Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “TOXOPLASMA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 973 records · Page 54Linked to original sources
PubMed1998

Identification and characterization of a Fc receptor activity on the Toxoplasma gondii tachyzoite.

The Immunoglobulin (Ig) binding capacity of Toxoplasma gondii tachyzoites was investigated using fluorescence flow-cytometry analysis. Polyclonal mouse, human and rat immunoglobulins without specific anti-Toxoplasma activity bound to parasites in a concentration-dependent manner, saturating them at circulating serum concentrations. The immunoglobulin class and subclass specificity of binding was investigated using irrelevant monoclonal antibodies. IgM, IgA and IgG reacted with the parasite membrane. The attachment of mouse IgM to the parasite surface was hampered by mouse IgG1, IgG2a, IgG2b and IgG3. The binding of mouse IgG was proportionally reduced with increasing concentrations of mouse monoclonal IgM. The binding of murine immunoglobulin was diminished when in presence of human IgG. Purified Fc- but not Fab portions of immunoglobulins, fixed to parasites. Using labelled calibrated beads, the Ig binding capacity of parasites was estimated to be 6900 +/- 500 sites per tachyzoite. The Kd of the T. gondii Fc Receptor (FcR) activity was determined at 1.4 +/- 0.1 microM (mean +/- SEM). Such FcR activity was reduced by phospholipase C, trypsin and pronase treatment of the parasites. These data show a low affinity FcR activity on T. gondii tachyzoites which recognizes Ig of different species and isotypes and is likely supported by a glycosyl-phosphatidylinositol (GPI)-anchored surface protein of the parasite.

Animals↗
PubMed1999

Interleukin-15 enhances host protection against acute Toxoplasma gondii infection in T-cell receptor alpha-/-deficient mice.

A potential role for T-cell receptor (TCR)-gamma(delta) cells in response to Toxoplasma gondii has been described. This study was undertaken to evaluate whether exogenous rIL-15 can enhance the production of gamma(delta) T cells in response to infection with T. gondii. For this, C57BL/6 and TCR alpha-gene deficient mice (alpha-/-) were vaccinated with Toxoplasma lysate antigen (TLA) in combination with interleukin (IL)-15. The cellular and humoral immune response was assessed following immunization. Administration of IL-15/TLA to alpha-/-mice lengthened survival time post lethal challenge. Several immunological parameters were increased in the alpha-/-mice following immunization with IL-15/TLA including serum immunoglobulin (Ig)G1 and IgG2a antibody titres and splenocyte lymphoproliferation in response to parasite antigen. Further, the CTL response to parasite infected target cells as well as the production of interferon gamma was enhanced by IL-15/TLA administration in the alpha-/-mice. These observations indicate that the gamma(delta) T cells response to this parasite can be enhanced by the administration of exogenous IL-15 in the presence of parasite lysate antigen.

Animals↗
PubMed2001

Evidence for the existence of a proteasome in Toxoplasma gondii: intracellular localization and specific peptidase activities.

The proteasome is a large intracellular protein complex whose main function is proteolytic removal of damaged proteins. It has recently been shown that the proteasome has a crucial role in the pathogenesis of protozoan parasites. We attempted to characterize the proteasome of T. gondii (RH strain). In immunoblot experiments, we showed that MCP231 monoclonal antibody, directed against the human 20S proteasome, labelled homologous proteins in T. gondii with a pattern similar to that observed in mammalian cells. The study of in vitro proteolytic activities showed that chymotrypsin-like activity (the only activity obtained with archaebacteria) was present in Toxoplasma, with Km and specific activity values close to those observed with eukaryotic cells. Immunofluorescence studies showed that the Toxoplasma proteasome predominated in the cytosol.

Animals↗
PubMed2004

Immune responses of different mouse strains after challenge with equivalent lethal doses of Toxoplasma gondii.

