bluuebunny/crossref_metadata_2025_split huggingface dataset:
GastricHelicobacterInfection Inhibits Development of Oral Tolerance to Food Antigens in Mice
Authors: Matysiak-Budnik Tamara , van Niel Guillaume , Mégraud Francis , Mayo Kathryn , Bevilacqua Claudia , Gaboriau-Routhiau Valérie , Moreau Marie-Christiane , Heyman Martine 
Published: August 2003

ABSTRACTThe increase in the transcellular passage of intact antigens across the digestive epithelium infected withHelicobacter pylorimay interfere with the regulation of mucosal immune responses. The aim of this work was to study the capacity ofHelicobacterinfection to inhibit the development of oral tolerance or to promote allergic sensitization and the capacity of a gastro-protective agent, rebamipide, to interfere with these processes in mice. Oral tolerance to ovalbumin (OVA) was studied in 48 C3H/He 4-week-old mice divided into four groups: (i) OVA-sensitized mice; (ii) OVA-“tolerized” mice (that is, mice that were rendered immunologically tolerant); (iii)H. felis-infected, OVA-tolerized mice; (iv) andH. felis-infected, OVA-tolerized, rebamipide-treated mice. Oral sensitization to hen egg lysozyme (HEL) was studied in 48 mice divided into four groups: (i) controls; (ii) HEL-sensitized mice; (iii)H. felis-infected, HEL-sensitized mice; and (iv)H. felis-infected, HEL-sensitized, rebamipide-treated mice. Specific anti-OVA or anti-HEL immunoglobulin E (IgE) and IgG1/IgG2a serum titers were measured by enzyme-linked immunosorbent assay. Additionally, the capacity of rebamipide to interfere with antigen presentation and T-cell activation in vitro, as well as absorption of rebamipide across the epithelial monolayer, was tested.H. felisinfection led to the inhibition of oral tolerance to OVA, but rebamipide prevented this inhibitive effect ofH. felis. H. felisinfection did not enhance the sensitization to HEL, but rebamipide inhibited the development of this sensitization. Moreover, rebamipide inhibited in a dose-dependent manner antigen presentation and T-cell activation in vitro and was shown to be able to cross the epithelium at a concentration capable of inducing this inhibitory effect. We conclude thatH. feliscan inhibit the development of oral tolerance to OVA in mice and that this inhibition is prevented by rebamipide.
Purification and Characterization of an Immunogenic Aminopeptidase ofBrucella melitensis
Authors: Contreras-Rodriguez Araceli , Ramirez-Zavala Bernardo , Contreras Andrea , Schurig Gerhardt G. , Sriranganathan Nammalwar , Lopez-Merino Ahide 
Published: August 2003

ABSTRACTAn immunogenic aminopeptidase was purified fromBrucella melitensisstrain VTRM1. The purification procedure consisted of ammonium sulfate fractionation and three chromatographic steps. This procedure resulted in a yield of 29% and a 144-fold increase in specific activity. The aminopeptidase appeared to be a monomeric enzyme with a molecular mass of 96 kDa and an isoelectric point of 4.8. Its activity was optimal at pH 7.0 at 40°C. The enzyme was strongly inhibited by EDTA, 1,10-phenathroline, and divalent cations (Zn2+and Hg2+), suggesting that this protein was a metalloaminopeptidase. The enzyme showed preference for alanine at the N termini of aminoacyl derivatives. TheKmvalues forl-alanine-p-nitroanilide (Ala-pNA) and Lys-pNA were 0.35 and 0.18 mM, respectively. The N-terminal sequence of aminopeptidase was used for a homologous search in the genomes ofB. melitensis16M andBrucella suis1330. The analysis revealed an exact match of the probe sequence (36 bp) with an open reading frame of 2,652 bp encoding a protein predicted to be alanyl aminopeptidase (aminopeptidase N). Collectively, these data suggest designation of theB. melitensisenzyme as an aminopeptidase N. The aminopeptidase was recognized by sera from patients with acute and chronic brucellosis, suggesting that the enzyme may have important diagnostic implications.
Mannose-Binding Lectin Is a Disease Modifier in Clinical Malaria and May Function as Opsonin forPlasmodium falciparum- Infected Erythrocytes
Authors: Garred Peter , Nielsen Morten A. , Kurtzhals Jørgen A.L. , Malhotra Rajneesh , Madsen Hans O. , Goka Bamenla Q. , Akanmori Bartholomew D. , Sim Robert B. , Hviid Lars 
Published: August 2003

