bluuebunny/crossref_metadata_2025_split huggingface dataset:
Macrophage Migration Inhibitory Factor Plays a Critical Role in Mediating Protection against the Helminth ParasiteTaenia crassiceps
Authors: Rodríguez-Sosa Miriam , Rosas Lucia E. , David John R. , Bojalil Rafael , Satoskar Abhay R. , Terrazas Luis I. 
Published: February 2003

ABSTRACTTo determine the role of endogenous migration inhibitory factor (MIF) in regulation of immune response during murine cysticercosis caused by the helminth parasiteTaenia crassiceps, we analyzed the course ofT. crassicepsinfection in MIF−/−BALB/c mice. MIF−/−mice were highly susceptible toT. crassicepsand developed significantly higher parasite loads compared to similarly infected MIF+/+mice. Throughout the course of infection,Taenia crassicepssoluble antigen-stimulated spleen cells from both MIF+/+and MIF−/−mice produced significant and comparable levels of interleukin-4 (IL-4), but those from MIF−/−mice produced significantly more IL-13, as well as gamma interferon (IFN-γ), suggesting that the susceptibility of MIF−/−mice toT. crassicepswas not due to the lack of IFN-γ production. Interestingly, low levels of both total and specific immunoglobulin G2a were observed in MIF−/−cysticercotic mice despite the high IFN-γ levels; in addition, peritoneal macrophages obtained fromT. crassiceps-infected MIF−/−mice at different time points failed to respond efficiently to stimulation in vitro with lipopolysaccharide plus IFN-γ and produced significantly lower levels of IL-12, tumor necrosis factor alpha, and NO compared to those from MIF+/+mice. These findings demonstrate that MIF plays a critical role in mediating protection againstT. crassicepsin vivo. Moreover, these findings also suggest that impaired macrophage function rather than the lack of Th1 development may be responsible for mediating susceptibility toT. crassiceps.
Structural Characterization of the N Terminus of IpaC from
Shigella flexneri
Authors: Harrington Amanda T. , Hearn Patricia D. , Picking Wendy L. , Barker Jeffrey R. , Wessel Andrew , Picking William D. 
Published: February 2003

ABSTRACT

The primary effector for
Shigella
invasion of epithelial cells is IpaC, which is secreted via a type III secretion system. We recently reported that the IpaC N terminus is required for type III secretion and possibly other functions. In this study, mutagenesis was used to identify an N-terminal secretion signal and to determine the functional importance of the rest of the IpaC N terminus. The 15 N-terminal amino acids target IpaC for secretion by
Shigella flexneri,
and placing additional amino acids at the N terminus does not interfere with IpaC secretion. Furthermore, amino acid sequences with no relationship to the native IpaC secretion signal can also direct its secretion. Deletions introduced beyond amino acid 20 have no effect on secretion and do not adversely affect IpaC function in vivo until they extend beyond residue 50, at which point invasion function is completely eliminated. Deletions introduced at amino acid 100 and extending toward the N terminus reduce IpaC's invasion function but do not eliminate it until they extend to the N-terminal side of residue 80, indicating that a region from amino acid 50 to 80 is critical for IpaC invasion function. To explore this further, the ability of an IpaC N-terminal peptide to associate in vitro with its translocon partner IpaB and its chaperone IpgC was studied. The N-terminal peptide binds tightly to IpaB, but the IpaC central hydrophobic region also appears to participate in this binding. The N-terminal peptide also associates with the chaperone IpgC and IpaB is competitive for this interaction. Based on additional biophysical data, we propose that a region between amino acids 50 and 80 is required for chaperone binding, and that the IpaB binding domain is located downstream from, and possibly overlapping, this region. From these data, we propose that the secretion signal, chaperone binding region, and IpaB binding domain are located at the IpaC N terminus and are essential for presentation of IpaC to host cells during bacterial entry; however, IpaC effector activity may be located elsewhere.
Phenotypic Switching in
Mycoplasma gallisepticum
Hemadsorption Is Governed by a High-Frequency, Reversible Point Mutation
Authors: Winner Florian , Markovà Ivana , Much Peter , Lugmair Albin , Siebert-Gulle Karin , Vogl Gunther , Rosengarten Renate , Citti Christine 
Published: February 2003

