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 613 records · Page 34Linked to original sources
PubMed1995

A Toxoplasma gondii-derived factor(s) stimulates immune downregulation: an in vitro model.

Suppression of the T-cell lymphoproliferative response and downregulation of interleukin 2 (IL-2) production by Toxoplasma gondii has been observed following in vivo infection. In this study, an experimental in vitro murine system was developed to evaluate the kinetics of these responses. Normal splenocytes from uninfected mice were stimulated with either concanavalin A or an anti-CD3 monoclonal antibody and cocultured with Toxoplasma tachyzoites either directly or separated by a transwell. A progressive decline in the lymphoproliferative response was observed as the concentration of parasites in culture increased. Neither heat-killed nor formaldehyde-fixed parasites stimulated this downregulatory response by the splenocytes. A decline in IL-2 production was associated with the decrease in lymphocyte proliferation. The addition of an antibody to IL-10 or heat-inactivated anti-Toxoplasma sera to the culture supernatant partially neutralized the inhibitory effect on lymphocyte proliferation. Cytokine analysis of the responder splenocytes demonstrated a decrease in the message for IL-2 and IL-2 receptor and an increase in IL-10. Together, these observations suggest that during in vitro culture in a murine system, parasite antigens that stimulate the release of a soluble factor(s), such as IL-10, that inhibits proliferation of mitogen-stimulated T cells are expressed.

Animals↗
PubMed1996

Attachment of Toxoplasma gondii to host cells is host cell cycle dependent.

The initial attachment of Toxoplasma tachyzoites to target host cells is an important event in the life cycle of the parasite and hence critical in the pathogenesis of this infection. The efficiency of Toxoplasma attachment to synchronized populations of Chinese hamster ovary cells and bovine kidney cells was investigated by using a glutaraldehyde-fixed host cell assay system. For both cell lines, parasite attachment increased as the synchronized host cells proceeded from the G1 phase to the mid-S phase and then decreased as the cells entered the G2-M boundary. Postulating that these differences in attachment reflect the upregulation of a specific receptor, polyclonal antibodies were generated against whole MDBK antigen at 0 and 4 h into the S phase. Both antisera were shown to inhibit parasite attachment to both synchronous and asynchronous host cell populations. However, the attachment blockade observed with the 4-h antiserum was significantly greater than that with the 0-h antiserum, completely abolishing the cell cycle-dependent increase in attachment found in control samples. These findings suggest that Toxoplasma tachyzoites bind specifically to a host cell receptor which is upregulated in the mid-S phase of the cell cycle.

Adhesiveness↗
PubMed1998

The surface of Toxoplasma tachyzoites is dominated by a family of glycosylphosphatidylinositol-anchored antigens related to SAG1.

Toxoplasma gondii is an Apicomplexan parasite with a complex life cycle that includes a rapidly dividing asexual stage known as the tachyzoite. The tachyzoite surface has been reported to comprise five major antigens, the most abundant of which is designated SAG1 (for surface antigen 1). At least one of the other four (SAG3) and another recently described minor antigen (SRS1 [for SAG1-related sequence 1]) have previously been shown to be structurally related to SAG1. To determine if further SAG1 homologs exist, we searched a Toxoplasma expressed sequence tag (EST) database and found numerous ESTs corresponding to at least three new genes related to SAG1. Like SAG1, these new SRS genes encode apparently glycosylphosphatidylinositol-anchored proteins that share several motifs and a set of conserved cysteine residues. This family appears to have arisen by divergence from a common ancestor under selection for the conservation of overall topology. The products of two of these new genes (SRS2 and SRS3) are shown to be expressed on the surface of Toxoplasma tachyzoites by immunofluorescence. We also identified strain-specific differences in relative expression levels. A total of 10 members of the SAG1 gene family have now been identified, which apparently include three of the five major surface antigens previously described and one antigen expressed only in bradyzoites. The function of this family may be to provide a redundant system of receptors for interaction with host cells and/or to direct the immune responses that limit acute T. gondii infections.

