EtOH-induced injury. Our data support several novel mechanisms where NF-kappaB can affect the molecular dynamics of the F-actin cytoskeleton and intestinal barrier integrity under conditions of EtOH injury. (1) EtOH induces disruption of the F-actin cytoskeleton and of intestinal barrier integrity, in part, through I-kappaBalpha degradation and NF-kappaB activation; (2) The mechanism underlying this pathophysiological effect of the NF-kappaB appears to involve instability of the assembly of the subunit components of actin network.

Identification of pH-regulated antigen 1 released from Candida albicans as the major ligand for leukocyte integrin alphaMbeta2

Candida albicans is a common opportunistic fungal pathogen and is the leading cause of invasive fungal disease in immunocompromised individuals. The induction of cell-mediated immunity to C. albicans is of critical importance in host defense and the prime task of cells of the innate immune system. We previously demonstrated that the integrin alpha(M)beta(2) (CD11b/CD18) is the major leukocyte receptor involved in C. albicans recognition, mediating both adhesive and migratory responses to the fungus. In the present study, we demonstrate that various C. albicans strains release a protease-sensitive activity into their conditioned medium that supports alpha(M)beta(2)-mediated cell adhesion and migration. The isolation and characterization of this protein was undertaken by two independent approaches: 1) immunoaffinity purification on a mAb raised to conditioned medium which blocked alpha(M)beta(2)-dependent adhesion and migration; and 2) affinity chromatography on purified alpha(M)beta(2). Each approach led to the isolation of the same protein, which was unequivocally identified as pH-regulated Ag 1 (Pra1p), based on mass spectrometry and amino acid sequence analyses. C. albicans mutant strains lacking Pra1p were unable to support leukocyte adhesion or migration. In a neutrophil-mediated fungal killing assay, such mutant strains were resistant to killing and/or phagocytosis. Addition of purified Pra1p or reagents that block alpha(M)beta(2) function prevented killing of Pra1p-expressing but not Pra1p-deficient strains of C. albicans. Together, these data indicate that Pra1p is a ligand of alpha(M)beta(2) on C. albicans and that the soluble form of Pra1p may assist the fungus in escaping host surveillance.

Regulation of oxidant-induced intestinal permeability by metalloprotease-dependent epidermal growth factor receptor signaling

Inflammatory bowel disease (IBD) affects more than 1 million Americans with more than 30,000 new cases diagnosed each year. IBD increases patient morbidity and susceptibility to colorectal cancer, yet its etiology remains unknown. Current models identify two key determinants of IBD pathogenesis: hyperpermeability of the gut epithelial barrier to bacterial products and an abnormal immune response to these products. Two factors seem critical for hyperpermeability: oxidant-induced stress and proinflammatory cytokines (e.g., tumor necrosis factor-alpha). The aim of this study was to investigate the role of oxidant stress-mediated transactivation of the epidermal growth factor receptor (EGFR) in intestinal hyperpermeability. This study used the Caco-2 human colonic epithelial cell in vitro model of intestinal epithelium. Cells were grown on inserts for permeability and signaling studies and glass coverslips for microscopy studies. show that oxidant-induced intestinal hyperpermeability can be blocked by specific inhibitors of the EGFR, tumor necrosis factor convertase (TACE) metalloprotease, transforming growth factor (TGF)-alpha, and mitogen-activated protein kinases, especially extracellular signal-regulated kinase 1/2. We also show that oxidant initiates these signaling events, in part by causing translocation of TACE to cell-cell contact zones. In this study, our data identify a novel mechanism for oxidant-induced intestinal hyperpermeability relevant to IBD. We propose a new intestinal permeability model in which oxidant transactivates EGFR signaling by activation of TACE and cleavage of precursor TGF-alpha. These data could have a significant effect on our view of IBD pathogenesis and provide new therapeutic targets for IBD treatment.

