bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contribution of Immune Activation to the Pathogenesis and Transmission of Human Immunodeficiency Virus Type 1 Infection
Authors: Lawn Stephen D. , Butera Salvatore T. , Folks Thomas M. 
Published: July 2002

SUMMARYThe life cycle of human immunodeficiency virus type 1 (HIV-1) is intricately related to the activation state of the host cells supporting viral replication. Although cellular activation is essential to mount an effective host immune response to invading pathogens, paradoxically the marked systemic immune activation that accompanies HIV-1 infection in vivo may play an important role in sustaining phenomenal rates of HIV-1 replication in infected persons. Moreover, by inducing CD4+cell loss by apoptosis, immune activation may further be central to the increased rate of CD4+cell turnover and eventual development of CD4+lymphocytopenia. In addition to HIV-1-induced immune activation, exogenous immune stimuli such as opportunistic infections may further impact the rate of HIV-1 replication systemically or at localized anatomical sites. Such stimuli may also lead to genotypic and phenotypic changes in the virus pool. Together, these various immunological effects on the biology of HIV-1 may potentially enhance disease progression in HIV-infected persons and may ultimately outweigh the beneficial aspects of antiviral immune responses. This may be particularly important for those living in developing countries, where there is little or no access to antiretroviral drugs and where frequent exposure to pathogenic organisms sustains a chronically heightened state of immune activation. Moreover, immune activation associated with sexually transmitted diseases, chorioamnionitis, and mastitis may have important local effects on HIV-1 replication that may increase the risk of sexual or mother-to-child transmission of HIV-1. The aim of this paper is to provide a broad review of the interrelationship between immune activation and the immunopathogenesis, transmission, progression, and treatment of HIV-1 infection in vivo.
Molecular Cloning and Analysis of a Putative Siderophore ABC Transporter from
Staphylococcus aureus
Authors: Morrissey Julie A. , Cockayne Alan , Hill Philip J. , Williams Paul 
Published: July 2002

ABSTRACT

From a mass-excised
Staphylococcus aureus
λZapII expression library, we cloned an operon encoding a novel ABC transporter with significant homology to bacterial siderophore transporter systems. The operon encodes four genes designated
sstA
, -
B
, -
C
, and -
D
encoding two putative cytoplasmic membrane proteins (
sstA
and
sstB
), an ATPase (
sstC
), and a membrane-bound 38-kDa lipoprotein (
sstD
). The
sst
operon is preceded by two putative Fur boxes, which indicated that expression of the
sst
operon was likely to be iron dependent. SstD was overexpressed in
Escherichia coli
, purified by Triton X-114 phase partitioning, and used to generate monospecific antisera in rats. Immunoblotting studies located SstD in the membrane fraction of
S. aureus
and showed that expression of the lipoprotein was reduced under iron-rich growth conditions. Triton X-114 partitioning studies on isolated membranes provided additional biochemical evidence that SstD in
S. aureus
is a lipoprotein. Immunoreactive polypeptides of approximately 38 kDa were detected in a wide range of staphylococcal species, but no antigenic homolog was detected in
Bacillus subtilis
. Expression of SstD in vivo was confirmed by immunoblotting studies with
S. aureus
recovered from a rat intraperitoneal chamber implant model. To further define the contribution of SstD in promoting growth of
S. aureus
in vitro and in vivo, we used antisense RNA technology to modulate expression of SstD. Expression of antisense
sstD
RNA in
S. aureus
resulted in a decrease in SstD expression under both iron-rich and iron-restricted growth conditions. However, this reduction in SstD levels did not affect the growth of
S. aureus
in vitro in an iron-limited growth medium or when grown in an intraperitoneal rat chamber implant model in vivo.
Inverse Relation between Disease Severity and Expression of the Streptococcal Cysteine Protease, SpeB, among Clonal M1T1 Isolates Recovered from Invasive Group A Streptococcal Infection Cases
Authors: Kansal Rita G. , McGeer Allison , Low Donald E. , Norrby-Teglund Anna , Kotb Malak 
Published: July 2002

