bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Cytotoxic Enterotoxin ofAeromonas hydrophilaInduces Proinflammatory Cytokine Production and Activates Arachidonic Acid Metabolism in Macrophages
Authors: Chopra A. K. , Xu X.-J. , Ribardo D. , Gonzalez M. , Kuhl K. , Peterson J. W. , Houston C. W. 
Published: July 2002

ABSTRACTAn aerolysin-related cytotoxic enterotoxin (Act) ofAeromonas hydrophilapossesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E2[PGE2]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1β (IL-1β) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE2coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE2, and Act produced AA from phospholipids by inducing group V secretory phospholipase A2. We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE2, could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-κB and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-κB and CREB. This is the first report of the detailed mechanisms of action of Act fromA. hydrophila.
Interdependency of Interleukin-10 and Interleukin-12 in Regulation of T-Cell Differentiation and Effector Function of Monocytes in Response to Stimulation withCryptococcus neoformans
Authors: Retini Cinzia , Kozel Thomas R. , Pietrella Donatella , Monari Claudia , Bistoni Francesco , Vecchiarelli Anna 
Published: July 2002

ABSTRACTWe previously demonstrated that the principal component of capsular material ofCryptococcus neoformans, glucuronoxylomannan (GXM), induces interleukin-10 (IL-10) secretion from human monocytes. Here we report that encapsulation of the yeast with GXM is able to down-regulate interleukin-12 (IL-12) production by monocytes that would normally occur in the absence of encapsulation. This phenomenon appeared to be the result of inhibition of the phagocytic process by encapsulation with GXM as well as of negative signals such as IL-10 secretion produced by interaction of GXM with leukocytes. Decreased secretion of IL-12 correlated with decreased release of gamma interferon (IFN-γ) from T cells, suggesting a role for encapsulation with GXM in hindering a T helper type 1 (Th1) response. This is supported by the ability of encapsulation with GXM to limit increased expression of B7-1 costimulatory molecules that otherwise might limit IL-10 secretion. Endogenous IL-10 played a critical role in modulatory activity associated with encapsulation with GXM. Blocking IL-10 with monoclonal antibody to IL-10 resulted in increased (i) IL-12 secretion, (ii) IFN-γ release from T cells, and (iii) killing ofC. neoformansby monocytes. These results suggest that encapsulation with GXM limits development of a protective Th1-type response, an inhibitory process in which IL-10 plays a critical role. Scavengers of GXM and/or IL-10 could be useful in a protective Th1-type response in patients with cryptococcosis.
Critical Role for Signal Transducer and Activator of Transcription Factor 6 in Mediating Intestinal Muscle Hypercontractility and Worm Expulsion inTrichinella spiralis-Infected Mice
Authors: Khan W. I. , Vallance B. A. , Blennerhassett P. A. , Deng Y. , Verdu E. F. , Matthaei K. I. , Collins S. M. 
Published: July 2002

ABSTRACTIntestinal nematode infections in rats or mice are accompanied by intestinal muscle hyper contractility that may contribute to parasite expulsion from the gut. Previous studies demonstrated that both the expulsion of nematode parasites and the associated muscle hyper contractility are dependent on CD4+T helper cells. Nevertheless, the precise immunological mechanism underlying changes in intestinal muscle function remains to be determined. In this study, we investigated the role of interleukin 4 (IL-4) and signal transducer and activator of transcription factor 6 (STAT6) in the development of intestinal muscle hypercontractility and worm expulsion by infecting IL-4 and STAT6-deficient mice withTrichinella spiralis. Worm expulsion was almost normal in IL-4-deficient mice but substantially delayed in STAT6-deficient mice. Consistent with delayed worm expulsion, we also observed a marked attenuation of carbachol-induced muscle contraction in STAT6-deficient mice but only a moderate decrease in muscle hypercontractility in IL-4-deficient mice. In addition, we also observed severe impairment of T helper type 2 cytokine responses and intestinal mucosal mastocytosis in STAT6-deficient mice, although some degree of intestinal tissue eosinophilia was evident in these animals. These results are consistent with the hypothesis that STAT6-dependent changes in intestinal muscle function contribute to host protection in nematode infection.
Induction of Lysogenic Bacteriophage and Phage-Associated Toxin from Group A Streptococci during Coculture with Human Pharyngeal Cells
Authors: Broudy Thomas B. , Pancholi Vijaykumar , Fischetti Vincent A. 
Published: July 2002

