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PubMed1990

Induction of tolerance to Toxoplasma gondii in newborn mice by maternal antibody.

To develop an animal model for analysing the suppressed immune response to Toxoplasma gondii in newborn humans with congenital toxoplasmosis, newborn mice from chronically infected mothers were inoculated intraperitoneally with bradyzoites of an avirulent strain. The newborn mice with maternal Toxoplasma antibodies showed a marked delay in the production of Toxoplasma antibodies when infected after birth. Many mice (11/13; 85%) developed a state of tolerance to T. gondii after disappearance of the maternal antibody, demonstrable by the absence of Toxoplasma antibody in their sera despite the fact that they were infected. The duration of tolerance differed between individuals, with two mice showing the longest tolerant state of 8 weeks. This murine model might be suitable for analysing the mechanism of suppressed immune response to T. gondii that has been observed in many human cases of congenital toxoplasmosis.

Animals↗

PubMed1994

Successful treatment of Toxoplasma gondii myocarditis in an AIDS patient.

Central nervous system disease due to Toxoplasma gondii is a common cause of morbidity and mortality in patients with the acquired immunodeficiency syndrome. Cardiac toxoplasmosis, however, has been described in only a limited number of cases. In a 45-year-old patient with symptoms suggestive of myocarditis, Toxoplasma gondii was detected in myocardial tissue obtained by biopsy. After the institution of appropriate antiprotozoal therapy, the patient recovered. This patient is believed to be the first patient to survive biopsy-proven myocarditis caused by Toxoplasma gondii. Cardiac toxoplasmosis should be ruled out in HIV-infected patients presenting with high fever and/or cardiorespiratory symptoms and exhibiting serologic evidence of prior exposure to Toxoplasma gondii as determined by a positive IgG EIA, especially if the CD4+ count is low and no systemic Pneumocystis carinii pneumonia prophylaxis has been administered. A high index of clinical suspicion and, if necessary, invasive diagnostic tests, including myocardial biopsies, are most important in making the correct diagnosis.

AIDS-Related Opportunistic Infections↗

PubMed1990

Comparison of dinucleotide frequency and codon usage in Toxoplasma and Plasmodium: evolutionary implications.

The weight-averaged observed/expected dinucleotide frequencies for the sum total of the coding regions of five Toxoplasma genes were compared with the same parameters previously determined for the coding regions of 21 Plasmodium genes. In addition, codon usage in the five Toxoplasma genes was compared with that in the 21 Plasmodium genes, and the percent distribution of amino acids in the Toxoplasma protein pool and the Plasmodium protein pool were compared with that in a general protein pool of 314 proteins. The results are consistent with the hypothesis that, contrary to currently held opinion, the genera Toxoplasma and Plasmodium are not especially closely related.

Animals↗

PubMed2004

Structure analysis of two Toxoplasma gondii and Neospora caninum satellite DNA families and evolution of their common monomeric sequence.

A family of repetitive DNA elements of approximately 350 bp-Sat350-that are members of Toxoplasma gondii satellite DNA was further analyzed. Sequence analysis identified at least three distinct repeat types within this family, called types A, B, and C. B repeats were divided into the subtypes B1 and B2. A search for internal repetitions within this family permitted the identification of conserved regions and the design of PCR primers that amplify almost all these repetitive elements. These primers amplified the expected 350-bp repeats and a novel 680-bp repetitive element (Sat680) related to this family. Two additional tandemly repeated high-order structures corresponding to this satellite DNA family were found by searching the Toxoplasma genome database with these sequences. These studies were confirmed by sequence analysis and identified: (1). an arrangement of AB1CB2 350-bp repeats and (2). an arrangement of two 350-bp-like repeats, resulting in a 680-bp monomer. Sequence comparison and phylogenetic analysis indicated that both high-order structures may have originated from the same ancestral 350-bp repeat. PCR amplification, sequence analysis and Southern blot showed that similar high-order structures were also found in the Toxoplasma-sister taxon Neospora caninum. The Toxoplasma genome database (http://ToxoDB.org ) permitted the assembly of a contig harboring Sat350 elements at one end and a long nonrepetitive DNA sequence flanking this satellite DNA. The region bordering the Sat350 repeats contained two differentially expressed sequence-related regions and interstitial telomeric sequences.