ABSTRACTThe streptococcal cysteine protease (SpeB) is one of the major virulence factors produced by group A streptococci (GAS). In this study we investigated if differences exist in SpeB production by clonally related M1T1 clinical isolates derived from patients with invasive infections. Twenty-nine of these isolates were from nonsevere cases and 48 were from severe cases, including streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis (NF) cases. The expression and amount of the 28-kDa SpeB protein produced were determined by quantitative Western blotting, and protease activity was measured by a fluorescent enzymatic assay. A high degree of variation in SpeB expression was seen among the isolates, and this variation seemed to correlate with the severity and/or clinical manifestation of the invasive infection. The mean amount of 28-kDa SpeB protein and cysteine protease activity produced by isolates from nonsevere cases was significantly higher than that from STSS cases (P= 0.001). This difference was partly due to the fact that 41% of STSS isolates produced little or no SpeB compared to only 14% of isolates recovered in nonsevere cases. Moreover, the cysteine protease activity among those isolates that expressed SpeB was significantly lower for STSS isolates than for isolates from nonsevere cases (P= 0.001). Increased SpeB production was also inversely correlated with intact M protein expression, and inhibition of cysteine protease activity blocked the cleavage of the surface M protein. Together, the data support the existence of both an “on-off” and a posttranslational regulatory mechanism(s) controlling SpeB production, and they suggest that isolates with thespeBgene in the “off” state are more likely to spare the surface M protein and to be isolated from cases of severe rather than nonsevere invasive infection. These findings may have important implications for the role of SpeB in host-pathogen interactions via regulation of the expression of GAS virulence genes and the severity of invasive disease.
A Novel Polymorphism in the Toll-Like Receptor 2 Gene and Its Potential Association with Staphylococcal Infection
Authors: Lorenz Eva , Mira Jean Paul , Cornish Kristyn L. , Arbour Nancy C. , Schwartz David A. 
Published: July 2002

ABSTRACTThe toll-like receptor 2 (TLR2) has gained importance as a major mammalian receptor for lipoproteins derived from the cell wall of a variety of bacteria, such asBorrelia burgdorferi,Treponema pallidum, andMycoplasma fermentans. We were interested in identifying mutations in the TLR2 gene that might prove to be associated with altered susceptibility to septic shock. We performed a mutation screen of the TLR2 gene using single-stranded conformational polymorphism in 110 normal, healthy study subjects and detected an Arg753Gln mutation in three individuals. No other missense mutations were detected in the TLR2 open reading frame. Functional studies demonstrate that the Arg753Gln polymorphism, in comparison to the wild-type TLR2 gene, is significantly less responsive to bacterial peptides derived fromB. burgdorferiandT. pallidum. In a septic shock population, the Arg753Gln TLR2 polymorphism occurred in 2 out of 91 septic patients. More importantly, both of the subjects with the TLR2 Arg753Gln polymorphism had staphylococcal infections. These findings suggest that a mutation in the TLR2 gene may predispose individuals to life-threatening bacterial infections.
Transmission Electron Microscopic Demonstration of Phagocytosis and Intracellular Processing of Segmented Filamentous Bacteria by Intestinal Epithelial Cells of the Chick Ileum
Authors: Yamauchi Koh-En , Snel Johannes 
Published: July 2002

ABSTRACT

Segmented filamentous bacteria (SFB) are autochthonous bacteria colonizing the ileum of many young animals by attaching to intestinal epithelial cells. These nonpathogenic bacteria strongly stimulate the mucosal immune system and induce intestinal epithelial cells to express major histocompatibility complex class II molecules. We tried to discover whether SFB are phagocytized and intracellularly processed by the host cells, which is indicative of antigen processing. The middle part of the ileum was extracted from 10- and 20-day-old broiler chicks (
Gallus gallus domesticus
). Samples were processed and examined by scanning and transmission electron microscopy (SEM and TEM, respectively). In SEM, no, few, medium, and dense SFB colonization levels were classified. In TEM of cells from animals with medium or dense SFB colonization levels, we could observe extracellular particles ranging from those only indenting the cell membrane to particles found in the cytoplasmatic area beyond the terminal web. These particles had a structural similarity with SFB that were floating freely in the intestinal lumen. Furthermore, we observed unlacing of the membrane and septum surrounding the extracellular particles and their incorporation into host cytoplasmatic components, which strongly suggests that these particles are phagocytized and intracellularly processed SFB. This conclusion is supported by TEM analysis of samples with no or few SFB, in which we failed to find these characteristic morphologies. The phagocytosis process described here could be an important trigger for the stimulating effect of SFB on the mucosal immune system.
Intercellular Communication in
Helicobacter pylori
:
luxS
Is Essential for the Production of an Extracellular Signaling Molecule
Authors: Forsyth Mark H. , Cover Timothy L. 
Published: July 2002