ABSTRACT

We found that when group A streptococci are cocultured with human pharyngeal cells, they upregulate and secrete a 25-kDa toxin, determined to be the bacteriophage-encoded streptococcal pyrogenic exotoxin C (SpeC). This prompted us to determine if the bacteriophage themselves are induced during coculture conditions. We found that bacteriophage induction does occur, resulting in the release of ∼10
5
phage particles during the 3-h coculture. Furthermore, we show that the bacteriophage induction event is mediated by a pharyngeal cell soluble factor for which we provide an initial characterization.
Gamma Interferon Prevents the Inhibitory Effects of Oxidative Stress on Host Responses toEscherichia coliInfection
Authors: Parmely Michael J. , Wang Fuan , Wright Douglas 
Published: July 2002

ABSTRACTOxidative stress occurs in animals challenged with bacterial endotoxin and can affect the expression of important host inflammatory genes. However, much less is known about the effects of oxidative stress on responses to gram-negative bacteria. The current study compared the effects of redox imbalance on hepatic responses of mice toEscherichia colibacteria versus purified endotoxic lipopolysaccharide (LPS). Oxidative stress induced by glutathione depletion virtually eliminated hepatic tumor necrosis factor alpha responses to bothE. coliand LPS. Inducible NO synthase (iNOS) and intercellular adhesion molecule-1 (ICAM-1) expression was also markedly inhibited by glutathione depletion in LPS-challenged mice, but was unaffected inE. coli-infected animals. Three findings suggested that gamma interferon (IFN-γ) production explained the differences between LPS and bacterial challenge. Glutathione depletion completely inhibited the IFN-γ response to LPS, but only partially inhibited IFN-γ production in infected mice. Exogenous IFN-γ restored iNOS and ICAM-1 responses to LPS in stressed mice. Conversely, IFN-γ-deficient, glutathione-depleted mice showed a marked decrease in iNOS and ICAM-1 expression when challenged withE. coli. These findings indicate that both the nature of the microbial challenge and the production of IFN-γ can be important in determining the effects of redox imbalance during gram-negative bacterial infections.
Interaction between Host Complement and Mosquito-Midgut-StagePlasmodium berghei
Authors: Margos Gabriele , Navarette Sandra , Butcher Geoff , Davies Alex , Willers Christine , Sinden Robert E. , Lachmann Peter J. 
Published: July 2002

ABSTRACTAfter ingestion by mosquitoes, gametocytes of malaria parasites become activated and form extracellular gametes that are no longer protected by the red blood cell membrane against immune effectors of host blood. We have studied the action of complement onPlasmodiumdevelopmental stages in the mosquito blood meal using the rodent malaria parasitePlasmodium bergheiand rat complement as a model. We have shown that in the mosquito midgut, rat complement components necessary to initiate the alternative pathway (factor B, factor D, and C3) as well as C5 are present for several hours following ingestion ofP. berghei-infected rat blood. In culture, 30 to 50% of mosquito midgut stages ofP. bergheisurvived complement exposure during the first 3 h of development. Subsequently, parasites became increasingly sensitive to complement lysis. To investigate the mechanisms involved in their protection, we tested for C3 deposition on parasite surfaces and whether host CD59 (a potent inhibitor of the complement membrane attack complex present on red blood cells) was taken up by gametes while emerging from the host cell. Between 0.5 and 22 h, 90% of Pbs21-positive parasites were positive for C3. While rat red and white blood cells stained positive for CD59, Pbs21-positive parasites were negative for CD59. In addition, exposure of parasites to rat complement in the presence of anti-rat CD59 antibodies did not increase lysis. These data suggest that parasite or host molecules other than CD59 are responsible for the protection of malaria parasites against complement-mediated lysis. Ongoing research aims to identify these molecules.
Exploitation of Interleukin-8-Induced Neutrophil Chemotaxis by the Agent of Human Granulocytic Ehrlichiosis
Authors: Akkoyunlu Mustafa , Malawista Stephen E. , Anguita Juan , Fikrig Erol 
Published: July 2002

