bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pseudomonas aeruginosa relA
Contributes to Virulence in
Drosophila melanogaster
Authors: Erickson David L. , Lines J. Louise , Pesci Everett C. , Venturi Vittorio , Storey Douglas G. 
Published: September 2004

ABSTRACT

The stringent response is a mechanism by which bacteria adapt to nutritional deficiencies through the production of the guanine nucleotides ppGpp and pppGpp, produced by the RelA enzyme. We investigated the role of the
relA
gene in the ability of an extracellular pathogen,
Pseudomonas aeruginosa
, to cause infection. Strains lacking the
relA
gene were created from the prototypical laboratory strain PAO1 as well as the mucoid cystic fibrosis isolate 6106, which lacks functional quorum-sensing systems. The absence of
relA
abolished the production of ppGpp and pppGpp under conditions of amino acid starvation. We found that strains lacking
relA
exhibited reduced virulence in a
D. melanogaster
feeding assay. In conditions of low magnesium, the
relA
gene enhanced production of the cell-cell signal
N
-[3-oxododecanoyl]-
l
-homoserine lactone, whereas
relA
reduced the production of the 2-heptyl-3-hydroxy-4-quinolone signal during serine hydroxamate induction of the stringent response. In the
relA
mutant, alterations in the
Pseudomonas
quinolone system pathways seemed to increase the production of pyocyanin and decrease the production of elastase. Deletion of
relA
also resulted in reduced levels of the RpoS sigma factor. These results suggest that adjustment of cellular ppGpp and pppGpp levels could be an important regulatory mechanism in
P. aeruginosa
adaptation in pathogenic relationships.
The ClpP Protease of
Streptococcus pneumoniae
Modulates Virulence Gene Expression and Protects against Fatal Pneumococcal Challenge
Authors: Kwon Hyog-Young , Ogunniyi A. David , Choi Moo-Hyun , Pyo Suhk-Neung , Rhee Dong-Kwon , Paton James C. 
Published: September 2004

ABSTRACT

Streptococcus pneumoniae
usually colonizes the nasopharynx of humans asymptomatically but occasionally translocates from this niche to the lungs, the brain, and the blood, causing potentially fatal infections. Spread to other host tissues requires a significant morphological change and the expression of virulence factors, such as capsular polysaccharide, and virulence proteins, such as pneumolysin (Ply), PspA, and CbpA. Modulation of the expression of pneumococcal virulence genes by heat shock and by heat shock proteins ClpL and ClpP, as well as the attenuation of virulence of a
clpP
mutant in a murine intraperitoneal infection model, was demonstrated previously. In this study, we further investigated the underlying mechanism of virulence attenuation by the
clpP
mutation. The half-lives of the mRNAs of
ply
and of the first gene of the serotype 2 capsule synthesis locus [
cps(2)A
] in the
clpP
mutant were more than twofold longer than those of the parent after heat shock, suggesting that the mRNA species were regulated posttranscriptionally by ClpP. In addition, the
clpP
mutant was defective in colonization of the nasopharynx and survival in the lungs of mice after intranasal challenge. The mutant was also killed faster than the parent in the murine macrophage RAW264.7 cell line, indicating that ClpP is required for colonization and intracellular survival in the host. Furthermore, fractionation studies demonstrated that ClpP was translocated into the cell wall after heat shock, and immunization of mice with ClpP elicited a protective immune response against fatal systemic challenge with
S. pneumoniae
D39, making ClpP a potential vaccine candidate for pneumococcal disease.
Internalization of
Staphylococcus aureus
by Human Keratinocytes
Authors: Kintarak Sompid , Whawell Simon A. , Speight Paul M. , Packer Samantha , Nair Sean P. 
Published: September 2004

ABSTRACT

Staphylococcus aureus
is among the most important human pathogens and causes various superficial and systemic infections. The ability of
S. aureus
to be internalized by, and survive within, host cells, such as keratinocytes, may contribute to the development of persistent or chronic infections and may finally lead to deeper tissue infections or dissemination. To examine the mechanisms of internalization of
S. aureus
by keratinocytes, isogenic mutants lacking fibronectin-binding proteins (FnBPs), a recombinant protein consisting of the fibronectin-binding domain of
S. aureus
FnBPs, and an anti-α5β1 antibody were used in cocultures with immortalized keratinocytes and primary keratinocytes. We found that internalization of
S. aureus
by immortalized keratinocytes requires bacterial FnBPs and is mediated by the major fibronectin-binding integrin α5β1. In contrast to internalization by immortalized keratinocytes, internalization of
S. aureus
by primary keratinocytes could occur through FnBP-dependent and -independent pathways.
S. aureus
clumping factor B (ClfB), which was recently determined to bind to epithelial cells, was not involved in the uptake of this bacterium by keratinocytes. The identification of an alternate uptake pathway, which is independent of
S. aureus
FnBPs and host cell α5β1, has important implications for the design of therapies targeted to bacterial uptake by host cells.
The Glycan-Rich Outer Layer of the Cell Wall ofMycobacterium tuberculosisActs as an Antiphagocytic Capsule Limiting the Association of the Bacterium with Macrophages
Authors: Stokes Richard W. , Norris-Jones Raymond , Brooks Donald E. , Beveridge Terry J. , Doxsee Dan , Thorson Lisa M. 
Published: September 2004