ABSTRACT

Mycoplasma gallisepticum
is a flask-shaped organism that commonly induces chronic respiratory disease in chickens and infectious sinusitis in turkeys. Phenotypic switching in
M. gallisepticum
hemadsorption (HA) was found to correlate with phase variation of the GapA cytadhesin concurrently with that of the CrmA protein, which exhibits cytadhesin-related features and is encoded by a gene located downstream of the
gapA
gene as part of the same transcription unit. In clones derived from strain R
low
, detailed genetic analyses further revealed that on-off switching in GapA expression is governed by a reversible base substitution occurring at the beginning of the
gapA
structural gene. In HA
−
variants, this event generates a stop codon that results in the premature termination of GapA translation and consequently affects the expression of CrmA. Sequences flanking the mutation spot do not feature any repeated motifs that could account for error-prone mutation via DNA slippage and the exact mechanism underlying this high-frequency mutational event remains to be elucidated. An HA
−
mutant deficient in producing CrmA, mHAD3, was obtained by disrupting the
crmA
gene by using transposition mutagenesis. Despite a fully functional
gapA
gene, the amount of GapA detected in this mutant was considerably lower than in HA
+
clonal variants, suggesting that, in absence of CrmA, GapA might be subjected to a higher turnover.
A Surface Amebic Cysteine Proteinase Inactivates Interleukin-18
Authors: Que Xuchu , Kim Soo-Hyun , Sajid Mohammed , Eckmann Lars , Dinarello Charles A. , McKerrow James H. , Reed Sharon L. 
Published: February 2003

ABSTRACTAmebiasis is a major cause of morbidity and mortality worldwide. Invasion byEntamoeba histolyticatrophozoites causes secretion of proinflammatory cytokines from host epithelial cells, leading to a local acute inflammatory response, followed by lysis of colonic cells. Extracellular cysteine proteinases from amebic trophozoites are key virulence factors and have a number of important interactions with host defenses, including cleavage of immunoglobulin G (IgG), IgA, and complement components C3 and C5. Amebic lysates have also been shown to activate the precursor to interleukin 1-beta (proIL-1β), mimicking the action of caspase-1. IL-18 is also a central cytokine, which induces gamma interferon (IFN-γ) and activates macrophages, one of the main host defenses against invading trophozoites. Because proIL-18 is also activated by caspase-1, we evaluated whether amebic proteinases had a similar effect. Instead, we found that recombinant proIL-18 was cleaved into smaller fragments by the complex of surface-associated and released amebic proteinases. To evaluate the function of an individual proteinase from the complex pool, we expressed an active surface proteinase, EhCP5, which is functional only inE. histolytica.Recombinant EhCP5 expressed inPichia pastorishad kinetic properties similar to those of the native enzyme with respect to substrate specificity and sensitivity to proteinase inhibitors. In contrast to the activation of proIL-1β by amebic lysates, the purified proteinase cleaved proIL-18 and mature IL-18 to biologically inactive fragments. These studies suggest that the acute host response and amebic invasion result from a complex interplay of parasite virulence factors and host defenses.E. histolyticamay block the host inflammatory response by a novel mechanism, inactivation of IL-18.
Intrapulmonary Expression of Macrophage Inflammatory Protein 1α (CCL3) Induces Neutrophil and NK Cell Accumulation and Stimulates Innate Immunity in Murine Bacterial Pneumonia
Authors: Zeng Xianying , Moore Thomas A. , Newstead Michael W. , Hernandez-Alcoceba Ruben , Tsai Wan C. , Standiford Theodore J. 
Published: February 2003

ABSTRACTMacrophage inflammatory protein 1α (MIP-1α) (CCL3) is an important mediator of leukocyte recruitment and activation in a variety of inflammatory states, including infection. A recombinant human type 5 adenovirus containing the murine MIP-1α cDNA (AdMIP-1α) was constructed to determine the effect of transient intrapulmonary expression of MIP-1α on leukocyte recruitment, activation, and bacterial clearance in a murine model ofKlebsiella pneumoniaepneumonia. The intratracheal administration of AdMIP-1α resulted in both time- and dose-dependent expression of MIP-1α mRNA and protein within the lung. Importantly, the intrapulmonary overexpression of MIP-1α resulted in a maximal 35- and 100-fold reduction in lung and blood bacterial burden, respectively, in animals cochallenged withK. pneumoniae, which was associated with a significant increase in neutrophil and activated NK cell accumulation. Furthermore, the transgenic expression of MIP-1α during bacterial pneumonia resulted in enhanced expression of gamma interferon mRNA, compared to that observed inKlebsiella-challenged animals pretreated with control vector. These findings indicate an important role for MIP-1α in the recruitment and activation of selected leukocyte populations in vivo and identify this cytokine as a potential immunoadjuvant to be employed in the setting of localized bacterial infection.
Reduced Glutathione Is Required for Pertussis Toxin Secretion by
Bordetella pertussis
Authors: Stenson Trevor H. , Patton Angela K. , Weiss Alison A. 
Published: February 2003

