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Victor J. Torres - One of the best experts on this subject based on the ideXlab platform.
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Counter inhibition between Leukotoxins attenuates Staphylococcus aureus virulence
Nature communications, 2015Co-Authors: Pauline Yoong, Victor J. TorresAbstract:Staphylococcus aureus subverts host defences by producing a collection of virulence factors including bi-component pore-forming Leukotoxins. Despite extensive sequence conservation, each Leukotoxin has unique properties, including disparate cellular receptors and species specificities. How these toxins collectively influence S. aureus pathogenesis is unknown. Here we demonstrate that the Leukotoxins LukSF-PV and LukED antagonize each other's cytolytic activities on leukocytes and erythrocytes by forming inactive hybrid complexes. Remarkably, LukSF-PV inhibition of LukED haemolytic activity on both human and murine erythrocytes prevents the release of nutrients required for in vitro bacterial growth. Using in vivo murine models of infection, we show that LukSF-PV negatively influences S. aureus virulence and colonization by inhibiting LukED. Thus, while S. aureus Leukotoxins can certainly injure immune cells, the discovery of Leukotoxin antagonism suggests that they may also play a role in reducing S. aureus virulence and maintaining infection without killing the host.
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CCR5 is a receptor for Staphylococcus aureus Leukotoxin ED
Nature, 2013Co-Authors: Francis Alonzo Iii, Lina Kozhaya, Stephen A. Rawlings, Tamara Reyes-robles, Ashley L. Dumont, David G. Myszka, Nathaniel R. Landau, Derya Unutmaz, Victor J. TorresAbstract:Pore-forming toxins are critical virulence factors for many bacterial pathogens and are central to Staphylococcus aureus- mediated killing of host cells. S. aureus encodes pore-forming bi-component Leukotoxins that are toxic towards neutrophils, but also specifically target other immune cells. Despite decades since the first description of staphylococcal leukocidal activity, the host factors responsible for the selectivity of Leukotoxins towards different immune cells remain unknown. Here we identify the human immunodeficiency virus (HIV) co-receptor CCR5 as a cellular determinant required for cytotoxic targeting of subsets of myeloid cells and T lymphocytes by the S. aureus Leukotoxin ED (LukED). We further demonstrate that LukED-dependent cell killing is blocked by CCR5 receptor antagonists, including the HIV drug maraviroc. Remarkably, CCR5-deficient mice are largely resistant to lethal S. aureus infection, highlighting the importance of CCR5 targeting in S. aureus pathogenesis. Thus, depletion of CCR5^+ leukocytes by LukED suggests a new immune evasion mechanism of S. aureus that can be therapeutically targeted. A Staphylococcus aureus Leukotoxin targets cells expressing the chemokine receptor CCR5, a mechanism for the specificity of Leukotoxins towards different immune cells. Staphylococcus aureus expresses Leukotoxins that preferentially kill neutrophils and other immune cells. Victor Torres and colleagues now show that Leukotoxin targets cells that express the chemokine receptor CCR5, providing the mechanistic basis for the specificity of this immune-evasion mechanism and suggesting possible therapeutic targets.
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staphylococcus aureus leucocidin ed contributes to systemic infection by targeting neutrophils and promoting bacterial growth in vivo
Molecular Microbiology, 2012Co-Authors: Francis Alonzo, Meredith A Benson, John W Chen, Richard P Novick, Bo Shopsin, Victor J. TorresAbstract:Bloodstream infection with Staphylococcus aureus is common and can be fatal. However, virulence factors that contribute to lethality in S. aureus bloodstream infection are poorly defined. We discovered that LukED, a commonly overlooked Leukotoxin, is critical for S. aureus bloodstream infection in mice. We also determined that LukED promotes S. aureus replication in vivo by directly killing phagocytes recruited to sites of hematogenously-seeded tissue. Furthermore, we established that murine neutrophils are the primary target of LukED, as the greater virulence of wild type S. aureus compared to a lukED mutant was abrogated by depleting neutrophils. The in vivo toxicity of LukED toward murine phagocytes is unique among S. aureus Leukotoxins, implying its crucial role in pathogenesis. Moreover, the tropism of LukED for murine phagocytes highlights the utility of murine models to study LukED pathobiology, including development and testing of strategies to inhibit toxin activity and control bacterial infection.
David J Kolodrubetz - One of the best experts on this subject based on the ideXlab platform.
