Pathophysiology of toxoplasmosis

Toxoplasma Shelph, a Phosphatase Located in the Parasite Endoplasmic Reticulum, Is Required for Parasite Virulence

Toxoplasma gondii is a single-celled parasitic eukaryote that evolved to successfully propagate in any nucleated cell. As with any other eukaryote, its life cycle is regulated by signaling pathways controlled by kinases and phosphatases. T. gondii encodes an atypical bacterial-like phosphatase absent from mammalian genomes, named Shelph, after its first identification in the psychrophilic bacterium Schewanella sp. Here, we demonstrate that Toxoplasma Shelph is an active phosphatase localized in the parasite endoplasmic reticulum. The phenotyping of a shelph knockout (KO) line showed a minor impairment in invasion on human fibroblasts, while the other steps of the parasite lytic cycle were not affected. In contrast with Plasmodium ortholog Shelph1, this invasion deficiency was not correlated with any default in the biogenesis of secretory organelles. However, Shelph-KO parasites displayed a much-pronounced defect in virulence in vivo. These phenotypes could be rescued by genetic complementation, thus supporting an important function for Shelph in the context of a natural infection. IMPORTANCE Toxoplasma gondii belongs to the Apicomplexa phylum, which comprises more than 5,000 species, among which is Plasmodium falciparum, the notorious agent of human malaria. Intriguingly, the Apicomplexa genomes encode at least one phosphatase closely related to the bacterial Schewanella phosphatase, or Shelph. To better understand the importance of these atypical bacterial enzymes in eukaryotic parasites, we undertook the functional characterization of T. gondii Shelph. Our results uncovered its subcellular localization and its enzymatic activity, revealed its subtle involvement during the tachyzoite invasion step of the lytic cycle, and more importantly, highlighted a critical requirement of this phosphatase for parasite propagation in mice. Overall, this study revealed an unexpected role for T. gondii Shelph in the maintenance of parasite virulence in vivo.

Anti-toxoplasma and Cytotoxic Activities of Holothuria leucospilota Extract and TiO2NPs In vitro and In vivo

BACKGROUND

An impressive treatment for toxoplasmosis is the combinatory use of sulfadiazine and pyrimethamine. However, both the drugs involve significant side effects and toxicity for the host. Therefore, the discovery of new anti-toxoplasma medications with high efficacy and less to no side effects is urgently needed.

OBJECTIVE

This study aimed to evaluate the anti-toxoplasmic effects of Holothuria leucospilota (H. leucospilota) extract and TiO₂NPs on the cell death of Toxoplasma gondii (T. gondii) tachyzoites in vitro and serum liver enzymes (AST, ALT, and ALP), and also to evaluate the immune response and production of IL-5, IFN-γ, and TNF-α in a mouse model.

MATERIALS AND METHODS

The cytotoxicity of TiO₂NPs and H. leucospilota extract against the tachyzoite of T. gondii was evaluated by the methyl thiazolyl tetrazolium (MTT) assay. The levels of serum TNF-α, IFN-γ, IL-5, and liver enzymes were measured, as well. All the groups were subjected to T. gondii, and the survival rate of experimental mice was evaluated.

RESULTS

Our findings suggested in vivo and in vitro anti-toxoplasmic activity of TiO₂NPs and H. leucospilota extract by inhibiting the proliferation and invasion of T. gondii tachyzoite. In addition, a significant increase in IFN-γ and TNF-α production was observed in mice treated with high doses of TiO₂NPs and H. leucospilota extract. However, IL-5 levels decreased in TiO₂NPs and H. leucospilota extract-treated mice. Our results also showed a highly significant increase (P < 0.05) in the levels of ALT, AST, and ALP in the groups injected with TiO₂NPs and H. leucospilota extract, but not the control group.

CONCLUSION

TiO₂NPs and H. leucospilota extract have greater anti-toxoplasma effects in vitro and in vivo. These two compounds could be considered as a candidate for use against toxoplasmosis, both therapeutically and prophylactically.

Immune response against toxoplasmosis-some recent updates RH: Toxoplasma gondii immune response

AIMS

Cytokines, soluble mediators of immunity, are key factors of the innate and adaptive immune system. They are secreted from and interact with various types of immune cells to manipulate host body's immune cell physiology for a counter-attack on the foreign body. A study was designed to explore the mechanism of Toxoplasma gondii (T. gondii) resistance from host immune response.

METHODS AND RESULTS

The published data on aspect of host (murine and human) immune response against T. gondii was taken from Google scholar and PubMed. Most relevant literature was included in this study. The basic mechanism of immune response starts from the interactions of antigens with host immune cells to trigger the production of cytokines (pro-inflammatory and anti-inflammatory) which then act by forming a cytokinome (network of cytokine). Their secretory equilibrium is essential for endowing resistance to the host against infectious diseases, particularly toxoplasmosis. A narrow balance lying between Th1, Th2, and Th17 cytokines (as demonstrated until now) is essential for the development of resistance against T. gondii as well as for the survival of host. Excessive production of pro-inflammatory cytokines leads to tissue damage resulting in the production of anti-inflammatory cytokines which enhances the proliferation of Toxoplasma. Stress and other infectious diseases (human immunodeficiency virus (HIV)) that weaken the host immunity particularly the cellular component, make the host susceptible to toxoplasmosis especially in pregnant women.

CONCLUSION

The current review findings state that in vitro harvesting of IL12 from DCs, Np and MΦ upon exposure with T. gondii might be a source for therapeutic use in toxoplasmosis. Current review also suggests that therapeutic interventions leading to up-regulation/supplementation of SOCS-3, IL12, and IFNγ to the infected host could be a solution to sterile immunity against T. gondii infection. This would be of interest particularly in patients passing through immunosuppression owing to any reason like the ones receiving anti-cancer therapy, the ones undergoing immunosuppressive therapy for graft/transplantation, the ones suffering from immunodeficiency virus (HIV) or having AIDS. Another imortant suggestion is to launch the efforts for a vaccine based on GRA6Nt or other similar antigens of T. gondii as a probable tool to destroy tissue cysts.

Evaluation of Adjuvant Effectiveness of Alum-Propranolol Mixture on the Immunogenicity of Excreted/Secreted Antigens of Toxoplasma gondii RH Strain

Purpose: The introduction of novel adjuvants is an important step in attempts to develop a safe and more efficient vaccine. The present study was performed to determine whether the use of a mixed beta-adrenergic receptor antagonist propranolol (PRP) and aluminum (alum), as an adjuvant, have efficacy for Toxoplasma gondii vaccine to induce protective immunity in a mouse model. Methods: Female BALB/c mice divided into five groups were immunized with excretorys-ecretory antigens (ESA) vaccine, alum-ESA vaccine, PRP-ESA vaccine, and alum-PRP ESA vaccine, as well as with phosphate buffered saline (PBS), as a negative control group. The immune responses were evaluated by lymphocyte proliferation assay for measuring delayedtype hypersensitivity (DTH) response and by cytokine assay for evaluating IFN-γ and IL-5 levels. The survival rate of mice in all groups was assessed during a three-week monitoring period after an intraperitoneal challenge with T. gondii tachyzoites. Results: The results showed that mice immunized with PRP, as an adjuvant, could secret a higher level of IFN-γ, which was significant in comparison to other groups. However, mice vaccinated with alum-precipitated ESA antigen had ability to produce an elevated level of IL-5 compared to other mouse groups (P ≤ 0.05). Moreover, alum-PRP co-administration together with ESA vaccine resulted in the longer survival of mice. Conclusion: The findings of this study revealed that the combination of alum-PRP adjuvants and ESA vaccine of T. gondii elicits both humoral and cellular immune responses, which are comparable to either alum or PRP alone.