ABSTRACT

The abilities of cysteine-containing compounds to support growth of
Bordetella pertussis
and influence pertussis toxin transcription, assembly, and secretion were examined. Cysteine is an essential amino acid for
B. pertussis
and must be present for protein synthesis and bacterial growth. However, cysteine can be metabolized to sulfate, and high concentrations of sulfate can selectively inhibit transcription of the virulence factors, including pertussis toxin, via the BvgAS two-component regulatory system in a process called modulation. In addition, pertussis toxin possesses several disulfide bonds, and the cysteine-containing compound glutathione can influence oxidation-reduction reactions and perhaps disulfide bond formation. Bacterial growth was not observed in the absence of a source of cysteine. Oxidized glutathione, as a sole source of cysteine, also did not support bacterial growth. Cysteine, cystine, and reduced glutathione did support bacterial growth, and none of these compounds caused modulation at the concentrations tested. Similar amounts of periplasmic pertussis toxin were detected regardless of the source of cysteine; however, in the absence of reduced glutathione, pertussis toxin was not efficiently secreted. Addition of the reducing agent dithiothreitol was unable to compensate for the lack of reduced glutathione and did not promote secretion of pertussis toxin. These results suggest that reduced glutathione does not affect the accumulation of assembled active pertussis toxin in the periplasm but plays a role in efficient pertussis toxin secretion by the bacterium.
Genetic Characterization and Immunogenicity of Coli Surface Antigen 4 from Enterotoxigenic
Escherichia coli
when It Is Expressed in a
Shigella
Live-Vector Strain
Authors: Altboum Zeev , Levine Myron M. , Galen James E. , Barry Eileen M. 
Published: February 2003

ABSTRACT

The genes that encode the enterotoxigenic
Escherichia coli
(ETEC) CS4 fimbriae,
csaA
, -
B
, -
C
, -
E
, and -
D
′, were isolated from strain E11881A. The
csa
operon encodes a 17-kDa major fimbrial subunit (CsaB), a 40-kDa tip-associated protein (CsaE), a 27-kDa chaperone-like protein (CsaA), a 97-kDa usher-like protein (CsaC), and a deleted regulatory protein (CsaD′). The predicted amino acid sequences of the CS4 proteins are highly homologous to structural and assembly proteins of other ETEC fimbriae, including CS1 and CS2, and to CFA/I in particular. The
csaA
, -
B
, -
C
, -
E
operon was cloned on a stabilized plasmid downstream from an osomotically regulated
ompC
promoter. pGA2-CS4 directs production of CS4 fimbriae in both
E
. coli DH5α and
Shigella flexneri
2a vaccine strain CVD 1204, as detected by Western blot analysis and bacterial agglutination with anti-CS4 immune sera. Electron-microscopic examination of
Shigella
expressing CS4 confirmed the presence of fimbriae on the bacterial surface. Guinea pigs immunized with CVD 1204(pGA2-CS4) showed serum and mucosal antibody responses to both the
Shigella
vector and the ETEC fimbria CS4. Among the seven most prevalent fimbrial antigens of human ETEC, CS4 is the last to be cloned and sequenced. These findings pave the way for CS4 to be included in multivalent ETEC vaccines, including an attenuated
Shigella
live-vector-based ETEC vaccine.
Isolation of Acid-Inducible Genes ofMycobacterium tuberculosiswith the Use of Recombinase-Based In Vivo Expression Technology
Authors: Saviola Beatrice , Woolwine Samuel C. , Bishai William R. 
Published: February 2003