Amino Acid Sequence↗
PubMed1999

Transformed Toxoplasma gondii tachyzoites expressing the circumsporozoite protein of Plasmodium knowlesi elicit a specific immune response in rhesus monkeys.

Toxoplasma gondii tachyzoites were transformed with the coding sequence of the circumsporozoite (CS) protein of the primate malaria parasite Plasmodium knowlesi. A single inoculation of live transformed tachyzoites elicited an antibody response directed against the immunodominant repeat epitope (EQPAAGAGG)2 of the P. knowlesi CS protein in rhesus monkeys. Notably, these animals failed to show a positive serum conversion against T. gondii. Antibodies against Toxoplasma antigens were detected only after a second inoculation with a higher number of transformed tachyzoites. This boost induced an increased antibody response against the P. knowlesi CS protein associated with immunoglobulin class switching, thus demonstrating the establishment of immunological memory. These results indicate that the Toxoplasma-derived CS protein is efficiently recognized by the monkey immune system and represents an immunodominant antigen in transformed parasites.

Amino Acid Sequence↗
PubMed2002

Mechanism of entry determines the ability of Toxoplasma gondii to inhibit macrophage proinflammatory cytokine production.

Macrophages (Mphi) infected with tachyzoites of the opportunistic protozoan Toxoplasma gondii are blocked in production of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-12 (IL-12) in response to lipopolysaccharide (LPS) triggering, and this is associated with parasite-induced inhibition of NFkappaB translocation. Here, we demonstrate a requirement for active invasion in the ability of the parasite to mediate suppression. Neither soluble tachyzoite antigen nor secreted products were suppressive, and heat-inactivated, antibody-coated tachyzoites, which efficiently entered the cell through receptor-mediated uptake, failed to inhibit LPS responses. Cytochalasin D, a drug blocking tachyzoite invasion of, but not adherence to, Mphi, severely curtailed Toxoplasma-induced suppression. In addition, parasite-induced nonresponsiveness, as measured by TNF-alpha production, was reversed by treating infected cells with the toxoplasmastatic drugs pyrimethamine and 6-thioxanthine prior to LPS stimulation. A divergence in IL-12 and TNF-alpha responses was found during extended incubation of tachyzoites and Mphi in that 24 h of incubation of infected Mphi resulted in IL-12, but not TNF-alpha, secretion, and production of the latter cytokine remained suppressed when these cells were subjected to LPS triggering. Our results demonstrate that active invasion and survival of the parasite within the parasitophorous vacuole are required to induce and maintain Mphi cytokine-specific nonresponsiveness to LPS. They also show that the effects of Toxoplasma on IL-12 and TNF-alpha production are nonidentical, with the parasite exerting a longer-lasting suppression of the latter.

Animals↗
PubMed2003

Protective mucosal Th2 immune response against Toxoplasma gondii by murine mesenteric lymph node dendritic cells.

Toxoplasma gondii, an obligate intracellular parasite pathogen which initially invades the intestinal epithelium before disseminating throughout the body, may cause severe sequelae in fetuses and life-threatening neuropathy in immunocompromised patients. Immune protection is usually thought to be performed through a systemic Th1 response; considering the route of parasite entry it is important to study and characterize the local mucosal immune response to T. gondii. Despite considerable effort, Toxoplasma-targeted vaccines have proven to be elusive using conventional strategies. We report the use of mesenteric lymph node dendritic cells (MLNDCs) pulsed ex vivo with T. gondii antigens (TAg) as a novel investigation approach to vaccination against T. gondii-driven pathogenic processes. Using a murine model, we demonstrate in two genetically distinct mouse strains (C57BL/6 and CBA/J) that adoptively transferred TAg-pulsed MLNDCs elicit a mucosal Toxoplasma-specific Th2-biased immune response in vivo and confer strong protection against infection. We also observe that MLNDCs mostly traffic to the intestine where they enhance resistance by reduction in the mortality and in the number of brain cysts. Thus, ex vivo TAg-pulsed MLNDCs represent a powerful tool for the study of protective immunity to T. gondii, delivered through its natural route of entry. These findings might impact the design of vaccine strategies against other invasive microorganisms known to be delivered through digestive tract.