ABSTRACTVariant alleles in the mannose-binding lectin (MBL) gene (mbl2) causing low levels of functional MBL are associated with susceptibility to different infections and are common in areas where malaria is endemic. Therefore, we investigated whether MBL variant alleles in 551 children from Ghana were associated with the occurrence and outcome parameters ofPlasmodium falciparummalaria and asked whether MBL may function as an opsonin forP. falciparum. No difference in MBL genotype frequency was observed between infected and noninfected children or between children with cerebral malaria and/or severe malarial anemia and children with uncomplicated malaria. However, patients with complicated malaria who were homozygous for MBL variant alleles had significantly higher parasite counts and lower blood glucose levels than their MBL-competent counterparts. Distinct calcium-dependent binding of MBL to the membrane ofP. falciparum-infected erythrocytes, which could be inhibited by mannose, was observed. Further characterization revealed that MBL reacted with aP. falciparumglycoprotein identical to the 78-kDa glucose-regulated stress protein ofP. falciparum. MBL seems to be a disease modifier in clinical malaria and to function as an opsonin for erythrocytes invaded byP. falciparumand may thus be involved in sequestration of the parasite, which in turn may explain the association between homozygosity for MBL variant alleles and high parasite counts.
SWR Mice Are Highly Susceptible to Pulmonary Infection with
Mycobacterium tuberculosis
Authors: Turner Oliver C. , Keefe Robert G. , Sugawara Isamu , Yamada Hiroyuki , Orme Ian M. 
Published: August 2003

ABSTRACT

Inbred mice differ in their abilities to control the growth of
Mycobacterium tuberculosis
in the lung and can as a result be regarded as either resistant or susceptible strains. In this study we report that the SWR mouse is both highly susceptible and in addition appears incapable of establishing a characteristic state of chronic disease after low-dose aerosol infection. In comparison to C57BL/6 mice, SWR mice were unable to contain the bacterial load in the lungs, resulting in progressive fatal disease. Histologic analysis of the lung tissue revealed evidence of a florid inflammatory cell response in the SWR mice leading to degeneration and necrosis and consolidation of a large percentage of the lung surface area. Digestion of infected lungs and analysis by flow cytometry demonstrated an initially similar but eventually higher number of lymphocytes accumulating in the SWR mice. Additionally, in contrast to the C57BL/6 mice, SWR mice had a significantly lower percentage of CD4 T cells in the lungs showing evidence of proliferation and positive intracellular staining for gamma interferon during the first two months of infection, and a lower percentage of both CD4 and CD8T cells exhibiting differentiation to an effector/memory phenotype during the first month of infection. We propose that further investigation of the SWR mouse may provide a new animal model for immunocompetent individuals apparently unable to effectively control the growth of
M. tuberculosis
in the lung.
Differential Role of MyD88 in Macrophage-Mediated Responses to Opportunistic Fungal Pathogens
Authors: Marr Kieren A. , Arunmozhi Balajee S. , Hawn Thomas R. , Ozinsky Adrian , Pham Uyenvy , Akira Shizuo , Aderem Alan , Conrad Liles W. 
Published: August 2003

