bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early Nonspecific Immune Responses and Immunity to Blood-Stage NonlethalPlasmodium yoeliiMalaria
Authors: Choudhury Hasib R. , Sheikh Nadeem A. , Bancroft Gregory J. , Katz David R. , de Souza J. Brian 
Published: July 2002

ABSTRACTThe early role of natural killer cells and gamma delta T cells in the development of protective immunity to the blood stage of nonlethalPlasmodium yoeliiinfection was studied. Splenic cytokine levels were measured 24 h after infection of natural killer cell-depleted immunodeficient and littermate mice or transiently T-cell-depleted normal mice. Splenic gamma interferon levels were significantly increased above background in immunodeficient and littermate mice 24 h after infection. Depletion of natural killer cells resulted in markedly depressed gamma interferon levels and poor control of parasitemia, particularly in severe combined immunodeficient mice. In the littermates, gamma interferon levels were partially reduced, but parasitemias were resolved normally. However, in athymic mice, natural killer cell depletion had no effect on gamma interferon production. Levels of tumor necrosis factor alpha were increased in all animals 24 h after infection, and responses were not affected by natural killer cell depletion. However, in T-cell-depleted animals, both gamma interferon and tumor necrosis factor alpha levels were decreased 24 h after infection, and depleted mice were unable to control their parasitemia. These results suggest that the early production of both cytokines is important in the early control of parasitemia and that both natural killer and gamma delta T cells contribute equally towards their production. The data also suggest that the subsequent resolution of infection requires early production of gamma interferon, which might act by switching on the appropriate T-helper-cell subsets and other essential parasitotoxic effector mechanisms.
Antigenic Variation ofAnaplasma marginaleby Expression of MSP2 Mosaics
Authors: Barbet Anthony F. , Lundgren Anna , Yi Jooyoung , Rurangirwa Fred R. , Palmer Guy H. 
Published: July 2002

ABSTRACTAnaplasma marginaleis a tick-borne pathogen, one of several closely related ehrlichial organisms that cause disease in animals and humans. TheseEhrlichiaspecies have complex life cycles that require, in addition to replication and development within the tick vector, evasion of the immune system in order to persist in the mammalian reservoir host. This complexity requires efficient use of the small ehrlichial genome.A. marginaleand related ehrlichiae express immunoprotective, variable outer membrane proteins that have similar structures and are encoded by polymorphic multigene families. We show here that the major outer membrane protein ofA. marginale, MSP2, is encoded on a polycistronic mRNA. The genomic expression site for this mRNA is polymorphic and encodes numerous amino acid sequence variants in bloodstream populations ofA. marginale. A potential mechanism for persistence is segmental gene conversion of the expression site to link hypervariablemsp2sequences to the promoter and polycistron.
Genetic and Functional Analysis of a PmrA-PmrB-Regulated Locus Necessary for Lipopolysaccharide Modification, Antimicrobial Peptide Resistance, and Oral Virulence of
Salmonella enterica
Serovar Typhimurium
Authors: Gunn John S. , Ryan Sara S. , Van Velkinburgh Jennifer C. , Ernst Robert K. , Miller Samuel I. 
Published: July 2002

ABSTRACT

The two-component regulatory system PmrA-PmrB confers resistance of
Salmonella
spp. to cationic antimicrobial peptides (AP) such as polymyxin (PM), bactericidal/permeability-increasing protein, and azurocidin. This resistance occurs by transcriptional activation of two loci termed
pmrE
and
pmrHFIJKLM
. Both
pmrE
and
pmrHFIJKLM
produce products required for the biosynthesis of lipid A with 4-aminoarabinose (Ara4N). Ara4N addition creates a more positively charged lipopolysaccharide (LPS) and thus reduces cationic AP binding. Experiments were conducted to further analyze the regulation of the
pmrHFIJKLM
operon and the role of this operon and the surrounding genomic region in LPS modification and antimicrobial peptide resistance. The
pmrHFIJKLM
genes are cotranscribed and over 3,000-fold regulated by PmrA-PmrB. The
pmrHFIJKLM
promoter bound PmrA, as determined by gel shift analysis, as did a 40-bp region of the PmrA-PmrB-regulated
pmrCAB
promoter. Construction of nonpolar mutations in the
pmrHFIJKLM
genes showed that all except
pmrM
were necessary for the Ara4N addition to lipid A and PM resistance. The flanking genes of the operon (
pmrG
and
pmrD
) were not necessary for PM resistance, but
pmrD
was shown to be regulated by the PhoP-PhoQ regulatory system. BALB/c mice inoculated with
pmrA
and
pmrHFIJKLM
mutant strains demonstrated virulence attenuation when the strains were administered orally but not when they were administered intraperitoneally, indicating that Ara4N addition may be important for resistance to host innate defenses within intestinal tissues.
Bacteroides fragilisNCTC9343 Produces at Least Three Distinct Capsular Polysaccharides: Cloning, Characterization, and Reassignment of Polysaccharide B and C Biosynthesis Loci
Authors: Coyne Michael J. , Kalka-Moll Wiltrud , Tzianabos Arthur O. , Kasper Dennis L. , Comstock Laurie E. 
Published: July 2002