Toxoplasma gondii: A possible etiologic agent for Alzheimer's disease

Toxoplasma gondii (T. gondii) is one of the most pervasive neurotropic pathogens causing different lesions in a wide variety of mammals as intermediate hosts, including humans. It is estimated that one-third of the world population is infected with T. gondii; however, for a long time, there has been much interest in the examination of the possible role of this parasite in the development of mental disorders, such as Alzheimer's disease (AD). T. gondii may play a role in the progression of AD using mechanisms, such as the induction of the host's immune responses, inflammation of the central nervous system (CNS), alteration in the levels of neurotransmitters, and activation of indoleamine-2,3-dyoxigenase. This paper presents an appraisal of the literature, reports, and studies that seek to the possible role of T. gondii in the development of AD. For achieving the purpose of the current study, a search of six English databases (PubMed, ScienceDirect, Web of Science, Scopus, ProQuest, and Google Scholar) was performed. The results support the involvement of T. gondii in the induction and development of AD. Indeed, T. gondii can be considered a risk factor for the development of AD and requires the special attention of specialists and patients. Furthermore, the results of this study may contribute to prevent or delay the progress of AD worldwide. Therefore, it is required to carry out further studies in order to better perceive the parasitic mechanisms in the progression of AD.

Immunological, histopathological, and ultrastructural evidence of steroid-induced reactivation of chronic murine toxoplasmosis

We developed a model of steroid-induced reactivation of chronic murine toxoplasmosis to mirror similar effects of steroids or other immunosuppressants in infected humans. Immunological, histopathological, and ultrastructural parameters were reported. Prior to steroid administration, mice were infected with 10 cysts of the Me49 strain of Toxoplasma gondii. Mice were treated with dexamethasone (DXM, 2.5 mg/kg/day in drinking water), alone or combined with Solu-Cortef (SOLU, 50 mg/kg by subcutaneous injection 3 times a week) for 7 weeks or left untreated as control. Histopathological changes and ultrastructural effects of steroids on the course of chronic toxoplasmosis were recorded. By electron microscopy, the brains of infected combined treated mice showed an increase in number of tachyzoites and bradyzoites, degeneration, and necrosis of neural cells and hydropic degeneration besides the observed rupture of toxoplasma cysts releasing free tachyzoites in brain tissue. DXM+SOLU-combined treatment also significantly increased mortality, mean brain cyst count as compared to infected untreated mice (P = .01 and). Moreover, 3/12 (25%) treated animals developed clinical signs of toxoplasmic encephalitis. This simple model of drug-induced reactivation of chronic toxoplasmosis permits investigation of host-parasite interaction and may be used for the evaluation of chemotherapeutics in immunocompromised infected patients.

Astrocytes promote a protective immune response to brain Toxoplasma gondii infection via IL-33-ST2 signaling

It is of great interest to understand how invading pathogens are sensed within the brain, a tissue with unique challenges to mounting an immune response. The eukaryotic parasite Toxoplasma gondii colonizes the brain of its hosts, and initiates robust immune cell recruitment, but little is known about pattern recognition of T. gondii within brain tissue. The host damage signal IL-33 is one protein that has been implicated in control of chronic T. gondii infection, but, like many other pattern recognition pathways, IL-33 can signal peripherally, and the specific impact of IL-33 signaling within the brain is unclear. Here, we show that IL-33 is expressed by oligodendrocytes and astrocytes during T. gondii infection, is released locally into the cerebrospinal fluid of T. gondii-infected animals, and is required for control of infection. IL-33 signaling promotes chemokine expression within brain tissue and is required for the recruitment and/or maintenance of blood-derived anti-parasitic immune cells, including proliferating, IFN-γ-expressing T cells and iNOS-expressing monocytes. Importantly, we find that the beneficial effects of IL-33 during chronic infection are not a result of signaling on infiltrating immune cells, but rather on radio-resistant responders, and specifically, astrocytes. Mice with IL-33 receptor-deficient astrocytes fail to mount an adequate adaptive immune response in the CNS to control parasite burden-demonstrating, genetically, that astrocytes can directly respond to IL-33 in vivo. Together, these results indicate a brain-specific mechanism by which IL-33 is released locally, and sensed locally, to engage the peripheral immune system in controlling a pathogen.

Protective immunity induced by a DNA vaccine cocktail expressing TgSAG1, TgROP2, and the genetic adjuvant HBsAg against Toxoplasma gondii infection

Toxoplasma gondii is an intracellular obligate parasitic protozoon that can infect all warm-blooded animals, causing zoonotic toxoplasmosis. So far, there is no commercial toxoplasmosis vaccine for human use. In the present study, we constructed a DNA vaccine cocktail which includes the surface protein (SAG1) and the rhoptry protein ROP2 denoted as pEGFP-N1-SAG1-ROP2. In order to improve the efficacy, HBsAg was used as a genetic adjuvant to construct pEGFP-N1-HBsAg-SAG1-ROP2. Two eukaryotic plasmids were transiently transfected into HEK293T cells and the expression was examined using fluorescence microscopy and western blotting. We then immunized Kunming mice intramuscularly with the DNA vaccine. After three immunizations, the immune response was evaluated by measuring antibody levels, cytokine production, percentages of CD4⁺ and CD8⁺ T lymphocytes, and the survival times of the T. gondii RH strain challenged mice. The results showed that the two DNA vaccines stimulated Th1 responses, and had a higher antibody titer, IL-2, IL-12, and IFN-γ levels, and percentage of CD4⁺ and CD8⁺ T lymphocytes than the control group. In addition, mice immunized with the pEGFP-N1-HBsAg-SAG1-ROP2 vaccine showed increased survival times compared with pEGFP-N1-SAG1-ROP2.

Anti-Toxoplasma Activities of the Hydroalcoholic Extract of Some Brassicaceae Species

Background:

Toxoplasma gondii (T. gondii) is a protozoan parasite that infects a wide range of warm-blooded animals and humans. The conventional anti-Toxoplasma treatments cause significant toxicity. Brassicaceae family contains several medicinal plants with anti-inflammatory, chemopreventive, insecticide, antibacterial, antiviral, and antiparasitic effects. In this study, the hydroalcoholic extract of some Brassicaceae species was investigated against T. gondiiin vitro.

Materials and Methods:

Seeds of Alyssum homolocarpum, Lepidium perfoliatum, Lepidium sativum, and aerial parts of Nasturtium officinale and Capsellabursa-pastoris were extracted by maceration method using 80% ethanol. Vero cells were treated with different concentrations (5–600 μg/mL) of the extracts and pyrimethamine (as positive control), and the cellular viability was verified. Next, Vero cells were infected by T. gondii tachyzoites (RH strain), and the viability of the infected cells was measured by a colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Results:

The 50% inhibitory concentration values were 5.1, 14.67, 32.49, 37.31, 71.35, and 2.63 μg/mL, and the selectivity indices were 8.06, 2.59, 0.74, 0.78, 0.65 (P < 0.05 compared with positive control), and 3.03 for L. sativum, L. perfoliatum, N. officinale, A. homolocarpum, C. bursa-pastoris, and pyrimethamine, respectively.