Increased matrix metalloproteinase-13 production with aging by human articular chondrocytes in response to catabolic stimuli

Chondrocyte anabolic activity has been shown to decline with aging, but catabolic activity has received little attention. In this study, the effect of aging on the chondrocyte catabolic response was determined by stimulating isolated human chondrocytes with fibronectin fragments (FN-f) or interleukin-1beta and measuring matrix metalloproteinase-13 (MMP-13) production as a catabolic response. A significant age-related increase in chondrocyte MMP-13 production was noted. FN-f stimulation of MMP-13 expression was blocked using a nuclear factor kappa-B (NFkappaB) inhibitor suggesting a role for NFkappaB in this chondrocyte catabolic response. Chondrocyte production of the NFkappaB-regulated cytokine interleukin-1beta was also found to increase with donor age in unstimulated cells. These results demonstrate a significant age-related increase in chondrocyte catabolic responsiveness which could contribute to the development of osteoarthritis in older adults.

theta Isoform of protein kinase C alters barrier function in intestinal epithelium through modulation of distinct claudin isotypes: a novel mechanism for regulation of permeability

Using monolayers of intestinal Caco-2 cells, we discovered that the isoform of protein kinase C (PKC), a member of the "novel" subfamily of PKC isoforms, is required for monolayer barrier function. However, the mechanisms underlying this novel effect remain largely unknown. Here, we sought to determine whether the mechanism by which PKC- disrupts monolayer permeability and dynamics in intestinal epithelium involves PKC--induced alterations in claudin isotypes. We used cell clones that we recently developed, clones that were transfected with varying levels of plasmid to either stably suppress endogenous PKC- activity (antisense, dominant-negative constructs) or to ectopically express PKC- activity (sense constructs). We then determined barrier function, claudin isotype integrity, PKC- subcellular activity, claudin isotype subcellular pools, and claudin phosphorylation. Antisense transfection to underexpress the PKC- led to monolayer instability as shown by reduced 1) endogenous PKC- activity, 2) claudin isotypes in the membrane and cytoskeletal pools ( downward arrowclaud-1, downward arrowclaud-4 assembly), 3) claudin isotype phosphorylation ( downward arrow phospho-serine, downward arrow phospho-threonine), 4) architectural stability of the claudin-1 and claudin-4 rings, and 5) monolayer barrier function. In these antisense clones, PKC- activity was also substantially reduced in the membrane and cytoskeletal cell fractions. In wild-type (WT) cells, PKC- (82 kDa) was both constitutively active and coassociated with claudin-1 (22 kDa) and claudin-4 (25 kDa), forming endogenous PKC-/claudin complexes. In a second series of studies, dominant-negative inhibition of the endogenous PKC- caused similar destabilizing effects on monolayer barrier dynamics, including claudin-1 and -4 hypophosphorylation, disassembly, and architectural instability as well as monolayer disruption. In a third series of studies, sense overexpression of the PKC- caused not only a mostly cytosolic distribution of this isoform (i.e., <12% in the membrane + cytoskeletal fractions, indicating PKC- inactivity) but also led to disruption of claudin assembly and barrier function of the monolayer. The conclusions of this study are that PKC- activity is required for normal claudin assembly and the integrity of the intestinal epithelial barrier. These effects of PKC- are mediated at the molecular level by changes in phosphorylation, membrane assembly, and/or organization of the subunit components of two barrier function proteins: claudin-1 and claudin-4 isotypes. The ability of PKC- to alter the dynamics of permeability protein claudins is a new function not previously ascribed to the novel subfamily of PKC isoforms.

theta Isoform of protein kinase C alters barrier function in intestinal epithelium through modulation of distinct claudin isotypes: a novel mechanism for regulation of permeability