ABSTRACTBacteroides fragilisproduces a capsular polysaccharide complex (CPC) that is directly involved in its ability to induce abscesses. Two distinct capsular polysaccharides, polysaccharide A (PS A) and PS B, have been shown to be synthesized by the prototype strain for the study of abscesses, NCTC9343. Both of these polysaccharides in purified form induce abscesses in animal models. In this study, we demonstrate that the CPC of NCTC9343 is composed of at least three distinct capsular polysaccharides: PS A, PS B, and PS C. A previously described locus contains genes whose products are involved in the biosynthesis of PS C rather than PS B as was originally suggested. The actual PS B biosynthesis locus was cloned, sequenced, and found to contain 22 genes in an operon-type structure. A mutant with a large chromosomal deletion of the PS B biosynthesis locus was created so that the contribution of PS B to the formation of abscesses could be assessed in a rodent model. Although purified PS B can induce abscesses, removal of this polysaccharide does not attenuate the organism's ability to induce abscesses.
A Protective Glycosylphosphatidylinositol-Anchored Membrane Protein ofPlasmodium yoeliiTrophozoites and Merozoites Contains Two Epidermal Growth Factor-Like Domains
Authors: Burns James M. , Belk Carla C. , Dunn Patricia D. 
Published: July 2002

ABSTRACTUsing sera from mice immunized and protected againstPlasmodium yoeliimalaria, we identified a novel blood-stage antigen gene,pypag-2. The 2.1-kbpypag-2cDNA contains a single open reading frame that encodes a 409-amino-acid protein with a predicted molecular mass of 46.8 kDa. Unlike many characterized plasmodial antigens, blocks of tandemly repeated amino acids are lacking in the pypAg-2 protein sequence. Recombinant pypAg-2, comprising the full-length protein minus the predicted N-terminal signal and C-terminal anchor sequences, was produced and used to raise a high-titer polyclonal rabbit antiserum. This antiserum was used to identify and characterize the native protein through immunoblotting, immunoprecipitation and immunofluorescence assays. Consistent with the presence of a glycosylphosphatidylinositol anchor, pypAg-2 fractionated with the detergent phase of Triton X-114-solubilized proteins and could be metabolically labeled with [3H]palmitic acid. By immunofluorescence, pypAg-2 expression was localized to both the trophozoite and merozoite membranes. Similar toPlasmodium falciparummerozoite surface protein 1, pypAg-2 contains two C-terminal epidermal growth factor (EGF)-like domains. Most importantly, immunization with recombinant pypAg-2 protected mice against lethalP. yoeliimalaria. Thus, pypAg-2 is a target of protective immune responses and represents a novel addition to the family of merozoite surface proteins that contain one or more EGF-like domains.
Augmentation of Nitric Oxide Production by Gamma Interferon in a Mouse Vascular Endothelial Cell Line and Its Modulation by Tumor Necrosis Factor Alpha and Lipopolysaccharide
Authors: Morikawa Akiko , Koide Naoki , Kato Yutaka , Sugiyama Tsuyoshi , Chakravortty Dipshikha , Yoshida Tomoaki , Yokochi Takashi 
Published: July 2002

ABSTRACTThe effect of gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), and lipopolysaccharide (LPS) on nitric oxide (NO) production in the mouse vascular aortic endothelial cell line END-D was examined. LPS, TNF-α, and a low concentration of IFN-γ inhibited NO production in END-D cells, while a high concentration of IFN-γ definitely enhanced it. The NO production induced by a high concentration of IFN-γ was further augmented by using IFN-γ in combination with LPS or TNF-α. In sequential incubations of LPS and IFN-γ, the enhancement of NO production required prior treatment with IFN-γ. Stimulation of END-D cells with a high concentration of IFN-γ led to the expression of inducible NO synthase (iNOS). The augmentation of NO production by IFN-γ alone or in combination with LPS or TNF-α was completely blocked by several inhibitors of iNOS. It was strongly suggested that a high concentration of IFN-γ itself enhanced NO production in END-D cells through inducing the expression of iNOS. LPS and TNF-α exclusively modulated the activity of iNOS once its expression was triggered by IFN-γ. On the other hand, a low concentration of IFN-γ, LPS, and TNF-α reduced NO production through down-regulating constitutive NOS (cNOS). The differential regulation of cNOS- and iNOS-mediated NO production by IFN-γ, TNF-α, and LPS is discussed.
Lack of CD4+T Cells Does Not Affect Induction of CD8+T-Cell Immunity againstEncephalitozoon cuniculiInfection
Authors: Moretto Magali , Casciotti Lori , Durell Brigit , Khan Imtiaz A. 
Published: July 2002