Adoptive Transfer↗
PubMed2004

TRAF6-dependent mitogen-activated protein kinase activation differentially regulates the production of interleukin-12 by macrophages in response to Toxoplasma gondii.

The production of interleukin-12 (IL-12) is critical to the development of innate and adaptive immune responses required for the control of intracellular pathogens. Many microbial products signal through Toll-like receptors (TLR) and activate NF-kappaB family members that are required for the production of IL-12. Recent studies suggest that components of the TLR pathway are required for the production of IL-12 in response to the parasite Toxoplasma gondii; however, the production of IL-12 in response to this parasite is independent of NF-kappaB activation. The adaptor molecule TRAF6 is involved in TLR signaling pathways and associates with serine/threonine kinases involved in the activation of both NF-kappaB and mitogen-activated protein kinase (MAPK). To elucidate the intracellular signaling pathways involved in the production of IL-12 in response to soluble toxoplasma antigen (STAg), wild-type and TRAF6(-/-) mice were inoculated with STAg, and the production of IL-12(p40) was determined. TRAF6(-/-) mice failed to produce IL-12(p40) in response to STAg, and TRAF6(-/-) macrophages stimulated with STAg also failed to produce IL-12(p40). Studies using Western blot analysis of wild-type and TRAF6(-/-) macrophages revealed that stimulation with STAg resulted in the rapid TRAF6-dependent phosphorylation of p38 and extracellular signal-related kinase, which differentially regulated the production of IL-12(p40). The studies presented here demonstrate for the first time that the production of IL-12(p40) in response to toxoplasma is dependent upon TRAF6 and p38 MAPK.

Animals↗
PubMed2005

Cell surface heparan sulfate promotes replication of Toxoplasma gondii.

Previous work suggests that cell surface heparan sulfate acts as a receptor for the Apicomplexan parasite Toxoplasma gondii. Using Chinese hamster ovary cell mutants defective in heparan sulfate biosynthesis, we show that heparan sulfate is necessary and sufficient for infectivity. Further, we demonstrate that the parasite requires N sulfation of heparan sulfate initiated by N-deacetylase/N-sulfotransferase-1, but 2-O sulfation and 6-O sulfation appear to be dispensable. In order to study the role of heparan sulfate in other cell types, we created a conditional allele for N-deacetylase/N-sulfotransferase-1 by using Cre-loxP technology. Mammary tumor cells lacking N-deacetylase/N-sulfotransferase-1 exhibited reduced toxoplasma infectivity like Chinese hamster ovary cell mutants. Surprisingly, heparin, chemically modified heparinoids, and monoclonal antibodies to heparan sulfate had no effect on toxoplasma infection. T. gondii attachment and invasion were unchanged in N-deacetylase/N-sulfotransferase-1-inactivated cells as well, but replication was reduced. Thus, heparan sulfate does not appear to function as a receptor for T. gondii but instead facilitates parasite replication postinvasion.

Animals↗
PubMed1968

Penetration-enhancing factor extracted from Toxoplasma gondii which increases its virulence for mice.

Fractionation of extracts of disintegrated Toxoplasma gondii resulted in preparations which, when tested in cell cultures, enhanced penetration of host cells by this parasite. The influence of the preparations on the virulence of the RH strain and on two naturally avirulent strains for mice was studied simultaneously with the in vitro studies. It was demonstrated that the preparations increased the virulence of Toxoplasma. Mice inoculated with the preparation plus Toxoplasma suffered earlier morbidity and had a greater mortality rate than the control animals. There was a direct correlation between the effect of the preparations on the cell-penetrating capacity of the parasites and the increase in virulence for mice, indicating that the same mechanism is operative in both the in vivo and in vitro systems observed.