ABSTRACTMycobacterium tuberculosis, the causative agent of tuberculosis, is a facultative intracellular pathogen that infects macrophages and other host cells. We show that sonication ofM. tuberculosisresults in the removal of material from the surface capsule-like layer of the bacteria, resulting in an enhanced propensity of the bacteria to bind to macrophages. This effect is observed with disparate murine and human macrophage populations though, interestingly, not with freshly explanted alveolar macrophages. Enhanced binding to macrophages following sonication is significantly greater within members of theM. tuberculosisfamily (pathogens) than within theMycobacterium aviumcomplex (opportunistic pathogens) or forMycobacterium smegmatis(saprophyte). Sonication does not affect the viability or the surface hydrophobicity ofM. tuberculosisbut does result in changes in surface charge and in the binding of mannose-specific lectins to the bacterial surface. The increased binding of sonicatedM. tuberculosiswas not mediated through complement receptor 3. These results provide evidence that the surface capsule on members of theM. tuberculosisfamily may be an important virulence factor involved in the survival ofM. tuberculosisin the mammalian host. They also question the view thatM. tuberculosisis readily ingested by any macrophage it encounters and support the contention thatM. tuberculosis, like many other microbial pathogens, has an antiphagocytic capsule that limits and controls the interaction of the bacterium with macrophages.
The Down-Regulation of Cathepsin G in THP-1 Monocytes after Infection withMycobacterium tuberculosisIs Associated with Increased Intracellular Survival of Bacilli
Authors: Rivera-Marrero Carlos A. , Stewart Julie , Shafer William M. , Roman Jesse 
Published: September 2004

ABSTRACTCathepsin G (CatG) is a serine protease found in the azurophilic granules of monocytes that is known to have antimicrobial properties, but its role inMycobacterium tuberculosisinfection is unknown. We found thatM. tuberculosisinfection of human THP-1 monocytic cells induced the down-regulation of CatG mRNA expression, as demonstrated by gene array analysis and reverse transcription-PCR. This was associated with a concomitant decrease in CatG protein and enzymatic activity. In contrast, the expression of lysosomal cathepsins B and D was up-regulated in infected cells. This effect was also observed when THP-1 cells were induced to differentiate into adherent macrophages by exposure to bacterial lipopolysaccharide (LPS). In agreement with this, CatG expression was null in adherent macrophages isolated from bronchoalveolar lavages and normal blood. We wanted to determine if the down-regulation of CatG would be relevant toM. tuberculosisinfection. First, we found that addition of CatG to THP-1 cells prior to infection resulted in decreased bacillary viability, presumably due to extracellular killing of bacilli. However, pretreatment of cells with LPS, which decreases intracellular CatG expression, resulted in increased bacillary viability. Second, we found that CatG cationic peptides killedM. tuberculosisbacilli and were five- to sevenfold more bactericidal than full-length CatG. These observations suggest thatM. tuberculosisinfection of human monocytic cells results in a “cathepsin switch” with down-regulation of CatG renderingM. tuberculosisbacilli more viable. Therefore, the down-regulation of CatG in macrophages is advantageous toM. tuberculosisbacilli and possibly is an important mechanism by whichM. tuberculosisis able to evade the host immune defenses.
Neither Neutrophils nor Reactive Oxygen Species Contribute to Tissue Damage duringPneumocystisPneumonia in Mice
Authors: Swain Steve D. , Wright Terry W. , Degel Peter M. , Gigliotti Francis , Harmsen Allen G. 
Published: September 2004