ABSTRACTCell-mediated immunity has been reported to play an important role in defense againstEncephalitozoon cuniculiinfection. Previous studies from our laboratory have underlined the importance of cytotoxic CD8+T lymphocytes (CTL) in survival of mice infected withE. cuniculi. In the present study, immune response againstE. cuniculiinfection in CD4+T-cell-deficient mice was evaluated. Similar to resistant wild-type animals, CD4−/−mice were able to resolveE. cuniculiinfection even at a very high challenge dose (5 × 107spores/mouse). Tissues from infected CD4−/−mice did not exhibit higher parasite loads in comparison to the parental wild-type mice. Conversely, at day 21 postinfection, susceptible CD8−/−mice had 1014times more parasites in the liver compared to control wild-type mice. Induction of the CD8+T-cell response in CD4−/−mice againstE. cuniculiinfection was studied. Interestingly, a normal antigen-specific CD8+T-cell response toE. cuniculiinfection was observed in CD4−/−mice (precursor proliferation frequency, 1/2.5 × 104versus 1/104in wild-type controls). Lack of CD4+T cells did not alter the magnitude of the antigen-specific CTL response (precursor CTL frequency; 1/1.4 × 104in CD4−/−mice versus 1/3 × 104in control mice). Adoptive transfer of immune CD8+T cells from both CD4−/−and wild-type animals prevented the mortality in CD8−/−mice.E. cuniculiinfection thus offers an example of an intracellular parasitic infection where CD8+T-cell immunity can be induced in the absence of CD4+T cells.
Suppression of Gamma Interferon Transcription and Production by Nematode Excretory-Secretory Antigen during Polyclonal Stimulation of Rat Lymph Node T Cells
Authors: Uchikawa Ryuichi , Matsuda Shinji , Arizono Naoki 
Published: July 2002

ABSTRACTAlthough certain helminth infections preferentially induce type 2 T-cell responses, the immunological mechanisms responsible for type 2 T-cell polarization remain unclear. In the present study, we investigated the effects of excretory-secretory (ES) antigen from the nematodeNippostrongylus brasiliensison cytokine production by mesenteric lymph node (MLN) cells isolated from naive rats. MLN cells produced considerable levels of gamma interferon (IFN-γ) during a 72-h stimulation with concanavalin A (ConA) or with immobilized anti-CD3 plus soluble anti-CD28 antibodies (anti-CD3/CD28). With either stimulation, 10 μg of ES antigen per ml significantly suppressed IFN-γ and interleukin-2 (IL-2) production without cytotoxic activity. The copresence of anti-IL-4, anti-IL-10, or transforming growth factor β (TGF-β) blocking antibodies did not alter the suppressive effect of ES antigen on IFN-γ production. ES antigen did not affect IL-10 production. Kinetic studies of the effect of ES antigen indicated that the antigen suppressed even ongoing IFN-γ production. Reverse transcription-PCR study showed that in the presence of ES antigen, IFN-γ mRNA expression by MLN cells was suppressed 6 and 12 h after ConA or anti-CD3/CD28 stimulation. ES antigen also significantly suppressed IFN-γ production by purified CD4+or CD8+T cells during anti-CD3/CD28 stimulation but did not affect IL-4 production by CD4+T cells. These findings suggested that the nematode antigen suppressed production of IFN-γ and IL-2 but not IL-4 or IL-10 production. ES antigen-mediated suppression of IFN-γ during the initiation of the immune response may provide a microenvironment that helps generation of type 2 T cells.
Human Neutrophil-Mediated Nonoxidative Antifungal Activity againstCryptococcus neoformans
Authors: Mambula Salamatu S. , Simons Elizabeth R. , Hastey Ryan , Selsted Michael E. , Levitz Stuart M. 
Published: July 2002