ABSTRACT

Individual bacteria of numerous species can communicate and coordinate their actions via the production, release, and detection of extracellular signaling molecules. In this study, we used the
Vibrio harveyi
luminescence bioassay to determine whether
Helicobacter pylori
produces such a factor. Cell-free conditioned media from
H. pylori
strains 60190 and 26695 each induced >100-fold-greater luminescence in
V. harveyi
than did sterile culture medium. The
H. pylori
signaling molecule had a molecular mass of <10 kDa, and its activity was unaffected by heating to 80°C for 5 min or protease treatment. The genome sequence of
H. pylori
26695 does not contain any gene predicted to encode an acyl homoserine lactone synthase but does contain an orthologue of
luxS
, which is required for production of autoinducer-2 (AI-2) in
V. harveyi
. To evaluate the role of
luxS
in
H. pylori
, we constructed
luxS
null mutants derived from
H. pylori
60190 and 26695. Conditioned media from the wild-type
H. pylori
strains induced >100-fold-greater luminescence in the
V. harveyi
bioassay than did conditioned medium from either mutant strain. Production of the signaling molecule was restored in an
H. pylori luxS
null mutant strain by complementation with a single intact copy of
luxS
placed in a heterologous site on the chromosome. In addition,
Escherichia coli
DH5α produced autoinducer activity following the introduction of an intact copy of
luxS
from
H. pylori
. Production of the signaling molecule by
H. pylori
was growth phase dependent, with maximal production occurring in the mid-exponential phase of growth. Transcription of
H. pylori vacA
also was growth phase dependent, but this phenomenon was not dependent on
luxS
activity. These data indicate that
H. pylori
produces an extracellular signaling molecule related to AI-2 from
V. harveyi
. We speculate that this signaling molecule may play a role in regulating
H. pylori
gene expression.
Stimulation ofBordetella pertussisAdenylate Cyclase Toxin Intoxication by Its Hemolysin Domain
Authors: Iwaki Masaaki , Kamachi Kazunari , Konda Toshifumi 
Published: July 2002

ABSTRACTThe internalization of the N-terminal catalytic domain ofBordetella pertussisadenylate cyclase toxin (ACT) across the cytoplasmic membrane has been considered to occur independently from protein-protein interactions which can lead to oligomerization required for hemolytic activity by its C-terminal hemolysin domain. Here we report that when added in excess, this hemolysin domain stimulates the internalization, suggesting the involvement of protein-protein interactions in cell-invasive activity of ACT, as well as its hemolytic activity.
Salmonella enterica
Serovar Pullorum Persists in Splenic Macrophages and in the Reproductive Tract during Persistent, Disease-Free Carriage in Chickens
Authors: Wigley P. , Berchieri A. , Page K. L. , Smith A. L. , Barrow P. A. 
Published: July 2002

ABSTRACT

Salmonella enterica
serovar Pullorum is worldwide a poultry pathogen of considerable economic importance, particularly in those countries with a developing poultry industry. In addition to the characteristic high mortality rates among young chicks, one of the features of
Salmonella
serovar Pullorum infection is that it persists for long periods in convalescent chicks in the absence of clinical disease. This can lead to colonization of the reproductive tract of chickens and at sexual maturity can result in infected progeny through transovarian transmission to eggs. The sites of
Salmonella
serovar Pullorum persistence in convalescent birds are not known, and the mechanisms of persistence are not understood. Here we show that
Salmonella
serovar Pullorum can persist in both the spleen and the reproductive tract for over 40 weeks following experimental infection in chickens. During the period of sexual maturity,
Salmonella
serovar Pullorum colonized both the ovary and the oviduct of hens and led to 6% of laid eggs being infected by
Salmonella
serovar Pullorum. The colonization of several different sites of the reproductive tract suggests that
Salmonella
serovar Pullorum may employ more than one mechanism of egg infection. Persistence occurred despite a strong humoral response, suggesting an intracellular site of infection. By use of a
Salmonella
serovar Pullorum strain containing a plasmid stably expressing green fluorescent protein, we demonstrated that the main site of carriage in the spleen is within macrophages. This raises interesting questions about the biology of
Salmonella
serovar Pullorum, including why there is an increase in bacterial numbers when birds become sexually mature and in particular how
Salmonella
serovar Pullorum avoids clearance by macrophages and whether it modulates the immune system in other ways.
Induction of Monocyte Chemoattractant Protein 1 byHelicobacter pyloriInvolves NF-κB
Authors: Mori Naoki , Ueda Atsuhisa , Geleziunas Romas , Wada Akihiro , Hirayama Toshiya , Yoshimura Teizo , Yamamoto Naoki 
Published: July 2002