Most immunological studies that utilize different strains of inbred mice following T. gondii infection fail to compensate for differences in host susceptibility to the size of the parasite innoculum. To address this concern, susceptible C57BL/6 and resistant CBA/J mice were orally infected with either an equivalent 50% lethal dose (LD50) of brain cysts of the 76K strain of T. gondii (15 cysts in C57BL/6, 400 cysts in CBA/J) or the same dose of parasites in each mouse strain. C57BL/6 mice receiving 400 cysts (LD50 of CBA/J mice) died post infection, whereas CBA/J mice that received 15 cysts (LD50 of C57BL/6 mice) survived. Parasite loads in the brains and serum Toxoplasma-specific IgG1 titers of LD50-infected C57BL/6 mice were significantly higher than those in LD50- or 15 cysts-infected CBA/J mice, whereas splenocyte proliferation to Toxoplasma antigen and the percentage of CD8 alpha+ T cells were reduced in LD50-infected C57BL/6 mice. In contrast, serum IgG2a and IgM titers, the percentage of gamma delta T cells and IFN-gamma expression of spleen of LD50-infected CBA/J mice were higher than those of either 15 cysts-infected CBA/J mice or LD50-infected C57BL/6 mice. These observations demonstrate that the immune response between LD50-infected C57BL/6 and CBA/J mice was more prominent when compared to C57BL/6 or CBA/J mice receiving the same parasite inoculum. These observations would suggest that caution must be excersized in the planning and interpretation of data when the size of the parasite inoculum has not been adjusted for mouse strain.

Animals↗
PubMedDate not supplied

Villitis of known origin: varicella and toxoplasma.

Chronic villitis is a common condition in human placentae. In some cases an infectious cause can be demonstrated, such as infection with cytomegalovirus and rubella virus. Most often it is of unknown aetiology, the so-called VUE (villitis of unknown aetiology). We describe two cases with identification of specific infectious agents, each demonstrating previously unreported findings, i.e. persistent varicella antigen in the villi in case 1, and presence of toxoplasma cysts in Wharton's jelly in case 2. The identification of the pathogens, varicella virus and toxoplasma, would easily have been overlooked in routine study of the placenta and were possible because of clinical suspicion.

Adult↗
PubMed1992

Induction of heat shock protein closely correlates with protection against Toxoplasma gondii infection.

Heat shock proteins (HSPs) are evolutionarily highly conserved polypeptides that appear to be produced by many cells to preserve cellular functions under a variety of conditions of stress, including infections. We report that a 65-kDa HSP is present in mouse peritoneal cells that have been infected with a low-virulence (Beverley) strain of Toxoplasma gondii, as determined by electroblot assay using a monoclonal antibody specific for microbial HSP65. This HSP is, however, not expressed when infection occurs with the high-virulence RH strain of T. gondii. Furthermore, HSP was demonstrable in mice that acquired resistance against infection with a lethal dose of bradyzoites of the Beverley strain or even of an inoculum of a highly virulent strain of T. gondii (RH). From these results, it can be suggested that HSPs play an important role in developing effective defenses that include effective immune responses against infection with Toxoplasma parasites in vivo.

Animals↗
PubMed1998

Nuclear-encoded proteins target to the plastid in Toxoplasma gondii and Plasmodium falciparum.

A vestigial, nonphotosynthetic plastid has been identified recently in protozoan parasites of the phylum Apicomplexa. The apicomplexan plastid, or "apicoplast," is indispensable, but the complete sequence of both the Plasmodium falciparum and Toxoplasma gondii apicoplast genomes has offered no clue as to what essential metabolic function(s) this organelle might perform in parasites. To investigate possible functions of the apicoplast, we sought to identify nuclear-encoded genes whose products are targeted to the apicoplast in Plasmodium and Toxoplasma. We describe here nuclear genes encoding ribosomal proteins S9 and L28 and the fatty acid biosynthetic enzymes acyl carrier protein (ACP), beta-ketoacyl-ACP synthase III (FabH), and beta-hydroxyacyl-ACP dehydratase (FabZ). These genes show high similarity to plastid homologues, and immunolocalization of S9 and ACP verifies that the proteins accumulate in the plastid. All the putatively apicoplast-targeted proteins bear N-terminal presequences consistent with plastid targeting, and the ACP presequence is shown to be sufficient to target a recombinant green fluorescent protein reporter to the apicoplast in transgenic T. gondii. Localization of ACP, and very probably FabH and FabZ, in the apicoplast implicates fatty acid biosynthesis as a likely function of the apicoplast. Moreover, inhibition of P. falciparum growth by thiolactomycin, an inhibitor of FabH, indicates a vital role for apicoplast fatty acid biosynthesis. Because the fatty acid biosynthesis genes identified here are of a plastid/bacterial type, and distinct from those of the equivalent pathway in animals, fatty acid biosynthesis is potentially an excellent target for therapeutics directed against malaria, toxoplasmosis, and other apicomplexan-mediated diseases.