ABSTRACTIt has long been appreciated that polymorphonuclear leukocytes (PMN) killCryptococcus neoformans, at least in part via generation of fungicidal oxidants. The aim of this study was to examine the contribution of nonoxidative mechanisms to the inhibition and killing ofC. neoformans. Treatment of human PMN with inhibitors and scavengers of respiratory burst oxidants only partially reversed anticryptococcal activity, suggesting that both oxidative and nonoxidative mechanisms were operative. To define the mediators of nonoxidative anticryptococcal activity, PMN were fractionated into cytoplasmic, primary (azurophil) granule, and secondary (specific) granule fractions. Incubation ofC. neoformanswith these fractions for 18 h resulted in percents inhibition of growth of 67.4 ± 3.4, 84.6 ± 4.4, and 29.2 ± 10.5 (mean ± standard error,n= 3), respectively. Anticryptococcal activity of the cytoplasmic fraction was abrogated by zinc and depletion of calprotectin. Antifungal activity of the primary granules was significantly reduced by pronase treatment, boiling, high ionic strength, and magnesium but not calcium. Fractionation of the primary granules by reverse phase high-pressure liquid chromatography on a C4column over an acetonitrile gradient revealed multiple peaks with anticryptococcal activity. Of these, peaks 1 and 6 had substantial fungistatic and fungicidal activity. Peak 1 was identified by acid-urea polyacrylamide gel electrophoresis (PAGE) and mass spectroscopy as human neutrophil proteins (defensins) 1 to 3. Analysis of peak 6 by sodium dodecyl sulfate-PAGE revealed multiple bands. Thus, human PMN have nonoxidative anticryptococcal activity residing principally in their cytoplasmic and primary granule fractions. Calprotectin mediates the cytoplasmic activity, whereas multiple proteins, including defensins, are responsible for activity of the primary granules.
Mononuclear Cell Recruitment, Granuloma Assembly, and Response to Treatment in Experimental Visceral Leishmaniasis: Intracellular Adhesion Molecule 1-Dependent and -Independent Regulation
Authors: Murray Henry W. 
Published: July 2002

ABSTRACTIn experimental visceral leishmaniasis, acquired resistance to intracellularLeishmania donovaniis Th1 cell cytokine dependent and largely mediated by gamma interferon (IFN-γ); the same response also permits conventional antimony (Sb) chemotherapy to express its leishmanicidal effect. Since the influxing blood monocyte (which utilizes endothelial cell ICAM-1 for adhesion and tissue entry) is a primary effector target cell for this cytokine mechanism, we tested the monocyte's role in host responsiveness to chemotherapy in mice with ICAM-1 gene disruptions. Mutant animals failed to develop any early granulomatous tissue response in the liver, initially supported high-level visceral parasite replication, and showed no killing after Sb treatment; the leishmanicidal response to a directly acting, alternative chemotherapeutic probe, amphotericin B, was intact. However, mutant mice proceeded to express a compensatory, ICAM-1-independent response leading to mononuclear cell influx and granuloma assembly, control over visceral infection, and the capacity to respond to Sb. Together, these results point to the recruitment of emigrant monocytes and mononuclear cell granuloma formation, mediated by ICAM-1-dependent and -independent pathways, as critical determinants of host responsiveness to conventional antileishmanial chemotherapy.
Staphylococcal Fibronectin Binding Protein Interacts with Heat Shock Protein 60 and Integrins: Role in Internalization by Epithelial Cells
Authors: Dziewanowska Katarzyna , Carson Andrew R. , Patti Joseph M. , Deobald Claudia F. , Bayles Kenneth W. , Bohach Gregory A. 
Published: July 2002