ABSTRACT

Toll-like receptors mediate macrophage recognition of microbial ligands, inducing expression of microbicidal molecules and cytokines via the adapter protein MyD88. We investigated the role of MyD88 in regulating murine macrophage responses to a pathogenic yeast (
Candida albicans
) and mold (
Aspergillus fumigatus
). Macrophages derived from bone marrow of MyD88-deficient mice (MyD88
−/−
) demonstrated impaired phagocytosis and intracellular killing of
C. albicans
compared to wild-type (MyD88
+/+
) macrophages. In contrast, ingestion and killing of
A. fumigatus
conidia was MyD88 independent. Cytokine production by MyD88
−/−
macrophages in response to
C. albicans
yeasts and hyphae was substantially decreased, but responses to
A. fumigatus
hyphae were preserved. These results provide evidence that MyD88 signaling is involved in phagocytosis and killing of live
C. albicans
, but not
A. fumigatus
. The differential role of MyD88 may represent one mechanism by which macrophages regulate innate responses specific to different pathogenic fungi.
Both the Fas Ligand and Inducible Nitric Oxide Synthase Are Needed for Control of Parasite Replication within Lesions in Mice Infected withLeishmania majorwhereas the Contribution of Tumor Necrosis Factor Is Minimal
Authors: Chakour Reza , Guler Reto , Bugnon Mélanie , Allenbach Cindy , Garcia Irène , Mauël Jacques , Louis Jacques , Tacchini-Cottier Fabienne 
Published: August 2003

ABSTRACTFollowing infection with the protozoan parasiteLeishmania major, C57BL/6 mice develop a small lesion that heals spontaneously. Resistance to infection is associated with the development of CD4+Th1 cells producing gamma interferon (IFN-γ) and tumor necrosis factor (TNF), which synergize in activating macrophages to their microbicidal state. We show here that C57BL/6 mice lacking both TNF and Fas ligand (FasL) (gldTNF−/−mice) infected withL. majorneither resolved their lesions nor controlledLeishmaniareplication despite the development of a strong Th1 response. Comparable inducible nitric oxide synthase (iNOS) activities were detected in lesions of TNF−/−,gldTNF−/−, andgldmice, but onlygldandgldTNF−/−mice failed to control parasite replication. Parasite numbers were high ingldmice and even more elevated ingldTNF−/−mice, suggesting that, in addition to iNOS, the Fas/FasL pathway is required for successful control of parasite replication and that TNF contributes only a small part to this process. Furthermore, FasL was shown to synergize with IFN-γ for the induction of leishmanicidal activity within macrophages infected withL. majorin vitro. Interestingly, TNF−/−mice maintained large lesion size throughout infection, despite being able to largely control parasite numbers. Thus, IFN-γ, FasL, and iNOS appear to be essential for the complete control of parasite replication, while the contribution of TNF is more important in controlling inflammation at the site of parasite inoculation.
Characterization of
Pseudomonas aeruginosa
Exoenzyme S as a Bifunctional Enzyme in J774A.1 Macrophages
Authors: Rocha Claudia L. , Coburn Jenifer , Rucks Elizabeth A. , Olson Joan C. 
Published: August 2003

ABSTRACT

Pseudomonas aeruginosa
exoenzyme S (ExoS) is a type III secretion (TTS) effector, which includes both a GTPase-activating protein (GAP) activity toward the Rho family of low-molecular-weight G (LMWG) proteins and an ADP-ribosyltransferase (ADPRT) activity that targets LMWG proteins in the Ras, Rab, and Rho families. The coordinate function of both activities of ExoS in J774A.1 macrophages was assessed by using
P. aeruginosa
strains expressing and translocating wild-type ExoS or ExoS defective in GAP and/or ADPRT activity. Distinct and coordinated functions were identified for both domains. The GAP activity was required for the antiphagocytic effect of ExoS and was linked to interference of lamellopodium and membrane ruffle formation. Alternatively, the ADPRT activity of ExoS altered cellular adherence and morphology and was linked to effects on filopodium formation. The cellular mechanism of ExoS GAP activity included an inactivation of Rac1 function, as determined in p21-activated kinase 1-glutathione
S
-transferase (GST) pull-down assays. The ADPRT activity of ExoS targeted Ras and RalA but not Rab or Rho proteins, and Ral binding protein 1-GST pull-down assays identified an effect of ExoS ADPRT activity on RalA activation. The results from these studies confirm the bifunctional nature of ExoS activity within macrophages when translocated by TTS.
Ehrlichia chaffeensis
and
Anaplasma phagocytophilum
Lack Genes for Lipid A Biosynthesis and Incorporate Cholesterol for Their Survival
Authors: Lin Mingqun , Rikihisa Yasuko 
Published: August 2003