Animals↗
PubMed1995

Biochemical and molecular characterization of nucleoside triphosphate hydrolase isozymes from the parasitic protozoan Toxoplasma gondii.

We have previously reported the presence of a novel nucleoside triphosphate hydrolase (NTPase) in the rapidly multiplying tachyzoite form of a virulent strain (RH) of Toxoplasma gondii. On further examination, it was found that the purified enzyme was not a single enzyme but was a mixture of two isozymes termed NTPase-I and NTPase-II. The two isozymes had similar molecular masses of approximately 240-270 kDa by gel filtration and contained four identical subunits of molecular mass 66-67 kDa by SDS-polyacrylamide gel electrophoresis. Both forms of the NTPase were activated by dithiothreitol, and NTPase-I had a specific activity 4.5-fold higher than NTPase-II in hydrolysis of ATP. The primary difference between these isozymes lies in their ability to hydrolyze nucleoside triphosphate versus diphosphate substrates. While NTPase-II hydrolyzed ATP to ADP and ADP to AMP at almost the same rate, NTPase-I hydrolyzed ADP to AMP at a much slower rate (0.7% of the rate for ATP). The complete cDNAs for NTPase-I and NTPase-II were sequenced and found to encode the same size predicted open reading frame of which only 16 of 628 amino acids differed between the two isozymes. Both forms of the NTPase contained an NH2-terminal hydrophobic signal peptide, consistent with our previous findings that these enzymes are secreted into the host cell vacuole occupied by the parasite. The gene encoding NTPase-II was found in all strains of Toxoplasma, while the NTPase-I was confined only to virulent strains. Expression of this highly active ATPase (NTPase-I) may contribute to intracellular survival and virulence of T. gondii.

Acid Anhydride Hydrolases↗
PubMed2001

Microarray analysis reveals previously unknown changes in Toxoplasma gondii-infected human cells.

Cells infected with the intracellular protozoan parasite Toxoplasma gondii undergo up-regulation of pro-inflammatory cytokines, organelle redistribution, and protection from apoptosis. To examine the molecular basis of these and other changes, gene expression profiles of human foreskin fibroblasts infected with Toxoplasma were studied using human cDNA microarrays consisting of approximately 22,000 known genes and uncharacterized expressed sequence tags. Early during infection (1-2 h), <1% of all genes show a significant change in the abundance of their transcripts. Of the 63 known genes in this group, 27 encode proteins associated with the immune response. These genes are also up-regulated by secreted, soluble factors from extracellular parasites indicating that the early response does not require parasite invasion. Later during infection, genes involved in numerous host cell processes, including glucose and mevalonate metabolism, are modulated. Many of these late genes are dependent on the direct presence of the parasite; i.e. secreted products from either the parasite or infected cells are insufficient to induce these changes. These results reveal several previously unknown effects on the host cell and lay the foundation for detailed analysis of their role in the host-pathogen interaction.

Animals↗
PubMed2001

The loss of cytoplasmic potassium upon host cell breakdown triggers egress of Toxoplasma gondii.

The ability of intracellular parasites to monitor the viability of their host cells is essential for their survival. The protozoan parasite Toxoplasma gondii actively invades nucleated animal cells and replicates in their cytoplasm. Two to 3 days after infection, the parasite-filled host cell breaks down and the parasites leave to initiate infection of a new cell. Parasite egress from the host cell is triggered by rupture of the host plasma membrane and the ensuing reduction in the concentration of cytoplasmic potassium. The many other changes in host cell composition do not appear be used as triggers. The reduction in the host cell [K(+)] appears to activate a phospholipase C activity in Toxoplasma that, in turn, causes an increase in cytoplasmic [Ca(2+)] in the parasite. The latter appears to be necessary and sufficient for inducing egress, as buffering of cytoplasmic Ca(2+) blocks egress and calcium ionophores circumvent the need for a reduction of host cell [K(+)] and parasite phospholipase C activation. The increase in [Ca(2+)](C) brings about egress by the activation of at least two signaling pathways: the protein kinase TgCDPK1 and the calmodulin-dependent protein phosphatase calcineurin.