ABSTRACTA better understanding of mycobacterial gene regulation under certain stress conditions (e.g., low pH) may provide insight into mechanisms of adaptation during infection. To identify mycobacterial promoters induced at low pH, we adapted the recombinase-based in vivo expression technology (RIVET) promoter trap system for use with mycobacteria. Our results show that the TnpR recombinase of transposon γδ is active inMycobacterium smegmatisandMycobacterium tuberculosis. We developed a method to perform sequential double selection with mycobacteria by using RIVET, with a kanamycin preselection and a sucrose postselection. A library ofM. tuberculosisDNA inserted upstream oftnpRwas created, and using the double selection, we identified two promoters which are upregulated at low pH. The promoter regions drive the expression of a gene encoding a putative lipase,lipF(Rv3487c), as well as a PE-PGRS gene,Rv0834c, in a pH-dependent manner in bothM. smegmatisandM. tuberculosis. The acid inducibility oflipFandRv0834cwas independent of the stress response sigma factor, SigF, as acid induction of the two genes in anM. tuberculosis sigFmutant strain was similar to that in the wild-type strain. No induction oflipForRv0834cwas observed during infection of J774 murine macrophages, an observation which is in agreement with previous reports on the failure of phagosomes containingM. tuberculosisto acidify.
CD40-CD40 Ligand Costimulation Is Not Required for Initiation and Maintenance of a Th1-Type Response toLeishmania majorInfection
Authors: Padigel Udaikumar M. , Farrell Jay P. 
Published: February 2003

ABSTRACTAlthough previous studies demonstrated a requirement for CD40-CD40 ligand (CD40L) interaction in the development of resistance toLeishmaniainfection, we recently showed that mice lacking the gene for CD40L (CD40L−/−mice) can controlLeishmania majorinfection when they are infected with reduced numbers of parasites. In this study, we examine the cytokine pattern in healing versus nonhealing CD40L−/−mice and investigated whether CD40 activation is required for resistance to reinfection. We observed that CD4+cells in healed CD40L−/−mice produce high levels of gamma interferon compared to cells from nonhealing, high-dose-inoculated mice. In addition, we observed a higher frequency of interleukin-12 (IL-12)- producing cells and a reduced number of IL-4-producing cells in mice infected with reduced numbers of parasites. Importantly, we found that healed CD40L−/−mice are highly resistant to reinfection with a large parasite inoculum. In addition, by comparing the cytokine patterns at an early and late stage of infection in nonhealing CD40L−/−mice, we demonstrated that nonhealing CD40L−/−mice produce a weak Th1-type response during the early stage of infection, but this response wanes as a Th2-type response emerges during late stages of infection. Anti-IL-4 antibody treatment, starting either at the beginning of infection or at week 4 postinfection enabled CD40L−/−mice to control a high-dose infection. Together, these results show that CD40-CD40L interaction, although important for IL-12 production in high-dose infections, is not required for either the development or maintenance of resistance in mice infected with reduced numbers of parasites.
Geographical Structure of Diversity and Differences between Symptomatic and Asymptomatic Infections for
Plasmodium falciparum
Vaccine Candidate AMA1
Authors: Cortés Alfred , Mellombo Mata , Mueller Ivo , Benet Ariadna , Reeder John C. , Anders Robin F. 
Published: February 2003

ABSTRACT

Plasmodium falciparum
apical membrane antigen 1 (AMA1) is a prime malaria vaccine candidate. Antigenic diversity within parasite populations is one of the main factors potentially limiting the efficacy of any asexual-stage vaccine, including one based on AMA1. The DNA coding for the most variable region of this antigen, domain I, was sequenced in 168 samples from the Wosera region of Papua New Guinea, including samples from symptomatic and asymptomatic infections. Neutrality tests applied to these sequences provided strong evidence of selective pressure operating on the sequence of
ama1
domain I, consistent with AMA1 being a target of protective immunity. Similarly, a peculiar pattern of geographical diversity and the particular substitutions found were suggestive of strong constraints acting on the evolution of AMA1 at the population level, probably as a result of immune pressure. In addition, a strong imbalance between symptomatic and asymptomatic infections was detected in the frequency of particular residues at certain polymorphic positions, pointing to AMA1 as being one of the determinants of the morbidity associated with a particular strain. The information yielded by this study has implications for the design and assessment of AMA1-based vaccines and provides additional data supporting the importance of AMA1 as a malaria vaccine candidate.
CD14- and Toll-Like Receptor-Dependent Activation of Bladder Epithelial Cells by Lipopolysaccharide and Type 1 PiliatedEscherichia coli
Authors: Schilling Joel D. , Martin Steven M. , Hunstad David A. , Patel Kunal P. , Mulvey Matthew A. , Justice Sheryl S. , Lorenz Robin G. , Hultgren Scott J. 
Published: February 2003