Using monolayers of intestinal Caco-2 cells, we discovered that the isoform of protein kinase C (PKC), a member of the "novel" subfamily of PKC isoforms, is required for monolayer barrier function. However, the mechanisms underlying this novel effect remain largely unknown. Here, we sought to determine whether the mechanism by which PKC- disrupts monolayer permeability and dynamics in intestinal epithelium involves PKC--induced alterations in claudin isotypes. We used cell clones that we recently developed, clones that were transfected with varying levels of plasmid to either stably suppress endogenous PKC- activity (antisense, dominant-negative constructs) or to ectopically express PKC- activity (sense constructs). We then determined barrier function, claudin isotype integrity, PKC- subcellular activity, claudin isotype subcellular pools, and claudin phosphorylation. Antisense transfection to underexpress the PKC- led to monolayer instability as shown by reduced 1) endogenous PKC- activity, 2) claudin isotypes in the membrane and cytoskeletal pools ( downward arrowclaud-1, downward arrowclaud-4 assembly), 3) claudin isotype phosphorylation ( downward arrow phospho-serine, downward arrow phospho-threonine), 4) architectural stability of the claudin-1 and claudin-4 rings, and 5) monolayer barrier function. In these antisense clones, PKC- activity was also substantially reduced in the membrane and cytoskeletal cell fractions. In wild-type (WT) cells, PKC- (82 kDa) was both constitutively active and coassociated with claudin-1 (22 kDa) and claudin-4 (25 kDa), forming endogenous PKC-/claudin complexes. In a second series of studies, dominant-negative inhibition of the endogenous PKC- caused similar destabilizing effects on monolayer barrier dynamics, including claudin-1 and -4 hypophosphorylation, disassembly, and architectural instability as well as monolayer disruption. In a third series of studies, sense overexpression of the PKC- caused not only a mostly cytosolic distribution of this isoform (i.e., <12% in the membrane + cytoskeletal fractions, indicating PKC- inactivity) but also led to disruption of claudin assembly and barrier function of the monolayer. The conclusions of this study are that PKC- activity is required for normal claudin assembly and the integrity of the intestinal epithelial barrier. These effects of PKC- are mediated at the molecular level by changes in phosphorylation, membrane assembly, and/or organization of the subunit components of two barrier function proteins: claudin-1 and claudin-4 isotypes. The ability of PKC- to alter the dynamics of permeability protein claudins is a new function not previously ascribed to the novel subfamily of PKC isoforms.

Critical role of the atypical {lambda} isoform of protein kinase C (PKC-{lambda}) in oxidant-induced disruption of the microtubule cytoskeleton and barrier function of intestinal epithelium

Oxidant injury to epithelial cells and gut barrier disruption are key factors in the pathogenesis of inflammatory bowel disease. Studying monolayers of intestinal (Caco-2) cells, we reported that oxidants disrupt the cytoskeleton and cause barrier dysfunction (hyperpermeability). Because the lambda isoform of protein kinase C (PKC-lambda), an atypical diacylglycerol-independent isozyme, is abundant in parental (wild type) Caco-2 cells and is translocated to the particulate fractions upon oxidant exposure, we hypothesized that PKC-lambda is critical to oxidative injury to the assembly and architecture of cytoskeleton and the intestinal barrier function. To this end, Caco-2 cells were transfected with an inducible plasmid, a tetracycline-responsive system, to create novel clones stably overexpressing native PKC-lambda. Other cells were transfected with a dominant-negative plasmid to stably inhibit the activity of native PKC-lambda. Cells were exposed to oxidant (H(2)O(2)) +/- modulators. Parental Caco-2 cells were treated similarly. We then monitored barrier function (fluorescein sulfonic acid clearance), microtubule cytoskeletal stability (confocal microscopy, immunoblotting), subcellular distribution of PKC-lambda (immunofluorescence, immunoblotting, immunoprecipitation), and PKC-lambda isoform activity (in vitro kinase assay). Monolayers were also processed to assess alterations in tubulin assembly, polymerized tubulin (S2, an index of cytoskeletal integrity), and monomeric tubulin (S1, an index of cytoskeletal disassembly) (polyacrylamide gel electrophoresis fractionation and immunoblotting. In parental cells, oxidant caused: 1) translocation of PKC-lambda from the cytosol to the particulate (membrane + cytoskeletal) fractions, 2) activation of native PKC-lambda, 3) tubulin pool instability (increased monomeric S1 and decreased polymerized S2), 4) disruption of cytoskeletal architecture, and 5) barrier dysfunction (hyperpermeability). In transfected clones, overexpression of the atypical (74 kDa) PKC-lambda isoform by itself ( approximately 3.2-fold increase) led to oxidant-like disruptive effects, including cytoskeletal and barrier hyperpermeability. Overexpressed PKC-lambda was mostly found in particulate cell fractions (with a smaller cytosolic distribution) indicating its activation. Disruption by PKC-lambda overexpression was also potentiated by oxidant challenge. Stable inactivation of endogenous PKC-lambda ( approximately 99.6%) by a dominant-negative protected against all measures of oxidant-induced disruption. We conclude that: 1) oxidant induces disruption of epithelial barrier integrity by disassembling the cytoskeleton, in large part, through the activation of PKC-lambda isoform; and 2) activation of PKC-lambda by itself appears to be sufficient for disruption of cellular cytoskeleton and monolayer barrier permeability. The unique ability to mediate an oxidant-like injury and cytoskeletal depolymerization and instability is a novel mechanism not previously attributed to the atypical subfamily of PKC isoforms.