ABSTRACTHelicobacter pyloristimulates secretion of monocyte chemoattractant protein 1 (MCP-1) from gastric epithelial cells. Secretion of this chemokine may be instrumental in monocyte infiltration of the gastric epithelium that characterizesH. pylorigastritis. The aim of this study was to identify the mechanism by whichH. pyloriinduces MCP-1 production. Induction of MCP-1 mRNA was assessed by reverse transcription-PCR. We used luciferase reporter assays to monitor activation of the MCP-1 gene promoter and electrophoretic mobility shift assays to explore binding of transcription factors to this promoter.H. pyloriinfection increased MCP-1 mRNA expression from gastric epithelial cells. Induction of MCP-1 mRNA relies on an intactcagpathogenicity island. We identified two closely spaced NF-κB-binding sites within the MCP-1 distal enhancer as required forH. pylori-induced MCP-1 gene transcription.H. pyloriinfection led to the specific activation of NF-κB complexes containing p50 and p65. Kinase-deficient mutants of NF-κB-inducing kinase (NIK) and IκB kinases (IKK) caused suppression of MCP-1 distal enhancer-dependent reporter activity followingH. pyloriinfection.H. pyloriinfection induces the activation of NF-κB via the NIK-IKK signaling complex, leading to MCP-1 gene transcription in gastric epithelial cells.
A Mutation in the
Corynebacterium glutamicum ltsA
Gene Causes Susceptibility to Lysozyme, Temperature-Sensitive Growth, and
l
-Glutamate Production
Authors: Hirasawa Takashi , Wachi Masaaki , Nagai Kazuo 
Published: July 2002

ABSTRACT

The
Corynebacterium glutamicum
mutant KY9714, originally isolated as a lysozyme-sensitive mutant, does not grow at 37°C. Complementation tests and DNA sequencing analysis revealed that a mutation in a single gene of 1,920 bp,
ltsA
(lysozyme and temperature sensitive), was responsible for its lysozyme sensitivity and temperature sensitivity. The
ltsA
gene encodes a protein homologous to the glutamine-dependent asparagine synthetases of various organisms, but it could not rescue the asparagine auxotrophy of an
Escherichia coli asnA asnB
double mutant. Replacement of the N-terminal Cys residue (which is conserved in glutamine-dependent amidotransferases and is essential for enzyme activity) by an Ala residue resulted in the loss of complementation in
C. glutamicum
. The mutant
ltsA
gene has an amber mutation, and the disruption of the
ltsA
gene caused lysozyme and temperature sensitivity similar to that in the KY9714 mutant.
l
-Glutamate production was induced by elevating growth temperature in the disruptant. These results indicate that the
ltsA
gene encodes a novel glutamine-dependent amidotransferase that is involved in the mechanisms of formation of rigid cell wall structure and in the
l
-glutamate production of
C. glutamicum
.
The
HTR1
Gene Is a Dominant Negative Mutant Allele of
MTH1
and Blocks Snf3- and Rgt2-Dependent Glucose Signaling in Yeast
Authors: Schulte Frank , Wieczorke Roman , Hollenberg Cornelis P. , Boles Eckhard 
Published: July 2002

ABSTRACT

Saccharomyces cerevisiae HTR1
mutants are severely impaired in the uptake of glucose. We have cloned dominant
HTR1
mutant alleles and show that they encode mutant forms of the Mth1 protein. Mth1 is shown to be involved in carbon source-dependent regulation of its own, invertase and hexose transporter gene expression. The mutant forms block the transduction of the Snf3- and Rgt2-mediated glucose signals upstream of the Rgt1 transcriptional regulator.
Disruption of
aldA
Influences the Developmental Process in
Myxococcus xanthus
Authors: Ward Mandy J. , Lew Helen , Zusman David R. 
Published: July 2002

ABSTRACT

Previously, we identified a gene (
aldA
) from
Myxococcus xanthus
, which we suggested encoded the enzyme alanine dehydrogenase on the basis of similarity to known Ald protein sequences (M. J. Ward, H. Lew, A. Treuner-Lange, and D. R. Zusman, J. Bacteriol. 180:5668–5675, 1998). In this study, we have confirmed that
aldA
does encode a functional alanine dehydrogenase, since it catalyzes the reversible conversion of alanine to pyruvate and ammonia. Whereas an
aldA
gene disruption mutation did not significantly influence the rate of growth or spreading on a rich medium, AldA was required for growth on a minimal medium containing
l
-alanine as the major source of carbon. Under developmental conditions, the
aldA
mutation caused delayed aggregation in both wild-type (DZ2) and FB (DZF1) strains. Poorly formed aggregates and reduced levels of spores were apparent in the DZ2
aldA
mutant, even after prolonged development.
A Second [2Fe-2S] Ferredoxin from
Sphingomonas
sp. Strain RW1 Can Function as an Electron Donor for the Dioxin Dioxygenase
Authors: Armengaud Jean , Gaillard Jacques , Timmis Kenneth N. 
Published: July 2002