Conclusion:

The results of this study demonstrated that the hydroalcoholic extracts of L. sativum and L. perfoliatum have the promising anti-Toxoplasma activity by growth inhibition of T. gondii tachyzoites in infected cells.

Toxoplasma gondii infection in two captive Patagonian maras

Toxoplasma gondii infection was diagnosed in 2 captive Patagonian maras (Dolichotis patagonum). One animal developed fatal systemic toxoplasmosis and had concurrent localized bacterial and fungal infections; its daughter remained clinically healthy. Microscopic findings included acute, coagulative necrosis, lymphohistiocytic inflammatory infiltrates, and extra- and intracellular parasites in the liver, myocardium, urinary bladder, and adrenal glands of the diseased animal. PCR and subsequent genotyping of parasites from fresh tissue from both cases revealed infection with T. gondii genotype II. Direct agglutination testing of blood from the healthy individual revealed high levels of T. gondii IgG antibodies. T. gondii is a potential cause of disease and lethality in captive and wild Patagonian maras, and toxoplasmosis should be considered when managing and providing veterinary care for this species.

Toxoplasma gondii excreted-secreted antigens suppress Foxp3 via PI3K-AKT-mTOR signaling pathway

Toxoplasma gondii excreted-secreted antigens (ESA) cause spontaneous abortion or fetal teratogenesis during the pregnancy in mice, especially in the early stage. Those adverse pregnancy outcomes are due to the deficit in regulatory T cells (Tregs). Forkhead box P3 (Foxp3), a critical transcription factor, modulates Tregs differentiation and its function. Besides, phosphatidylinositol 3-kinase-protein kinase B-mammalian target of rapamycin (PI3K-AKT-mTOR) signaling network is implicated in interfering with Foxp3 induction. We previously demonstrated that ESA diminished the number of Tregs and inhibited its function. And ESA suppressed Foxp3 expression via the attenuation of transforming growth factor β RII/Smad2/Smad3/Smad4 pathway. The current study aimed to investigate whether the PI3K-AKT-mTOR signaling network is involved in Foxp3 downregulation induced by ESA. We found that ESA upregulated PI3K, P-AKT, mTOR, and P-mTOR. Knockdown of PI3K cooperated with ESA to restore Foxp3 expression mediated by ESA. This suppressive role of ESA on Foxp3 expression was abrogated by AKT inhibitor. In addition, neutralization of Toll-like receptor 4 could restore the expression of Foxp3, PI3K, and its downstream effectors induced by ESA. Collectively, the findings indicated that ESA inhibited Foxp3 expression via the upregulation of PI3K-AKT-mTOR signaling pathway.

Targeted Delivery of Toxoplasma gondii Antigens to Dendritic Cells Promote Immunogenicity and Protective Efficiency against Toxoplasmosis

Toxoplasmosis is a major public health problem and the development of a human vaccine is of high priority. Efficient vaccination against Toxoplasma gondii requires both a mucosal and systemic Th1 immune response. Moreover, dendritic cells play a critical role in orchestrating the innate immune functions and driving specific adaptive immunity to T. gondii. In this study, we explore an original vaccination strategy that combines administration via mucosal and systemic routes of fusion proteins able to target the major T. gondii surface antigen SAG1 to DCs using an antibody fragment single-chain fragment variable (scFv) directed against DEC205 endocytic receptor. Our results show that SAG1 targeting to DCs by scFv via intranasal and subcutaneous administration improved protection against chronic T. gondii infection. A marked reduction in brain parasite burden is observed when compared with the intranasal or the subcutaneous route alone. DC targeting improved both local and systemic humoral and cellular immune responses and potentiated more specifically the Th1 response profile by more efficient production of IFN-γ, interleukin-2, IgG2a, and nasal IgA. This study provides evidence of the potential of DC targeting for the development of new vaccines against a range of Apicomplexa parasites.

Influence of indigenous microbiota on experimental toxoplasmosis in conventional and germ-free mice

Toxoplasmosis represents one of the most common zoonoses worldwide. Its agent, Toxoplasma gondii, causes a severe innate pro-inflammatory response. The indigenous intestinal microbiota promotes host animal homoeostasis and may protect the host against pathogens. Germ-free (GF) animals provide an important tool for the study of interactions between host and microbiota. In this study, we assessed the role of indigenous microorganisms in disease development utilizing a murine toxoplasmosis model, which includes conventional (CV) and GF NIH Swiss mice. CV and GF mice orally inoculated with T. gondii had similar survival curves. However, disease developed differently in the two animal groups. In CV mice, intestinal permeability increased and levels of intestinal pro-inflammatory cytokines were altered. In GF animals, there were discrete epithelial degenerative changes and mucosal oedema, but the liver and lungs displayed significant lesions. We conclude that, despite similar survival curves, CV animals succumb to an exaggerated inflammatory response, whereas GF mice fail to produce an adequate systemic response.

CD103+ CD8 T Cells in the Toxoplasma-Infected Brain Exhibit a Tissue-Resident Memory Transcriptional Profile

During chronic infection, memory T cells acquire a unique phenotype and become dependent on different survival signals than those needed for memory T cells generated during an acute infection. The distinction between the role of effector and memory T cells in an environment of persistent antigen remains unclear. Here, in the context of chronic Toxoplasma gondii infection, we demonstrate that a population of CD8 T cells exhibiting a tissue-resident memory (T_RM) phenotype accumulates within the brain. We show that this population is distributed throughout the brain in both parenchymal and extraparenchymal spaces. Furthermore, this population is transcriptionally distinct and exhibits a transcriptional signature consistent with the T_RM observed in acute viral infections. Finally, we establish that the CD103⁺ T_RM population has an intrinsic capacity to produce both IFN-γ and TNF-α, cytokines critical for parasite control within the central nervous system (CNS). The contribution of this population to pro-inflammatory cytokine production suggests an important role for T_RM in protective and ongoing immune responses in the infected CNS.

Accession number: GSE95105

Regulatory T Cells Promote Myositis and Muscle Damage in Toxoplasma gondii Infection

The coordination of macrophage polarization is essential for the robust regenerative potential of skeletal muscle. Repair begins with a phase mediated by inflammatory monocytes (IM) and proinflammatory macrophages (M1), followed by polarization to a proregenerative macrophage (M2) phenotype. Recently, regulatory T cells (Tregs) were described as necessary for this M1 to M2 transition. We report that chronic infection with the protozoan parasite Toxoplasma gondii causes a nonresolving Th1 myositis with prolonged tissue damage associated with persistent M1 accumulation. Surprisingly, Treg ablation during chronic infection rescues macrophage homeostasis and skeletal muscle fiber regeneration, showing that Tregs can directly contribute to muscle damage. This study provides evidence that the tissue environment established by the parasite could lead to a paradoxical pathogenic role for Tregs. As such, these findings should be considered when tailoring therapies directed at Tregs in inflammatory settings.