ABSTRACT

Ehrlichia chaffeensis
and
Anaplasma phagocytophilum
are agents of human monocytic and granulocytic ehrlichioses, respectively. They are extremely sensitive to mechanical stress and are pleomorphic gram-negative bacteria. Membrane incorporation of cholesterol from the eukaryotic host is known to be essential for other fragile and pleomorphic bacteria and mycoplasmas that lack a cell wall. Thus, we tested whether cholesterol is required for
E. chaffeensis
and
A. phagocytophilum
. Using a freeze fracture technique and biochemical analysis, these bacteria were found to contain significant levels of membrane cholesterol. These bacteria lack genes for cholesterol biosynthesis or modification. However, host cell-free bacteria had the ability to take up directly exogenous cholesterol or NBD-cholesterol, a fluorescent cholesterol derivative. Treatment of the bacteria with cholesterol extraction reagent methyl-β-cyclodextrin caused their ultrastructural changes. Furthermore, pretreatment of the bacteria with methyl-β-cyclodextrin or NBD-cholesterol deprived these bacteria of the ability to infect leukocytes, thus killing these obligate intracellular bacteria. Analysis of
E. chaffeensis
and
A. phagocytophilum
genome sequences revealed that these bacteria lack all genes for the biosynthesis of lipid A and most genes for the biosynthesis of peptidoglycan, which confer structural strength to gram-negative bacteria. Taken together, these results suggest that human ehrlichiosis agents became cholesterol dependent due to the loss of these genes. As the first report of gram-negative bacteria incorporating cholesterol for survival, these findings offer insight into the unique nature of their parasitism and imply that cholesterol is important in the control of human ehrlichioses.
A Family of
acr
-Coregulated
Mycobacterium tuberculosis
Genes Shares a Common DNA Motif and Requires Rv3133c (
dos
R or
dev
R) for Expression
Authors: Florczyk Matthew A. , McCue Lee Ann , Purkayastha Anjan , Currenti Egidio , Wolin Meyer J. , McDonough Kathleen A. 
Published: August 2003

ABSTRACT

Previous work has shown that the divergently transcribed
Mycobacterium tuberculosis
genes
acr
(
hspX
, Rv2031c) and
acg
(Rv2032) are induced under conditions of shallow standing culture and low oxygen and intracellularly within macrophages. We used a combination of computational and experimental methods to identify promoters for eight additional genes that are regulated in a similar manner and that comprise an
acr
-coregulated promoter (ACP) family. Transcriptional regulation of these ACP family members was evaluated by using a plasmid-based promoter-green fluorescent protein fusion system and flow cytometry. All promoters showed increased expression in shallow standing versus shaking cultures, in low- versus high-oxygen conditions, and intracellularly within macrophages versus extracellularly in tissue culture medium. However, there were quantitative differences in expression among promoters and among conditions for each promoter. A conserved 18-bp palindromic sequence motif was identified in all ACPs by Gibbs sampling-based computational analyses. Two such motifs overlap regions in the
acr
and
acg
promoters that were previously shown to be required for their expression. In addition, we found that 5% carbon dioxide was required for growth of
Mycobacterium bovis
BCG under microaerophilic (1.3% O
2
) culture conditions and fully prevented the growth cessation typically associated with rapid removal of oxygen. These findings are likely to be relevant to the in vivo environment and will contribute to our understanding of the pathogenesis of tuberculosis infection.
Calcineurin Is Essential for Virulence in
Candida albicans
Authors: Bader Teresa , Bodendorfer Barbara , Schröppel Klaus , Morschhäuser Joachim 
Published: August 2003