Animals↗
PubMed1985

Demonstration of Toxoplasma antigen containing complexes in active toxoplasmosis.

With an enzyme-linked immunosorbent assay antigen, specific circulating immune complexes (CIC) were demonstrated in experimental and human toxoplasmosis. In experimentally infected mice, CIC became demonstrable as soon as antibodies appeared after fatal infection. When a nonvirulent strain of Toxoplasma was used CIC remained detectable for several weeks. This period was characterized by clinically healthy animals with increasing antibody titers and by cysts growing in the brains of the animals, indicating a subacute stage of the toxoplasma infection. In the human sera, a surprisingly high percentage of CIC was demonstrated. Both immunoglobulin G (IgG) and IgM were found in the CIC; however, IgG was seen in the majority. If the humans were grouped according to other serological results, such as a combination with IgM antibodies, circulating antigens, or both, or a positive complement fixation test, increasingly more CIC were observed. When sera were selected from patients with clinical symptoms generally associated with toxoplasmosis, more CIC were also again demonstrated. On the contrary, in healthy individuals (blood donors), CIC were also regularly observed, suggesting that exacerbations of latent infections or reinfections may regularly occur without leading to clinical signs. In conclusion, we propose that the interpretation of a positive CIC test requires great care but may provide useful information about the activity of a toxoplasma infection.

Animals↗
PubMed1988

Antigen(s) responsible for immunoglobulin G responses specific for the acute stage of Toxoplasma infection in humans.

An agglutination test for immunoglobulin G (IgG) Toxoplasma antibodies with acetone-fixed tachyzoites (AC antigens; AC agglutination test) was positive only with sera from patients during the acute stage of their infection. In contrast, when the test was performed with Formalin-fixed tachyzoites (HS antigens; HS agglutination test), positive results were obtained during both the acute and chronic (latent) stages of the infection. Studies were performed to define the antigen(s) of T. gondii which are detected by IgG antibodies present only during the acute stage of the infection. Sera of mice immunized with AC antigens recognized predominantly 10 antigens of tachyzoites by immunoblot analysis. Sera from individuals with the acute but not chronic infection reacted strongly with these same 10 antigens in immunoblots. Sera of mice immunized with HS antigens recognized more Toxoplasma antigens on immunoblots than did mouse AC antibodies. Absorption of the latter with HS antigens removed detectable reactivity of AC antibodies in immunoblots and in the AC and HS agglutination tests, suggesting that AC antigens are a selected portion of HS antigens. AC antigens were specific for tachyzoites in that AC antibodies reacted with the cell membranes of both forms of the organism in an indirect fluorescent-antibody test. Tachyzoite-specific antigen(s) appear to be useful in differentiating between the acute and chronic stages of Toxoplasma infection through their detection by IgG antibodies.

Acute Disease↗
PubMed1990

Rapid prenatal diagnosis of congenital Toxoplasma infection by using polymerase chain reaction and amniotic fluid.

Infection of pregnant women with Toxoplasma gondii places the developing fetus at risk for congenital infection. We report a prospective study of 43 documented cases of acute maternal Toxoplasma infections acquired during gestation in which the polymerase chain reaction (PCR) was evaluated for diagnosis of fetal infection and compared with the current standard methods. On the basis of direct lysis of pelleted amniotic fluid cells followed by amplification of a gene sequence specific for T. gondii, PCR correctly identified the presence of T. gondii in five of five samples of amniotic fluid from four proven cases of congenital infection. PCR also detected three of five positive cases from a nonprospective group. The two diagnostic methods of comparable speed, detection of specific immunoglobulin M from fetal blood and and inoculation of amniotic fluid into tissue culture, correctly identified only 3 and 4 of the 10 positive samples, respectively. The considerably more time-consuming methods of mouse inoculation of amniotic fluid and fetal blood both detected 7 of 10 positive samples. There were no false-positive diagnoses by any of the methods. Therefore, detection of T. gondii by PCR appears to be the most promising method for prenatal diagnosis of congenital Toxoplasma infection, since it is both extremely rapid and highly sensitive.

