T lymphocyte-dependent effector mechanisms of immunity to Toxoplasma gondii

Activity of isoflavone biochanin A in chronic experimental toxoplasmosis: impact on inflammation

Toxoplasma gondii is a worldwide prevalent parasite. The infection has been linked to variable inflammatory effects including neuroinflammation. Biochanin A (BCA) is an isoflavone, known for its anti-inflammatory and anti-oxidative properties. In this study, we examined the effect of BCA on the brain and liver inflammatory lesions in a murine model with chronic toxoplasmosis. Mice were divided in to six groups: non-infected control, non-infected BCA-treated, and four infected groups with Toxoplasmagondii Me49-type II cystogenic strain: infected control, BCA (50 mg/kg/day)-treated, combined BCA/cotrimoxazole-treated and cotrimoxazole (370 mg/kg/day) alone-treated. Gene expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and inducible nitric oxide synthase (iNOS) was evaluated by quantitative real-time PCR in the brain and liver tissues. In the infected control group, an upregulation of TNF-α and IL-1β mRNA expression levels was found. However, a downregulation of iNOS expression was detected in the brain of infected control mice. In both BCA- and combined-treated groups, the brain and liver tissues showed significantly reduced inflammatory lesions compared to the infected control mice with inhibited TNF-α and IL-1β mRNA levels. The iNOS expression levels in the brain tissues of BCA group were significantly higher than the levels of the infected control group. BCA alone or combined significantly reduced T. gondii cyst count in the brain tissues. In conclusion, the anti-inflammatory activity of BCA was demonstrated in the brain tissues of mice with chronic toxoplasmosis with decreased TNF-α and IL-1β expression levels and increased iNOS expression levels.

Immunomodulatory effects of Inonotus obliquus polysaccharide on splenic lymphocytes infected with Toxoplasma gondii via NF-κB and MAPKs pathways

CONTEXT

As a medicinal and edible fungus, Inonotus obliquus has been traditionally used to prevent and treat various ailments. Inonotus obliquus polysaccharide (IOP) isolated from I. obliquus processes many biological activities, our series of in vivo studies have shown that IOP protects against Toxoplasma gondii infection.

OBJECTIVE

This study aimed to investigate the in vitro immunomodulatory effects and its mechanisms of IOP on mouse splenic lymphocytes infected with T. gondii.

MATERIALS AND METHODS

Mouse splenic lymphocytes were infected with T. gondii tachyzoites, and treated with different concentrations of IOP. The levels of cytokines and chemokines were measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). The expression of toll-like receptor 2 (TLR2) and TLR4, and the modulation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways were determined by Western blot.

RESULTS

IOP significantly decreased the over-release of cytokine interleukin-1 beta (IL-1β), IL-4, IL-6, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) in supernatant from T. gondii-infected splenic lymphocytes. IOP also effectively inhibited the overexpression of cytokines and chemokine macrophage inflammatory protein-1 (MIP-1) and monocyte chemoattractant protein-1 (MCP-1) mRNA. Furthermore, IOP down-regulated TLR2 and TLR4 expressions and inhibited the over-phosphorylation of NF-κB p65 and inhibitor κBα (IκBα) in NF-κB signaling pathway and p38, c-Jun N-terminal kinase (JNK) in MAPKs signaling pathway. By observing the effect of IOP on TNF-α secretion after pretreatment with specific inhibitors, it was further confirmed that IOP was involved in the regulation of NF-κB, p38, and JNK signaling pathways.

CONCLUSIONS

These data indicate that IOP can inhibit the excessive inflammatory response caused by T. gondii infection through modulating NF-κB, p38, and JNK signaling pathways, and thus plays the in vitro anti-T. gondii role.

Lymphotoxin β Receptor: a Crucial Role in Innate and Adaptive Immune Responses against Toxoplasma gondii

The lymphotoxin β receptor (LTβR) plays an essential role in the initiation of immune responses to intracellular pathogens. In mice, the LTβR is crucial for surviving acute toxoplasmosis; however, until now, a functional analysis was largely incomplete. Here, we demonstrate that the LTβR is a key regulator required for the intricate balance of adaptive immune responses. Toxoplasma gondii-infected LTβR-deficient (LTβR^−/−) mice show globally altered interferon-γ (IFN-γ) regulation, reduced IFN-γ-controlled host effector molecule expression, impaired T cell functionality, and an absent anti-parasite-specific IgG response, resulting in a severe loss of immune control of the parasites. Reconstitution of LTβR^−/− mice with toxoplasma immune serum significantly prolongs survival following T. gondii infection. Notably, analysis of RNA-seq data clearly indicates a specific effect of T. gondii infection on the B cell response and isotype switching. This study uncovers the decisive role of the LTβR in cytokine regulation and adaptive immune responses to control T. gondii.

Targeted Transcriptomic Analysis of C57BL/6 and BALB/c Mice During Progressive Chronic Toxoplasma gondii Infection Reveals Changes in Host and Parasite Gene Expression Relating to Neuropathology and Resolution

Toxoplasma gondii is a resilient parasite that infects a multitude of warm-blooded hosts and results in a lifelong chronic infection requiring continuous responses by the host. Chronic infection is characterized by a balanced immune response and neuropathology that are driven by changes in gene expression. Previous research pertaining to these processes has been conducted in various mouse models, and much knowledge of infection-induced gene expression changes has been acquired through the use of high throughput sequencing techniques in different mouse strains and post-mortem human studies. However, lack of infection time course data poses a prominent missing link in the understanding of chronic infection, and there is still much that is unknown regarding changes in genes specifically relating to neuropathology and resulting repair mechanisms as infection progresses throughout the different stages of chronicity. In this paper, we present a targeted approach to gene expression analysis during T. gondii infection through the use of NanoString nCounter gene expression assays. Wild type C57BL/6 and BALB/c background mice were infected, and transcriptional changes in the brain were evaluated at 14, 28, and 56 days post infection. Results demonstrate a dramatic shift in both previously demonstrated and novel gene expression relating to neuropathology and resolution in C57BL/6 mice. In addition, comparison between BALB/c and C57BL/6 mice demonstrate initial differences in gene expression that evolve over the course of infection and indicate decreased neuropathology and enhanced repair in BALB/c mice. In conclusion, these studies provide a targeted approach to gene expression analysis in the brain during infection and provide elaboration on previously identified transcriptional changes and also offer insights into further understanding the complexities of chronic T. gondii infection.