ABSTRACT

Calcineurin is a conserved Ca
2+
-calmodulin-activated, serine/threonine-specific protein phosphatase that regulates a variety of physiological processes, e.g., cell cycle progression, polarized growth, and adaptation to salt and alkaline pH stresses. In the pathogenic yeast
Cryptococcus neoformans
, calcineurin is also essential for growth at 37°C and virulence. To investigate whether calcineurin plays a role in the virulence of
Candida albicans
, the major fungal pathogen of humans, we constructed
C. albicans
mutants in which both alleles of the
CMP1
gene, encoding the calcineurin catalytic subunit, were deleted. The
C. albicans
Δ
cmp1
mutants displayed hypersensitivity to elevated Na
+
, Li
+
, and Mn
2+
concentrations and to alkaline pH, phenotypes that have been described after calcineurin inactivation in the related yeast
Saccharomyces cerevisiae
. Unlike
S. cerevisiae
calcineurin mutants, which exhibit reduced susceptibility to high Ca
2+
concentrations, growth of
C. albicans
was inhibited in the presence of 300 mM CaCl
2
after the deletion of
CMP1
, demonstrating that there are also differences in calcineurin-mediated cellular responses between these two yeast species. In contrast to
C. neoformans
, inactivation of calcineurin did not cause temperature sensitivity in
C. albicans
. In addition, hyphal growth, an important virulence attribute of
C. albicans
, was not impaired in the Δ
cmp1
mutants under a variety of inducing conditions. Nevertheless, the virulence of the mutants was strongly attenuated in a mouse model of systemic candidiasis, demonstrating that calcineurin signaling is essential for virulence in
C. albicans
.
Evidence for a Melanin Cell Wall Component in
Pneumocystis carinii
Authors: Icenhour Crystal R. , Kottom Theodore J. , Limper Andrew H. 
Published: August 2003

ABSTRACT

Fluorescein isothiocyanate-labeled monoclonal antibodies specific for fungal melanin were used in this study to visualize melanin-like components of the
Pneumocystis carinii
cell wall. A colorimetric enzyme assay confirmed these findings. This is the first report of melanin-like pigments in
Pneumocystis
.
Intracellular Expression of the Plasmid-Encoded Toxin from Enteroaggregative
Escherichia coli
Authors: Sui Bao Quan , Dutta Pinaki R. , Nataro James P. 
Published: August 2003

ABSTRACT

The plasmid-encoded toxin (Pet) from enteroaggregative
Escherichia coli
is a serine protease autotransporter that acts as an enterotoxin and cytotoxin. When applied to epithelial cells in culture, purified toxin induces cell elongation and rounding, followed by exfoliation of cells from the substratum. These effects are accompanied by loss of actin stress fibers and electrophysiologic changes. Although it has been hypothesized that Pet has an intracellular site of action, evidence for this is indirect. In addition, Pet has recently been shown to cleave spectrin in vitro and in vivo. If Pet requires intracellular localization to execute its toxic effects, then intracellular expression of the protein could induce cytopathic effects similar to those observed when the toxin is applied to the cell surface. To test this hypothesis, we expressed the mature Pet toxin (comprising only the passenger domain of the Pet precursor) in the cytoplasm of HEp-2 cells by using mammalian expression vectors. Separately, we expressed the Pet passenger domain mutated at the catalytic serine (PetS260A), a construct that has been reported to lack toxic effects. Forty-eight hours after transient transfection of pcDNA3.1-
pet
in HEp-2 cells, we observed cell elongation and other morphological changes similar to those induced by applied toxin. Cells transfected with pcDNA3.1 vector alone appeared normal, while cells expressing the PetS260A mutant displayed similar (though less pronounced) changes compared with those in cells expressing pcDNA3.1-
pet
. Notably, intracellular expression of Pet was accompanied by condensation of the spectrin cytoskeleton. These studies corroborate an intracellular site of action for the Pet toxin, further implicate a role for spectrin in Pet intoxication, and provide a powerful tool for Pet structure and function analyses.
Accumulation of
Clostridium perfringens
Epsilon-Toxin in the Mouse Kidney and Its Possible Biological Significance
Authors: Tamai Eiji , Ishida Tetsuya , Miyata Shigeru , Matsushita Osamu , Suda Hirofumi , Kobayashi Shoji , Sonobe Hiroshi , Okabe Akinobu 
Published: August 2003