Amniocentesis↗
PubMed1990

Differential agglutination test for diagnosis of recently acquired infection with Toxoplasma gondii.

We evaluated the recently described differential agglutination test (HS/AC test) to differentiate recently acquired toxoplasma infections from those acquired in the more distant past in sera obtained from 38 patients with carefully defined symptomatic and asymptomatic infections. AC antigens detect acute-phase-specific immunoglobulin G (IgG) antibodies against Toxoplasma gondii tachyzoites that are formed only during the acute stage of infection in humans. The HS/AC test correctly identified recently acquired infections in patients with toxoplasmic lymphadenopathy or asymptomatic infections (including infections in 7 women who seroconverted during gestation) in 31 of 33 patients. We also studied 15 individuals who had been infected for at least 2 years. In that group, only 13% had an acute pattern in the HS/AC test. However, the wide range in times from infection (from 2 to 14 years) did not allow for an estimate of when the pattern in the HS/AC test changed from acute to not acute. These results reveal that in the appropriate clinical situation, when both IgG and IgM tests are positive and a question still remains about the acuteness of infection, the HS/AC test may be useful for differentiating between toxoplasma infections acquired recently and those acquired in the more distant past.

Agglutination Tests↗
PubMed1996

Multicenter evaluation of a fluorometric enzyme immunocapture assay to detect toxoplasma-specific immunoglobulin M in dried blood filter paper specimens from newborns.

An easy-to-perform fluorometric enzyme immunocapture assay (FEIA) was developed by Labsystems, Helsinki, Finland, to detect toxoplasma-specific immunoglobulin M (IgM) in dried blood spots. Assay materials were distributed to two sites that have programs in place designed to identify infants born with congenital toxoplasma infection: the Statens Serum Institut, Copenhagen, Denmark, and the New England Regional Newborn Screening Program, Boston, Mass. Each site tested over 700 dried blood samples from healthy newborns to define a cutoff at the 99.5 percentile (5 enzyme immunounits for Copenhagen and 4 enzyme immunounits for Boston). Each site then applied its own cutoff of interpret results for dried blood spots prepared from either adults with serology suggestive of acute infection (Copenhagen) or infants determined to be congenitally infected on the basis of serological criteria (Boston). In Copenhagen, 35 of 38 adult samples were either positive to a small degree or borderline positive for IgA. These samples thus may not represent acute infection. In Boston, of 26 congenitally infected infants, 22 were positive by FEIA. The four infant specimens not positive by FEIA were either negative or borderline positive by the standard Boston assay. These results demonstrate that the IgM FEIA is a potential alternative to other filter paper assay for toxoplasma-specific IgM currently in use for newborns.

Adult↗
PubMed1996

Diagnostic implications of kinetics of immunoglobulin M and A antibody responses to Toxoplasma gondii.

We evaluated immunoglobulin M (IgM) and IgA assays that could improve the predictive value for recently acquired toxoplasma infection for patients with positive screening test results. Follow-up sera were collected from 82 patients whose initial serum specimen had a reactive anti-Toxoplasma gondii IgM result. According to the evolution of the immune response, patients were divided retrospectively into two groups: one in which a recent infection was unlikely and the other one with an evolving immune response suggestive of recent toxoplasma infection. All IgM and one of three IgA assays used in the study are suitable for screening pregnant patients, with a negative predictive value of 100%. The predictive value of positive results is much lower because of the low prevalence of acute toxoplasmosis in pregnant women and the long persistence of IgM after acute infection. In the present study, all except one IgM enzyme immunoassay remained positive well beyond 6 months after the initial sample was tested. The IgM immunofluorescence test had the shortest persistence of positivity in most cases. IgA tests were either too insensitive or remained reactive too long to be useful for screening pregnant patients. Interpreting enzyme immunoassays with modified cutoff values and the combination of two tests could improve the predictive value of positive results to about 80% in terms of recent infection.

