SEARCH · PubMed Health

Results for “TOXOPLASMA”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMed2001

Residual infection of 15 toxoplasma strains in the brain of rats fed cysts.

Thirty-seven groups of 4-32 Wistar rats were 2-10(3) cysts of 15 Toxoplasma strains. After 2 months, the rats were euthanized and their brains screened for Toxoplasma cysts and bioassayed in mice if negative. The brains of 323 of 411 rats (78.6%) were found to be infected 2 months after inoculation with Toxoplasma cysts. Two hundred cysts were necessary to infect nearly 90% of the rats. With lower doses, only 60% of the rats had residual brain infection. Brain cysts were formed only in 146 of 411 rats (35.5%). The numbers of cysts formed were in the order of tens to hundreds, only occasionally one or two thousands. The mean percentage of rats with brain cysts, and the number of cysts formed in rat brains by different inocula, increased with higher doses of cysts and then declined. This pattern is difficult to explain and similar results regarding the number of cysts formed have been published. In relation to the mean percentage of rats infected, there appears to be a plateau in infection with the higher inocula. Neither the number of rats with cysts in their brains nor the numbers of cysts formed were dependent on the Toxoplasma strain used, with the exception of one strain. Instead, individual variations were marked, and are presumably related to variations in the individual genetic resistance to Toxoplasma infection in the rat. The information gathered is considered a preliminary step for a rat model of immunity against acquired toxoplasmosis.

Animals↗

PubMed2003

Cellular immunity to Toxoplasma gondii in congenitally infected newborns and immunocompetent infected hosts.

The aim of this study was to determine the frequency of anergy to Toxoplasma gondii in congenitally infected newborns and immunocompetent infected individuals. Specific anergy to Toxoplasma has been reported previously, especially in cases of congenital toxoplasmosis. Whole blood from 592 immunocompetent patients with suspected toxoplasmosis was cultured in the presence of soluble Toxoplasma antigen for 7 days. Activated T lymphocytes were detected by flow cytometry. In patients over 1 year of age, the percentage of soluble Toxoplasma antigen-stimulated T cells expressing the interleukin-2 receptor CD25 was higher in infected patients than in uninfected subjects (40.0+/-18.3% vs. 1.8+/-2.0%, P<0.0001). No differences were detected between seroconverters, i.e. those with recent rises in IgM and IgG antibodies, and those with acquired or congenital toxoplasmosis. Similar results were observed when congenitally infected ( n=38) and uninfected ( n=89) children under 1 year of age were compared (17.6+/-9.2% vs. 3.0+/-4.9%, P<0.0001). The sensitivity and specificity values of CD25 detection for diagnosis of congenital toxoplasmosis in infants were 95% and 89%, respectively, at a threshold value of 7% above control culture. The results show that specific cellular immunity is detectable in virtually all Toxoplasma-infected patients, including newborns. Detection of CD25 constitutes a simple, sensitive and specific test for diagnosis of congenital toxoplasmosis.

Animals↗

PubMed1987

Macrophage-mediated suppression of immune responses in Toxoplasma-infected mice. III. Suppression of antibody responses to parasite itself.

In acute Toxoplasma infection, anti-sheep erythrocytes (SRBC) antibody responses were strongly suppressed in the infected C57BL/6 mice, and the mice produced low titers of only 2-mercaptoethanol (2-ME)-sensitive antibodies but not 2-ME-resistant antibodies. By contrast, the infected BALB/c mice produced much higher titers of both 2-ME-sensitive and -resistant anti-SRBC antibodies than the infected C57BL/6 mice. In anti-Toxoplasma antibody responses, the 2-ME-resistant antibody titers were significantly lower in the infected C57BL/6 mice than in the BALB/c mice in the early phase of infection, suggesting that the suppressive effect of Toxoplasma infection affects antibody responses to Toxoplasma itself as well as to the unrelated antigen, SRBC. A histological study revealed that in the infected C57BL/6 mice, a large number of acid phosphatase-positive, macrophage-like cells infiltrated into the follicles of their spleens, and an involution of follicles occurred in the acute phase of infection. This histological change was not observed in the infected BALB/c mice. The infected C57BL/6 mice, which had the suppressed anti-Toxoplasma antibody responses, made five times as many as cysts in their brains as compared with the BALB/c mice at the fifth week of infection.