Virus-Like Nanoparticle Vaccine Confers Protection against Toxoplasma gondii

The inner membrane complex (IMC) of Toxoplasma gondii as a peripheral membrane system has unique and critical roles in parasite replication, motility and invasion. Disruption of IMC sub-compartment protein produces a severe defect in T. gondii endodyogeny, the form of internal cell budding. In this study, we generated T. gondii virus-like particle particles (VLPs) containing proteins derived from IMC, and investigated their efficacy as a vaccine in mice. VLP vaccination induced Toxoplasma gondii-specific total IgG, IgG1 and IgG2a antibody responses in the sera and IgA antibody responses in the feces. Upon challenge infection with a lethal dose of T. gondii (ME49), all vaccinated mice survived, whereas all naïve control mice died. Vaccinated mice showed significantly reduced cyst load and cyst size in the brain. VLP vaccination also induced IgA and IgG antibody responses in feces and intestines, and antibody-secreting plasma cells, mixed Th1/Th2 cytokines and CD4+/CD8+ T cells from spleen. Taken together, these results indicate that non-replicating VLPs containing inner membrane complex of T. gondii represent a promising strategy for the development of a safe and effective vaccine to control the spread of Toxoplasma gondii infection.

Caspase-11 Modulates Inflammation and Attenuates Toxoplasma gondii Pathogenesis

Toxoplasma gondii is an obligate intracellular parasite that is the etiologic agent responsible for toxoplasmosis. Infection with T. gondii results in activation of nucleotide binding domain and leucine rich repeat containing receptors (NLRs). NLR activation leads to inflammasome formation, the activation of caspase-1, and the subsequent cleavage of IL-1β and IL-18. Recently, a noncanonical inflammasome has been characterized which functions through caspase-11 and appears to augment many biological functions previously considered to be dependent upon the canonical inflammasome. To better elucidate the function of this noncanonical inflammasome in toxoplasmosis, we utilized Asc (-/-) and Casp11 (-/-) mice and infected these animals with T. gondii. Our data indicates that caspase-11 modulates the innate immune response to T. gondii through a mechanism which is distinct from that currently described for the canonical inflammasome. Asc (-/-) mice demonstrated increased disease pathogenesis during the acute phase of T. gondii infection, whereas Casp11 (-/-) mice demonstrated significantly attenuated disease pathogenesis and reduced inflammation. This attenuated host response was associated with reduced local and systemic cytokine production, including diminished IL-1β. During the chronic phase of infection, caspase-11 deficiency resulted in increased neuroinflammation and tissue cyst burden in the brain. Together, our data suggest that caspase-11 functions to protect the host by enhancing inflammation during the early phase of infection in an effort to minimize disease pathogenesis during later stages of toxoplasmosis.

Removal of extracellular Toxoplasma gondii tachyzoites from suspended cell culture

Tachyzoites of Toxoplasma gondii, an obligate intracellular parasite, actively invade a broad spectrum of cell types. T. gondii infects leukocytes and spreads to distant organs such as the brain, lungs and muscles. However, the mechanism of T. gondii transmission from infected leukocytes to peripheral organs is unknown. To show the dynamics of infected leukocytes and intracellular parasites in vivo, previous studies have prepared T. gondii-infected leukocytes and injected them into circulation in experimental animals. However, when the infected leukocytes are prepared in vitro, some extracellular tachyzoites remain in the leukocyte cell culture because it is almost impossible to wash out these extracellular tachyzoites. These extracellular tachyzoites may distort experimental results. In this study, we report a method for removing extracellular tachyzoites from leukocyte culture suspension using antibody-conjugated magnetic beads. Using this method, extracellular tachyzoites in suspension cell culture can be effectively eliminated.

Pathological changes in acute experimental toxoplasmosis with Toxoplasma gondii strains obtained from human cases of congenital disease

There is a lack of studies using Toxoplasma gondii strains isolated from human patients. Here, we present a pathological study of three strains obtained from human cases of congenital toxoplasmosis in Brazil using inbred mice after oral infection with 10 tissue cysts. Multiplex-nested PCR-RFLP of eleven loci revealed atypical genotypes commonly found in Brazil: toxodb #8 for TgCTBr5 and TgCTBr16 strains and toxodb #11 for the TgCTBr9 strain. BALB/c and C57BL/6 mice were evaluated for survival and histological changes during the acute phase of the disease. All mice inoculated with the non-virulent TgCTBR5 strain survived after 30 days, although irreversible tissue damage was found. In contrast, no mice were resistant to infection with the highly virulent TgCTBR9 strain. The TgCTBr16 strain resulted in 80% survival in mice. However, this strain presented low infectivity, especially by the oral route of infection. Despite being identified with the same genotype, TgCTBr5 and TgCTBr16 strains showed biological differences. Histopathologic analysis revealed liver and lungs to be the most affected organs, and the pattern of tissue injury was similar to that found in mice inoculated perorally with strains belonging to clonal genotypes. However, there was a variation in the intensity of ileum lesions according to T. gondii strain and mouse lineage. C57BL/6 mice showed higher susceptibility than BALB/c for histological lesions. Taken together, these results revealed that the pathogenesis of T. gondii strains belonging to atypical genotypes can induce similar tissue damage to those from clonal genotypes, although intrinsic aspects of the strains seem critical to the induction of ileitis in the infected host.

Induction of interferon-stimulated genes by IRF3 promotes replication of Toxoplasma gondii

Innate immunity is the first line of defense against microbial insult. The transcription factor, IRF3, is needed by mammalian cells to mount innate immune responses against many microbes, especially viruses. IRF3 remains inactive in the cytoplasm of uninfected cells; upon virus infection, it gets phosphorylated and then translocates to the nucleus, where it binds to the promoters of antiviral genes and induces their expression. Such genes include type I interferons (IFNs) as well as Interferon Stimulated Genes (ISGs). IRF3-/- cells support enhanced replication of many viruses and therefore, the corresponding mice are highly susceptible to viral pathogenesis. Here, we provide evidence for an unexpected pro-microbial role of IRF3: the replication of the protozoan parasite, Toxoplasma gondii, was significantly impaired in IRF3-/- cells. In exploring whether the transcriptional activity of IRF3 was important for its pro-parasitic function, we found that ISGs induced by parasite-activated IRF3 were indeed essential, whereas type I interferons were not important. To delineate the signaling pathway that activates IRF3 in response to parasite infection, we used genetically modified human and mouse cells. The pro-parasitic signaling pathway, which we termed PISA (Parasite-IRF3 Signaling Activation), activated IRF3 without any involvement of the Toll-like receptor or RIG-I-like receptor pathways, thereby ruling out a role of parasite-derived RNA species in activating PISA. Instead, PISA needed the presence of cGAS, STING, TBK1 and IRF3, indicating the necessity of DNA-triggered signaling. To evaluate the physiological significance of our in vitro findings, IRF3-/- mice were challenged with parasite infection and their morbidity and mortality were measured. Unlike WT mice, the IRF3-/- mice did not support replication of the parasite and were resistant to pathogenesis caused by it. Our results revealed a new paradigm in which the antiviral host factor, IRF3, plays a cell-intrinsic pro-parasitic role.