ABSTRACTNeutrophils are implicated in the damage of lung tissue in many disease states, including infectious diseases and environmental insults. These effects may be due to oxidative or nonoxidative functions of the neutrophil or both. We examined the role of neutrophils in pulmonary damage during infection with the opportunistic fungal pathogenPneumocystissp. in four mouse models of neutrophil dysfunction. These were (i) a knockout of the gp91phoxcomponent of NADPH oxidase, in which reactive oxygen species (ROS) production is greatly reduced; (ii) a double knockout of gp91phoxand inducible nitric oxide synthase, in which ROS and nitric oxide production is greatly decreased; (iii) a knockout of the chemokine receptor CXCR2, in which accumulation of intra-alveolar neutrophils is severely diminished; and (iv) antibody depletion of circulating neutrophils in wild-type mice with the monoclonal antibody RB6. Surprisingly, in each case, indicators of pulmonary damage (respiratory rates, arterial oxygen partial pressures, and intra-alveolar albumin concentrations) were the same in knockout mice and comparable wild-type mice. Therefore, whereas neutrophils are a valid correlative marker of lung damage duringPneumocystisinfection, neither neutrophils nor ROS appear to be the causative agent of tissue damage. We also show that there is no difference inPneumocystisburdens between wild-type and knockout mice, which supports the idea that neutrophils do not have a major role in the clearance of this organism.
NF-κB- and AP-1-Mediated Induction of Human Beta Defensin-2 in Intestinal Epithelial Cells byEscherichia coliNissle 1917: a Novel Effect of a Probiotic Bacterium
Authors: Wehkamp Jan , Harder Jürgen , Wehkamp Kai , Meissner Birte Wehkamp-von , Schlee Miriam , Enders Corinne , Sonnenborn Ulrich , Nuding Sabine , Bengmark Stig , Fellermann Klaus , Schröder Jens Michael , Stange Eduard F. 
Published: September 2004

ABSTRACTLittle is known about the defensive mechanisms induced in epithelial cells by pathogenic versus probiotic bacteria. The aim of our study was to compare probiotic bacterial strains such asEscherichia coliNissle 1917 with nonprobiotic, pathogenic and nonpathogenic bacteria with respect to innate defense mechanisms in the intestinal mucosal cell. Here we report thatE. colistrain Nissle 1917 and a variety of other probiotic bacteria, including lactobacilli—in contrast to more than 40 differentE. colistrains tested—strongly induce the expression of the antimicrobial peptide human beta-defensin-2 (hBD-2) in Caco-2 intestinal epithelial cells in a time- and dose-dependent manner. Induction of hBD-2 throughE. coliNissle 1917 was further confirmed by activation of the hBD-2 promoter and detection of the hBD-2 peptide in the culture supernatants ofE. coliNissle 1917-treated Caco-2 cells. Luciferase gene reporter analyses and site-directed mutagenesis experiments demonstrated that functional binding sites for NF-κB and AP-1 in the hBD-2 promoter are required for induction of hBD-2 throughE. coliNissle 1917. Treatment with the NF-κB inhibitor Helenalin, as well as with SP600125, a selective inhibitor of c-Jun N-terminal kinase, blocked hBD-2 induction byE. coliNissle 1917 in Caco-2 cells. SB 202190, a specific p38 mitogen-activated protein kinase inhibitor, and PD 98059, a selective inhibitor of extracellular signal-regulated kinase 1/2, were ineffective. This report demonstrates that probiotic bacteria may stimulate the intestinal innate defense through the upregulation of inducible antimicrobial peptides such as hBD-2. The induction of hBD-2 may contribute to an enhanced mucosal barrier to the luminal bacteria.
CD28 Costimulation Is Required for the Expression of T-Cell-Dependent Cell-Mediated Immunity against Blood-StagePlasmodium chabaudiMalaria Parasites
Authors: Rummel Thomas , Batchelder Joan , Flaherty Patrick , LaFleur GayeLyn , Nanavati Payal , Burns James M. , Weidanz William P. 
Published: September 2004