Putative biomarkers for early diagnosis and prognosis of congenital ocular toxoplasmosis

In the present study we have evaluated the performance of several immunological biomarkers for early diagnosis and prognosis of congenital toxoplasmosis. Our results showed that ex vivo serum levels of CXCL9, and the frequencies of circulating CD4⁺CD25⁺ T-cells and T. gondii-specific IFN-γ⁺CD4⁺ T-cells measured 30–45 days after birth presented high accuracy to distinguish T. gondii-infected infants from healthy age-matched controls (Global Accuracy/AUC = 0.9; 0.9 and 0.8, respectively). Of note was the enhanced performance (Accuracy = 96%) achieved by using a combined stepwise analysis of CD4⁺CD25⁺ T-cells and CXCL9. In addition, high global accuracy (AUC = 0.9) with elevated sensitivity (Se = 98%) was also reached by using the total frequency of in vitro IFN-γ-producing T. gondii-specific T-cells (∑ IFN-γ⁺ CD4⁺ & CD8⁺) as a biomarker of congenital toxoplasmosis. Furthermore, the analysis of in vitro T. gondii-specific IL5⁺CD4⁺ T-cells and IFN-γ⁺NK-cells displayed a high accuracy for early prognosis of ocular lesion in infant with congenital toxoplasmosis (Global Accuracy/AUC = 0.8 and 0.9, respectively). Together, these findings support the relevance of employing the elements of the cell-mediated immune response as biomarkers with potential to endorse early diagnosis and prognosis of congenital ocular toxoplasmosis to contribute for a precise clinical management and effective therapeutic intervention.

Global status of Toxoplasma gondii infection and associated risk factors in people living with HIV

OBJECTIVE

Toxoplasma infection remains as the most common cause of focal brain lesions among people living with HIV (PLHIV) despite the decline in opportunistic infections with the introduction of antiretroviral treatment. This study was conducted to provide a summary of evidence about the seroprevalence of Toxoplasma gondii and prevalence of active T. gondii infection and associated risk factors among PLHIV.

DESIGN

Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Scopus, PubMed, Science Direct and EMBASE were searched from 1997 to July 2018. All peer-reviewed original research articles describing T. gondii infection among PLHIV with different diagnostic methods were included.

METHODS

Incoherence and heterogeneity between studies were quantified by I index and Cochran's Q test. Publication and population bias were assessed with funnel plots and Egger's regression asymmetry test. All statistical analyses were performed using StatsDirect.

RESULTS

In total, 111 studies from 37 countries assessing 66 139 blood samples were included in this study. The pooled prevalence of T. gondii infection among PLHIV was 3.24% by IgM and 26.22% by molecular methods using the random-effects model. Pooled seroprevalence of T. gondii by IgG was 44.22%. There was a relationship between Toxoplasma prevalence and sex, raw meat consumption, contact with cat and knowledge about toxoplasmosis.

CONCLUSION

High Toxoplasma seroprevalence among PLHIV observed in this study emphasizes the need for implementing screening and prophylaxis tailored to the local context. Owing to the serious and significant clinical manifestations of the parasite in case of reactivation, early identification of seropositivity for initiating prophylaxis among those with a CD4 cell count of less than 200 cells/ml is recommended.

Research on the effect and mechanism of antimicrobial peptides HPRP-A1/A2 work against Toxoplasma gondii infection

With increasing antibiotic resistance and drug safety concerns, novel therapeutics are urgently needed. Antimicrobial peptides are promising candidates that could address the spread of multidrug-resistant pathogens. HPRP-A1/A2 are known to display antimicrobial activity against gram-negative bacteria, gram-positive bacteria and some pathogenic fungi, but whether HPRP-A1/A2 work on Toxoplasma gondii (T gondii) is unknown. In this study, we found that the viability of tachyzoites that received HPRP-A1/A2 treatment was significantly decreased, and there was a reduction in the adhesion to and invasion of macrophages by tachyzoites after HPRP-A1/A2 treatment. HPRP-A1/A2 damaged the integrity of tachyzoite membranes, as characterized by membrane disorganization in and cytoplasm outflow from tachyzoites. In addition, in vivo injection with HPRP-A1/A2 resulted in a significantly decreased number of tachyzoites and an accelerated Th1/Tc1 response, and elicited pro-inflammatory cytokines in T gondii-infected mice. Furthermore, HPRP-A1/A2-treated splenocytes exhibited a significantly increased Tc1/Th1 response, and HPRP-A1/A2-stimulated macrophages inhibited the growth of carboxyfluorescein succinimidyl amino ester (CFSE)-labelled tachyzoites, which had higher TNF-α/IL-12 mRNA levels. Altogether, these results imply that HPRP-A1/A2 are effective against T gondii through damaging the structure of tachyzoites and inducing a protective immune response, which could offer an alternative approach against T gondii infection.