Animals↗

PubMed2005

Evolution of plant-like crystalline storage polysaccharide in the protozoan parasite Toxoplasma gondii argues for a red alga ancestry.

Single-celled apicomplexan parasites are known to cause major diseases in humans and animals including malaria, toxoplasmosis, and coccidiosis. The presence of apicoplasts with the remnant of a plastid-like DNA argues that these parasites evolved from photosynthetic ancestors possibly related to the dinoflagellates. Toxoplasma gondii displays amylopectin-like polymers within the cytoplasm of the dormant brain cysts. Here we report a detailed structural and comparative analysis of the Toxoplasma gondii, green alga Chlamydomonas reinhardtii, and dinoflagellate Crypthecodinium cohnii storage polysaccharides. We show Toxoplasma gondii amylopectin to be similar to the semicrystalline floridean starch accumulated by red algae. Unlike green plants or algae, the nuclear DNA sequences as well as biochemical and phylogenetic analysis argue that the Toxoplasma gondii amylopectin pathway has evolved from a totally different UDP-glucose-based metabolism similar to that of the floridean starch accumulating red alga Cyanidioschyzon merolae and, to a lesser extent, to those of glycogen storing animals or fungi. In both red algae and apicomplexan parasites, isoamylase and glucan-water dikinase sequences are proposed to explain the appearance of semicrystalline starch-like polymers. Our results have built a case for the separate evolution of semicrystalline storage polysaccharides upon acquisition of photosynthesis in eukaryotes.

Amino Acid Sequence↗

PubMed2006

Regulation of microglial cell responses in murine Toxoplasma encephalitis by CD200/CD200 receptor interaction.

Under autoimmune inflammatory conditions within the brain, evidence suggests that neurons downregulate microglial activation through CD200/CD200R interaction, which reduces disease severity. To gain insight into the regulation of intracerebral immune reactions by resident brain cells in chronic cerebral infections, the expression of the CD200 antigen and the CD200R as well as the functional role of CD200/CD200R interactions were characterized in murine Toxoplasma encephalitis. In the normal brain of C57BL/6 wild type mice, CD200 was ubiquitously expressed on neurons, their axons, cerebral endothelial cells, and plexus macrophages. CD200R was expressed at very low levels on cerebral macrophages and microglia without differences between CD200-/- and wild type mice. Infection of C57BL/6 mice with Toxoplasma gondii induced an upregulation of CD200R on microglia and of CD200 on blood vessel endothelial cells. In Toxoplasma encephalitis of CD200-/- mice, microglial cell numbers strongly increased due to an enhanced proliferation indicated by increased Ki-67 immunoreactivity. In addition, microglial activation was increased in CD200-/- mice as evidenced by a further upregulation of already high MHC class II levels as well as an increased expression of the anti-parasitic effector molecules, TNF and iNOS. The increased microglial cell activation resulted in a reduced intracerebral parasite burden and an increased survival rate. Thus, in Toxoplasma encephalitis, microglial activity was regulated via CD200/CD200R-mediated interaction further pointing to an intrinsic regulation of brain resident cells under inflammatory CNS conditions.

Animals↗

PubMed2003

Immunological comparison of 124 isolates of Toxoplasma gondii.

We tested 124 isolates of Toxoplasma gondii, as determined morphologically and by their ability to elicit antibodies in the dye test with the RH strain of Toxoplasma in mice. They were compared for their capacity to immunize CF-1 mice against isolate T-1, and T-1 immune mice for their capacity to resist each of the 123 other isolates. Of the 125 isolates, 52 had been isolated in the continental USA, 33 in Central America, 15 in Europe, 9 in Hawaii, five in Japan, two in Taiwan, five in Australia, one in Indonesia, one in Tunisia, and one was of unknown origin. Complete cross-immunity was found. This suggests that only one immunotype of Toxoplasma is prevalent in the United States, and perhaps all over the earth. Vaccines are likely to immunize against most or all Toxoplasma isolates.