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mlc is a transcriptional activator with a key role in integrating cyclic amp receptor protein and integration host factor regulation of Leukotoxin rna synthesis in aggregatibacter actinomycetemcomitans
Journal of Bacteriology, 2013Co-Authors: Catherine Childress, Alex Burgum, Linda Phillips, Leigh A Feuerbacher, David J KolodrubetzAbstract:ABSTRACT Aggregatibacter actinomycetemcomitans, a periodontal pathogen, synthesizes Leukotoxin (LtxA), a protein that helps the bacterium evade the host immune response. Transcription of the ltxA operon is induced during anaerobic growth. The cyclic AMP (cAMP) receptor protein (CRP) indirectly increases ltxA expression, but the intermediary regulator is unknown. Integration host factor (IHF) binds to and represses the Leukotoxin promoter, but neither CRP nor IHF is responsible for the anaerobic induction of ltxA RNA synthesis. Thus, we have undertaken studies to identify other regulators of Leukotoxin transcription and to demonstrate how these proteins work together to modulate Leukotoxin synthesis. First, analyses of ltxA RNA expression from defined Leukotoxin promoter mutations in the chromosome identify positions −69 to −35 as the key control region and indicate that an activator protein modulates Leukotoxin transcription. We show that Mlc, which is a repressor in Escherichia coli, functions as a direct transcriptional activator in A. actinomycetemcomitans; an mlc deletion mutant reduces Leukotoxin RNA synthesis, and recombinant Mlc protein binds specifically at the −68 to −40 region of the Leukotoxin promoter. Furthermore, we show that CRP activates ltxA expression indirectly by increasing the levels of Mlc. Analyses of Δ mlc , Δ ihf , and Δ ihf Δ mlc strains demonstrate that Mlc can increase RNA polymerase (RNAP) activity directly and that IHF represses ltxA RNA synthesis mainly by blocking Mlc binding. Finally, a Δ ihf Δ mlc mutant still induces ltxA during anaerobic growth, indicating that there are additional factors involved in Leukotoxin transcriptional regulation. A model for the coordinated regulation of Leukotoxin transcription is presented.
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Repression of aerobic Leukotoxin transcription by integration host factor in Aggregatibacter actinomycetemcomitans.
Research in microbiology, 2010Co-Authors: David J Kolodrubetz, Linda Phillips, Alex BurgumAbstract:Aggregatibacter actinomycetemcomitans has been implicated as the primary etiologic agent in localized aggressive periodontitis. This bacterium produces a Leukotoxin which may help the bacterium evade the host immune response. Leukotoxin transcription is induced when A. actinomycetemcomitans is grown anaerobically, as in the periodontal pocket. Previously, a 35 bp oxygen-response-element (ORE) was shown to be responsible for oxygen regulation at the Leukotoxin promoter. However, the gene’s transcription is not controlled by Fnr or ArcA, the major oxygen regulators in other bacteria. To identify the potentially novel protein(s) that regulate Leukotoxin transcription, protein extracts of A. actinomycetemcomitans were tested for ORE binding by mobility shift assays; one ORE-specific binding complex was found. Standard fractionation protocols and protein sequencing identified the ORE binding protein as integration host factor (IHF). DNaseI protection assays showed that the IHF binding site overlaps the first half of the ORE. To assess the effect of IHF on Leukotoxin synthesis, an A. actinomycetemcomitans deletion mutant in ihfB was constructed and characterized. Interestingly, Leukotoxin RNA and protein synthesis was de-repressed in the ihf mutant, although Leukotoxin synthesis in still oxygen-regulated in the mutant cells. Thus, IHF plays a direct role in repressing Leukotoxin transcription, but another protein is also involved in regulating Leukotoxin expression in response to oxygen.
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Molecular genetics and the analysis of Leukotoxin in A. actinomycetemcomitans
Journal of Periodontology, 1996Co-Authors: David J KolodrubetzAbstract:The primary pathogen involved in certain forms of early-onset periodontitis is A. actinomycetemcomitans. Among its numerous potential virulence factors is a Leukotoxin that kills certain host defense cells. In order to analyze the regulation and in vivo function of Leukotoxin and other virulence factors in A. actinomycetemcomitans, molecular genetic approaches are being established. Although there has been significant progress in developing plasmids and bacteriophage as E. colilA. actinomycetemcomitans shuttle vectors, more work needs to be done. Tn5-based transposon mutagenesis has been shown to work in this organism. Targeted mutagenesis is now possible in A. actinomycetemcomitans; exogenously introduced DNA recombines efficiently with the homologous chromosomal locus. These techniques have been applied to studies of Leukotoxin. Targeted mutagenesis has been used to construct Leukotoxin negative mutants that are otherwise isogenic with their Leukotoxin-producing parent strain. These mutants can be teste...