Animals↗

PubMed2005

Toxoplasma gondii: identification of a putative nitric oxide synthase motif DNA sequence.

Nitric oxide (NO) plays an important role as a mediator of the immune response to intracellular pathogens in mice; however discordant results were obtained in in vitro human cell lines experiments. Thus, we found that nitrite levels (nitric oxide derivatives) were increased in presence of Toxoplasma but not with IFN gamma plus LPS treatment during Toxoplasma infection of a human monocyte cell line THP1 and Griess assays confirmed that Toxoplasma alone has a nitrite production that was surprisingly increased by the most common inhibitor of nitric oxide synthase (NOS) in mammals. To look for genomic sequences that code for NOS gene in Toxoplasma, which could explain this production of NO derivatives, specific NOS motifs were sought by bioinformatics methods. A putative NOS motif sequence was found in one contig of the Toxoplasma genome (). Specific primers amplified a segment of 270 bp in RT-PCR assay, indicating that it is a transcription gene in the tachyzoite stage. Our results are the first description of the existence and transcription of a putative NOS DNA sequence in a pathogenic protozoan.

Amino Acid Motifs↗

PubMed2003

Organisation and sequence determination of glutamine-dependent carbamoyl phosphate synthetase II in Toxoplasma gondii.

Carbamoyl phosphate synthetase II encodes the first enzymic step of de novo pyrimidine biosynthesis. Carbamoyl phosphate synthetase II is essential for Toxoplasma gondii replication and virulence. In this study, we characterised the primary structure of a 28kb gene encoding Toxoplasma gondii carbamoyl phosphate synthetase II. The carbamoyl phosphate synthetase II gene was interrupted by 36 introns. The predicted protein encoded by the 37 carbamoyl phosphate synthetase II exons was a 1,687 amino acid polypeptide with an N-terminal glutamine amidotransferase domain fused with C-terminal carbamoyl phosphate synthetase domains. This bifunctional organisation of carbamoyl phosphate synthetase II is unique, so far, to protozoan parasites from the phylum Apicomplexa (Plasmodium, Babesia, Toxoplasma) or zoomastigina (Trypanosoma, Leishmania). Apicomplexan parasites possessed the largest carbamoyl phosphate synthetase II enzymes due to insertions in the glutamine amidotransferase and carbamoyl phosphate synthetase domains that were not present in the corresponding gene segments from bacteria, plants, fungi and mammals. The C-terminal allosteric regulatory domain, the carbamoyl phosphate synthetase linker domain and the oligomerisation domain were also distinct from the corresponding domains in other species. The novel C-terminal regulatory domain may explain the lack of activation of Toxoplasma gondii carbamoyl phosphate synthetase II by the allosteric effector 5-phosphoribosyl 1-pyrophosphate. Toxoplasma gondii growth in vitro was markedly inhibited by the glutamine antagonist acivicin, an inhibitor of glutamine amidotransferase activity typically associated with carbamoyl phosphate synthetase II, guanosine monophosphate synthetase, or CTP synthetase.

Animals↗

PubMed1983

Secretion from the rhoptries of Toxoplasma gondii during host-cell invasion.

To determine whether the rhoptries of Toxoplasma gondii play a role in the invasion of host cells by this parasite, we inoculated toxoplasmas into the peritoneal cavities of normal mice and into macrophage cultures, fixed the specimens at various intervals thereafter, and analyzed them by electron microscopy. We found that during host-cell invasion, the rhoptry membrane fused with the anterior limiting membrane of the toxoplasma, producing an opening to the exterior. Since such openings were formed when the host-cell membrane was disrupted, it appears that the rhoptries may secrete a lytic product that facilitates invasion through the host-cell membrane. Such a "penetration-enhancing factor" was previously isolated from lysed toxoplasmas (Lycke and Norrby, 1966). Occasionally, when secretion was incomplete, masses of tubules were found in the rhoptries, sometimes as soon as 15 sec after the toxoplasms had been injected into mice. Similar tubules were found in the parasitophorous vacuole that was formed 10-15 min later, and such tubules are typical of vacuoles containing replicating parasites. Because these tubules are in continuity with the vacuolar membrane, it appears to be a hybrid membrane, composed in part of toxoplasma products. We speculate that the hybrid nature of the vacuolar membrane prevents it from fusing with the lysosomes of phagocytes and thereby contributes to the intracellular survival of the parasites.