Toxoplasma gondii antigen SAG2A differentially modulates IL-1β expression in resistant and susceptible murine peritoneal cells

The cell surface of Toxoplasma gondii is covered by antigens (SAGs) from the SRS family anchored by glycosylphosphatidylinositol (GPI) and includes antigens from the SAG2 family. Among these, the SAG2A surface antigen shows great potential in activating humoral responses and has been used in characterizing the acute phase of infection and in the serological diagnosis of toxoplasmosis. In this study, we aimed to evaluate rSAG2A-induced proteins in BALB/c and C57BL/c mice macrophages and to evaluate the phenotypic polarization induced in the process. We treated the peritoneal macrophages from mouse strains that were resistant or susceptible to T. gondii with rSAG2A to analyze their proteomic profile by mass spectrometry and systems biology. We also examined the gene expression of these cells by RT-qPCR using the phenotypic markers of M1 and M2 macrophages. Differences were observed in the expression of proteins involved in the inflammatory process in both resistant and susceptible cells, and macrophages were preferentially induced to obtain a pro-inflammatory immune response (M1) via the overexpression of IL-1β in mice susceptible to this parasite. These data suggest that the SAG2A antigen induces phenotypic and classical activation of macrophages in both resistant and susceptible strains of mice during the acute phase of the disease.

Strain- and Dose-Dependent Reduction of Toxoplasma gondii Burden in Pigs Is Associated with Interferon-Gamma Production by CD8+ Lymphocytes in a Heterologous Challenge Model

Toxoplasma gondii is a worldwide prevalent parasite of humans and animals. The global infection burden exceeds yearly one million disability-adjusted life years (DALY's) in infected individuals. Therefore, effective preventive measures should be taken to decrease the risk of infection in humans. Although human toxoplasmosis is predominantly foodborne by ingestion of tissue cysts in meat from domestic animals such as pigs, the incidence risk is difficult to estimate due to the lack of screening of animals for infection and insights in location and persistence of the parasite in the tissues. Hence, experimental infections in pigs can provide more information on the risk for zoonosis based on the parasite burden in meat products intended for human consumption and on the immune responses induced by infection. In the present study, homo- and heterologous infection experiments with two distinct T. gondii strains (IPB-LR and IPB-Gangji) were performed. The humoral and cellular immune responses, the presence of viable parasites and the parasite load in edible meat samples were evaluated. In homologous infection experiments the parasite persistence was clearly strain-dependent and inversely correlated with the infection dose. The results strongly indicate a change in the amount of parasite DNA and viable cysts in porcine tissues over time. Heterologous challenge infections demonstrated that IPB-G strain could considerably reduce the parasite burden in the subsequent IPB-LR infection. A strong, however, not protective humoral response was observed against GRA7 and TLA antigens upon inoculation with both strains. The in vitro IFN-γ production by TLA-stimulated PBMCs was correlated with the infection dose and predominantly brought about by CD3⁺CD4^-CD8α^bright T-lymphocytes. The described adaptive cellular and humoral immune responses in pigs are in line with the induced or natural infections in mice and humans. Previous studies underscored the heterogeneity of T. gondii strains and the corresponding virulence factors. These findings suggest the potential of the IPB-G strain to elicit a partially protective immune response and to reduce the parasite burden upon a challenge infection. The IPB-G strain could be used as a promising tool in limiting the number of viable parasites in edible tissues and, hence, in lowering the risk for human toxoplasmosis.

Unconventional Peptide Presentation by Major Histocompatibility Complex (MHC) Class I Allele HLA-A*02:01: BREAKING CONFINEMENT

Peptide antigen presentation by major histocompatibility complex (MHC) class I proteins initiates CD8⁺ T cell-mediated immunity against pathogens and cancers. MHC I molecules typically bind peptides with 9 amino acids in length with both ends tucked inside the major A and F binding pockets. It has been known for a while that longer peptides can also bind by either bulging out of the groove in the middle of the peptide or by binding in a zigzag fashion inside the groove. In a recent study, we identified an alternative binding conformation of naturally occurring peptides from Toxoplasma gondii bound by HLA-A*02:01. These peptides were extended at the C terminus (PΩ) and contained charged amino acids not more than 3 residues after the anchor amino acid at PΩ, which enabled them to open the F pocket and expose their C-terminal extension into the solvent. Here, we show that the mechanism of F pocket opening is dictated by the charge of the first charged amino acid found within the extension. Although positively charged amino acids result in the Tyr-84 swing, amino acids that are negatively charged induce a not previously described Lys-146 lift. Furthermore, we demonstrate that the peptides with alternative binding modes have properties that fit very poorly to the conventional MHC class I pathway and suggest they are presented via alternative means, potentially including cross-presentation via the MHC class II pathway.

Early detection of Toxoplasma gondii infection by using a interferon gamma release assay: A review

Antibody-based serological tests are currently the most common diagnostic methods for detection of Toxoplasma gondii; however, these tests bear several limitations. Recently, Interferon-gamma release assay (IGRA), a T-cell-based test, was introduced as an in vitro test for detection of T. gondii infection. Few studies have investigated the potential role of cell immunity in diagnosis of toxoplasmosis. IGRA accurately distinguished infected from uninfected individuals, showing strong lymphocyte activation after in vitro stimulation with T. gondii antigens, even during the first days of life. IGRA is an easy-operation and low-cost method to measure cell mediated immunity against T. gondii. The results of this review underline the importance of evaluating cellular immunity to establish an early diagnosis particularly for congenital toxoplasmosis. Therefore, ELISA-based IGRA holds the potential to become a useful diagnostic tool for early detection of T. gondii infection.