ABSTRACTThe agent of human granulocytic ehrlichiosis (HGE) is an obligate intracellular bacterium with a tropism for neutrophils; however, the mechanisms of bacterial dissemination are not yet understood. Interleukin-8 (IL-8) is a chemokine that induces neutrophil migration to sites of infection for host defense against pathogens. We now show that HGE bacteria, and the HGE-44 protein, induce IL-8 secretion in a promyelocytic (HL-60) cell line that has been differentiated along the neutrophil lineage with retinoic acid and in neutrophils. Infected HL-60 cells also demonstrate upregulation of CXCR2, an IL-8 receptor, but not CXCR1. Human neutrophils migrate towardsEhrlichiasp.-infected cells in a chemotaxis chamber assay, and this movement can be blocked with antibodies to IL-8. Finally, immunocompetent and severe combined immunodeficient mice administered CXCR2 antisera, and CXCR2−/−mice that lack the human IL-8 receptor homologue, are much less susceptible to granulocytic ehrlichiosis than are control animals. These results demonstrate that HGE bacteria induce IL-8 production by host cells and, paradoxically, appear to exploit this chemokine to enhance infection.
The Efficiency of the Translocation ofMycobacterium tuberculosisacross a Bilayer of Epithelial and Endothelial Cells as a Model of the Alveolar Wall Is a Consequence of Transport within Mononuclear Phagocytes and Invasion of Alveolar Epithelial Cells
Authors: Bermudez Luiz E. , Sangari Felix J. , Kolonoski Peter , Petrofsky Mary , Goodman Joseph 
Published: July 2002

ABSTRACTThe mechanism(s) by whichMycobacterium tuberculosiscrosses the alveolar wall to establish infection in the lung is not well known. In an attempt to better understand the mechanism of translocation and create a model to study the different stages of bacterial crossing through the alveolar wall, we established a two-layer transwell system.M. tuberculosisH37Rv was evaluated regarding the ability to cross and disrupt the membrane.M. tuberculosisinvaded A549 type II alveolar cells with an efficiency of 2 to 3% of the initial inoculum, although it was not efficient in invading endothelial cells. However, bacteria that invaded A549 cells were subsequently able to be taken up by endothelial cells with an efficiency of 5 to 6% of the inoculum. When incubated with a bicellular transwell monolayer (epithelial and endothelial cells),M. tuberculosistranslocated into the lower chamber with efficiency (3 to 4%).M. tuberculosiswas also able to efficiently translocate across the bicellular layer when inside monocytes. Infected monocytes crossed the barrier with greater efficiency when A549 alveolar cells were infected withM. tuberculosisthan when A549 cells were not infected. We identified two potential mechanisms by whichM. tuberculosisgains access to deeper tissues, by translocating across epithelial cells and by traveling into the blood vessels within monocytes.
Functional Variation of the Antigen I/II Surface Protein in
Streptococcus mutans
and
Streptococcus intermedius
Authors: Petersen F. C. , Assev S. , van der Mei H. C. , Busscher H. J. , Scheie A. A. 
Published: July 2002

ABSTRACT

Although
Streptococcus intermedius
and
Streptococcus mutans
are regarded as members of the commensal microflora of the body,
S. intermedius
is often associated with deep-seated purulent infections, whereas
S. mutans
is frequently associated with dental caries. In this study, we investigated the roles of the
S. mutans
and
S. intermedius
antigen I/II proteins in adhesion and modulation of cell surface characteristics. By using isogenic mutants, we show that the antigen I/II in
S. mutans
, but not in
S. intermedius
, was involved in adhesion to a salivary film under flowing conditions, as well as in binding to rat collagen type I. Binding to human fibronectin was a common function associated with the
S. mutans
and
S. intermedius
antigen I/II. Adhesion of
S. mutans
or
S. intermedius
to human collagen types I or IV was negligible. Hydrophobicity, as measured by water contact angles, and zeta potentials were unaltered in the
S. intermedius
mutant. The
S. mutans
isogenic mutants, on the other hand, exhibited more positive zeta potentials at physiological pH values than did the wild type. The results indicate common and species-specific roles for the antigen I/II in mediating the attachment of
S. mutans
and
S. intermedius
to host components and in determining cell surface properties.
Association of a Determinant on Mouse Chromosome 18 with Experimental SeverePlasmodium bergheiMalaria
Authors: Nagayasu Eiji , Nagakura Koichi , Akaki Mayumi , Tamiya Gen , Makino Satoshi , Nakano Yamaji , Kimura Minoru , Aikawa Masamichi 
Published: July 2002