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The regulation of Leukotoxin production in Actinobacillus actinomycetemcomitans strain JP2.
Advances in dental research, 1995Co-Authors: J. Spitznagel, Ellen Kraig, David J KolodrubetzAbstract:Actinobacillus actinomycetemcomitans (A.a.) can produce a potent Leukotoxin that is thought to be involved in evasion of the host immune response. In order to understand the role of A.a. and its Leukotoxin in the initiation and progression of periodontal disease, it is important determine how the expression of A.a. virulence factors might be regulated by the local periodontal micro-environment. To facilitate the measurement of Leukotoxin levels, a Leukotoxin-β-galactosidase gene fusion was constructed and recombined into the chromosome of A.a. strain JP2 at the Leukotoxin locus. The resulting strain, AAM17, produces β-galactosidase under control of the Leukotoxin promoter. It also produces Leukotoxin, since integration of the gene fusion into the chromosome was designed to produce a duplication of the Leukotoxin gene. This strain was used to measure the change in Leukotoxin level in response to alterations in two environmental signals: iron concentration and oxygen tension. When AAM17 was grown in iron-li...
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Directed genomic integration in Actinobacillus actinomycetemcomitans: generation of defined Leukotoxin-negative mutants.
Infection and immunity, 1995Co-Authors: David J Kolodrubetz, Linda Phillips, P. J. Ezzo, Ellen KraigAbstract:To develop targeted gene integration in the periodontal pathogen Actinobacillus actinomycetemcomitans, a ColE1-based, spectinomycin-resistant plasmid containing a segment of the Leukotoxin gene was electroporated into strain JP2. In all of the stable spectinomycin-resistant transformants that arose, the plasmid had recombined into the genomic Leukotoxin locus since ColE1-based vectors cannot replicate extrachromosomally in A. actinomycetemcomitans. Directed genomic integration was then used to construct a Leukotoxin-negative strain by transforming the Leukotoxin-producing strain JP2 with a ColE1-based plasmid containing an internal fragment of the Leukotoxin gene. Cytotoxicity assays proved that these transformants had < 0.1% of the Leukotoxin activity of the parental strain. These results demonstrate that integration-based approaches can be used for generating isogenic mutants in specific virulence genes in A. actinomycetemcomitans.
Gilles Prévost - One of the best experts on this subject based on the ideXlab platform.
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internalization of staphylococcal Leukotoxins that bind and divert the c5a receptor is required for intracellular ca2 mobilization by human neutrophils
Cellular Microbiology, 2015Co-Authors: Mira Y Tawk, Gilles Prévost, Bernard Poulain, Jean-louis Bossu, Cristina Potrich, Gaelle Zimmermannmeisse, T Bourcier, Mauro Dalla Serra, Emmanuel JoverAbstract:A growing number of receptors, often associated with the innate immune response, are being identified as targets for bacterial toxins of the beta-stranded pore-forming family. These findings raise the new question of whether the receptors are activated or merely used as docking points facilitating the formation of a pore. To elucidate whether the Staphylococcus aureus Panton-Valentine leukocidin and the Leukotoxin HlgC/HlgB act through the C5a receptor (C5aR) as agonists, antagonists or differ from the C5a complement-derived peptide, their activity is explored on C5aR-expressing cells. Both Leukotoxins equally bound C5aR in neutrophils and in stable transfected U937 cells and initiated mobilization of intracellular Ca(2+) . HlgC/HlgB requires the presence of robust intracellular acidic Ca(2+) stores in order to evoke a rise in free [Ca(2+) ]i , while the LukS-PV/LukF-PV directly altered reticular Ca(2+) stores. Intracellular target specificity is conferred by the F-subunit associated to the S-subunit binding the receptor. Furthermore, internalization of the two Leukotoxin components (S- and F-subunits) associated to C5aR is required for the initiation of [Ca(2+) ]i mobilization. Electrophysiological recordings on living cells demonstrated that LukS-PV/LukF-PV does not alter the membrane resistance of C5aR-expressing cells. The present observations suggest that part of the pore-forming process occurs in distinct intracellular compartments rather than at the plasma membrane.