Effect of route of infection on outcome of Toxoplasma gondii infection in hu-PBL SCID mice

Toxoplasma gondii (T. gondii) causes serious infection, especially in immunocompromised hosts. The relevance of animal models of toxoplasmosis to human disease is unclear, but have indicated that the route of Toxoplasma infection may affect the outcome. A humanized model of toxoplasmosis of immunocompromised mice (i.e. hu-PBL SCID), using the intraperitoneal (IP) route demonstrated long-term engraftment of human cells and worsening of inflammation compared to controls. In this study, we examined the effect of route of infection on this hu-PBL SCID model using a Toxoplasma strain (i.e. DAG) isolated from an immunocompromised human. Oral infection led to an asymptomatic infection, whereas animals infected by the IP route succumbed more quickly to infection. Human cells, detected through species-specific β-actin mRNA, were not as prominent in IP-infected animals as compared to orally infected and uninfected animals. There was evidence of control of toxoplasmosis in some orally infected animals, and this was associated with the presence of human cells in multiple tissues. Thus, the route of infection dramatically affects the outcome of infection, either by affecting parasite replication or expansion of human immune cells. Further studies of oral Toxoplasma infection using hu-PBL SCID mice may help in developing chemotherapies and immunotherapeutic strategies for toxoplasmosis.

Toxoplasmosis

Toxoplasma gondii, an Apicomplexan, is a pathogic protozoan that can infect the central nervous system. Infection during pregnancy can result in a congenial infection with severe neurological sequelae. In immunocompromised individuals reactivation of latent neurological foci can result in encephalitis. Immunocompetent individuals infected with T. gondii are typically asymptomatic and maintain this infection for life. However, recent studies suggest that these asymptomatic infections may have effects on behavior and other physiological processes. Toxoplasma gondii infects approximately one-third of the world population, making it one of the most successful parasitic organisms. Cats and other felidae serve as the definite host producing oocysts, an environmentally resistant life cycle stage found in cat feces, which can transmit the infection when ingested orally. A wide variety of warm-blooded animals, including humans, can serve as the intermediate host in which tissue cysts (containing bradyzoites) develop. Transmission also occurs due to ingestion of the tissue cysts. There are three predominant clonal lineages, termed Types I, II and III, and an association with higher pathogenicity with the Type I strains in humans has emerged. This chapter presents a review of the biology of this infection including the life cycle, transmission, epidemiology, parasite strains, and the host immune response. The major clinical outcomes of congenital infection, chorioretinitis and encephalitis, and the possible association of infection of toxoplasmosis with neuropsychiatric disorders such as schizophrenia, are reviewed.

Toxoplasma gondii excretory secretory antigenic proteins of diagnostic potential

Infection with Toxoplasma gondii is widespread and important in humans, especially pregnant women and immunosuppressed patients. A panel of tests is usually required for diagnosis toxoplasmosis. Excretory secretory antigen (ESA) is highly immunogenic, and thus it is a good candidate for investigation into new infection markers. ESA was prepared from tachyzoites of RH strain of T. gondii by mice intraperitoneal infection. Sera were obtained from several categories of individuals who differed in their status of anti-Toxoplasma IgM, IgG and IgG avidity antibodies. The ESA was subjected to SDS-PAGE, two-dimensional gel electrophoresis and Western blot analysis. Antigenic bands of approximate molecular weights of 12, 20 and 30 kDa, when probed with anti-human IgM-HRP and IgA-HRP, showed good potential as infection markers. The highest sensitivity of the bands was 98.7% with combination of IgM and IgA blots with sera of patients with anti-Toxoplasma IgM+ IgG+. The specificities were 84% and 70% with sera from other infections and healthy controls in IgM blots and IgA blots respectively. By mass spectrometry, the 12 kDa protein was identified as thioredoxin. The two top proteins identified for 20 kDa molecule were microneme protein 10 and dense granule protein 7; whereas that for 30 kDa were phosphoglycerate mutase 1 and phosphoglycerate mutase.

Development of high-throughput methods to quantify cysts of Toxoplasma gondii

Toxplasma is a protozoan parasite, which forms persistent cysts in tissues of chronically infected animals and humans. Cysts can reactivate leading to severe pathologies. They also contribute to the transmission of Toxoplasma infection in humans by ingestion of undercooked meat. Classically, the quantification of cyst burden in tissues uses microscopy methods, which are laborious and time consuming. Here, we have developed automated protocols to quantify cysts, based on flow cytometry or high-throughput microscopy. Brains of rodents infected with cysts of Prugniaud strain were incubated with the FITC-Dolichos biflorus lectin and analyzed by flow cytometry and high-throughput epifluorescence microscopy. The comparison of cyst counts by manual epifluorescence microscopy to flow cytometry or to high-throughput epifluorescence microscopy revealed a good correlation (r = 0.934, r = 0.993, P < 0.001 respectively). High-throughput epifluorescence microscopy was found to be more specific and sensitive than flow cytometry and easier to use for large series of samples. This reliable and easy protocol allow the specific detection of Toxoplasma cysts in brain, even at low concentrations; it could be a new way to detect them in water and in contaminate food.

Molecular markers of susceptibility to ocular toxoplasmosis, host and guest behaving badly

Infection with Toxoplasma gondii results in retinochoroiditis in 6% to 20% of immunocompetent individuals. The outcome of infection is the result of a set of interactions involving host genetic background, environmental, and social factors, and the genetic background of the parasite, all of which can be further modified by additional infections or even reinfection. Genes that encode several components of the immune system exhibit polymorphisms in their regulatory and coding regions that affect level and type of expression in response to stimuli, directing the immune response into different pathways. These variant alleles have been associated with susceptibility to immune-mediated diseases and with severity of pathology. We have investigated polymorphisms in several of these genes, identified as candidates for progression to retinochoroiditis caused by toxoplasmosis, namely chemokine (C-C motif) receptor 5 (CCR5), toll-like receptor-2 (TLR2), and TLR4. Furthermore, because interleukin-12 (IL-12) has been shown to be fundamental both in mice and in man to control a protective response against T. gondii, molecules that have a key function in IL-12 production will be emphasized in this review, in addition to discussing the importance of the genetic background of the parasite in the establishment of ocular disease.

Regulation of CD8+ T cell responses to infection with parasitic protozoa

There are over 10,000 species of parasitic protozoa, a subset of which can cause considerable disease in humans. Here we examine in detail the complex immune response generated during infection with a subset of these parasites: Trypanosoma cruzi, Leishmania sp., Toxoplasma gondii, and Plasmodium sp. While these particular species perhaps represent the most studied parasites in terms of understanding how T cells function during infection, it is clear that the lessons learned from this body of work are also relevant to the other protozoa known to induce a CD8(+) T cell response. This review will highlight some of the key studies that established that CD8(+) T cells play a major role in protective immunity to protozoa, the factors that promote the generation as well as maintenance of the CD8(+) T cell response during these infections, and draw attention to some of the gaps in our knowledge. Moreover, the development of new tools, including MHC-Class I tetramer reagents and the use of TCR transgenic mice or genetically modified parasites, has provided a better appreciation of how parasite specific CD8(+) T cell responses are initiated and new insights into their phenotypic plasticity.

Toxoplasma gondii: the role of IFN-gamma, TNFRp55 and iNOS in inflammatory changes during infection

In order to examine the role of IFN-gamma, TNFRp55 and iNOS in inflammatory reaction during toxoplasmosis, IFN-gamma(-/-), TNFRp55(-/-) and iNOS(-/-) mice were experimentally infected with Toxoplasma gondii ME-49 strain. The organs of the mice were evaluated for histology and immunohistochemistry in detection of tissue parasitism and iNOS positive cells. IFN-gamma(-/-) mice presented mild inflammation in peripheral organs associated with a high parasitism and mortality in the acute phase of infection. In contrast, the peripheral organs of WT, TNFRp55(-/-) and iNOS(-/-) mice, presented a significant inflammatory reaction and low tissue parasitism in the same period of infection. The inflammatory lesions and tissue parasitism were increased and more severe in the Central Nervous System (CNS) of TNFRp55(-/-) and iNOS(-/-) with a progression of infection, when compared to WT mice. In these knockout animals, the inflammatory changes were associated with low levels or no expression of iNOS in TNFRp55(-/-) and iNOS(-/-) mice, respectively.

