(1/2611) Disruption of the Toxoplasma gondii bradyzoite-specific gene BAG1 decreases in vivo cyst formation.
The bradyzoite stage of the Apicomplexan protozoan parasite Toxoplasma gondii plays a critical role in maintenance of latent infection. We reported previously the cloning of a bradyzoite-specific gene BAG1/hsp30 (previously referred to as BAG5) encoding a cytoplasmic antigen related to small heat shock proteins. We have now disrupted BAG1 in the T. gondii PLK strain by homologous recombination. H7, a cloned null mutant, and Y8, a control positive for both cat and BAG1, were chosen for further characterization. Immunofluorescence and Western blot analysis of bradyzoites with BAG1 antisera demonstrated expression of BAG1 in the Y8 and the PLK strain but no expression in H7. All three strains expressed a 116 kDa bradyzoite cyst wall antigen, a 29 kDa matrix antigen and the 65 kDa matrix reactive antigen MAG1. Mice inoculated with H7 parasites formed significantly fewer cysts than those inoculated with the Y8 and the PLK strains. H7 parasites were complemented with BAG1 using phleomycin selection. Cyst formation in vivo for the BAG1-complemented H7 parasites was similar to wild-type parasites. We therefore conclude that BAG1 is not essential for cyst formation, but facilitates formation of cysts in vivo. (+info)
(2/2611) Chemokine secretion of human cells in response to Toxoplasma gondii infection.
The ubiquitous protozoan parasite Toxoplasma gondii is a major cause of morbidity and mortality in neonates and immunocompromised hosts. Both acute invasion and reactivation of latent infection result in an inflammatory reaction with lymphocytes, macrophages, and neutrophils. The mechanisms responsible for triggering the local host response to toxoplasmosis are not fully understood. Infection of monolayers of human HeLa epithelial cells and fibroblasts with T. gondii resulted in a marked increase in the expression of interleukin-8 (IL-8)-specific mRNA and secretion of the proinflammatory and chemoattractant cytokines interleukin-8 (IL-8), GROalpha, and MCP-1. Host cell invasion and lysis were required for this response, as tachyzoite lysates alone had no effect on IL-8 secretion. IL-8 release was dependent on the release of soluble host cell factors: IL-1alpha in HeLa cells and an additional mediator in fibroblasts. HT-29 epithelial cells, which lack IL-1alpha or another IL-8-inducing activity, did not release IL-8 after infection, although they were efficiently infected with T. gondii and increased IL-8 secretion in response to added IL-1alpha. These data suggest that proinflammatory chemokine secretion is an important host cell response to toxoplasmosis and that the release of IL-1alpha and other mediators from lysed host cells is critical for this chemokine response. (+info)
(3/2611) 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. (+info)
(4/2611) Inhibition of inducible nitric oxide synthase exacerbates chronic cerebral toxoplasmosis in Toxoplasma gondii-susceptible C57BL/6 mice but does not reactivate the latent disease in T. gondii-resistant BALB/c mice.
Infection of C57BL/6 mice with Toxoplasma gondii leads to progressive and ultimately fatal chronic Toxoplasma encephalitis (TE). Genetic deletion or inhibition of inducible nitric oxide synthase (iNOS) from the beginning of infection increased the number of T. gondii cysts in the brain and markedly reduced the time-to-death in this mouse strain. In the present study, we addressed whether iNOS also contributes to the control of intracerebral parasites in a clinically stable latent infection that develops in T. gondii-resistant BALB/c mice after resolution of the acute phase of TE. iNOS was expressed in the inflammatory cerebral infiltrates of latently infected BALB/c mice, but the number of iNOS+ cells was significantly lower than in the brains of chronically infected T. gondii-susceptible C57BL/6 mice. In BALB/c mice with latent TE (> 30 days of infection), treatment with the iNOS inhibitors L-N6-iminoethyl-lysine or L-nitroarginine-methylester for < or = 40 days did not result in an increase of the intracerebral parasitic load and a reactivation of the disease, despite the presence of iNOS-suppressive inhibitor levels in the brain. However, L-nitroarginine-methylester treatment had remarkably toxic effects and induced a severe wasting syndrome with high mortality. In contrast to BALB/c mice, L-N6-iminoethyl-lysine treatment rapidly exacerbated the already established chronic TE of C57BL/6 mice. Thus, the containment of latent toxoplasms in T. gondii-resistant BALB/c mice is independent of iNOS, whereas the temporary control of intracerebral parasites in T. gondii-susceptible C57BL/6 mice with chronic TE requires iNOS activity. (+info)
(5/2611) Specific antibody-dependent killing of Toxoplasma gondii by normal macrophages.