Animals↗

PubMed1990

Toxoplasma gondii: immunocytochemistry of four immunodominant antigens with monoclonal antibodies.

Four monoclonal antibodies in which diagnostic usefulness has been observed, concerning congenital, acquired, and reactivated toxoplasmosis, were raised against Toxoplasma gondii tachyzoïtes in order to localize immunodominant antigens. On immunoblots, it appears that McAb IV47, McAB GII9, McAb II38, and McAb IE10 identify families of proteins with estimated molecular weights of 28-30 kDa, 30 kDa, 45-50 kDa, and 66-70 kDa, respectively. By immunogold preembedding techniques one can observe an homogeneous labeling of the outer pellicle of the tachyzoïtes with the McAb GII9 and IV47 and a light labeling with the McAb II38 and IE10. The three-dimensional observation of cell surface antigens is performed by applying a modified metal extraction replica method, i.e., A plasma polymerization method of glow discharge by Tanaka (1979). By immunogold preembedding techniques [with saponin permeabilization (0.1%)], and by immunogold postembedding techniques, a labeling of the rhoptries is observed with McAb GII9 and McAb IV47 but essentially all label is found with McAb II38 and IE10. With McAb GII9 a uniform labeling is observed on the cell surface. By immunoenzymatic techniques (peroxidase) a cell surface labeling is observed with the four McAb. Intracellular Toxoplasma, the outer pellicle, and the vesicles of the network (elaborated by Toxoplasma in parasitophorous vacuole) are also labeled with McAb IE10. These results indicate that McAb GII9 recognizes antigens of the antigen family (P 30) located on the cell surface and in the rhoptries. The antigen recognized by McAb IV47 is essentially located on and beneath the Toxoplasma cell surface membrane, and McAb II38 and IE10 identify preferentially rhoptry proteins.

Animals↗

PubMed1983

Identification of antigenic components of Toxoplasma gondii by an immunoblotting technique.

Proteins of Toxoplasma gondii were separated by SDS-polyacrylamide gel electrophoresis with subsequent transfer to a nitrocellulose sheet by electrophoretic blotting. Immunologically reactive polypeptides were detected by human sera with previously known toxoplasma antibody levels. Heavy chain-specific, peroxidase-conjugated anti-human immunoglobulins were used as the indicator antibodies for the separate identification of IgG and IgM reactive polypeptides. IgG toxoplasma antibodies reacted with several antigens of Mr approximately 27 000-67 000, while toxoplasma-specific IgM seemed to detect only a few polypeptides. The Mr of 35 000 for the dominating IgM reactive polypeptide was observed.

Antibodies↗

PubMed1993

In-vitro synthesis of antibodies to Toxoplasma gondii by lymphocytes from HIV-1-infected patients.

Toxoplasma-specific in-vitro antibody production by peripheral blood lymphocytes (PBL) was investigated in 124 adults infected with human immunodeficiency virus (HIV-1). PBL from 20 of 21 patients with cerebral toxoplasmosis showed spontaneous in-vitro secretion of antibodies to Toxoplasma gondii antigens. Among 103 HIV-1-infected patients without signs or symptoms of toxoplasmosis, PBL from 19 produced toxoplasma-specific antibodies in vitro; 5 of these patients, who discontinued prophylaxis for toxoplasmic encephalitis, showed in-vitro antibody production 3-15 months before the diagnosis of toxoplasmic encephalitis. In-vitro production of toxoplasma-specific antibodies could improve the diagnosis of toxoplasmic encephalitis in HIV-1-infected patients.

AIDS-Related Opportunistic Infections↗

PubMed1989

Western blot analyses and LD50 determinations of Toxoplasma gondii isolates.

Western blot analysis of tachyzoite detergent extracts revealed striking similarities and only minor differences in the antigenic profiles of four isolates, including one new isolate of Toxoplasma gondii. At least nine common protein bands with molecular weights ranging from 14,000-108,000 were recognized by all antitoxoplasma antisera. Differences existed primarily between molecular weights 28,000 and 33,000. The LD50 determinations showed that strains of laboratory mice were affected differently by the various Toxoplasma isolates used in this study. Results indicate a need for further investigations into whether there are true strain differences of Toxoplasma gondii or simply different isolates of the same strain of this single species in the genus Toxoplasma.