CD8+ T cell immunity in an encephalitis model of Toxoplasma gondii infection

Toxoplasma gondii infection induces a robust CD8 T cell immunity in the infected host, which is critical for keeping chronic infection under control. IFNγ production and cytolytic activity exhibited by CD8 T cells are critical functions needed to prevent the reactivation of latent infection. Paradoxically, the susceptible mice infected with the parasite develop encephalitis irrespective of the presence of vigorous CD8 T cell immunity. Recent studies from our laboratory have demonstrated that these animals have defect in the memory CD8 T cell population, which become dysfunctional due to exhibition of inhibitory receptors like PD-1. Although the blockade of PD-1-PDL-1 pathway rescues the CD8 response, PD-1(hi) expressing cells are refractory to the treatment. In this review, we discuss the development of CD8 memory response during chronic infection, mechanism responsible for their dysfunctionality, and possible therapeutic measures that can be taken to reverse the process.

Interferon-gamma expression and infectivity of Toxoplasma infected tissues in experimentally infected sheep in comparison with pigs

Livestock animals are a potential risk for transmission of toxoplasmosis to humans. Sheep and pigs still remain an important source because their meat is often eaten undercooked which has been regarded as a major route of infection in many countries. Moreover, porcine tissues are processed in many food products. In the current study, the IFN-gamma (T-helper 1 cells), IL-4 (Th2 cells) and IL-10 mRNA (Treg cells) expression by blood mononuclear cells, and the serum antibody response against Toxoplasma gondii total lysate antigen, recombinant T. gondii GRA1, rGRA7, rMIC3 and rEC2, a chimeric antigen composed of MIC2, MIC3 and SAG1, was studied in sheep the first two months after a T. gondii infection and compared with these responses in pigs. At the end of this period, the parasite distribution in heart, brain and two skeletal muscles in sheep was compared with this in pigs. Whereas the parasite distribution was similar in sheep and pigs, the antibody response differed considerably. In sheep, antibodies appeared against all tested T. gondii antigens, but mainly against rGRA7, rMIC3234307 and TLA whereas in pigs only rGRA7-specific antibodies could be demonstrated. Also, the cytokine response differed. Both in sheep and pigs an IFN-gamma response occurred which seemed to be a slightly more pronounced in sheep. In sheep, also IL-10 and IL-4 mRNA expression showed an increase, but later than IFN-gamma and with more variation. However, in pigs no such increase was seen. As concerning diagnosis, results indicate that serum antibodies against GRA7 in live sheep and pigs and heart tissue for bioassay and qPCR in slaughtered animals are the best targets to demonstrate presence of T. gondii infection.

TgMAPK1 is a Toxoplasma gondii MAP kinase that hijacks host MKK3 signals to regulate virulence and interferon-γ-mediated nitric oxide production

The parasite Toxoplasma gondii controls tissue-specific nitric oxide (NO), thereby augmenting virulence and immunopathology through poorly-understood mechanisms. We now identify TgMAPK1, a Toxoplasma mitogen-activated protein kinase (MAPK), as a virulence factor regulating tissue-specific parasite burden by manipulating host interferon (IFN)-γ-mediated inducible nitric oxide synthase (iNOS). Toxoplasma with reduced TgMAPK1 expression (TgMAPK1(lo)) demonstrated that TgMAPK1 facilitates IFN-γ-driven p38 MAPK activation, reducing IFN-γ-generated NO in an MKK3-dependent manner, blunting IFN-γ-mediated parasite control. TgMAPK1(lo) infection in wild type mice produced ≥ten-fold lower parasite burden versus control parasites with normal TgMAPK1 expression (TgMAPK1(con)). Reduced parasite burdens persisted in IFN-γ KO mice, but equalized in normally iNOS-replete organs from iNOS KO mice. Parasite MAPKs are far less studied than other parasite kinases, but deserve additional attention as targets for immunotherapy and drug discovery.

Foxp4 is dispensable for T cell development, but required for robust recall responses

Transcription factors regulate T cell fates at every stage of development and differentiation. Members of the Foxp family of forkhead transcription factors are essential for normal T lineage development; Foxp3 is required for T regulatory cell generation and function, and Foxp1 is necessary for generation and maintenance of naïve T cells. Foxp4, an additional member of the Foxp family, is highly homologous to Foxp1 and has been shown to dimerize with other Foxp proteins. We report the initial characterization of Foxp4 in T lymphocytes. Foxp4 is expressed in both thymocytes and peripheral CD4⁺ and CD8⁺ T cells. We used a CD4Cre mediated approach to evaluate the cell autonomous role for Foxp4 in murine T lymphocytes. T cell development, peripheral cellularity and cell surface phenotype are normal in the absence of Foxp4. Furthermore, Foxp3⁺ T regulatory cells develop normally in Foxp4 deficient animals and naïve Foxp4 deficient CD4 T cells can differentiate to inducible T regulatory cells in vitro. In wild-type T cells, expression of Foxp4 increases following activation, but deletion of Foxp4 does not affect T cell proliferative responses or in vitro effector T cell differentiation. In vivo, despite effective control of Toxoplasma gondii and acute lymphocytic choriomeningitis virus infections, effector cytokine production during antigen specific recall responses are reduced in the absence of Foxp4. We conclude that Foxp4 is dispensable for T cell development, but necessary for normal T cell cytokine recall responses to antigen following pathogenic infection.

The Toxoplasma gondii peptide AS15 elicits CD4 T cells that can control parasite burden

The apicomplexan parasite Toxoplasma gondii can cause severe disease in immunocompromised individuals. Previous studies in mice have focused largely on CD8(+) T cells, and the role of CD4 T cells is relatively unexplored. Here, we show that immunization of the C57BL/6 strain of mice, in which the immunodominant CD8 T cell response to the parasite dense-granule protein GRA6 cannot be generated, leads to a prominent CD4 T cell response. To identify the CD4 T cell-stimulating antigens, we generated a T. gondii-specific, lacZ-inducible, CD4 T cell hybridoma and used it as a probe to screen a T. gondii cDNA library. We isolated a cDNA encoding a protein of unknown function that we call CD4Ag28m and identified the minimal peptide, AS15, which was presented by major histocompatibility complex (MHC) class II molecules to the CD4 T cells. Immunization of mice with the AS15 peptide provided significant protection against subsequent parasite challenge, resulting in a lower parasite burden in the brain. Our findings identify the first CD4 T cell-stimulating peptide that can confer protection against toxoplasmosis and provide an important tool for the study of CD4 T cell responses and the design of effective vaccines against the parasite.