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Internalization of staphylococcal Leukotoxins that bind and divert the C5a receptor is required for intracellular Ca(2+) mobilization by human neutrophils
Cellular Microbiology, 2015Co-Authors: Mira Tawk, Gilles Prévost, Bernard Poulain, Tristan Bourcier, Gaëlle Zimmermann - Meisse, Jean-louis Bossu, Cristina Potrich, Mauro Dalla Serra, Emmanuel JoverAbstract:A growing number of receptors, often associated with the innate immune response, are being identified as targets for bacterial toxins of the beta-stranded pore-forming family. These findings raise the new question of whether the receptors are activated or merely used as docking points facilitating the formation of a pore. To elucidate whether the Staphylococcus aureus Panton-Valentine leukocidin and the Leukotoxin HlgC/HlgB act through the C5a receptor (C5aR) as agonists, antagonists or differ from the C5a complement-derived peptide, their activity is explored on C5aR-expressing cells. Both Leukotoxins equally bound C5aR in neutrophils and in stable transfected U937 cells and initiated mobilization of intracellular Ca(2+) . HlgC/HlgB requires the presence of robust intracellular acidic Ca(2+) stores in order to evoke a rise in free [Ca(2+) ]i , while the LukS-PV/LukF-PV directly altered reticular Ca(2+) stores. Intracellular target specificity is conferred by the F-subunit associated to the S-subunit binding the receptor. Furthermore, internalization of the two Leukotoxin components (S- and F-subunits) associated to C5aR is required for the initiation of [Ca(2+) ]i mobilization. Electrophysiological recordings on living cells demonstrated that LukS-PV/LukF-PV does not alter the membrane resistance of C5aR-expressing cells. The present observations suggest that part of the pore-forming process occurs in distinct intracellular compartments rather than at the plasma membrane.
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staphylococcal Leukotoxins trigger free intracellular ca2 rise in neurones signalling through acidic stores and activation of store operated channels
Cellular Microbiology, 2013Co-Authors: Emmanuel Jover, Mira Y Tawk, Benoitjoseph Laventie, Bernard Poulain, Gilles PrévostAbstract:Headache, muscle aches and chest pain of mild to medium intensity are among the most common clinical symptoms in moderate Staphylococcus aureus infections, with severe infections usually associated with worsening pain symptoms. These nociceptive responses of the body raise the question of how bacterial infection impinges on the nervous system. Does S. aureus, or its released virulence factors, act directly on neurones? To address this issue, we evaluated the potential effects on neurones of certain bi-component Leukotoxins, which are virulent factors released by the bacterium. The activity of four different Leukotoxins was verified by measuring the release of glutamate from rat cerebellar granular neurones. The bi-component γ-haemolysin HlgC/HlgB was the most potent Leukotoxin, initiating transient rises in intracellular Ca2+ concentration in cerebellar neurones and in primary sensory neurones from dorsal root ganglia, as probed with the Fura-2 Ca2+ indicator dye. Using pharmacological antagonists of receptors and Ca2+ channels, the variations in intracellular Ca2+ concentration were found independent of the activation of voltage-operatedCa2+ channels or glutamate receptors. Drugs targeting Sarco-Endoplasmic Reticulum Ca2+-ATPase (SERCA) or H+-ATPase and antagonists of the store-operated Ca2+ entry complex blunted, or significantly reduced, the Leukotoxin-induced elevation in intracellular Ca2+. Moreover, activation of the ADP-ribosyl cyclase CD38 was also required to initiate the release of Ca2+ from acidic stores. These findings suggest that, prior to forming a pore at the plasma membrane, Leukotoxin HlgC/HlgB triggers a multistep process which initiates the release of Ca2+ from lysosomes, modifies the steady-state level of reticular Ca2+ stores and finally activates the Store-Operated Calcium Entry complex.