ABSTRACTMice suppress the parasitemia of acute blood-stagePlasmodium chabaudimalaria by an antibody- or T-cell-dependent cell-mediated mechanism of immunity (AMI and CMI, respectively) or by both mechanisms. To determine whether CD28 costimulation is required for expression of these polar immune responses, we first compared the time courses ofP. chabaudimalaria in CD28-deficient (CD28−/−) and CD28-intact (CD28+/+) mice. Acute infections in both knockout (KO) and control mice followed similar time courses, with the period of descending parasitemia being prolonged ∼2 weeks in KO mice followed by intermittent low-grade chronic parasitemia. Infected CD28−/−mice produced primarily the immunoglobulin M antibody, which upon passive transfer provided partial protection againstP. chabaudichallenge, suggesting that the elimination of blood-stage parasites by CD28−/−mice was achieved by AMI. To determine whether CD28−/−costimulation is required for the expression of CMI against the parasite, we compared the time courses of parasitemia in B-cell-deficient double-KO (JH−/−× CD28−/−) mice and control (JH−/−× CD28+/+) mice. Whereas control mice suppressed parasitemia to subpatent levels within ∼2 weeks postinoculation, double-KO mice developed high levels of parasitemia of long-lasting duration. Although not required for the suppression of acuteP. chabaudiparasitemia by AMI, CD28 costimulation is essential for the elimination of blood-stage parasites by CMI.
Reduced Expression of Gamma Interferon in Serum and Marked Lymphoid Depletion Induced by
Porphyromonas gingivalis
Increase Murine Morbidity and Mortality due to Cytomegalovirus Infection
Authors: Stern Jacob , Shai Ela , Zaks Batia , Halabi Amal , Houri-Haddad Yael , Shapira Lior , Palmon Aaron 
Published: September 2004

ABSTRACT

Porphyromonas gingivalis
, a gram-negative anaerobe, is a major etiological agent of severe forms of periodontal disease. Although periodontal disease is considered a localized disease, accumulating evidence indicates that it may lead to a predisposition to a decline in immunocompetence. Human cytomegalovirus (CMV) commonly infects all human populations without producing significant clinical symptoms. Immunocompromised patients usually develop a primary or reactivated CMV infection, which is associated with high rates of morbidity and mortality. The aim of this study was to determine whether
P. gingivalis
increases animal susceptibility to CMV infection. Mice were inoculated with CMV and infected locally with
P. gingivalis
3 days after the virus inoculation. Mortality rates were monitored, and traces of viral DNA and bacterial infection were detected systemically by using real-time PCR. Local and systemic cytokine secretion was measured, and histological sections were used to assess the pathological state of infected organs.
P. gingivalis
- and CMV-coinfected mice showed dramatically higher mortality rates than mice infected with
P. gingivalis
or CMV only. Although the organs of coinfected mice exhibited decreased viral titers, distinct necrosis and tissue damage were more evident in the livers and spleens of these mice than in those of mice infected with CMV only. Furthermore, systemic gamma interferon levels were decreased in coinfected mice, and marked lymphoid depletion was observed in their necrotic organs. In parallel control
Escherichia coli
-CMV coinfection experiments, the mortality and pathological results were the same as those found in mice infected with CMV only. Our results suggest a specific influence of
P. gingivalis
on the mouse immune response, causing increased susceptibility to CMV infection.
Differential Expression of Toll-Like Receptors 2 and 4 in Tissues of the Human Female Reproductive Tract
Authors: Pioli Patricia A. , Amiel Eyal , Schaefer Todd M. , Connolly John E. , Wira Charles R. , Guyre Paul M. 
Published: September 2004

ABSTRACT
Toll-like receptor (TLR) signal transduction is a central component of the innate immune response to pathogenic challenge. Although recent studies have begun to elucidate differences in acquired immunity in tissues of the human female reproductive tract, there is a relative paucity of work regarding innate defense mechanisms. We investigated TLR mRNA and protein expression in tissues of the human female reproductive tract. Constitutive mRNA expression of TLRs 1 to 6 was observed in fallopian tubes, uterine endometrium, cervix, and ectocervix. Furthermore, transcripts of the signaling adapter MyD88 and the accessory molecule CD14 were also detected in all tissues assayed. Quantitative analysis of TLR2 mRNA levels revealed highest expression of this molecule in fallopian tube and cervical tissues, followed by endometrium and ectocervix. In contrast to TLR2, TLR4 expression declined progressively along the tract, with highest expression in the upper tissues (fallopian tubes and endometrium), followed by cervix and ectocervix. In addition to mRNA, protein expression of TLR2 and TLR4 was also documented in these tissues. These data suggest that TLRs are differentially expressed in distinct compartments of the female reproductive tract and may provide insight regarding the regulation of inflammation and immunity within the tract.
A Spontaneous Translational Fusion ofBacillus cereusPlcR and PapR Activates Transcription of PlcR-Dependent Genes inBacillus anthracisvia Binding with a Specific Palindromic Sequence
Authors: Pomerantsev Andrei P. , Pomerantseva Olga M. , Leppla Stephen H. 
Published: September 2004