Animals↗

PubMed1980

Mouse spleen cell-derived toxoplasma growth inhibitory factor: its separation from macrophage migration inhibitory factor.

Spleen cells from hyperimmunized mice infected with Toxoplasma gondii were cultured in vitro with Toxoplasma specific antigen. The supernatant produced from the cells were termed lymphokines (LKs). The LKs were divided into 4 major fractions, namely: LKs-I, LKs-II, LKs-III and LKs-IV, according to the elution pattern on Sephadex G-100 gel columns. Partially purified LKs contained 2 MIF peaks, namely: MIF-I in LKs-II fraction and MIF-II in LKs-IV fraction. In this study, Toxoplasma growth inhibitory factor (Toxo-GIF), which inhibits the multiplication of Toxoplasma within non-immune macrophages in vitro, was separated by the same method as MIF separation, i.e. Sephadex G-100 gel filtration. Toxo-GIF activity was present in the LKs-II fraction in which MIF-I was also detected with a calculated molecular weight of 30,000 to 40,000. This murine LKs inhibited Toxoplasma multiplication only in murine macrophages but not in guinea pig macrophages or canine monocytes. Cytotoxic substances against macrophages were observed in the LKs-IV fraction, however, no Toxo-GIF was present in this fraction which in addition contained MIF-II with a calculated molecular weight of 3,000 to 5,000.

Animals↗

PubMed1985

Requirement for calcium ions in antibody-dependent complement-mediated cytolysis of Toxoplasma gondii.

The mechanism of antibody-dependent complement-mediated cytolysis of Toxoplasma organisms was studied by using a selective chelating agent for Ca++, ethyleneglycol-bis (beta-aminoethyl ether)-N,N-tetraacetic acid (EGTA). Toxoplasma organisms were lysed by treatment with human serum containing anti-Toxoplasma antibodies and with fresh human-plasma at 37 degrees C for 1 h. The reaction was prevented by heat treatment of the fresh plasma at 56 degrees C for 30 min, confirming that the cytolysis of Toxoplasma organisms had been mediated by an activation of complement. The lytic reaction was completely inhibited by an addition of EGTA at final concentrations of more than 2.5 mM. Addition of Ca++ cleared the inhibitory effect of EGTA on the reaction. These results demonstrate that the antibody-dependent complement-mediated cytolysis of Toxoplasma organisms requires the presence of Ca++, indicating that the reaction is mediated by an activation of the classical complement pathway.

Animals↗

PubMed1994

Stable DNA transformation in the obligate intracellular parasite Toxoplasma gondii by complementation of tryptophan auxotrophy.

The protozoan parasite Toxoplasma gondii infects a wide range of vertebrate hosts and is an important opportunistic pathogen in immunocompromised humans. Although Toxoplasma is amenable to both biochemical and cellular experimental approaches, the molecular basis of its success as an intracellular parasite is poorly understood. To provide a system for molecular genetic analyses, we have developed a stable DNA transformation system for Toxoplasma based on complementation of its naturally occurring tryptophan auxotrophy. Complementation was accomplished by expressing the Escherichia coli trpB gene, encoding the beta subunit of tryptophan synthase (EC 4.2.1.20), the enzyme that catalyzes the formation of tryptophan from indole plus serine. Transformants were obtained by electroporation of a plasmid, called SAG1/trpB, containing the trpB gene flanked by Toxoplasma surface antigen 1 (SAG1) gene sequences and selection for growth on indole. Transformants were obtained with circular forms of the SAG1/trpB plasmid with efficiencies of 10(-4) per cell. Transformation with either circular or linear SAG1/trpB resulted in integration into the genome at distinct, nonhomologous sites. Trp+ transformants typically contained tandemly repeated copies of the SAG1/trpB plasmid and were stable in the absence of continued selection. The Trp phenotype provides a dominant selectable marker that should allow expression of foreign or altered genes in Toxoplasma and facilitate molecular analyses of genes important for intracellular survival.