The placenta: a main role in congenital toxoplasmosis?

Systemic infections, such as toxoplasmosis, acquired during pregnancy can lead to placental infection and have profound effects on the mother-to-child relationship and the success of pregnancy. Placental permeability to Toxoplasma gondii is a main parameter that determines parasite transmission to the foetus, and the use of antibiotics to decrease placental parasite load and prevent congenital toxoplasmosis has been suggested for decades. Although parasitological examination of the placenta at birth is commonly used to diagnose neonatal congenital toxoplasmosis, this approach can be controversial. Here we argue in favour of placental examination for both diagnostic and epidemiological purposes.

Evaluation of Toxoplasma gondii as a live vaccine vector in susceptible and resistant hosts

Background

Toxoplasma gondii has been shown to trigger strong cellular immune responses to heterologous antigens expressed by the parasite in the inbred mouse model [1]. We studied the immune response induced by T. gondii as an effective vaccine vector in chickens and rabbits.

Results

T. gondii RH strain was engineered to express the yellow fluorescent protein (YFP) in the cytoplasm. A subcutaneous injection of the transgenic T. gondii YFP in chickens afforded partial protection against the infection of transgenic E. tenella YFP. T. gondii YFP induced low levels of antibodies to YFP in chickens, suggesting that YFP specific cellular immune response was probably responsible for the protective immunity against E. tenella YFP infection. The measurement of T-cell response and IFN-γ production further confirmed that YFP specific Th1 mediated immune response was induced by T. gondii YFP in immunized chickens. The transgenic T. gondii stimulated significantly higher YFP specific IgG titers in rabbits than in chickens, suggesting greater immunogenicity in a T. gondii susceptible species than in a resistant species. Priming with T. gondii YFP and boosting with the recombinant YFP can induce a strong anti-YFP antibody response in both animal species.

Conclusions

Our findings suggest that T. gondii can be used as an effective vaccine vector and future research should focus on exploring avirulent no cyst-forming strains of T. gondii as a live vaccine vector in animals.

IFN-γ expression and infectivity of Toxoplasma infected tissues are associated with an antibody response against GRA7 in experimentally infected pigs

Toxoplasma gondii, an obligate intracellular parasite, can be transmitted to humans via the consumption of infected meat. However, there are currently no veterinary diagnostic tests available for the screening of animals at slaughter. In the current work, we investigated whether cytokine responses in the blood, and antibody responses against recombinant T. gondii GRA1, GRA7, MIC3 proteins and a chimeric antigen EC2 encoding MIC2-MIC3-SAG1, are associated with the infectivity of porcine tissues after experimental infection with T. gondii. Two weeks after experimental infection of conventional 5-week-old seronegative pigs, an IFN-γ response was detected in the blood, with a kinetic profile that followed the magnitude of the GRA7 antibody response. Antibody responses to GRA1, MIC3 and EC2 were very weak or absent up to 6 weeks post infection. Antibodies against GRA7 occurred in all infected animals and were associated with the presence of the parasite in tissues at euthanasia a few months later, as demonstrated by quantitative real-time PCR and isolation by bio-assay. Remarkably, although brain and heart tissue remained infectious, musculus gastrocnemius and musculus longissimus dorsi were found clear of infectious parasites 6 months after experimental infection. Seropositive response in a GRA7 ELISA indicates a Toxoplasma infection in pigs and is predictive of the presence of infectious cysts in pig heart and brain. This new ELISA is a promising tool to study the prevalence of Toxoplasma infection in pigs. Clearance of the infection in certain pig tissues suggests that the risk assessment of pig meat for human health needs further evaluation.

Toxoplasma gondii cyclophilin 18 regulates the proliferation and migration of murine macrophages and spleen cells

Toxoplasma gondii is an intracellular parasite that shows a unique capacity to infect a variety of cell types in warm-blooded animals. It can invade and survive well inside immune cells, such as macrophages, that disseminate the parasite around the body because of their migratory properties. The aim of the present study was to evaluate the role of T. gondii cyclophilin 18 (TgCyp18) in the proliferation and migration of macrophages and spleen cells (mainly T lymphocytes) in order to understand the effects of TgCyp18 on the dynamics of the infection. A high dose of TgCyp18 enhanced the proliferation of macrophages and spleen cells in a cysteine-cysteine chemokine receptor 5 (CCR5)-independent way. In contrast, TgCyp18 controlled the migration of macrophages and spleen cells in dose- and CCR5-dependent manners. Our data suggest that TgCyp18 recruits cells and enhances the growth of host cells at the site of infection for maintenance of the interaction between the parasite and host.