ABSTRACTExperimental severe malaria (ESM; also known as experimental cerebral malaria) is an acute lethal syndrome caused by infection withPlasmodium bergheiANKA and associated with coma and other neurological manifestations in mice. Various inbred strains of mice exhibit differences in susceptibility to the development of ESM. For example, C57BL/6 mice are highly susceptible and DBA/2 mice are relatively resistant. We report here the results of a genomewide scan for host genomic regions that control resistance to ESM in DBA/2 mice using an F2intercross population of susceptible and resistant strains. A region of mid-chromosome 18 was found to be a major determinant of resistance to ESM.
Pressure Regulation of Soluble Cytochromes
c
in a Deep-Sea Piezophilic Bacterium,
Shewanella violacea
Authors: Yamada Mitsunori , Nakasone Kaoru , Tamegai Hideyuki , Kato Chiaki , Usami Ron , Horikoshi Koki 
Published: July 2002

ABSTRACT

Two
c
-type cytochromes from the soluble fraction of a deep-sea moderately piezophilic bacterium,
Shewanella violacea
, were purified and characterized, and the genes coding for these cytochromes were cloned and sequenced. One of the cytochromes, designated cytochrome
c
A
, was found to have a molecular mass of approximately 8.3 kDa, and it contained one heme
c
per molecule. The other, designated cytochrome
c
B
, was found to have a molecular mass of approximately 23 kDa, and it contained two heme
c
molecules per protein molecule. The amount of cytochrome
c
B
expressed in cells grown at high hydrostatic pressure (50 MPa) was less than that in cells grown at atmospheric pressure, whereas cytochrome
c
A
was constitutively expressed under all pressure conditions examined. The results of Northern blotting analysis were consistent with the above-mentioned observations and suggested that the pressure regulation of cytochrome
c
B
gene expression occurred at the transcriptional level. These results suggest that the components of the respiratory chain of moderately piezophilic
S. violacea
could be exchanged according to the growth pressure conditions.
Characterization of a
Bordetella pertussis
Diaminopimelate (DAP) Biosynthesis Locus Identifies
dapC
, a Novel Gene Coding for an
N
-Succinyl-
l,l
-DAP Aminotransferase
Authors: Fuchs Thilo M. , Schneider Boris , Krumbach Karin , Eggeling Lothar , Gross Roy 
Published: July 2002

ABSTRACT

The functional complementation of two
Escherichia coli
strains defective in the succinylase pathway of
meso
-diaminopimelate (
meso
-DAP) biosynthesis with a
Bordetella pertussis
gene library resulted in the isolation of a putative
dap
operon containing three open reading frames (ORFs). In line with the successful complementation of the
E. coli dapD
and
dapE
mutants, the deduced amino acid sequences of two ORFs revealed significant sequence similarities with the DapD and DapE proteins of
E. coli
and many other bacteria which exhibit tetrahydrodipicolinate succinylase and
N
-succinyl-
l,l
-DAP desuccinylase activity, respectively. The first ORF within the operon showed significant sequence similarities with transaminases and contains the characteristic pyridoxal-5′-phosphate binding motif. Enzymatic studies revealed that this ORF encodes a protein with
N
-succinyl-
l,l
-DAP aminotransferase activity converting
N
-succinyl-2-amino-6-ketopimelate, the product of the succinylase DapD, to
N
-succinyl-
l,l
-DAP, the substrate of the desuccinylase DapE. Therefore, this gene appears to encode the DapC protein of
B. pertussis
. Apart from the pyridoxal-5′-phosphate binding motif, the DapC protein does not show further amino acid sequence similarities with the only other known enzyme with
N
-succinyl-
l,l
-DAP aminotransferase activity, ArgD of
E. coli
.
Physical Morphology and Surface Properties of Unsaturated
Pseudomonas putida
Biofilms
Authors: Auerbach Ilene D. , Sorensen Cody , Hansma Helen G. , Holden Patricia A. 
Published: July 2002