ABSTRACTThe gram-negative bacteriumEscherichia coliis the leading cause of urinary tract infection. The interaction between type 1 piliatedE. coliand bladder epithelial cells leads to the rapid production of inflammatory mediators, such as interleukin-6 (IL-6) and IL-8. Conflicting reports have been published in the literature regarding the mechanism by which uroepithelial cells are activated by type 1 piliatedE. coli. In particular, the role of lipopolysaccharide (LPS) in these responses has been an area of significant debate. Much of the data arguing against LPS-mediated activation of bladder epithelial cells have come from studies using a renal epithelial cell line as an in vitro model of the urinary epithelium. In this report, we analyzed three bladder epithelial cell lines and demonstrated that they all respond to LPS. Furthermore, the LPS responsivity of the cell lines directly correlated with their ability to generate IL-6 afterE. colistimulation. The LPS receptor complex utilized by the bladder epithelial cell lines included CD14 and Toll-like receptors, and signaling involved the activation of NF-κB and p38 mitogen-activated protein kinase. Also, reverse transcription-PCR analysis demonstrated that bladder epithelial cells express CD14 mRNA. Thus, the molecular machinery utilized by bladder epithelial cells for the recognition ofE. coliis very similar to that described for traditional innate immune cells, such as macrophages. In contrast, the A498 renal epithelial cell line did not express CD14, was hyporesponsive to LPS stimulation, and demonstrated poor IL-6 responses toE. coli.
Role of the
Brucella suis
Lipopolysaccharide O Antigen in Phagosomal Genesis and in Inhibition of Phagosome-Lysosome Fusion in Murine Macrophages
Authors: Porte Françoise , Naroeni Aroem , Ouahrani-Bettache Safia , Liautard Jean-Pierre 
Published: February 2003

ABSTRACT

Brucella
species are gram-negative, facultative intracellular bacteria that infect humans and animals. These organisms can survive and replicate within a membrane-bound compartment inside professional and nonprofessional phagocytic cells. Inhibition of phagosome-lysosome fusion has been proposed as a mechanism for intracellular survival in both cell types. However, the molecular mechanisms and the microbial factors involved are poorly understood. Smooth lipopolysaccharide (LPS) of
Brucella
has been reported to be an important virulence factor, although its precise role in pathogenesis is not yet clear. In this study, we show that the LPS O side chain is involved in inhibition of the early fusion between
Brucella suis
-containing phagosomes and lysosomes in murine macrophages. In contrast, the phagosomes containing rough mutants, which fail to express the O antigen, rapidly fuse with lysosomes. In addition, we show that rough mutants do not enter host cells by using lipid rafts, contrary to smooth strains. Thus, we propose that the LPS O chain might be a major factor that governs the early behavior of bacteria inside macrophages.
Lymphoid Follicle-Dense Mucosa at the Terminal Rectum Is the Principal Site of Colonization of Enterohemorrhagic
Escherichia coli
O157:H7 in the Bovine Host
Authors: Naylor Stuart W. , Low J. Christopher , Besser Thomas E. , Mahajan Arvind , Gunn George J. , Pearce Michael C. , McKendrick Iain J. , Smith David G. E. , Gally David L. 
Published: February 2003

ABSTRACT

Escherichia coli
O157:H7 causes bloody diarrhea and potentially fatal systemic sequelae in humans. Cattle are most frequently identified as the primary source of infection, and
E. coli
O157:H7 generally colonizes the gastrointestinal tracts of cattle without causing disease. In this study, persistence and tropism were assessed for four different
E. coli
O157:H7 strains. Experimentally infected calves shed the organism for at least 14 days prior to necropsy. For the majority of these animals, as well as for a naturally colonized animal obtained from a commercial beef farm, the highest numbers of
E. coli
O157:H7 were found in the feces, with negative or significantly lower levels detected in lumen contents taken from the gastrointestinal tract. Detailed examination demonstrated that in these individuals the majority of tissue-associated bacteria were adherent to mucosal epithelium within a defined region extending up to 5 cm proximally from the recto-anal junction. The tissue targeted by
E. coli
O157:H7 was characterized by a high density of lymphoid follicles. Microcolonies of the bacterium were readily detected on the epithelium of this region by immunofluorescence microscopy. As a consequence of this specific distribution,
E. coli
O157:H7 was present predominately on the surface of the fecal stool. In contrast, other
E. coli
serotypes were present at consistent levels throughout the large intestine and were equally distributed in the stool. This is a novel tropism that may enhance dissemination both between animals and from animals to humans. The accessibility of this site may facilitate simple intervention strategies.