IL-33 receptor (T1/ST2) signalling is necessary to prevent the development of encephalitis in mice infected with Toxoplasma gondii

T1/ST2 is an immunoregulatory protein of the IL-1 receptor family that has recently been reported as being a component of the IL-33 receptor. IL-33 is a newly described cytokine known to amplify the Th2 response and reduce production of Th1 cytokines. The function of T1/ST2 during Toxoplasma gondii infection is as yet undescribed. Given the requirement of a balanced type 1/type 2 response for effective control of parasite number and immunopathology, it is likely that T1/ST2 may play a part in aiding this process. Accordingly, we have shown that T1/ST2 mRNA transcripts are upregulated in the brains of mice infected with T. gondii and that mice deficient in T1/ST2 demonstrated increased susceptibility to infection with T. gondii that correlated with increased pathology and greater parasite burden in the brains. Real-time PCR analysis of cerebral cytokine levels revealed increased mRNA levels of iNOS, IFN-gamma and TNF-alpha in infected T1/ST2(-/-) mice. These effects were independent of changes in IL-10 production. This study provides the first evidence of a specific role for IL-33 receptor signalling in the brain as well as highlighting the requirement of this mechanism in limiting infection with an intracellular parasite.

Functional characterization of in vivo effector CD4(+) and CD8(+) T cell responses in acute Toxoplasmosis: an interplay of IFN-gamma and cytolytic T cells

Development of prophylactic vaccines against Toxoplasma gondii is based on the observation that latently infected subjects are protected against secondary infection during pregnancy. Cocktail DNA vaccines have been shown to provide high resistance to parasite challenge, and latently infected mice are protected against acute disease. In order to characterize the associated Th1 cellular immune responses in vivo, we used H2-K(k) bone marrow macrophage cell lines constitutively expressing T. gondii GRA1, GRA7 or ROP2 antigens, for the in vivo characterization of antigen-specific T cells in an antigenic challenge model, and as target cells in an in vivo CTL assay. In latently infected C3H/HeN mice, CD4(+) and CD8(+) T cells were recruited to the peritoneal cavity after i.p. challenge with these syngeneic cell lines. GRA1 and GRA7-specific T cells from infected mice were IFN-gamma(+) FasL(-) CD107(-). No IFN-gamma or lytic markers were observed against ROP2. In cocktail DNA vaccinated C3H/HeN mice, the response was restricted to GRA1-specific CD8(+) IFN-gamma(-) FasL(-) CD107(+) T cells. Target cells expressing GRA1 and GRA7, but not ROP2, were efficiently killed in an in vivo CTL assay in latently infected mice, while in DNA vaccinated mice only lysis of GRA1 expressing target cells was observed. Both forms of immunization, DNA vaccination and latent infection, completely protected mice against acute Toxoplasmosis. The results obtained in this work suggest that distinct in vivo cytolytic effector mechanisms are at work in DNA vaccinated and latently infected mice, but both converge to protect against acute toxoplasmosis.

Diagnosis of congenital toxoplasmosis by using a whole-blood gamma interferon release assay

Congenital toxoplasmosis in newborns is generally subclinical, but infected infants are at risk of developing ocular lesions. Diagnosis at birth relies mainly on serological tests. Cell-mediated immunity plays the major role in resistance to infection but is not routinely investigated for diagnostic purposes. Here, we describe a simple test based on the gamma interferon (IFN-gamma) response after stimulation of whole blood by crude parasitic antigens. One milliliter of heparinized blood was centrifuged; plasma was kept for routine serological tests, and pellets were resuspended in culture medium. After 24 h of culture in the presence of crude Toxoplasma gondii antigen, the cells were centrifuged and the supernatant was assayed for IFN-gamma. For 62 infants under 1 year of age born to mothers who were infected during pregnancy, the sensitivity and specificity of the test were 94% (with positive results for 16 of 17 infected infants) and 98% (with negative results for 44 of 45 uninfected infants), respectively. The false-negative result was for a treated baby who gave positive results after the withdrawal of treatment. The false positive was obtained for a 3-month-old baby. For a cohort of 124 congenitally infected patients between 1 and 30 years of age, the sensitivity of the assay was 100%. We present a simple test based on IFN-gamma secretion to assess cell-mediated immunity in toxoplasmosis. As only 1 ml of blood is required to investigate humoral and cellular immunity, our assay is well adapted for the study of congenital toxoplasmosis in infants. Using purified antigens or recombinant peptides may improve the test performance.

Improvement of a dendritic cell-based therapeutic cancer vaccine with components of Toxoplasma gondii

The use of dendritic cells (DCs) as a cellular adjuvant is a promising approach to the immunotherapy of cancer. It has previously been demonstrated that DCs pulsed ex vivo with Toxoplasma gondii antigens trigger a systemic Th1-biased specific immune response and induce protective and specific antitoxoplasma immunity. In the present study, we demonstrate that tumor antigen-pulsed DCs matured in the presence of Toxoplasma gondii components induce a potent antitumor response in a mouse model of fibrosarcoma. Bone-marrow derived DCs (BMDCs) were cultured in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4. After 5 days, tumor lysates with or without the T. gondii lysate were added to the culture for another 2 days. The cytokine production in the BMDC culture and the coculture supernatants of DCs and splenic cells was evaluated. For immunization, 7 days after tumor challenge, different groups of BALB/c mice received different kinds of DCs subcutaneously around the tumor site. Tumor growth was monitored, and 2 weeks after DC immunotherapy, the cytotoxic activity and the infiltration of CD8(+) T cells were monitored in different groups. According to the findings, immunotherapy with T. gondii-matured DCs led to a significant increase in the activity of cytotoxic T cells and decreased the rate of growth of the tumor in immunized animals. Immature DCs did not cause any change in cytotoxic activity or the tumor growth rate compared to that in the healthy controls. The current study suggests that a specific antitumor immune response can be induced by DCs matured with T. gondii components and provide the basis for the use of T. gondii in DC-targeted clinical therapies.

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.