Animals↗

PubMedDate not supplied

The importance of trophozoites in transmission of toxoplasmosis: survival and pathogenity of Toxoplasma gondii trophozoites in liquid media.

It has been generally assumed that Toxoplasma gondii trophozoites cannot survive long outside the body, and that toxoplasmosis is transmitted by transplacental infection, cysts and oocysts. We tested the survival and pathogenicity of separated Toxoplasma trophozoites in saline, colostrum, and solutions of albumen and serum, and the penetration of Toxoplasma trophozoites from infected secretions through mucous membranes of nose, conjunctiva, and mouth. The trophozoites survived 24 h in saline, 3 days in 3.5% serum albumen, 3 days in colostrum, and 17-43 days in serum solutions. The infectivity of the trophozoites was highest after nasal instillation, second highest after instillation into conjunctiva, and lowest after instillation into the mouth. The infective dose was calculated. The results show that Toxoplasma trophozoites survive and remain infectious for a relatively long time in biological liquid media and can easily penetrate mucous membranes, and suggest a revised hypothesis for the transmission of Toxoplasmosis with the trophozoites as one important source of infection.

Animals↗

PubMed1996

Toxoplasma invasion of mammalian cells is powered by the actin cytoskeleton of the parasite.

Toxoplasma gondii is an obligate intracellular parasite that invades a wide range of vertebrate host cells. We demonstrate that invasion is critically dependent on actin filaments in the parasite, but not the host cell. Invasion into cytochalasin D (CD)-resistant host cells was blocked by CD, while parasite mutants invaded wild-type host cells in the presence of drug. CD resistance in Toxoplasma was mediated by a point mutation in the single-copy actin gene ACT1. Transfection of the mutant act1 allele into wild-type Toxoplasma conferred motility and invasion in the presence of CD. We conclude that host cell invasion by Toxoplasma, and likely by related Apicomplexans, is actively powered by an actin-based contractile system in the parasite.

Actin Cytoskeleton↗

PubMed1987

Higher yields and increased purity of in vitro grown Toxoplasma gondii.

An improved method for in vitro cultivation of Toxoplasma gondii is described. Commonly, confluent cell monolayers are infected with Toxoplasma; higher yields and an increased purity could be obtained instead when host cells were immediately infected after subculture: Depending on the initial parasite inoculum 2-3 fold increased multiplication rates were achieved and simultaneously the amount of host cell debris was reduced to 10-20 per cent compared to that deriving from infected cell monolayers. This may be ascribed to a facilitated invasion of host cells by Toxoplasma when the cell's glycocalyx is irritated by trypsinization and to a more far-reaching exploitation of young separated host cells in contrast to cells of monolayers. Moreover, the Toxoplasma trophozoites could be harvested from tissue culture already four days after infection without any change of medium, which makes the method very economical.

Animals↗

PubMed1987

Modification of growth rate of Toxoplasma gondii by continuous passage in immune mice.

Growth of the RH strain of Toxoplasma gondii, is suppressed in mice immunized with Toxoplasma antigens. At the second passage, the growth of T. gondii harvested from immune mice is suppressed more strongly in immune mice than that of T. gondii from control mice. After 52 passages in immune mice, the growth of T. gondii was still suppressed in immune mice than in control mice. T. gondii did not possess ability of antigenic variation (Pfefferkorn et al., 1983). After vaccination with the S-273 strain of T. gondii, mice were challenged twice with the RH strain. Cysts in brains caused death of all mice by inoculation at the 1st, 2nd, 3rd, 4th and 8th week after the second challenge of the RH strain. But the cysts from mice at the 16th and 30th week have decreased virulence, causing death in only 2 out of 4 and 1 out of 4 mice, respectively. Virulence of cysts had no definite relationship to Toxoplasma antibodies by indirect latex agglutination test and the numbers of cysts per brain. Growth variation of T. gondii is proposed under unfavourable conditions as in mice immunized with Toxoplasma antigens or vaccinated with the S-273 strain.