Animals↗
PubMed2002

Selection and identification of dense granule antigen GRA3 by Toxoplasma gondii whole genome phage display.

Toxoplasma gondii is a ubiquitous, unicellular, eukaryotic parasite with a complex intracellular life cycle capable of invading and chronically infecting a wide variety of vertebrate host species, including man. Although normally opportunistic in healthy adults, it is a lethal pathogen in immunocompromised humans, particularly in AIDS patients. We present the application of a genomic phage display as a tool for the direct identification of antigens with potential value in diagnosis and/or as subunit vaccine components. Using a polycosmid cloning strategy, we constructed a large phagemid display library (>10(9) independent clones) of mixed short genomic restriction fragments (< or = 500 bp) of T. gondii genomic DNA (80 Mbp genome size) fused to gene III of the filamentous phage M13. Biopanning of the library with monoclonal Toxoplasma antibodies resulted in the isolation and identification of an epitope of GRA3, an antigen located in the dense granules of T. gondii tachyzoites. The reactivity of the phage displaying the GRA3 epitope with the monoclonal antibody was confirmed by an enzyme-linked immunosorbent assay. These results demonstrate the accessibility of midsized eukaryotic genomes to display technology and the feasibility to screen these whole genome display libraries with antibodies for isolating novel antigenic determinants.

Amino Acid Sequence↗
PubMed2002

Functional analysis of Toxoplasma gondii protease inhibitor 1.

We have characterized a Kazal family serine protease inhibitor, Toxoplasma gondii protease inhibitor 1 (TgPI-1), in the obligate intracellular parasite Toxoplasma gondii. TgPI-1 contains four inhibitor domains predicted to inhibit trypsin, chymotrypsin, and elastase. Antibodies against recombinant TgPI-1 detect two polypeptides, of 43 and 41 kDa, designated TgPI-1(43) and TgPI-1(41), in tachyzoites, bradyzoites, and sporozoites. TgPI-1(43) and TgPI-1(41) are secreted constitutively from dense granules into the excreted/secreted antigen fraction as well as the parasitophorous vacuole that T. gondii occupies during intracellular replication. Recombinant TgPI-1 inhibits trypsin, chymotrypsin, pancreatic elastase, and neutrophil elastase. Immunoprecipitation studies with anti-rTgPI-1 antibodies reveal that recombinant TgPI-1 forms a complex with trypsin that is dependent on interactions with the active site of the protease. TgPI-1 is the first anti-trypsin/chymotrypsin inhibitor to be identified in bradyzoites and sporozoites, stages of the parasite that would be exposed to proteolytic enzymes in the digestive tract of the host.

Amino Acid Sequence↗
PubMed2005

Biology and epidemiology of Toxoplasma gondii in man and animals.

Toxoplasma gondii is a coccidian parasite which utilizes felids as definitive hosts, and which has an unusually wide intermediate host range. The parasite was initially described by Nicolle and Manceaux in 1908 from the rodent, Ctenodactylus gundi. Infection with T. gondii is one of the most common parasitic infections of man and other warm-blooded animals. It has been found worldwide from Alaska to Australia. Nearly one-third of humanity has been exposed to this parasite; serologic surveys indicate that T. gondii infections are common in wild carnivores, including pigs, bears, felids, fox, raccoons, and skunks. Clinical and subclinical toxoplasmosis has been reported from wild cervids, ungulates, marsupials, monkeys, and marine mammals. Southern sea otter populations have been severely impacted by Toxoplasma infections.

Animals↗
PubMed1998

Congenital toxoplasma gondii infection diagnosed by PCR amplification of peripheral mononuclear blood cells from a child and mother.

A case of congenital toxoplasmosis is presented, where diagnosis by PCR amplification of Toxoplasma gondii DNA from peripheral blood led to early treatment of the infant and seemingly normal brain development despite the presence of intracranial calcifications at birth. The mother, who experienced a subclinical infection during pregnancy, was PCR-positive for toxoplasma DNA in a sample of peripheral blood drawn after delivery.