Adolescent↗
PubMed1997

Detection of immunoglobulin G (IgG) and IgM antibodies to Toxoplasma gondii: evaluation of four commercial immunoassay systems.

A comparative evaluation of the following commercial immunoassays for the determination of antibodies to Toxoplasma gondii was performed: Behring Diagnostics OPUS Toxo G and Toxo M, Abbott Diagnostics IMX Toxo-IgG 2.0 and Toxo-IgM, Sanofi Diagnostics Pasteur Platelia Toxo IgG and Toxo IgM, and bioMérieux Vitek VIDAS Toxo IgG and IgM. Of 676 specimens that were tested for Toxoplasma-specific immunoglobulin G (IgG) antibodies, 26% were reactive by all methods while 8% displayed some discrepancy. Of 718 specimens that were tested for Toxoplasma-specific IgM antibodies, 3% were reactive by all methods while 10% displayed some discrepancy. Analysis of discrepant specimens revealed performance shortcomings with all IgM-specific assays. The impact of such shortcomings is magnified in a population with a low prevalence of toxoplasmosis.

Animals↗
PubMed2002

VIDAS test for avidity of Toxoplasma-specific immunoglobulin G for confirmatory testing of pregnant women.

Because congenital toxoplasmosis is almost solely the result of maternal infection acquired during gestation, it is critical to determine whether infection during pregnancy has occurred. In the United States, definitive diagnosis of the acute infection and the time of its occurrence have been compromised by a lack of systematic screening and the fact that only a single serum sample is submitted for testing. In studies in Europe, and depending on the method used, the demonstration of high-avidity immunoglobulin G (IgG) toxoplasma antibodies has been shown to exclude infection having occurred in the first 3 to 5 months of pregnancy. We investigated the usefulness of determining the avidity of IgG toxoplasma antibodies with a VIDAS kit (herein referred to as the VIDAS Toxo-IgG avidity kit, the VIDAS kit essentially rules out acute infection having occurred within the 4 prior months) in the setting of a reference serology laboratory in the United States. Sera (132 samples) from 132 women in the first 16 weeks of pregnancy were chosen because at least one test in the toxoplasma serological profile (TSP) suggested or was equivocal for a recently acquired infection. High-avidity antibodies were demonstrated in 75% of 99 sera positive with the IgM enzyme-linked immunosorbent assay (ELISA) and 31.3% of 16 sera with acute TSP results. A significant percentage of sera with equivocal results wtih the IgM ELISA or TSP also had high-avidity test results. Of 39 women for whom treatment with spiramycin had been suggested to attempt to prevent congenital transmission, 19 (48.7%) had high-avidity antibodies. These findings highlight the value of the VIDAS IgG avidity kit when used in combination with the TSP to exclude recent infection, especially when only a single serum sample is available.

Acute Disease↗
PubMed2003

Use of an immunoglobulin G avidity assay based on recombinant antigens for diagnosis of primary Toxoplasma gondii infection during pregnancy.

The objective of this work was to develop an antibody-specific immunoglobulin G (IgG) avidity assay to discriminate between acute and latent phases of Toxoplasma gondii infection by using recombinant antigens. One hundred twenty-one serum samples from women who developed IgG antibodies against Toxoplasma during pregnancy were used. The IgG avidities of antibodies directed against epitopes carried by fragments of GRA3, GRA7, MIC3, and SAG1 antigens were measured by performing parallel enzyme immunoassays. The avidity index for Toxoplasma-specific antibodies against a homogeneous mixture of recombinant GRA3, GRA7, MIC3, and SAG1 antigens correlated closely with the IgG avidity of antibodies against lysed whole-cell T. gondii antigen. The avidity assay performed with the recombinant MIC3 antigen highlighted the presence of avidity low-antibodies IgG exclusively in sera collected within 2 months after primary infection. The presence of T. gondii-specific, low-avidity IgG antibodies against recombinant MIC3 antigen can be used to determine the point of infection with T. gondii within a 2-month time frame after infection.

Animals↗