Further analysis of protection induced by the MIC3 DNA vaccine against T. gondii: CD4 and CD8 T cells are the major effectors of the MIC3 DNA vaccine-induced protection, both Lectin-like and EGF-like domains of MIC3 conferred protection

The present study was conducted mainly to evaluate the contribution of the cellular and the humoral responses in protection conferred by the MIC3 DNA vaccine (pMIC3i) that was proved as a potent vaccine against toxoplasmosis. We performed the adoptive transfer of CD4(+) and CD8(+) T lymphocytes from pMIC3i immunized mice to naive ones and the role of humoral immunity was evaluated by in vitro invasion assays. We also constructed plasmids encoding the EGF-like domains and the Lectin-like domain of MIC3, to define which domains of MIC3 are involved in the protection. Furthermore, the adjuvant effect of the GM-CSF-expressing vector (granulocyte-macrophage colony-stimulating factor) required the precise temporal and spatial codelivery of GM-CSF with antigen, thus, we constructed a bicistronic plasmid expressing MIC3 and GM-CSF. In conclusion, the protection induced by pMIC3i was mainly mediated by CD4(+) and CD8(+) T lymphocytes and both EGF and Lectin domains of MIC3 conferred protection. Furthermore, the codelivery of GM-CSF by a bicistronic plasmid appeared to be a most effective way for enhancing the adjuvant properties of GM-CSF.

CCR2 receptor is essential to activate microbicidal mechanisms to control Toxoplasma gondii infection in the central nervous system

Chemokines comprise a structurally related family of cytokines that regulate leukocyte trafficking. Because infection with Toxoplasma gondii can induce an important inflammatory reaction that, if left uncontrolled, can lead to death, we investigated the role of the chemokine receptor CCR2 in T. gondii infection. We orally infected CCR2(-/-) mice with five ME-49 T. gondii cysts and monitored morbidity, survival, and immune response thereafter. The CCR2(-/-) mice displayed higher susceptibility to infection as all mice died on day 28 after infection. Despite similar Th1 responses, a more evident anti-inflammatory response was induced in the peripheral organs of CCR2(-/-) mice compared with wild-type C57BL/6 mice. Additionally, CCR2(-/-) mice presented greater parasitism and a milder inflammatory reaction in their peripheral organs with lesser CD4(+) and MAC-1(+) and greater CD8(+) cell migration. The parasite load decreased in these organs in CCR2(-/-) mice but remained uncontrolled in the central nervous system. Additionally, we observed down-regulated inducible nitric oxide synthase expression in peripheral organs from CCR2(-/-) mice that was associated with a small nitric oxide production by spleen macrophages. In conclusion, in the absence of CCR2, another mechanism is activated to control tissue parasitism in peripheral organs. Nevertheless, CCR2 is essential for the activation of microbicidal mediators that control T. gondii replication in the central nervous system.

Cellular and molecular physiopathology of congenital toxoplasmosis: the dual role of IFN-gamma

Toxoplasma gondii is one of the few pathogens that can cross the placenta. Frequency and severity of transmission vary with gestational age. While the control of acquired toxoplasmosis is already well explored, the control of materno-foetal transmission of the parasite remains almost unknown. This is partly due to the lack of an animal model to study this process. This review summarises the studies which have been undertaken and shows that the mouse is a valuable model despite obvious differences to the human case. The paramount role of the cellular immune response has been shown by several experiments. However, IFN-gamma has a dual role in this process. While its beneficial effects in the control of toxoplasmosis are well known, it also seems to have transmission-enhancing effects and can also directly harm the developing foetus. The ultimate goal of these studies is to develop a vaccine which protects both mother and foetus. Therefore, it is useful to study the mechanisms of natural resistance against transmission during a secondary infection. In this setting, the process is more complicated, involving both cellular and also humoral components of the immune system. In summary, even if the whole process is far from being elucidated, important insights have been gained so far which will help us to undertake rational vaccine research.

Death receptor ligation or exposure to perforin trigger rapid egress of the intracellular parasite Toxoplasma gondii

The obligate intracellular parasite Toxoplasma gondii chronically infects up to one-third of the global population, can result in severe disease in immunocompromised individuals, and can be teratogenic. In this study, we demonstrate that death receptor ligation in T. gondii-infected cells leads to rapid egress of infectious parasites and lytic necrosis of the host cell, an active process mediated through the release of intracellular calcium as a consequence of caspase activation early in the apoptotic cascade. Upon acting on infected cells via death receptor- or perforin-dependent pathways, T cells induce rapid egress of infectious parasites able to infect surrounding cells, including the Ag-specific effector cells.

Inhibition of Lewis lung carcinoma growth by Toxoplasma gondii through induction of Th1 immune responses and inhibition of angiogenesis

Toxoplasma gondii is an obligate intracellular protozoan parasite that induces antitumor activity against certain types of cancers. However, little information is available regarding the immunologic mechanisms that regulate these effects. For this purpose, C57BL/6 mice were administered either the T. gondii Me49 strain orally or Lewis lung carcinoma (LLC) cells intramuscularly. Survival rates, tumor size, histopathology, and immune responses were determined for each group, and angiogenesis was evaluated by in vivo Matrigel plug assay. Toxoplasma-infected (TG-injected) mice survived the entire experimental period, whereas cancer cell-bearing (LLC-injected) mice died within six weeks. Mice injected with both T. gondii and cancer cells (TG/LLC-injected group) showed significantly increased survival rates, CD8+ T-cell percentages, IFN-gamma mRNA expression levels, serum IgG2a titers, and CTL responses as compared to the LLC-injected mice. In addition, angiogenesis in the TG/LLC-injected mice was notably inhibited. These effects in TG/LCC-injected mice were similar or were increased by the addition of an adjuvant, Quil-A. However, TG/LLC-injected mice showed decreased percentages of CD4+ and CD8+ T cells, IFN-gamma mRNA expression levels, and serum IgG1 and IgG2a titers as compared to TG-injected mice. Taken together, our results demonstrate that T. gondii infection inhibits tumor growth in the Lewis lung carcinoma mouse model through the induction of Th1 immune responses and antiangiogenic activity.