ABSTRACT

We reported previously that internalization of
Staphylococcus aureus
by nonprofessional phagocytes involves an interaction between fibronectin (Fn) binding protein (FnBP) and the host cell, resulting in signal transduction, tyrosine kinase activity, and cytoskeletal rearrangement (K. Dziewanowska, J. M. Patti, C. F. Deobald, K. W. Bayles, W. R. Trumble, and G. A. Bohach, Infect. Immun. 67:4673–4678, 1999). The goal of the present study was to identify the host molecules responsible for uptake of the organism through an interaction with FnBP. First, Fn was required for internalization. Addition of small amounts of exogenous Fn stimulated the uptake of
S. aureus
by HEp-2 cells, which are deficient in Fn synthesis. Fn antibodies blocked internalization of the organism by MAC-T cell monolayers, a bovine epithelial cell line which expresses Fn. Second, a monoclonal antibody (MAb) specific for β
1
integrins dramatically reduced
S. aureus
invasion, suggesting that the formation of a Fn bridge linking the host cell β
1
integrin and FnBP precedes internalization. However, ligand blotting of cell membrane proteins with a functional fragment of FnBP consistently identified an additional ∼55-kDa receptor on both human and bovine epithelial cells. This protein was purified and identified by N-terminal microsequencing as heat shock protein 60 (Hsp60). The interaction between FnBP and Hsp60 also occurred when the whole cells were used. Cell membrane localization of Hsp60 was confirmed by biotinylation with an agent nonpermeable to the cell membrane. Pretreatment of epithelial cells with a MAb specific for eukaryotic Hsp60 significantly reduced internalization of
S. aureus
. Combined, these results suggest that the FnBP binds directly to both Hsp60 and Fn and is linked to β
1
integrins through a Fn bridge. The simultaneous involvement of Fn and two host cell ligands, β
1
integrins and Hsp60, suggests that FnBP is a multifunctional adhesin that mediates internalization in a manner similar to that proposed for OpaA, the
Neisseria gonorrhoeae
FnBP homolog (J. P. M. van Putten, T. D. Duensing, and R. L. Cole, Mol. Microbiol. 29:369–379, 1998).
Role of Catalase in
Campylobacter jejuni
Intracellular Survival
Authors: Day William A. , Sajecki Jaime L. , Pitts Todd M. , Joens Lynn A. 
Published: July 2002

ABSTRACT

The ability of
Campylobacter jejuni
to penetrate normally nonphagocytic host cells is believed to be a key virulence determinant. Recently, kinetics of
C. jejuni
intracellular survival have been described and indicate that the bacterium can persist and multiply within epithelial cells and macrophages in vitro. Studies conducted by Pesci et al. indicate that superoxide dismutase contributes to intraepithelial cell survival, as isogenic
sod
mutants are 12-fold more sensitive to intracellular killing than wild-type strains. These findings suggest that bacterial factors that combat reactive oxygen species enable the organism to persist inside host cells. Experiments were conducted to determine the contribution of catalase to
C. jejuni
intracellular survival. Zymographic analysis indicated that
C. jejuni
expresses a single catalase enzyme. The gene encoding catalase (
katA
) was cloned via functional complementation, and an isogenic
katA
mutant strain was constructed. Kinetic studies indicate that catalase provides resistance to hydrogen peroxide in vitro but does not play a role in intraepithelial cell survival. Catalase does however contribute to intramacrophage survival. Kinetic studies of
C. jejuni
growth in murine and porcine peritoneal macrophages demonstrated extensive killing of both wild-type and
katA
mutant strains shortly following internalization. Long-term cultures (72 h postinfection) of infected phagocytes permitted recovery of viable wild-type
C. jejuni
; in contrast, no viable
katA
mutant bacteria were recovered. Accordingly, inhibition of macrophage nitric oxide synthase or NADPH oxidase permitted recovery of
katA
mutant
C. jejuni
. These observations indicate that catalase is essential for
C. jejuni
intramacrophage persistence and growth and suggest a novel mechanism of intracellular survival.
Essential Role of Platelet-Activating Factor in Control ofLeishmania(Leishmania)amazonensisInfection
Authors: Lonardoni Maria Valdrinez Campana , Russo Momtchillo , Jancar Sonia 
Published: July 2002

ABSTRACTIn the present study we investigated the role of platelet-activating factor (PAF) and prostaglandins in experimentalLeishmania(Leishmania)amazonensisinfection and the relationship between these mediators and nitric oxide (NO) production. Mouse peritoneal macrophages elicited with thioglicolate were infected with leishmania amastigotes, and the infection index determined 48 h later. The course of infection was monitored for 5 weeks in mice infected in the footpad with promastigotes by measuring the footpad swelling and parasite load in regional lymph nodes and spleen. The addition of PAF to C57BL/6 mouse macrophages significantly inhibited parasite growth and induced NO production. Treatment of macrophages with a selective PAF antagonist, WEB2086, increased the infection, indicating that endogenously produced PAF regulates macrophage ability to control leishmania infection. This effect of PAF was abolished by addition of the inhibitor of NO synthesis, L-NAME, to the cultures. The addition of prostaglandin E2significantly increased the infection and NO production. Treatment with cyclo-oxygenase inhibitor, indomethacin, reduced the infection and PAF-induced release of NO. Thus, the increased NO production induced by PAF seems to be mediated by prostaglandins. The more-selective inhibitors of cyclo-oxygenase 2, nimesulide and NS-398, had no significant effect. Thus, antileishmanial activity correlates better with the presence of PAF or absence of prostaglandins than with NO production. In vivo treatment with PAF antagonists significantly increased leishmania lesions, as well as the parasite load, in regional lymph nodes and spleens. These findings indicate that PAF is essential for the control of leishmania infection.