Fibronectin fragment activation of proline-rich tyrosine kinase PYK2 mediates integrin signals regulating collagenase-3 expression by human chondrocytes through a protein kinase C-dependent pathway

Fibronectin fragments (FN-f), including the 110-kDa fragment that binds the alpha5beta1 integrin, stimulate collagenase-3 (MMP-13) production and cartilage destruction. In the present study, treatment of chondrocytes with the 110-kDa FN-f or an activating antibody to the alpha5beta1 integrin was found to increase tyrosine autophosphorylation (Tyr-402) of the proline-rich tyrosine kinase-2 (PYK2) without significant change in autophosphorylation (Tyr-397) of focal adhesion kinase (FAK). The tyrosine kinase inhibitor tyrphostin A9, shown previously to block a PYK2-dependent pathway, blocked the FN-f-stimulated increase in MMP-13, whereas tyrphostin A25 did not. FN-f-stimulated PYK2 phosphorylation and MMP-13 production was also blocked by reducing intracellular calcium levels. Adenovirally mediated overexpression of wild type but not mutant PYK2 resulted in increased MMP-13 production. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate stimulated PYK2 phosphorylation and MMP-13 production. MMP-13 expression stimulated by either phorbol 12-myristate 13-acetate or FN-f was blocked by PKC inhibitors including the PKCdelta inhibitor rottlerin. Furthermore, PKCdelta translocation from cytosol to membrane was noted within 5 min of stimulation with FN-f. Immortalized human chondrocytes, transiently transfected with MMP-13 promoter-luciferase reporter constructs, showed increased promoter activity after FN-f treatment that was inhibited by co-transfection with either of two dominant negative mutants of PYK2 (Y402F and K457A). No inhibition was seen after cotransfection with wild type PYK2, a dominant negative of FAK (FRNK) or empty vector plasmid. FN-f-stimulated MMP-13 promoter activity was also inhibited by chemical inhibitors of ERK, JNK, and p38 mitogen-activated protein (MAP) kinases or by co-transfection of dominant negative MAP kinase mutant constructs. These studies have identified a novel pathway for the MAP kinase regulation of MMP-13 production which involves FN-f stimulation of the alpha5beta1 integrin and activation of the nonreceptor tyrosine kinase PYK2 by PKC, most likely PKCdelta

Fibronectin fragments and blocking antibodies to alpha2beta1 and alpha5beta1 integrins stimulate mitogen-activated protein kinase signaling and increase collagenase 3 (matrix metalloproteinase 13) production by human articular chondrocytes

OBJECTIVE

To determine if integrin-mediated signaling results in activation of chondrocyte mitogen-activated protein (MAP) kinases that lead to increased expression of matrix metalloproteinase 13 (MMP-13; collagenase 3), a potent mediator of cartilage matrix degradation.

METHODS

Human articular chondrocytes isolated from normal ankle and knee cartilage obtained from tissue donors were cultured in monolayers. The cells were treated with a 120-kd fibronectin fragment (FN-f) that binds the alpha5beta1 integrin or with antibodies to specific integrin receptors. Activation of MAP kinases was determined by immunoblotting with phosphospecific antibodies. MMP production was measured by gelatin zymography, and MMP-13 production and activation were determined by immunoblotting and by a fluorogenic peptide assay.

RESULTS

Human articular chondrocytes were found to respond to the 120-kd FN-f and to adhesion-blocking antibodies to the alpha2beta1 and alpha5beta1 integrins with increased phosphorylation of the extracellular signal-regulated kinase 1 (ERK1)/ERK2, c-Jun N-terminal kinase (JNK), and p38 MAP kinases. Intact FN and integrin-blocking antibodies to alpha1, alpha3, and alphaVbeta3 and a nonblocking alpha5 antibody had no effect. After MAP kinase activation, increased phosphorylation of c-Jun and the nuclear factor kappaB inhibitor was noted, followed by increased pro- and activated MMP-13 in the conditioned media. Inhibitors of mitogen-activated protein kinase kinase, p38, and JNK were each able to inhibit increased MMP-13 production, while the interleukin-1 receptor antagonist (IL-1Ra) protein did not. However, the IL-1Ra partially inhibited FN-f-induced activation of MMP-13.