Animals↗

PubMed1998

Development of a stable episomal shuttle vector for Toxoplasma gondii.

The rapid developments in the molecular genetics of Toxoplasma gondii have far reaching implications in treatment and vaccination strategies for this as well as closely related pathogens such as Plasmodium. Although stable transformation of this parasite through homologous and illegitimate genomic integration has provided many of the tools necessary for genetic analysis, subsequent manipulations of the DNA have proven laborious. This report describes the selection and subsequent characterization of a Toxoplasma sequence that permits the episomal maintenance of bacterial plasmids in this parasite. This sequence was isolated from the Toxoplasma genome through selection for episomal stability of a pUC19-based library in the absence of a selectable marker. A 500-base pair fragment was determined to possess the stabilization activity. Transformations of Toxoplasma using vectors possessing this fragment, referred to as EMS (episomal maintenance sequence), demonstrated an elevated stable transformation frequency compared with the vector alone. Mutants deficient in hypoxanthine-xanthine-guanine phosphoribosyltransferase activity were used as a test to see if this gene could be selected from a genomic library using a vector containing the EMS. The success of this test demonstrates the utility of EMS-containing vectors in complementation strategies and the ability of such constructs bearing large fragments of the Toxoplasma genome to be maintained episomally.

Animals↗

PubMed2001

Toxoplasma gondii attachment to host cells is regulated by a calmodulin-like domain protein kinase.

The role of calcium-dependent protein kinases in the invasion of Toxoplasma gondii into its animal host cells was analyzed. KT5926, an inhibitor of calcium-dependent protein kinases in other systems, is known to block the motility of Toxoplasma tachyzoites and their attachment to host cells. In vivo, KT5926 blocks the phosphorylation of only three parasite proteins, and in parasite extracts only a single KT5926-sensitive protein kinase activity was detected. This activity was calcium-dependent but did not require calmodulin. In a search for calcium-dependent protein kinases in Toxoplasma, two members of the class of calmodulin-like domain protein kinases (CDPKs) were detected. TgCDPK2 was only expressed at the mRNA level in tachyzoites, but no protein was detected. TgCDPK1 protein was expressed in Toxoplasma tachyzoites and cofractionated precisely with the peak of KT5926-sensitive protein kinase activity. TgCDPK1 kinase activity was calcium-dependent but did not require calmodulin or phospholipids. TgCDPK1 was found to be inhibited effectively by KT5926 at concentrations that block parasite attachment to host cells. In vitro, TgCDPK1 phosphorylated three parasite proteins that migrated identical to the three KT5926-sensitive phosphoproteins detected in vivo. Based on these observations, a central role is suggested for TgCDPK1 in regulating Toxoplasma motility and host cell invasion.

Alkaloids↗

PubMed2005

The opportunistic pathogen Toxoplasma gondii deploys a diverse legion of invasion and survival proteins.

Host cell invasion is an essential step during infection by Toxoplasma gondii, an intracellular protozoan that causes the severe opportunistic disease toxoplasmosis in humans. Recent evidence strongly suggests that proteins discharged from Toxoplasma apical secretory organelles (micronemes, dense granules, and rhoptries) play key roles in host cell invasion and survival during infection. However, to date, only a limited number of secretory proteins have been discovered, and the full spectrum of effector molecules involved in parasite invasion and survival remains unknown. To address these issues, we analyzed a large cohort of freely released Toxoplasma secretory proteins by using two complementary methodologies, two-dimensional electrophoresis/mass spectrometry and liquid chromatography/electrospray ionization-tandem mass spectrometry (MudPIT, shotgun proteomics). Visualization of Toxoplasma secretory products by two-dimensional electrophoresis revealed approximately 100 spots, most of which were successfully identified by protein microsequencing or matrix-assisted laser desorption ionization-mass spectrometry analysis. Many proteins were present in multiple species suggesting they are subjected to substantial post-translational modification. Shotgun proteomic analysis of the secretory fraction revealed several additional products, including novel putative adhesive proteins, proteases, and hypothetical secretory proteins similar to products expressed by other related parasites including Plasmodium, the etiologic agent of malaria. A subset of novel proteins were re-expressed as fusions to yellow fluorescent protein, and this initial screen revealed shared and distinct localizations within secretory compartments of T. gondii tachyzoites. These findings provided a uniquely broad view of Toxoplasma secretory proteins that participate in parasite survival and pathogenesis during infection.