Whole genome sequencing of a natural recombinant Toxoplasma gondii strain reveals chromosome sorting and local allelic variants

Extensive sequence analysis of eight Toxoplasma gondii isolates from Uganda has revealed chromosome sorting and local allelic variants.

Background

Toxoplasma gondii is a zoonotic parasite of global importance. In common with many protozoan parasites it has the capacity for sexual recombination, but current evidence suggests this is rarely employed. The global population structure is dominated by a small number of clonal genotypes, which exhibit biallelic variation and limited intralineage divergence. Little is known of the genotypes present in Africa despite the importance of AIDS-associated toxoplasmosis.

Results

We here present extensive sequence analysis of eight isolates from Uganda, including the whole genome sequencing of a type II/III recombinant isolate, TgCkUg2. 454 sequencing gave 84% coverage across the approximate 61 Mb genome and over 70,000 single nucleotide polymorphisms (SNPs) were mapped against reference strains. TgCkUg2 was shown to contain entire chromosomes of either type II or type III origin, demonstrating chromosome sorting rather than intrachromosomal recombination. We mapped 1,252 novel polymorphisms and clusters of new SNPs within coding sequence implied selective pressure on a number of genes, including surface antigens and rhoptry proteins. Further sequencing of the remaining isolates, six type II and one type III strain, confirmed the presence of novel SNPs, suggesting these are local allelic variants within Ugandan type II strains. In mice, the type III isolate had parasite burdens at least 30-fold higher than type II isolates, while the recombinant strain had an intermediate burden.

Conclusions

Our data demonstrate that recombination between clonal lineages does occur in nature but there is nevertheless close homology between African and North American isolates. The quantity of high confidence SNP data generated in this study and the availability of the putative parental strains to this natural recombinant provide an excellent basis for future studies of the genetic divergence and of genotype-phenotype relationships.

Disruption of the Toxoplasma gondii parasitophorous vacuole by IFNgamma-inducible immunity-related GTPases (IRG proteins) triggers necrotic cell death

Toxoplasma gondii is a natural intracellular protozoal pathogen of mice and other small mammals. After infection, the parasite replicates freely in many cell types (tachyzoite stage) before undergoing a phase transition and encysting in brain and muscle (bradyzoite stage). In the mouse, early immune resistance to the tachyzoite stage is mediated by the family of interferon-inducible immunity-related GTPases (IRG proteins), but little is known of the nature of this resistance. We reported earlier that IRG proteins accumulate on intracellular vacuoles containing the pathogen, and that the vacuolar membrane subsequently ruptures. In this report, live-cell imaging microscopy has been used to follow this process and its consequences in real time. We show that the rupture of the vacuole is inevitably followed by death of the intracellular parasite, shown by its permeability to cytosolic protein markers. Death of the parasite is followed by the death of the infected cell. The death of the cell has features of pyronecrosis, including membrane permeabilisation and release of the inflammatory protein, HMGB1, but caspase-1 cleavage is not detected. This sequence of events occurs on a large scale only following infection of IFNgamma-induced cells with an avirulent strain of T. gondii, and is reduced by expression of a dominant negative mutant IRG protein. Cells infected by virulent strains rarely undergo necrosis. We did not find autophagy to play any role in the key steps leading to the death of the parasite. We conclude that IRG proteins resist infection by avirulent T. gondii by a novel mechanism involving disruption of the vacuolar membrane, which in turn ultimately leads to the necrotic death of the infected cell.

BALB/c mice resistant to Toxoplasma gondii infection proved to be highly susceptible when previously infected with Myocoptes musculinus fur mites

The immune response induced by Toxoplasma gondii is characterized by Th1 immune mechanisms. We previously demonstrated that C57BL/6 mice infested with Myocoptes musculinus and infected with T. gondii by intraperitoneal route undergo accelerated mortality according to Th2 immune mechanisms induced by the acarian. To evaluate whether infection with M. musculinus influences T. gondii-induced Th1 response in a resistant mouse lineage, BALB/c, which develops latent chronic toxoplasmosis in a way similar to that observed in immunocompetent humans, this study was done. The animals were infected with T. gondii ME-49 strain 1 month after M. musculinus infestation, being the survival and the immune response monitored. The double-infected displayed higher mortality rate if compared with the mono-infected mice. In addition, infection with M. musculinus changed the T. gondii-specific immune response, converting BALB/c host to a susceptible phenotype. Spleen cells had increased the levels of IL-4 in double-infected mice. This alteration was associated with severe pneumonia, encephalitis and wasting condition. In addition, a higher tissue parasitism was observed in double-infected animals. It can be concluded that infection with these two contrasting parasites, M. musculinus and T. gondii, may convert an immunocompetent host into a susceptible one, and such a host will develop severe toxoplasmosis.

Induction and regulation of host cell-mediated immunity by Toxoplasma gondii

Toxoplasma gondii is a highly infectious intracellular parasite which, if left unchecked by the immune system, rapidly overwhelms its intermediate hosts, as illustrated by the pathogenesis of toxoplasmic encephalitis in patients with AIDS. In order to insure both its host's and consequently its own survival simultaneously, T. gondii induces a potent gamma-interferon (IFN-gamma)-dependent cell-mediated immunity early in infection that controls the replication of the protozoan and facilitates transformation into the dormant cyst stage. The protective IFN-gamma is derived from three sources: natural killer cells; and CD4+ and CD8+ T lymphocytes, which can partially compensate for each other in knockout mice lacking the appropriate major histocompatibility complex-restricting elements. At least two properties of the parasite appear to be responsible for the early induction of these effector cells. The first is a hydrophobic molecule (or group of related molecules) that triggers interleukin 12 (IL-12), tumour necrosis factor alpha and IL-1beta synthesis in macrophages. This response can also promote HIV replication in the same cells. The second is a superantigen activity that drives IFN-gamma-producing Vbeta5+ CD8+ T cells. These potentially lethal responses are later regulated through the triggering of IL-10 and by the induction of anergy in the superantigen-stimulated Vbeta5+ T cell population.

IL-13 pre-treatment of murine peritoneal macrophages increases their anti-Toxoplasma gondii activity induced by lipopolysaccharides

Th1 cytokines and microbial lipopolysaccharides (LPS) activate macrophages to produce inflammatory mediators and effector molecules. Althrough Th2 cytokines often have an opposite action to Th1 cytokines and down-modulate the inflammatory response of macrophages, they can induce a distinct alternative activation that is beneficial in host defence. In this study, we report that IL-13 enhances the anti-Toxoplasma activity of LPS-activated murine macrophages. The inhibition of parasite proliferation was not related to reduced Toxoplasma gondii penetration into the cells, nor to the conversion of tachyzoites into bradyzoites. Used alone, IL-13 triggers the polarisation of macrophages towards type 2. However, in LPS-activated macrophages, we show the priming capacity of this cytokine to enhance the expression of inducible nitric oxide synthase (iNOS), a major marker of type 1 macrophages. This effect of IL-13 was not dependent on the activation state of macrophages (resident versus thioglycolate-elicited) or the timing of pre-treatment. We demonstrate a correlation between the enhancement of NO production and upgrading of the microbicidal effectiveness of the macrophages. Thus, both Th2 and Th1 cytokines could activate macrophages to control infections.