ABSTRACT

Unsaturated biofilms of
Pseudomonas putida
, i.e., biofilms grown in humid air, were analyzed by atomic force microscopy to determine surface morphology, roughness, and adhesion forces in the outer and basal cell layers of fresh and desiccated biofilms. Desiccated biofilms were equilibrated with a 75.5% relative humidity atmosphere, which is far below the relative humidity of 98 to 99% at which these biofilms were cultured. In sharp contrast to the effects of drying on biofilms grown in fluid, we observed that drying caused little change in morphology, roughness, or adhesion forces in these unsaturated biofilms. Surface roughness for moist and dry biofilms increased approximately linearly with increasing scan sizes. This indicated that the divides between bacteria contributed more to overall roughness than did extracellular polymeric substances (EPS) on individual bacteria. The EPS formed higher-order structures we termed mesostructures. These mesostructures are much larger than the discrete polymers of glycolipids and proteins that have been previously characterized on the outer surface of these gram-negative bacteria.
Mycobacterium smegmatis
Has Two Pyrazinamidase Enzymes, PncA and PzaA
Authors: Guo Ming , Sun Zhonghe , Zhang Ying 
Published: July 2002

ABSTRACT

The
Mycobacterium smegmatis pncA
gene, encoding nicotinamidase/pyrazinamidase, was identified. While it was similar to counterparts from other mycobacteria, the
M. smegmatis
PncA had little homology to the other
M. smegmatis
pyrazinamidase/nicotinamidase, encoded by the
pzaA
gene. Transformation of
Mycobacterium bovis
strain BCG with
M. smegmatis pncA
or
pzaA
conferred susceptibility to pyrazinamide.
Mapping of the
Cryptococcus neoformans MAT
α Locus: Presence of Mating Type-Specific Mitogen-Activated Protein Kinase Cascade Homologs
Authors: Karos M. , Chang Y. C. , McClelland C. M. , Clarke D. L. , Fu J. , Wickes B. L. , Kwon-Chung K. J. 
Published: July 2002

ABSTRACT

In this study we investigated the relationship between the
MAT
α locus of
Cryptococcus neoformans
and several
MAT
α-specific mitogen-activated protein (MAP) kinase signal transduction cascade genes, including
STE12
α,
STE11
α, and
STE20
α. To resolve the location of the genes, we screened a cosmid library of the
MAT
α strain B-4500 (JEC21), which was chosen for the
C. neoformans
genome project. We isolated several overlapping cosmids spanning a region of about 71 kb covering the entire
MAT
α locus. It was found that
STE12
α,
STE11
α, and
STE20
α are imbedded within the locus rather than closely linked to the locus. Furthermore, three copies of
MF
α, the mating type α-pheromone gene, a
MAT
α-specific myosin gene, and a pheromone receptor (
CPR
α) were identified within the locus. We created a physical map, based on the restriction enzyme
Bam
HI, and identified both borders of the
MAT
α locus. The
MAT
α locus of
C. neoformans
is approximately 50 kb in size and is one of the largest mating type loci reported among fungi with a one-locus, two-allele mating system.
Measuring Virulence Factor Expression by the Pathogenic Bacterium
Photorhabdus luminescens
in Culture and during Insect Infection
Authors: Daborn Phillip J. , Waterfield Nicholas , Blight Mark A. , Ffrench-Constant Richard H. 
Published: July 2002

ABSTRACT

During insect infection
Photorhabdus luminescens
emits light and expresses virulence factors, including insecticidal toxin complexes (Tcs) and an RTX-like metalloprotease (Prt). Using quantitative PCR and protein assays, we describe the expression patterns of these factors both in culture and during insect infection and compare them to the associated bacterial growth curves. In culture, light and active Prt protease are produced in stationary phase. Tca also appears in stationary phase, whereas Tcd is expressed earlier. These patterns seen in a culture flask are strikingly similar to those observed during insect infection. Thus, in an infected insect, bacteria grow exponentially until the time of insect death at ≈48 h, when both light and the virulence factors Prt protease and Tca are produced. In contrast, Tcd appears much earlier in insect infection. However, at present, the biological significance of this difference in timing of the production of the two toxins in unclear. This is the first documentation of the expression of Tcs and Prt in an insect and highlights the malleability of
Photorhabdus
as a model system for bacterial infection.