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lukm lukf pv is the most active staphylococcus aureus Leukotoxin on bovine neutrophils
Microbes and Infection, 2006Co-Authors: Maria.b Barrio, Pascal Rainard, Gilles PrévostAbstract:Staphylococcus aureus is a ubiquitous pathogen causing infections in humans and domestic animals. It is often associated with bovine mastitis. Among secreted virulence factors, the Leukotoxins constitute a family of toxins composed of two distinct subunits (class S and F proteins) which induce first Ca2+ influx and subsequent pore formation that allows ethidium entry. As mastitis-causing isolates harbor the genes of at least two, and often three Leukotoxins, we compared the biological activities of the purified Leukotoxins whose genes are found in mastitis-causing isolates on bovine polymorphonuclear neutrophils (PMN): spreading on a solid support, calcium influx and ethidium entry. In the spreading assay, the homologous pair LukM/LukF'-PV was the most active Leukotoxin. Within each class, either S or F, subunits were interchangeable and generated Leukotoxins with different specific activity. LukM was also very active when associated with heterologous F subunits. A similar ranking of homologous pairs was also found in the ethidium entry assay: LukM/LukF'-PV > HlgA/HlgB > HlgC/HlgB > LukE/LukD = LukEv/LukDv. In the Ca2+ flux assay, LukM/F'-PV was the most active pair, but gamma-hemolysin (Hlg) was also very efficient. LukEv/Dv was more active (twofold) than LukE/D in the spreading assay, but the two variants showed similar activities in the other two assays. Supposing that spreading and ethidium entry (pore formation) reflect toxic activities on bovine PMN, and Ca2+ influx cell activation, LukM/F'-PV was by far the most cytotoxic Leukotoxin, but it was closely followed by gamma-hemolysin for PMN activation. These results suggest that LukM/F'-PV may constitute a particular virulence attribute of mastitis-causing S. aureus strains.
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LukM/LukF '-PV is the most active Staphylococcus aureus Leukotoxin on bovine neutrophils
Microbes and Infection, 2006Co-Authors: Maria.b Barrio, Pascal Rainard, Gilles PrévostAbstract:Staphylococcus aureus is a ubiquitous pathogen causing infections in humans and domestic animals. It is often associated with bovine mastitis. Among secreted virulence factors, the Leukotoxins constitute a family of toxins composed of two distinct subunits (class S and F proteins) which induce first Ca2+ influx and subsequent pore formation that allows ethidium entry. As mastitis-causing isolates harbor the genes of at least two, and often three Leukotoxins, we compared the biological activities of the purified Leukotoxins whose genes are found in mastitis-causing isolates on bovine polymorphonuclear neutrophils (PMN): spreading on a solid support, calcium influx and ethidium entry. In the spreading assay, the homologous pair LukM/LukF′-PV was the most active Leukotoxin. Within each class, either S or F, subunits were interchangeable and generated Leukotoxins with different specific activity. LukM was also very active when associated with heterologous F subunits. A similar ranking of homologous pairs was also found in the ethidium entry assay: LukM/LukF′-PV > HlgA/HlgB > HlgC/HlgB > LukE/LukD = LukEv/LukDv. In the Ca2+ flux assay, LukM/F′-PV was the most active pair, but γ-hemolysin (Hlg) was also very efficient. LukEv/Dv was more active (twofold) than LukE/D in the spreading assay, but the two variants showed similar activities in the other two assays. Supposing that spreading and ethidium entry (pore formation) reflect toxic activities on bovine PMN, and Ca2+ influx cell activation, LukM/F′-PV was by far the most cytotoxic Leukotoxin, but it was closely followed by γ-hemolysin for PMN activation. These results suggest that LukM/F′-PV may constitute a particular virulence attribute of mastitis-causing S. aureus strains.
Anders Johansson - One of the best experts on this subject based on the ideXlab platform.
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The role of Aggregatibacter actinomycetemcomitans and its Leukotoxin in periodontitis
Journal of Oral Microbiology, 2017Co-Authors: Anders Johansson, Rolf Claesson, Carola Hoglund Aberg, Mark Lindholm, Jan OscarssonAbstract:ABSTRACTAggregatibacter actinomycetemcomitans is a Gram-negative periodontitis-associated bacterium that expresses a toxin that selectively affects leukocytes. Leukotoxin is encoded by an operon belonging to the core genome of this bacterial species. Variations in the expression of the Leukotoxin have been reported, and a specific clonal type (JP2) of this bacterium with enhanced Leukotoxin expression has been identified. Experimental studies have shown that Leukotoxin, besides to kill leukocytes, also activates a substantial pro-inflammatory response in these cells. Characterization of clinical isolates from individuals with different geographic origin, age and periodontal status linked carriership of highly leukotoxic A. actinomycetemcomitans to disease. These highly virulent bacteria are of serotype b and have several common phenotypic and genetic features. Based on a great genetic diversity, A. actinomycetemcomitans can be distributed into a high number of different genotypes with various virulence ca...