Protozoal meningoencephalitis in sea otters (Enhydra lutris): a histopathological and immunohistochemical study of naturally occurring cases

Protozoal meningoencephalitis is considered to be an important cause of mortality in the California sea otter (Enhydra lutris). Thirty nine of 344 (11.3%) California (CA) and Washington state (WA) sea otters examined from 1985 to 2004 had histopathological evidence of significant protozoal meningoencephalitis. The aetiological agents and histopathological changes associated with these protozoal infections are described. The morphology of the actively multiplicative life stages of the organisms (tachyzoites for Toxoplasma gondii and merozoites for Sarcocystis neurona) and immunohistochemical labelling were used to identify infection with S. neurona (n=22, 56.4%), T. gondii (n=5, 12.8%) or dual infection with both organisms (n=12, 30.8%). Active S. neurona was present in all dual infections, while most had only the latent form of T. gondii. In S. neurona meningoencephalitis, multifocal to diffuse gliosis was widespread in grey matter and consistently present in the molecular layer of the cerebellum. In T. gondii meningoencephalitis, discrete foci of gliosis and malacia were more widely separated, sometimes incorporated pigment-laden macrophages and mineral, and were found predominantly in the cerebral cortex. Quiescent tissue cysts of T. gondii were considered to be incidental and not a cause of clinical disease and mortality. Protozoal meningoencephalitis was diagnosed more frequently in the expanding population of WA sea otters (10 of 31, 32.3%) than in the declining CA population (29 of 313, 9.3%). Among sea otters with protozoal meningoencephalitis, those that had displayed neurological signs prior to death had active S. neurona encephalitis, supporting the conclusion that S. neurona is the most significant protozoal pathogen in the central nervous system of sea otters.

Toxoplasma gondii: expression and characterization of a recombinant protein containing SAG1 and GRA2 in Pichia pastoris

Toxoplasma gondii is an obligate intracellular protozoan which infects most species of warm-blooded animals and causes toxoplasmosis. Previous immunological and immunization studies have demonstrated the potential role of T. gondii antigens SAG1 and GRA2 as a vaccine candidate. In the present study, we have cloned, expressed, and purified a recombinant protein SAG1-GRA2 in Pichia pastoris. Results showed that P. pastoris was a robust system producing a large amount of highly purified and biological activity protein. BALB/c mice immunized with SAG1-GRA2 elicited stronger humoral and cellular responses in comparison to control groups. This immunization resulted in an enhanced Th1 immune response as measured by IgG2a antibody production and increased splenocyte IFN-gamma production, whereas no IL-4 was detected. After a lethal challenge with the highly virulent T. gondii RH strain, a prolonged survival time in SAG1-GRA2-immunized mice was observed in comparison to control groups. Our data demonstrate that SAG1-GRA2 triggered a protective response against toxoplasmosis. Therefore, SAG1-GRA2 protein might be a good candidate for the further development of a multiantigenic vaccine.

An opposite role is exerted by the acarian Myocoptes musculinus in the outcome of Toxoplasma gondii infection according to the route of the protozoa inoculation

Infection with Toxoplasma gondii leads to a Th1 immune response. Alternatively, the acarian Myocoptes musculinus induces a disease in BALB/c mice that involves Th2 immune mechanisms. In this study, we investigated whether infestation by M. musculinus induces Th2 immune response in C57BL/6 mice and if this response influences the T. gondii-induced Th1 response when mice are inoculated by intraperitoneal or oral route. The animals were infected with M. musculinus and one month later with T. gondii ME-49 strain and the survival and immune response were monitored. The co-infected animals displayed higher mortality rate and the spleen cells showed a decreased IFN-gamma and elevated IL-4 and IL-5 production. These changes were associated with severe pneumonia and wasting condition. On the other hand, when mice were orally infected with 100 T. gondii cysts, co-infection prolonged the survival rates and ameliorated intestinal lesions in association with a significant drop in IFN-gamma levels in sera. These results indicate the interference of Th2 response induced by M. musculinus in a T. gondii-induced Th1 response. Altogether, these data demonstrate the profound interactions between the immune response induced against unrelated organisms T. gondii and M. musculinus, and suggest that this type of interactions may impact clinical disease.

The role of dopamine in Toxoplasma-induced behavioural alterations in mice: an ethological and ethopharmacological study

Toxoplasma gondii, a cosmopolitan protozoan parasite, is known to induce behavioural alterations in rodents and may exert an effect on human personality and behaviour. The mechanism of parasite-induced alterations in host behaviour has not been described, but it was hypothesized that development of Toxoplasma tissue cysts in the brain could affect the dopaminergic neuromodulatory system. In this study, we tested the effect of latent Toxoplasma infection on mouse behaviour associated with activity of the dopaminergic system, i.e. locomotion in a novel environment and exploration test. Additionally, we examined the behavioural response of Toxoplasma-infected mice to a selective dopamine uptake inhibitor, GBR 12909. In both genders, Toxoplasma infection decreased locomotion in the open field. Infected females displayed an increased level of exploration in the holeboard test. GBR 12909 induced suppression in holeboard-exploration in the infected males, but had an opposite effect on the controls. These results suggest an association between Toxoplasma gondii infection and changes in the dopaminergic neuromodulatory system.

Genetic divergence of Toxoplasma gondii strains associated with ocular toxoplasmosis, Brazil

Brazilian strains of T. gondii differ from lineages in North America and Europe; these differences may underlie severe ocular disease.

Previous studies have shown a high prevalence of toxoplasmosis and the frequent occurrence of ocular disease in Brazil. To identify the genotypes of parasite strains associated with ocular disease, we compared 25 clinical and animal isolates of Toxoplasma gondii from Brazil to previously characterized clonal lineages from North America and Europe. Multilocus nested polymerase chain reaction analysis was combined with direct sequencing of a polymorphic intron to classify strains by phylogenetic methods. The genotypes of T. gondii strains isolated from Brazil were highly divergent when compared to the previously described clonal lineages. Several new predominant genotypes were identified from different regions of Brazil, including 2 small outbreaks attributable to foodborne or waterborne infection. These findings show that the genetic makeup of T. gondii is more complex than previously recognized and suggest that unique or divergent genotypes may contribute to different clinical outcomes of toxoplasmosis in different localities.

Immunization with MIC1 and MIC4 induces protective immunity against Toxoplasma gondii

Host cell invasion by Toxoplasma gondii is tightly coupled to the apical release of micronemal proteins (MIC). In this work, we evaluated the protective effect encountered in C57BL/6 mice immunized with MIC1 and MIC4 purified from soluble tachyzoite antigens by affinity to immobilized lactose. The immunized mice presented high serum levels of IgG1 and IgG2b specific antibodies. MIC1/4-stimulated spleen cells from immunized mice produced IL-2, IL-12, IFN-gamma, IL-10, but not IL-4, suggesting the induction of a polarized Th1 type immune response. When orally challenged with 40 cysts of the ME49 strain, the immunized mice had 68% fewer brain cysts than the control mice. Immunization was associated with 80% survival of the mice challenged with 80 cysts, contrasting with 100% mortality of the non-immunized mice in the acute phase. In this phase, there was much lower parasitism in the lungs and small intestine of the immunized mice, and they did not exhibit the early-stage signs of intestinal necrosis, which was clearly detected in the control mice. Our data demonstrate that MIC1 and MIC4 triggered a protective response against toxoplasmosis, and that these antigens are targets for the further development of a vaccine.