Animals↗

PubMed1999

Risk factors for Toxoplasma infection in pregnancy: a case-control study in France.

Each year an estimated 4900 cases of primary Toxoplasma infection occur in pregnant women in France, a country with a high prevalence. Since 1992 all pregnant women at risk of Toxoplasma infection have been required to undergo monthly serological testing. This case-control study, the first of its kind in France, was undertaken to identify risk factors for Toxoplasma infection during pregnancy, with a view to improving primary prevention among non-immune pregnant women. A total of 80 pregnant women who seroconverted to Toxoplasma were matched with 80 pregnant women who had repeatedly negative tests. The women were interviewed by telephone, using a standardized questionnaire, to determine socio-demographic characteristics, exposure to possible risk factors and the type of information on prevention received during pregnancy. The risk factors for Toxoplasma infection included in a multivariate analysis were poor hand hygiene (OR = 9.9; 95%CI: 0.8-125), consumption of undercooked beef (OR = 5.5; 95%CI: 1.1-27), having a pet cat (OR =4.5; 95%CI: 1.0-19.9), frequent consumption of raw vegetables outside the home (OR = 3.1; 95%,CI: 1.2-7.7) and consumption of undercooked lamb (OR = 3.1; 95%CI: 0.85-14). Receipt of documentary advice on prevention was associated with a lower risk of infection. Prevention campaigns among pregnant women in France could be improved and should focus on eating habits, hand hygiene and cats.

Adult↗

PubMed1979

Macrophage oxygen-dependent antimicrobial activity. I. Susceptibility of Toxoplasma gondii to oxygen intermediates.

A sensitive method for evaluating extracellular parasite viability was used to determine the in vitro susceptibility of virulent Toxoplasma gondii to selected oxygen intermediates. By acridine orange fluorescent staining criteria, toxoplasmas were resistant to up to either 10(-3) M reagent H2O2 or H2O2 generated by glucose-glucose oxidase. In keeping with a lack of sensitivity to H2O2, toxoplasmas contained endogenous catalase (5.7 x 10(-4) Baudhuin units/10(6) organisms). The addition of a peroxidase and halide, however, markedly accelerated killing and lowered the H2O2 requirement by 1,000-fold. In contrast, toxoplasmas were promptly killed after exposure to products generated by xanthine (1.5 x 10(-4) M) and xanthine oxidase (50 micrograms). The inhibition of this system's microbicidal activity by scavengers of O2- (superoxide dismutase) and H2O2 (catalase) indicated that although neither O2- nor H2O2 were toxoplasmacidal, their interaction was required for parasite killing. Quenching OH. and 1O2, presumed products of O2--H2O2 interaction, by mannitol, benzoate, diazabicyclooctane, and histidine, also inhibited toxoplasma killing by xanthine-xanthine oxidase. These findings suggested that O2- and H2O2 functioned in precursor roles and that OH. and 1O2 were toxoplasmacidal. The capacity of normal peritoneal macrophages to pinocytose an oxygen intermediate scavenger, soluble catalase, was also demonstrated. Appreciable extraphagosomal concentrations of catalase were achieved by exposing macrophages to 1 mg/ml of the enzyme for 3 h. Maintenance of high intracellular levels required constant exposure because interiorized catalase was rapidly degraded.

Acridine Orange↗

PubMed2001

Immune recovery under highly active antiretroviral therapy is associated with restoration of lymphocyte proliferation and interferon-gamma production in the presence of Toxoplasma gondii antigens.