CONCLUSION

Integrin-mediated MAP kinase signaling stimulated by FN-f is associated with increased production and release of pro- and active MMP-13. Autocrine production of IL-1 appears to result in additional MMP-13 activation. These processes may play a key role in feedback loops responsible for progressive cartilage degradation in arthritis.

Lymphocyte adhesion to Candida albicans

Adherence of lymphocytes to the fungus is the first step in the direct lymphocyte-mediated antifungal effect against Candida albicans. In this study we identified macrophage-1 antigen (Mac-1) (CD11b/CD18, alpha(M)/beta(2)) as the lymphocyte surface structure responsible for the adhesion of activated lymphocytes to the hyphal form of the fungus. Antibodies specific for epitopes of the alpha-subunit (CD11b) and the beta(2)-subunit (CD18) of Mac-1 were shown to completely eliminate lymphocyte adhesion to C. albicans hyphae. Lymphocyte adhesion to C. albicans was also inhibited significantly by known ligands of Mac-1, including the extracellular matrix proteins laminin and fibrinogen, as well as engineered peptides containing arginine-glycine-aspartic acid sequences and the disintegrin echistatin. N-Acetyl-D-glucosamine and beta-glucan, which inhibit Mac-1-mediated adhesion to the yeast, blocked lymphocyte adhesion to hyphae. NIH 3T3 fibroblast transfectants expressing human CD11b/CD18 bound to C. albicans, and their binding was inhibited by antibodies specific for CD11b/CD18. Finally, antibodies specific for CD11b/CD18 effectively inhibited the capacity of activated lymphocytes to have an antifungal effect against hyphae. Our results clearly identify Mac-1 (CD11b/CD18) as the lymphocyte surface structure that mediates activated lymphocyte adhesion to C. albicans and the resultant antifungal effect of the lymphocytes.

Integrin alpha(M)beta(2)-mediated cell migration to fibrinogen and its recognition peptides

Leukocyte migration is the hallmark of inflammation, and integrin α_Mβ₂ and its ligand fibrinogen (Fg) are key participants in this cellular response. Cells expressing wild-type or mutant α_Mβ₂ and Fg or its derivatives have been used to dissect the molecular requirements for this receptor–ligand pair to mediate cell migration. The major conclusions are that (a) Fg, its D fragment, and its P1 and P2 α_Mβ₂ recognition peptides support a chemotactic response; (b) when the I domain of α_L was replaced with the I domain of α_M, the chimeric receptor supported cell migration to Fg; however, the α_M subunit, containing the I domain but lacking the β₂ subunit, supported migration poorly, thus, the α_MI domain is necessary but not sufficient to support chemotaxis, and efficient migration requires the β₂ subunit and α_MI domain; and (c) in addition to supporting cell migration, P2 enhanced α_Mβ₂-mediated chemotaxis to Fg and the P1 peptide. This activation was associated with exposure of the activation-dependent epitope recognized by monoclonal antibody 7E3 and was observed also with human neutrophils. Taken together, these data define specific molecular requirements for α_Mβ₂ to mediate cell migration to Fg derivatives and assign a novel proinflammatory activity to the P2 peptide.

Interaction of the Fungal Pathogen Candida albicans with Integrin CD11b/CD18: Recognition by the I Domain Is Modulated by the Lectin-Like Domain and the CD18 Subunit

Interactions of microorganisms with integrins are central to the host defense mechanisms. The leukocyte integrin CD11b/CD18 is the principal adhesion receptor on leukocytes for Candida albicans, a major opportunistic pathogen. In this study we have investigated the roles of three regions within the receptor, the inserted (I) and lectin-like domains within the CD11b subunit, and the CD18 subunit, in CD11b/CD18-C. albicans interactions. We report four major findings. 1) A mutation in CD18 exerts a dominant negative effect on the function of the CD11b/CD18 complex. This interpretation is based on the observation that in the absence of CD18, the CD11b subunit alone binds C. albicans well, but a single point mutation at Ser138 of CD18 abolishes CD11b/CD18 binding of the fungus. 2) The lectin-like domain is not sufficient for CD11b/CD18-C. albicans interactions. Rather, the lectin-like domain appears to influence CD11b/CD18 binding activity by modulating the function of the I domain. 3) The I domain is the primary binding site for C. albicans in the receptor and is sufficient to support an efficient interaction. 4) We have identified specific amino acid sequences within the I domain that engage the microorganism. Compared with other ligands of CD11b/CD18, C. albicans has some unique as well as common contact sites within the I domain of the receptor. Such unique contact sites may underlie the ability of C. albicans to modulate CD11b/CD18 function and raise the possibility for selective interference of the microorganism-host leukocyte interactions.