Innate refractoriness of the Lewis rat to toxoplasmosis is a dominant trait that is intrinsic to bone marrow-derived cells

Toxoplasmosis is a ubiquitous parasitic infection causing a wide spectrum of diseases. It is usually asymptomatic but can lead to severe ocular and neurological disorders. Among the small-animal models available to study factors that determine susceptibility to toxoplasmosis, the rat appears to be rather similar to humans, particularly in terms of resistance to acute infection. Here, we demonstrate that the Lewis (LEW) rat strain displays an unexpected refractoriness to Toxoplasma infection. Complete resistance was assessed by both negative anti-Toxoplasma serology and lack of detection of the parasite during the course of infection. In this model, sex, age, major histocompatibility complex, and inoculum size had no effect on resistance. Interestingly, progeny from F(1) hybrid crosses between Fischer (F344) or Brown Norway susceptible rats and LEW resistant rats were also fully resistant, showing a dominant effect of the gene or set of genes. Furthermore, resistance of the LEW rat was shown to be dependent on hematopoietic cells and partially abrogated by neutralization of endogenous gamma interferon. To our knowledge, this is the first observation of a rodent strain that is refractory to Toxoplasma infection. This model is therefore an attractive and powerful tool to dissect host genetic factors involved in susceptibility to toxoplasmosis.

Oral immunization with a live recombinant attenuated Salmonella typhimurium protects mice against Toxoplasma gondii

The natural site of infection for T. gondii is the mucosal surface of the intestine, so the protective immunity obtained after natural infection with T. gondii points to the importance of developing a vaccine that stimulates mucosal defences. In this study, an aroA- and aroD- attenuated strain of Salmonella typhimurium (BRD509) has been used to deliver the recombinant eukaryotic plasmid pSAG(1-2)/CTA2/B expressing a multi-antigenic gene encoding SAG1 and SAG2 of T. gondii linked to A2/B subunits of cholera toxin as a candidate oral T. gondii vaccine. Immunoblot analysis showed compound gene expression in HeLa cells in vitro and intragastric immunization of mice with the recombinant salmonella resulted in the induction of humoral and Th1 type cellular immune responses and afforded protection against RH strain T. gondii challenge. Anti-T. gondii IgG values increased markedly in the BRD509/pSAG(1-2)-CTA2/B immunized group; these values were significantly higher than those in the negative controls (P = 0.008). With CTA2/B genetic adjuvant, the T. gondii-specific response was predominantly Th1, indicating that the CTA(2)/B genetic adjuvant was able to overcome the strong Th2-bias of the antigen (IgG2a >> IgG1). Antigen-specific T cell proliferative responses and CTL activity were significantly enhanced when cholera toxin CTA2/B genetic adjuvant was used (P = 0.009; P = 0.006). Culture supernatants from antigen-stimulated splenocytes from mice in these groups were also examined by ELISA for Th1- and Th2-type cytokines; mean IFN-gamma levels produced after oral immunization with BRD509/pSAG(1-2)-CTA2/B were about nine-fold higher than after immunization with BRD509/pSAG(1-2) (P = 0.007). On the other hand, the levels of IL-4 were low for all groups and no increase was seen in the presence of CTA2/B genetic adjuvant. When the immunized mice were intraperitoneally challenged with 10(3) tachyzoites of the highly virulent RH strain, the survival time of the mice immunized with BRD509/pSAG(1-2)-CTA2/B was markedly longer than other groups (P = 0.003) and a 40% survival rate was achieved. This is the first report that demonstrates that an oral attenuated salmonella DNA vaccine can induce protective immunity against the acute phase of T. gondii infection.

Transepithelial migration of Toxoplasma gondii involves an interaction of intercellular adhesion molecule 1 (ICAM-1) with the parasite adhesin MIC2

Toxoplasma gondii crosses non-permissive biological barriers such as the intestine, the blood-brain barrier and the placenta thereby gaining access to tissues where it most commonly causes severe pathology. Herein we show that in the process of migration Toxoplasma initially concentrates around intercellular junctions and probably uses a paracellular pathway to transmigrate across biological barriers. Parasite transmigration required viable and actively motile parasites. Interestingly, the integrity of host cell barriers was not altered during parasite transmigration. As intercellular adhesion molecule 1 (ICAM-1) is upregulated on cellular barriers during Toxoplasma infection, we investigated the role of this receptor in parasite transmigration. Soluble human ICAM-1 and ICAM-1 antibodies inhibited transmigration of parasites across cellular barriers implicating this receptor in the process of transmigration. Furthermore, human ICAM-1 immunoprecipitated the mature form of the parasite adhesin MIC2 present on the parasite surface, indicating that this interaction may contribute to cellular migration. These findings reveal that Toxoplasma exploits the natural cell trafficking pathways in the host to cross cellular barriers and disseminate to deep tissues.

CD11c- and CD11b-expressing mouse leukocytes transport single Toxoplasma gondii tachyzoites to the brain

The protozoan parasite Toxoplasma gondii enters hosts through the intestinal mucosa and colonizes distant tissues such as the brain, where its progeny persists for a lifetime. We investigated the role of CD11c- and CD11b-expressing leukocytes in T. gondii transport during the early step of parasitism from the mouse small intestine and during subsequent parasite localization in the brain. Following intragastric inoculation of cyst-containing parasites in mice, CD11c+ dendritic cells from the intestinal lamina propria, the Peyer patches, and the mesenteric lymph nodes were parasitized while in the blood, parasites were associated with the CD11c- CD11b+ monocytes. Using adoptive transfer experiments, we demonstrated that these parasitized cells triggered a parasitic process in the brain of naive recipient mice. Ex vivo analysis of parasitized leukocytes showed that single tachyzoites remained at the cell periphery, often surrounded by the host cell plasma membrane, but did not divide. Using either a dye that labels circulating leukocytes or an antibody known to prevent CD11b+ circulating leukocytes from leaving the microvascular bed lumen, and chimeric mice in which the hematopoietic cells expressed the green fluorescent protein, we established that T. gondii zoites hijacked CD11b+ leukocytes to reach the brain extravascular space.

Attachment and invasion ofToxoplasma gondiiandNeospora caninumto epithelial and fibroblast cell linesin vitro

Attachment and invasion ofToxoplasma gondiiandNeospora caninumto a cat and a dog fibroblast cell line and 2 epithelial cell lines (a cat kidney and Vero) were comparedin vitrousing fluorescence antibody methodology. In addition, trypsin treatment of tachyzoites was used to determine whether protein molecules were essential to the process of invasion. The results show that bothT. gondiiandN. caninuminvaded all 4 cell lines, and that pre-treatment ofT. gondiitachyzoites with trypsin caused an increase in the ability of the parasite to invade these host cells. FurthermoreT. gondii, in comparison toN. caninum, invaded all 4 cell lines at greater levels. The results here support the conclusion that bothT. gondiiandN. caninumhave the ability to invade a variety of cell types including both dog and cat cells, and questions the utility of Vero cells as an appropriate host cell forin vitrostudies on the biology of these taxa.