Animals↗
PubMed2002

How to detect current toxoplasma infection.

This study seeks to identify the best way to detect current toxoplasma infection for district general hospital laboratories. One hundred 'ordinary' and 174 'difficult' sera are categorised into either an 'evidence' or 'no evidence' group for current toxoplasma infection. Twelve test protocols are investigated using different combinations of one whole antibody latex test (Eiken Toxoreagent), one in-house specific IgG enzyme-linked immunosorbent assay (ELISA) and three specific IgM assays (Toxo-ISAGA, in-house BAM ELISA IgM and Toxonostika ELISA M). The Eiken latex and in-house IgG assays produced significantly fewer false-negative results than were obtained with the single IgM test or the IgG and IgM test protocols (P<0.05), but a greater number of false-positive results (102/274 and 115/274, respectively). Of the IgM assay test protocols, the three IgM assays in combination produced the least number of false-negative results (1/274). However, a significantly greater number of false-positive results were produced than with one or two IgM tests or an IgG and any IgM test in combination (P<0.001). We recommend testing with three IgM tests, or a whole antibody (Eiken) or IgG-specific assay, and that positive or clinically important negative samples be referred to a reference laboratory for confirmation.

Animals↗
PubMed2003

Strategies for detecting toxoplasma immunity.

A strategy for identifying toxoplasma immunity in pregnancy must provide good evidence of immunity but not falsely reassure; that for immunocompromised patients should identify immunity and also the risk of reactivated toxoplasmosis. Using sera from both of these patient groups, the performance of an in-house IgG EIA and two commonly used commercial assays (Abbott AxSYM Toxo-G and Eiken latex test) were compared with the dye test. False-positive results were obtained using the IgG enzyme immunoassay (EIA) and AxSYM Toxo-G, and false negatives using all three screen tests. During pregnancy, positive results may falsely reassure, and patients should be tested for toxoplasma-specific IgM to differentiate between current infection and immunity. In immunocompromised patients, positive results indicate immunity but negative results do not exclude it; these should be tested by dye test. Despite these reservations, we have demonstrated that immunity screening can be performed within a district general hospital.

Animals↗
PubMed1999

Molecular search of new active drugs against Toxoplasma gondii.

Molecular connectivity has been applied to the search of new compounds with activity against the protozoan Toxoplasma gondii, using a stepwise linear discriminant analysis (SLDA) which is able to classify a compound according its activity either as active or as inactive. Among the selected compounds, andrographolide and dibenzotiophene sulfone stand out, both with IC50 values lower than 1 microgram/ml, which are comparable to these of drugs such as sulfamethoxazole, pyrimethamine and trimethoprim, with IC50 values equal to 1.1, 0.04 and 2.31 micrograms/ml, respectively. These results confirm the usefulness of our topological approach for the selection and design of new-lead drugs active against Toxoplasma gondii.

Animals↗
PubMed2000

The plastid of Toxoplasma gondii is divided by association with the centrosomes.

Apicomplexan parasites harbor a single nonphotosynthetic plastid, the apicoplast, which is essential for parasite survival. Exploiting Toxoplasma gondii as an accessible system for cell biological analysis and molecular genetic manipulation, we have studied how these parasites ensure that the plastid and its 35-kb circular genome are faithfully segregated during cell division. Parasite organelles were labeled by recombinant expression of fluorescent proteins targeted to the plastid and the nucleus, and time-lapse video microscopy was used to image labeled organelles throughout the cell cycle. Apicoplast division is tightly associated with nuclear and cell division and is characterized by an elongated, dumbbell-shaped intermediate. The plastid genome is divided early in this process, associating with the ends of the elongated organelle. A centrin-specific antibody demonstrates that the ends of dividing apicoplast are closely linked to the centrosomes. Treatment with dinitroaniline herbicides (which disrupt microtubule organization) leads to the formation of multiple spindles and large reticulate plastids studded with centrosomes. The mitotic spindle and the pellicle of the forming daughter cells appear to generate the force required for apicoplast division in Toxoplasma gondii. These observations are discussed in the context of autonomous and FtsZ-dependent division of plastids in plants and algae.

Aniline Compounds↗