Interaction of the fungal pathogen Candida albicans with integrin CD11b/CD18: recognition by the I domain is modulated by the lectin-like domain and the CD18 subunit

Interactions of microorganisms with integrins are central to the host defense mechanisms. The leukocyte integrin CD11b/CD18 is the principal adhesion receptor on leukocytes for Candida albicans, a major opportunistic pathogen. In this study we have investigated the roles of three regions within the receptor, the inserted (I) and lectin-like domains within the CD11b subunit, and the CD18 subunit, in CD11b/CD18-C. albicans interactions. We report four major findings. 1) A mutation in CD18 exerts a dominant negative effect on the function of the CD11b/CD18 complex. This interpretation is based on the observation that in the absence of CD18, the CD11b subunit alone binds C. albicans well, but a single point mutation at Ser138 of CD18 abolishes CD11b/CD18 binding of the fungus. 2) The lectin-like domain is not sufficient for CD11b/CD18-C. albicans interactions. Rather, the lectin-like domain appears to influence CD11b/CD18 binding activity by modulating the function of the I domain. 3) The I domain is the primary binding site for C. albicans in the receptor and is sufficient to support an efficient interaction. 4) We have identified specific amino acid sequences within the I domain that engage the microorganism. Compared with other ligands of CD11b/CD18, C. albicans has some unique as well as common contact sites within the I domain of the receptor. Such unique contact sites may underlie the ability of C. albicans to modulate CD11b/CD18 function and raise the possibility for selective interference of the microorganism-host leukocyte interactions.

Lymphocytes utilize CD11b/CD18 for adhesion to Candida albicans

Large granular lymphocytes require adherence to hyphae of Candida albicans to inhibit growth of this fungus. This study was undertaken to identify the lymphocyte surface structures that mediate this adhesion. Monoclonal antibodies specific for epitopes of the alpha subunit (CD11b) and the beta 2 subunit (CD18) of Mac-1 eliminated lymphocyte adhesion to C. albicans hyphae. Significant inhibition of lymphocyte adhesion to C. albicans was also achieved with known protein ligands of Mac-1. These proteins included the extracellular matrix proteins vitronectin, laminin, and fibrinogen as well as two engineered peptides containing RGD (arginine-glycine-aspartic acid) sequences. Carbohydrates including N-acetyl-D-glucosamine which have been demonstrated to inhibit Mac-l-mediated adhesion to whole yeast and yeast zymosan also blocked lymphocyte adhesion to hyphae. These results identify Mac-1 (CD11b/CD18) as the surface structure that mediates lymphocyte adhesion to C. albicans. A model is proposed for lymphocyte Mac-1 activation by microbial ligands.

A quantitative radiometric assay to measure mammalian cell binding to hyphae of Candida albicans

A rapid and reproducible assay has been developed to measure the capacity of lymphocytes to bind to Candida albicans. Lymphocytes that bound to C. albicans were either the large granular lymphocyte cell line, YT, or interleukin-2 activated lymphocytes. Lymphocyte binding was assessed as the associated radioactivity of 51Cr-labeled lymphocytes with preformed hyphae. The assay was sensitive to detection of 0.6 lymphocytes/one hyphal form at one half maximal lymphocyte binding capacity. The assay correlated well with direct microscopic assessment of lymphocyte binding to C. albicans and provided quantitative radiometric data. Although the assay was developed for the assessment of lymphocyte adhesion to C. albicans, it can be used to measure binding of other mammalian cells (e.g., polymorphonuclear leukocytes) to this fungus. In addition, the assay may be used to identify molecules involved in the adhesion of lymphocytes and other mammalian cells to C. albicans.