ABSTRACT

In this paper we show that
Clostridium perfringens
epsilon-toxin accumulates predominantly in the mouse kidney, where it is distributed mainly in glomeruli, capillaries, and collecting ducts. Although some pycnotic and exfoliated epithelial cells were observed in distal tubuli and collecting ducts, there were no findings indicative of severe renal injury. Bilateral nephrectomy increased the mouse lethality of the toxin, suggesting that the kidney contributes to the host defense against the lethal toxicity of epsilon-toxin.
Intracellular Survival of
Streptococcus pyogenes
in Polymorphonuclear Cells Results in Increased Bacterial Virulence
Authors: Medina Eva , Rohde Manfred , Chhatwal Gursharan S. 
Published: August 2003

ABSTRACT

It has recently been shown that survival within phagocytic cells constitutes an additional strategy used by
Streptococcus pyogenes
to evade the host defenses. Here we provide evidence that
S. pyogenes
can escape from the phagosome into the cytoplasm of phagocytic cells. Furthermore, intracellular bacteria seem to undergo phenotypic switching that results in much more virulent microorganisms.
Two-Component Systems of
Helicobacter pylori
Contribute to Virulence in a Mouse Infection Model
Authors: Panthel Klaus , Dietz Patricia , Haas Rainer , Beier Dagmar 
Published: August 2003

ABSTRACT

Helicobacter pylori
encodes three histidine kinases and five response regulators belonging to the family of two-component regulatory systems which are involved in transcriptional control. Here we demonstrate that isogenic mutants of
H. pylori
P76 with deletions of the response regulator open reading frame (ORF) HP1365 and ORFs HP244, HP165, and HP1364 encoding histidine kinases are unable to colonize the stomachs of BALB/c mice, suggesting an essential role of these systems in the regulation of important virulence properties of
H. pylori
. Furthermore, we demonstrate that the genes under the control of the P
HP1408
and P
HP119
promoters which are regulated by the two-component system HP166-HP165 are not essential for single mutant colonization of mice but are required under competitive colonization conditions.
Role of Periplasmic Peptidylprolyl Isomerases in
Salmonella enterica
Serovar Typhimurium Virulence
Authors: Humphreys Sue , Rowley Gary , Stevenson Andrew , Kenyon William J. , Spector Michael P. , Roberts Mark 
Published: August 2003

ABSTRACT

FkpA is a peptidylprolyl isomerase whose expression is regulated by the alternative sigma factor, sigma factor E (σ
E
). In contrast to the results of a previous report, inactivation of
fkpA
was found to have only a minor effect on the ability of
Salmonella enterica
serovar Typhimurium to invade and survive within epithelial and macrophage cell lines and cause infection in mice. However, an effect of the
fkpA
mutation on serovar Typhimurium virulence was seen if the mutation was combined with mutations in
surA
or
htrA
, two other σ
E
-regulated genes, which encode proteins involved in protein folding and/or degradation in the periplasm.