Animals↗

PubMed1988

Isoenzyme studies on Toxoplasma gondii isolates using isoelectric focusing.

Zymogram analysis using isoelectric focusing on polyacrylamide gels was performed to characterize and distinguish two Toxoplasma gondii isolates ("strains" BK and RH). The activity of the following 14 enzymes in the cell lysates was investigated: IDH, MDH, ME, 6PG, G6P, LDH, IPO, HEX, PGM, EST, ALP, ACP, LAP, and PGI. Nine enzymes (IDH, G6P, LDH, HEX, PGM, EST, ALP, ACP, and PGI) showed distinct and reproducible banding patterns, and four of them (IDH, G6P, EST, PGI) enabled a reliable distinction of the two Toxoplasma gondii isolates. A contamination of the parasite extracts with host proteins could be excluded by comparison of the enzyme activities of the Toxoplasma isolates with mouse peritoneal exudate cells. Isoenzyme analysis proved to be a helpful method for a characterization and a distinction of Toxoplasma gondii isolates.

Animals↗

PubMed1999

Infection with Toxoplasma gondii RH and Prugniaud strains in mice, rats and nude rats: kinetics of infection in blood and tissues related to pathology in acute and chronic infection.

Since mice and rats are the most studied models of experimental toxoplasmosis, the aim of this work was to analyze the outcome of Toxoplasma infection in mice, rats and congenitally athymic nude rats; for this purpose, the parasitic load in different organs and the anatomic-pathological characteristics of infection were investigated in these animals. The data obtained after infection with two different strains and stages of Toxoplasma gondii (RH tachyzoites and Prugniaud cysts) concerned the following organs: brain, mesenteric lymph nodes, blood, spleen, heart, lungs, diaphragm and liver. In Fischer rats, the infection with either the Prugniaud or the RH strains displayed similar characteristics: after a peak in the parasite load, a complete disappearance of parasites was observed, except in the brain of Prugniaud strain-infected rats where toxoplasmas were evidenced throughout the experiment. In OF1 mice, where infection by the RH tachyzoites was lethal, infection with the Prugniaud strain led to survival; the parasitic burden peaked in the different organs and was then undetectable, except in the brain where toxoplasmas were still present during the chronic phase. Like mice, nude rats did not survive to the RH infection. Interestingly, for all the animals the observed histopathological changes in the infected organs, although more or less obvious in the acute phase, were not very severe in almost all cases. For instance, mice, although more susceptible to infection than rats, did not present more severe lesions. They consisted in a discrete inflammation with some focal areas of necrosis in some organs such as brain, liver and heart. Our results support the assumption that rats and nude rats constitute interesting experimental models relevant to either human acute toxoplasmosis, chronic toxoplasmosis, or disseminated toxoplasmosis in AIDS patients.

Acute Disease↗

PubMed2003

Drugs used in the treatment of schizophrenia and bipolar disorder inhibit the replication of Toxoplasma gondii.

The exact mechanisms of action of some antipsychotics and mood stabilizers have not been elucidated. Response to these medications can vary among individuals. Recent studies indicate that infection with the parasite Toxoplasma gondii may contribute to the symptoms of schizophrenia in some individuals. We investigated commonly used antipsychotic and mood stabilizing medications for their ability to inhibit the replication of this organism. We employed a system for testing compounds for in vitro activity against T. gondii. Human fibroblasts (HFF) were treated with test compounds and then exposed to Toxoplasma that has been genetically modified to express cytoplasmic beta-galactosidase. Inhibition by the drugs was determined by spectrophotometric analysis of colorimetric reactions. We tested 12 neuroleptic compounds and found that of these, the antipsychotic haloperidol and the mood stabilizer valproic acid most effectively inhibit Toxoplasma growth in vitro. Valproic acid inhibited the parasite at a concentration below that found in the cerebrospinal fluid and blood of individuals being treated with this medication and displayed synergistic activity with haloperidol and with trimethoprim, an antibiotic commonly used to treat Toxoplasma infections.Several medications used to treat schizophrenia and bipolar disorder have the ability to inhibit the in vitro replication of T. gondii.

Animals↗