ABSTRACTTransformation ofBacillus anthraciswith plasmid pUTE29-plcR-papRcarrying the nativeBacillus cereus plcR-papRgene cluster did not activate expression ofB. anthracishemolysin genes, even though these are expected to be responsive to activation by the global regulator PlcR. To further characterize the action of PlcR, we examined approximately 3,000B. anthracistransformants containing pUTE29-plcR-papRand found a single hemolytic colony. The hemolytic strain contained a plasmid having a spontaneousplcR-papRintergenic region deletion. Transformation of the resulting plasmid pFP12, encoding a fused PlcR-PapR protein, into the nonhemolyticB. anthracisparental strain produced strong activation ofB. anthracishemolysins, including phosphatidylcholine-specific phospholipase C and sphingomyelinase. The fused PlcR-PapR protein present in a lysate ofB. anthraciscontaining pFP12 bound strongly and specifically to the double-stranded palindrome 5′-TATGCATTATTTCATA-3′ that matches the consensus PlcR-binding site. In contrast, native PlcR protein in a lysate from aB. anthracisstrain expressing large amounts of this protein did not demonstrate binding with the palindrome. The results suggest that the activation of PlcR by binding of a PapR pentapeptide as normally occurs inBacillus thuringiensisandB. cereuscan be mimicked by tethering the peptide to PlcR in a translational fusion, thereby obviating the need for PapR secretion, extracellular processing, retrieval into the bacterium, and binding with PlcR.
The B Subunit ofEscherichia coliHeat-Labile Enterotoxin Induces Both Caspase-Dependent and -Independent Cell Death Pathways in CD8+T Cells
Authors: Salmond Robert J. , Williams Rachel , Hirst Timothy R. , Williams Neil A. 
Published: September 2004

ABSTRACTThe nontoxic B subunit ofEscherichia coliheat-labile enterotoxin (EtxB) is a potent immunomodulatory molecule that acts both as an adjuvant and to stimulate immune deviation processes, resulting in the suppression of Th1-associated inflammatory responses. The ability of EtxB to alter immune reactivity is dependent on its ability to modulate immune cell function through binding to cell surface molecules, the principal receptor of which is the ubiquitous GM1-ganglioside. EtxB activates B cells and antigen-presenting cells and induces the selective apoptosis of murine CD8+T cells. We postulated that these effects are mediated by the induction of intracellular signaling pathways following EtxB-receptor interaction. We have previously shown that CD8+T-cell apoptosis induced by EtxB results from the activation of the transcription factor NF-κB and caspases. Here we report that while caspase activity is required for apoptosis, additional features of cell death are caspase independent. EtxB induces a rapid loss of mitochondrial membrane potential and cell viability that are unaffected by caspase inhibitors. In addition, our data suggest that these processes are independent of the activity of Bax and Bcl-2 but are mediated by nitric oxide synthase.
Dysregulated Inflammatory Response toCandida albicansin a C5-Deficient Mouse Strain
Authors: Mullick Alaka , Elias Miria , Picard Serge , Bourget Lucie , Jovcevski Orce , Gauthier Susan , Tuite Ashleigh , Harakidas Penelope , Bihun Craig , Massie Bernard , Gros Philippe 
Published: September 2004

ABSTRACTExperimental infection of inbred mouse strains withCandida albicansprovides a good model system to identify host genetic determinants that regulate onset of, response to, and ultimate outcome of disseminated candidiasis. The A/J mouse strain is exquisitely sensitive to infection withC. albicans, while the C57BL/6J strain is relatively resistant, as measured by survival following intravenous injection ofCandidablastospores. This differential susceptibility is caused by an A/J-specific loss-of-function mutation in the C5 component of the complement pathway. C5 plays several critical roles in host response to infection, including target lysis and phagocyte recruitment. Therefore, to determine which of its functions were required for host resistance to candidiasis, a detailed comparative analysis of pathophysiology and host response to acuteC. albicansinfection was conducted in A/J and C57BL/6J mice. C5-sufficient C57BL/6J mice were found to succumb late in infection due to severe kidney pathology, typified by fungal replication and robust neutrophil-based inflammatory response associated with extensive tissue damage. In contrast, A/J mice were moribund within 24 h postinfection but displayed little if any kidney damage despite an inability to mobilize granulocytes and a high fungal load in the kidney. Rather, C5 deficiency in A/J mice was associated with higher levels of circulating cytokines tumor necrosis factor alpha, interleukin-6, monocyte chemotactic protein 1 (MCP-1), MCP-5, and eotaxin in response toC. albicans. Transfer of the C5-defective allele from A/J onto a C57BL/6J genetic background in recombinant congenic strain BcA17 recapitulated the phenotypic aspects of the susceptibility of A/J mice toC. albicans, confirming the causative role of C5 deficiency in the dysregulated cytokine response.