ABSTRACT

The first step in the degradation of dibenzofuran and dibenzo-
p
-dioxin by
Sphingomonas
sp. strain RW1 is carried out by dioxin dioxygenase (DxnA1A2), a ring-dihydroxylating enzyme. An open reading frame (
fdx3
) that could potentially specify a new ferredoxin has been identified downstream of
dxnA1A2
, a two-cistron gene (J. Armengaud, B. Happe, and K. N. Timmis, J. Bacteriol. 180:3954–3966, 1998). In the present study, we report a biochemical analysis of Fdx3 produced in
Escherichia coli
. This third ferredoxin thus far identified in
Sphingomonas
sp. strain RW1 contained a putidaredoxin-type [2Fe-2S] cluster which was characterized by UV-visible absorption spectrophotometry and electron paramagnetic resonance spectroscopy. The midpoint redox potential of this ferredoxin (E′
0
= −247 ± 10 mV versus normal hydrogen electrode at pH 8.0) is similar to that exhibited by Fdx1 (−245 mV), a homologous ferredoxin previously characterized in
Sphingomonas
sp. strain RW1. In in vitro assays, Fdx3 can be reduced by RedA2 (a reductase similar to class I cytochrome P-450 reductases), previously isolated from
Sphingomonas
sp. strain RW1. RedA2 exhibits a

K
m

value of 3.2 ± 0.3 μM for Fdx3. In vivo coexpression of
fdx3
and
redA2
with
dxnA1A2
confirmed that Fdx3 can serve as an electron donor for the dioxin dioxygenase.
Azotobacter vinelandii
Aldehyde Dehydrogenase Regulated by ς
54
: Role in Alcohol Catabolism and Encystment
Authors: Gama-Castro Socorro , Núñez Cinthia , Segura Daniel , Moreno Soledad , Guzmán Josefina , Espı́n Guadalupe 
Published: July 2002

ABSTRACT

Encystment in
Azotobacter vinelandii
is induced by
n
-butanol or β-hydroxybutyrate (BHB). We identified a gene, encoding an aldehyde dehydrogenase, that was named
aldA
. An
aldA
mutation impaired bacterial growth on
n
-butanol, ethanol, or hexanol as the sole carbon source. Expression of
aldA
increased in cells shifted from sucrose to
n
-butanol and was shown to be dependent on the alternative ς
54
factor. A mutation in
rpoN
encoding the ς
54
factor also impaired growth on alcohols. Encystment on
n
-butanol, but not on BHB, was impaired in
aldA
or
rpoN
mutants, indicating that
n
-butanol is not an inducer of encystment by itself but must be catabolized in order to induce encystment.
The Alternative Electron Acceptor Tetrathionate Supports B
12
-Dependent Anaerobic Growth of
Salmonella enterica
Serovar Typhimurium on Ethanolamine or 1,2-Propanediol
Authors: Price-Carter Marian , Tingey Justin , Bobik Thomas A. , Roth John R. 
Published: July 2002

ABSTRACT

Synthesis of cobalamin de novo by
Salmonella enterica
serovar Typhimurium strain LT2 and the absence of this ability in
Escherichia coli
present several problems. This large synthetic pathway is shared by virtually all salmonellae and must be maintained by selection, yet no conditions are known under which growth depends on endogenous B
12
. The cofactor is required for degradation of 1,2-propanediol and ethanolamine. However, cofactor synthesis occurs only anaerobically, and neither of these carbon sources supports anaerobic growth with any of the alternative electron acceptors tested thus far. This paradox is resolved by the electron acceptor tetrathionate, which allows
Salmonella
to grow anaerobically on ethanolamine or 1,2-propanediol by using endogenously synthesized B
12
. Tetrathionate provides the only known conditions under which simple
cob
mutants (unable to make B
12
) show a growth defect. Genes involved in this metabolism include the
ttr
operon, which encodes tetrathionate reductase. This operon is globally regulated by OxrA (Fnr) and induced anaerobically by a two-component system in response to tetrathionate.
Salmonella
reduces tetrathionate to thiosulfate, which it can further reduce to H
2
S, by using enzymes encoded by the genes
phs
and
asr
. The genes for 1,2-propanediol degradation (
pdu
) and B
12
synthesis (
cob
), along with the genes for sulfur reduction (
ttr
,
phs,
and
asr
), constitute more than 1% of the
Salmonella
genome and are all absent from
E. coli
. In diverging from
E. coli
,
Salmonella
acquired some of these genes unilaterally and maintained others that are ancestral but have been lost from the
E. coli
lineage.