The requirement for specificity of antibody-dependent inhibition or killing of intracellular Toxoplasma gondii trophozoites by normal mouse peritoneal macrophages was evaluated in vitro using light microscopy and autoradiography. Anti-toxoplasma antibody in the presence of 'accessory factor' rendered extracellular T. gondii trophozoites non-viable and non-infectious for cells, whereas exposure of extracellular trophozoites to heat-inactivated immune serum did not appear to damage the parasites. Although pretreatment of extracellular trophozoites with heat-inactivated immune serum neither diminished nor prevented infection of normal mouse peritoneal macrophages, it did confer upon macrophages the ability to inhibit or kill the organisms once they were intracellular. In contrast, pretreatment of trophozoites with either heat-inactivated normal or Besnoitia jellisoni immune serum did not enable normal macrophages to inhibit or kill T. gondii; rather, such organisms multiplied intracellularly in normal macrophages. Thus, pretreatment with specific antibody alone prepared T. gondii trophozoites for intracellular destruction by normal mouse peritoneal macrophages. These results suggest that spesific antibody acting in concert with normal macrophages may play a role in controlling infection with T. gondii. (+info)
(6/2611) Recombinant bactericidal/permeability-increasing protein (rBPI21) in combination with sulfadiazine is active against Toxoplasma gondii.
The activity of recombinant bactericidal/permeability-increasing protein (rBPI21), alone or in combination with sulfadiazine, on the intracellular replication of Toxoplasma gondii was assessed in vitro and in mice with acute toxoplasmosis. rBPI21 markedly inhibited the intracellular growth of T. gondii in human foreskin fibroblasts (HFFs). Following 72 h of exposure, the 50% inhibitory concentration of rBPI21 for T. gondii was 2.6 micrograms/ml, whereas only slight cytotoxicity for HFF cells was observed at the concentrations tested. Subsequent mathematical analyses revealed that the combination of rBPI21 with sulfadiazine yielded slight to moderate synergistic effects against T. gondii in vitro. Infection of mice orally with C56 cysts or intraperitoneally (i.p.) with RH tachyzoites resulted in 100% mortality, whereas prolongation of the time to death or significant survival (P = 0.002) was noted for those animals treated with 5 to 20 mg of rBPI21 per kg of body weight per day. Treatment with rBPI21 in combination with sulfadiazine resulted in significant (P = 0.0001) survival of mice infected i.p. with tachyzoites but not of mice infected orally with T. gondii cysts. These results indicate that rBPI21 is active in vitro and in vivo against T. gondii and that its activity is significantly enhanced when it is used in combination with sulfadiazine. To our knowledge, this is the first report of the activity of rBPI21 against a protozoan parasite. (+info)
(7/2611) Toxoplasma gondii antibody titers in sera of children admitted to the Seoul National University Children's Hospital.
A total of 542 children under 10 years of age, admitted to the Seoul National University Children's Hospital, was examined for antibody titers of Toxoplasma gondii using indirect latex agglutination (ILA) test. Among them, 7.7% showed positive titers higher than 1:32, without significant difference between males (7.3%) and females (8.5%). The seropositive rate increased with age although the statistical significance was negligible (0.05 < P < 0.1). By residential areas, the prevalence appeared higher among children from southern provinces (Kyongsang-do and Cholla do) than those from other areas, but the statistical significance was also very low (0.05 < P < 0.1). When the seropositive cases were analyzed by coincidental diseases, the prevalence was significantly higher in patients with congenital diseases than in patients with non-congenital diseases (P < 0.05). The results showed that the seropositive rate of toxoplasmosis in children examined was not high compared with other endemic countries. Some correlations are suggested between toxoplasmosis and congenital anomalies in Korea. (+info)
(8/2611) Effector cells of both nonhemopoietic and hemopoietic origin are required for interferon (IFN)-gamma- and tumor necrosis factor (TNF)-alpha-dependent host resistance to the intracellular pathogen, Toxoplasma gondii.
Although interferon (IFN)-gamma-activated, mononuclear phagocytes are considered to be the major effectors of resistance to intracellular pathogens, it is unclear how they control the growth of microorganisms that reside in nonhemopoietic cells. Pathogens within such cells may be killed by metabolites secreted by activated macrophages or, alternatively, directly controlled by cytokine-induced microbicidal mechanisms triggered within infected nonphagocytic cells. To distinguish between these two basic mechanisms of cell-mediated immunity, reciprocal bone marrow chimeras were constructed between wild-type and IFN-gamma receptor-deficient mice and their survival assessed following infection with Toxoplasma gondii, a protozoan parasite that invades both hemopoietic and nonhemopoietic cell lineages. Resistance to acute and persistent infection was displayed only by animals in which IFN-gamma receptors were expressed in both cellular compartments. Parallel chimera experiments performed with tumor necrosis factor (TNF) receptor-deficient mice also indicated a codependence on hemopoietic and nonhemopoietic lineages for optimal control of the parasite. In contrast, in mice chimeric for inducible nitric oxide synthase (iNOS), an enzyme associated with IFN-gamma-induced macrophage microbicidal activity, expression by cells of hemopoietic origin was sufficient for host resistance. Together, these findings suggest that, in concert with bone marrow-derived effectors, nonhemopoietic cells can directly mediate, in the absence of endogenous iNOS, IFN-gamma- and TNF-alpha-dependent host resistance to intracellular infection. (+info)