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The role of Aggregatibacter actinomycetemcomitans and its Leukotoxin in periodontitis
Taylor & Francis Group, 2017Co-Authors: Anders Johansson, Rolf Claesson, Carola Hoglund Aberg, Mark Lindholm, Jan OscarssonAbstract:Aggregatibacter actinomycetemcomitans is a Gram-negative periodontitis-associated bacterium that expresses a toxin that selectively affects leukocytes. Leukotoxin is encoded by an operon belonging to the core genome of this bacterial species. Variations in the expression of the Leukotoxin have been reported, and a specific clonal type (JP2) of this bacterium with enhanced Leukotoxin expression has been identified. Experimental studies have shown that Leukotoxin, besides to kill leukocytes, also activates a substantial pro-inflammatory response in these cells. Characterization of clinical isolates from individuals with different geographic origin, age and periodontal status linked carriership of highly leukotoxic A. actinomycetemcomitans to disease. These highly virulent bacteria are of serotype b and have several common phenotypic and genetic features. Based on a great genetic diversity, A. actinomycetemcomitans can be distributed into a high number of different genotypes with various virulence capacities. It can be concluded that carriership of highly leukotoxic bacteria is associated with a significantly increased risk for initiation of aggressive forms of periodontitis
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effects of aggregatibacter actinomycetemcomitans Leukotoxin on neutrophil migration and extracellular trap formation
Journal of Oral Microbiology, 2016Co-Authors: Josefine Hirschfeld, Anders Johansson, Helen Roberts, Iain L C Chapple, Marijo Parcina, Soren Jepsen, Rolf ClaessonAbstract:Background : Aggressive periodontitis is associated with the presence of Aggregatibacter actinomycetemcomitans , a Leukotoxin (Ltx)-producing periodontal pathogen. Ltx has the ability to lyse white blood cells including neutrophils. Objectives : This study was aimed at investigating the interactions between neutrophils and Ltx with regard to the chemotactic properties of Ltx and the release of neutrophil extracellular traps (NETs). Methods : Neutrophils from healthy blood donors were isolated and incubated for 30 min and 3 h with increasing concentrations of Ltx (1, 10, and 100 ng/mL) as well as with A. actinomycetemcomitans strains (NCTC 9710 and HK 1651) producing different levels of Ltx. Formation of NETs and cell lysis were assessed by microscopy, fluorescence-based assays, and measurement of released lactate dehydrogenase. Neutrophil migration in response to different Ltx gradients was monitored by real-time video microscopy, and image analysis was performed using ImageJ software. Results : Although Ltx (10 and 100 ng/mL) and the leukotoxic A. actinomycetemcomitans strain HK 1651 lysed some neutrophils, other cells were still capable of performing NETosis in a concentration-dependent manner. Low doses of Ltx and the weakly leukotoxic strain NCTC 9710 did not lead to neutrophil lysis, but did induce some NETosis. Furthermore, all three concentrations of Ltx enhanced random neutrophil movement; however, low directional accuracy was observed compared with the positive control (fMLP). Conclusions : The results indicate that Ltx acts both as a neutrophil activator and also causes cell death. In addition, Ltx directly induces NETosis in neutrophils prior to cell lysis. In future studies, the underlying pathways involved in Ltx-meditated neutrophil activation and NETosis need to be investigated further. Keywords: Leukotoxin; Aggregatibacter actinomycetemcomitans; neutrophils; NETs; migration; chemotaxis; aggressive periodontitis (Published: 8 November 2016) Citation: Journal of Oral Microbiology 2016, 8: 33070 - http://dx.doi.org/10.3402/jom.v8.33070
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detection of a 640 bp deletion in the aggregatibacter actinomycetemcomitans Leukotoxin promoter region in isolates from an adolescent of ethiopian origin
Journal of Oral Microbiology, 2015Co-Authors: Rolf Claesson, Jan Gudmundson, Carola Hoglund Aberg, Dorte Haubek, Anders JohanssonAbstract:The expression of the Leukotoxin of Aggregatibacter actinomycetemcomitans is regulated by the Leukotoxin promoter. A 530-bp deletion or an 886-bp insertion sequence (IS) element in this region has earlier been described in highly leukotoxic isolates. Here, we report on highly leukotoxic isolate with a 640-bp deletion, which was detected in an adolescent of Ethiopian origin. Keywords: leukotoxicity; deletion; JP2; aggressive periodontitis; geographic spreading; Africa (Published: 13 April 2015) Citation: Journal of Oral Microbiology 2015, 7 : 26974 - http://dx.doi.org/10.3402/jom.v7.26974
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pathogenicity of the highly leukotoxic jp2 clone of aggregatibacter actinomycetemcomitans and its geographic dissemination and role in aggressive periodontitis