The in vitro lymphocyte proliferative response (LPR) and interferon (IFN)-gamma production in the presence of Toxoplasma antigen were evaluated in 97 human immunodeficiency virus (HIV)-1-infected patients with CD4 cell counts of <100 cells/microL (group 1), currently >300 cells/microL but previously <100 cells/microL (group 2), or always >300 cells/microL (group 3) and in 28 non-HIV-infected blood donors (group 4), all seropositive to Toxoplasma. In group 2, 81% of patients had a positive LPR, versus 20% in group 1 (P<10(-3)). IFN-gamma production was greater in group 2 than in group 1 (922 vs. 0 Deltapg/mL; P=10(-4)). Multivariate analysis found a significant association between a positive LPR to Toxoplasma antigen and a CD4 count >300 cells/microL (odds ratio [OR], 16.3; 95% confidence interval [CI], 5.3-50.2) and anti-Toxoplasma IgG titer >150 IU/mL (OR, 5; 95% CI, 1.6-15.2). Immune reconstitution under highly active antiretroviral therapy was associated with a restoration of immune responses against Toxoplasma.

Adult↗

PubMed1979

Activity of human blood leukocytes against Toxoplasma gondii.

Previous reports on the ability of Toxoplasma gondii to multiply within human mononuclear phagocytes have supported the concept that the phagocytes may protect Toxoplasma from antibody and act as a transport mechanism for dissemination of the organism throughout the body. However, after phagocytosis of viable Toxoplasma, greater than 80% of freshly isolated human peripheral blood monocytes and 50% of polymorphonuclear leukocytes rapidly destroyed these intracellular organisms. Virtually no replication of Toxoplasma occurred within these cells, as determined by microscopic examination and by uptake of [3H]uracil. These results suggested that circulating phagocytes from humans restrict rather than facilitate the initial dissemination of Toxoplasma.

Animals↗

PubMed1987

Murine spleen and lymph node cellular composition and function during cyclophosphamide and splenectomy induced resistance to Toxoplasma gondii.

Murine toxoplasmosis caused by a low virulence, cyst-forming strain of Toxcoplasma gondii (Pe strain) is characterized by splenomegaly, lymphadenopathy, decreased delayed-type hypersensitivity (DTH), and the presence of toxoplasma cysts in brain tissue. Cyclophosphamide (CY) in a single dose of 100 mg/kg injected 3 days before infection, or splenectomy 3 weeks before infection, augmented DTH and decreased the number of toxoplasma brain cysts. CY-induced augmentation of resistance during the first 3 weeks of murine toxoplasmosis was associated with: (1) an increase in mononuclear phagocytes and a decrease in T lymphocytes (including Lyt2+ cells) in spleens and lymph nodes; (2) suppressed toxoplasma antigen induced proliferation of cultured spleen cells: (3) augmentation of antigen induced proliferation of cultured lymph node cells; and (4) low levels of interferon-gamma production in both spleen and lymph node cultures. The best correlate of the enhanced in-vivo effects of CY was proliferation of nylon wool-purified lymph node cells to toxoplasma antigen. The presence of Lyt2+ cells in lymph nodes of toxoplasma infected mice inhibited maximal proliferation.

Animals↗

PubMed1997

Anti-Toxoplasma gondii immunoglobulins A and G in human saliva and serum.

Paired human saliva and serum samples from 60 individuals were tested for specific IgA and IgG antibodies to Toxoplasma gondii. The study in both fluids was carried out by indirect immunoenzymatic assay (ELISA). Saline antigenic extract of T. gondii was used to coat plastic surfaces upon which the samples were then incubated; monospecific conjugates of anti-IgA and anti-IgG-peroxidase were then incubated with the samples after a washing procedure to separate the unbound antibodies. The enzymatic activity was measured and the results expressed in terms of ELISA index. Toxoplasma-specific IgG antibodies were detected in 43 of the serum samples (71.7%) and in 12 of the saliva samples (20.0%) whereas Toxoplasma-specific IgA antibodies were detected in 18 of the serum samples (30.0%) and in 12 of the saliva samples (20.0%). No association was observed when the Toxoplasma-specific IgG reactive and non-reactive serum samples were compared with the reactive and non-reactive saliva samples for this class of immunoglobulin. On the other hand, a significant association was observed when the Toxoplasma-specific IgA reactive and non-reactive serum samples were compared with the reactive and non-reactive saliva for this type of antibody. In conclusion, our results show that the detection of salivary IgA reflects the serum level of this isotype but salivary IgG does not. Moreover, the isolated detection of salivary IgG may not contribute to epidemiological studies of chronic toxoplasmic infections.

Adult↗