Journal of Oral Microbiology, 2014Co-Authors: Dorte Haubek, Anders JohanssonAbstract:For decades, Aggregatibacter actinomycetemcomitans has been associated with aggressive forms of periodontitis in adolescents. In the middle of the 1990s, a specific JP2 clone of A. actinomycetemcomitans , belonging to the cluster of serotype b strains of A. actinomycetemcomitans and having a number of other characteristics, was found to be strongly associated with aggressive forms of periodontitis, particularly in North Africa. Although several longitudinal studies still point to the bacterial species, A. actinomycetemcomitans as a risk factor of aggressive periodontitis, it is now also widely accepted that the highly leukotoxic JP2 clone of A. actinomycetemcomitans is implicated in rapidly progressing forms of aggressive periodontitis. The JP2 clone strains are highly prevalent in human populations living in Northern and Western parts of Africa. These strains are also prevalent in geographically widespread populations that have originated from the Northwest Africa. Only sporadic signs of a dissemination of the JP2 clone strains to non-African populations have been found despite Africans living geographically widespread for hundreds of years. It remains an unanswered question if a particular host tropism exists as a possible explanation for the frequent colonization of the Northwest African population with the JP2 clone. Two exotoxins of A. actinomycetemcomitans are known, Leukotoxin (LtxA) and cytolethal distending toxin (Cdt). LtxA is able to kill human immune cells, and Cdt can block cell cycle progression in eukaryotic cells and thus induce cell cycle arrest. Whereas the Leukotoxin production is enhanced in JP2 clone strains thus increasing the virulence potential of A. actinomycetemcomitans , it has not been possible so far to demonstrate such a role for Cdt. Lines of evidence have led to the understanding of the highly leukotoxic JP2 clone of A. actinomycetemcomitans as an aetiological factor of aggressive periodontitis. Patients, who are colonized with the JP2 clone, are likely to share this clone with several family members because the clone is transmitted through close contacts. This is a challenge to the clinicians. The patients need intense monitoring of their periodontal status as the risk for developing severely progressing periodontal lesions are relatively high. Furthermore, timely periodontal treatment, in some cases including periodontal surgery supplemented by the use of antibiotics, is warranted. Preferably, periodontal attachment loss should be prevented by early detection of the JP2 clone of A. actinomycetemcomitans by microbial diagnostic testing and/or by preventive means. Keywords: Virulence factors; spreading; geographical dissemination; Leukotoxin; cytolethal distending toxin; host response (Published: 14 August 2014) Citation: Journal of Oral Microbiology 2014, 6 : 23980 - http://dx.doi.org/10.3402/jom.v6.23980
Emmanuel Jover - One of the best experts on this subject based on the ideXlab platform.
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internalization of staphylococcal Leukotoxins that bind and divert the c5a receptor is required for intracellular ca2 mobilization by human neutrophils
Cellular Microbiology, 2015Co-Authors: Mira Y Tawk, Gilles Prévost, Bernard Poulain, Jean-louis Bossu, Cristina Potrich, Gaelle Zimmermannmeisse, T Bourcier, Mauro Dalla Serra, Emmanuel JoverAbstract:A growing number of receptors, often associated with the innate immune response, are being identified as targets for bacterial toxins of the beta-stranded pore-forming family. These findings raise the new question of whether the receptors are activated or merely used as docking points facilitating the formation of a pore. To elucidate whether the Staphylococcus aureus Panton-Valentine leukocidin and the Leukotoxin HlgC/HlgB act through the C5a receptor (C5aR) as agonists, antagonists or differ from the C5a complement-derived peptide, their activity is explored on C5aR-expressing cells. Both Leukotoxins equally bound C5aR in neutrophils and in stable transfected U937 cells and initiated mobilization of intracellular Ca(2+) . HlgC/HlgB requires the presence of robust intracellular acidic Ca(2+) stores in order to evoke a rise in free [Ca(2+) ]i , while the LukS-PV/LukF-PV directly altered reticular Ca(2+) stores. Intracellular target specificity is conferred by the F-subunit associated to the S-subunit binding the receptor. Furthermore, internalization of the two Leukotoxin components (S- and F-subunits) associated to C5aR is required for the initiation of [Ca(2+) ]i mobilization. Electrophysiological recordings on living cells demonstrated that LukS-PV/LukF-PV does not alter the membrane resistance of C5aR-expressing cells. The present observations suggest that part of the pore-forming process occurs in distinct intracellular compartments rather than at the plasma membrane.
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Internalization of staphylococcal Leukotoxins that bind and divert the C5a receptor is required for intracellular Ca(2+) mobilization by human neutrophils
Cellular Microbiology, 2015Co-Authors: Mira Tawk, Gilles Prévost, Bernard Poulain, Tristan Bourcier, Gaëlle Zimmermann - Meisse, Jean-louis Bossu, Cristina Potrich, Mauro Dalla Serra, Emmanuel JoverAbstract:A growing number of receptors, often associated with the innate immune response, are being identified as targets for bacterial toxins of the beta-stranded pore-forming family. These findings raise the new question of whether the receptors are activated or merely used as docking points facilitating the formation of a pore. To elucidate whether the Staphylococcus aureus Panton-Valentine leukocidin and the Leukotoxin HlgC/HlgB act through the C5a receptor (C5aR) as agonists, antagonists or differ from the C5a complement-derived peptide, their activity is explored on C5aR-expressing cells. Both Leukotoxins equally bound C5aR in neutrophils and in stable transfected U937 cells and initiated mobilization of intracellular Ca(2+) . HlgC/HlgB requires the presence of robust intracellular acidic Ca(2+) stores in order to evoke a rise in free [Ca(2+) ]i , while the LukS-PV/LukF-PV directly altered reticular Ca(2+) stores. Intracellular target specificity is conferred by the F-subunit associated to the S-subunit binding the receptor. Furthermore, internalization of the two Leukotoxin components (S- and F-subunits) associated to C5aR is required for the initiation of [Ca(2+) ]i mobilization. Electrophysiological recordings on living cells demonstrated that LukS-PV/LukF-PV does not alter the membrane resistance of C5aR-expressing cells. The present observations suggest that part of the pore-forming process occurs in distinct intracellular compartments rather than at the plasma membrane.
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staphylococcal Leukotoxins trigger free intracellular ca2 rise in neurones signalling through acidic stores and activation of store operated channels
Cellular Microbiology, 2013Co-Authors: Emmanuel Jover, Mira Y Tawk, Benoitjoseph Laventie, Bernard Poulain, Gilles PrévostAbstract:Headache, muscle aches and chest pain of mild to medium intensity are among the most common clinical symptoms in moderate Staphylococcus aureus infections, with severe infections usually associated with worsening pain symptoms. These nociceptive responses of the body raise the question of how bacterial infection impinges on the nervous system. Does S. aureus, or its released virulence factors, act directly on neurones? To address this issue, we evaluated the potential effects on neurones of certain bi-component Leukotoxins, which are virulent factors released by the bacterium. The activity of four different Leukotoxins was verified by measuring the release of glutamate from rat cerebellar granular neurones. The bi-component γ-haemolysin HlgC/HlgB was the most potent Leukotoxin, initiating transient rises in intracellular Ca2+ concentration in cerebellar neurones and in primary sensory neurones from dorsal root ganglia, as probed with the Fura-2 Ca2+ indicator dye. Using pharmacological antagonists of receptors and Ca2+ channels, the variations in intracellular Ca2+ concentration were found independent of the activation of voltage-operatedCa2+ channels or glutamate receptors. Drugs targeting Sarco-Endoplasmic Reticulum Ca2+-ATPase (SERCA) or H+-ATPase and antagonists of the store-operated Ca2+ entry complex blunted, or significantly reduced, the Leukotoxin-induced elevation in intracellular Ca2+. Moreover, activation of the ADP-ribosyl cyclase CD38 was also required to initiate the release of Ca2+ from acidic stores. These findings suggest that, prior to forming a pore at the plasma membrane, Leukotoxin HlgC/HlgB triggers a multistep process which initiates the release of Ca2+ from lysosomes, modifies the steady-state level of reticular Ca2+ stores and finally activates the Store-Operated Calcium Entry complex.