Vaccination against murine toxoplasmosis using recombinant Toxoplasma gondii SAG3 antigen alone or in combination with Quil A

PURPOSE

Surface antigen 3 (SAG3) of Toxoplasma gondii is very similar in structure to the major surface antigen 1 (SAG1). Although numerous studies have supported the importance of SAG1 in protection against T. gondii infection, few reports exist on SAG3.

MATERIALS AND METHODS

Glutathione-S-transferase (GST)-fused SAG3 of T. gondii (rSAG3) were immunized into BALB/c mice alone or in combination with Quil A (rSAG3/Quil A), and then evaluated the protective immunity in vivo and in vitro against murine toxoplasmosis.

RESULTS

Immunization with rSAG3 or rSAG3/Quil A resulted in significantly more survival days and fewer brain cysts after challenge with T. gondii compared to an infected control group. Mice immunized with rSAG3 alone or in combination with Quil A produced significantly more specific IgG2a antibody, whereas specific IgG1 antibody titers did not increase. The percentage of CD8+ T cells, IFN-gamma mRNA expression, and nitric oxide production significantly increased in rSAG3- and rSAG3/Quil A-immunized mice.

CONCLUSION

These results indicate that vaccination with Toxoplasma rSAG3 results in partial protective immunity against T. gondii infection through induction of a Th1-type immune response, and that protective immunity is accelerated by the modulating effects of Quil A.

1,25(OH)2D3 inhibits in vitro and in vivo intracellular growth of apicomplexan parasite Toxoplasma gondii

The hormonal form of vitamin D, 1,25-dyhydroxyvitamin D3 (1,25(OH)2D3), is implicated in a wide range of functions other than its classical role in calcium and phosphorous homeostasis. When Toxoplasma gondii-infected BALB/c mice were treated with 1,25(OH)2D3, they succumb to death sooner than their counterparts. But they showed less parasite burden in tissues which was further supported by mild pathological lesions. As an effort to understand the physiological mechanism for the above observation an in vitro study was performed. Fewer parasites were observed when 1,25(OH)2D3 pre-treated murine intestinal epithelial cells were challenged with parasites. Moreover, the observed inhibition was dose-dependent and had a maximum effect with 10(-7)M of 1,25(OH)2D3. However, no observable difference was observed, when pre-incubated parasites were added to cells suggesting that the observed inhibition was a result of an effect from 1,25(OH)2D3 on Toxoplasma intracellular growth. Our data support the notion that 1,25(OH)2D3 may inhibit intra cellular T. gondii parasite proliferation in vivo and in vitro.

Age-dependent impairment of functional helper T cell responses to immunodominant epitopes of Toxoplasma gondii antigens in congenitally infected individuals

Human infection with Toxoplasma gondii is generally asymptomatic in immunocompetent adults while it causes significant morbidity in congenitally infected children. Cell mediated immunity plays the main role in host resistance to T. gondii infection and a Th1 cytokine profile is necessary for protection and control of infection. The present work focused on comparing the helper T cell response to the GRA1 antigen of the parasite between children with congenital toxoplasmosis and healthy adults with acquired infection. We demonstrated that in young children with congenital infection the specific T cell response to parasite antigens is impaired and that such hypo-responsiveness is restored during childhood. Also, we provided clear evidence that in individuals with congenital toxoplasmosis the acquisition of functional helper T cell responses is disease-unrelated and indistinguishable in terms of strength, epitope specificity, and cytokine profile from the corresponding responses in immunocompetent adults with asymptomatic acquired T. gondii infection.

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.

A human origin type II strain of Toxoplasma gondii causing severe encephalitis in mice

Despite its capacity for sexual reproduction and global distribution, Toxoplasma gondii has a highly clonal structure, with the majority of isolates belonging to three distinct clonal types. Congenital toxoplasmosis has been associated with type I and type II strains. We here present the first characterization of a T. gondii strain (BGD1) from South-East Europe, isolated from the umbilical blood of a 24-week-old fetus in Serbia. Genotyping, performed by PCR-RFLP using a set of nested PCR markers (5'SAG2, 3'SAG2, BTUB, SAG3, and GRA6), showed that the BGD1 strain possessed a type II genotype. The cytokine patterns in Swiss-Webster mice inoculated with brain cysts of BGD1 and the prototype type II ME49 strain were similar until 180 days post-infection, with highly elevated IFN-gamma, IL-12 and IL-10 by d7 and decreasing thereafter. While both strains induced pneumonia and hepatitis in acute infection (d14), chronic infection (d56) was characterized, in addition to hepatitis, by severe meningoencephalitis, associated with numerous brain cysts. Thus, the BGD1 strain of T. gondii has type II genotypic and immunologic characteristics, but unlike other type II strains of human origin, induces severe encephalitis, making it an alternative to the sheep-derived ME49 strain for experimental models of infection.

Crystal Structure of the Complex between the Monomeric Form of Toxoplasma gondii Surface Antigen 1 (SAG1) and a Monoclonal Antibody that Mimics the Human Immune Response

Toxoplasma gondii, the intracellular parasite responsible for toxoplasmosis infects more than one-third of the world population and can be life-threatening for fetuses and immunocompromised patients. The surface protein SAG1 is an important immune target, which provides a strong immune response against the invasive tachyzoite while the other forms of the parasite, devoid of SAG1 at their surface, are multiplying. In addition to this role as a "hot spot" decoy, SAG1 is predicted to act as an adhesin during host-cell attachment through its binding to proteoglycans. To begin to understand the relationships between SAG1 epitopes and the ligand-binding site, we have solved the crystal structure of the monomeric form of T.gondii SAG1 complexed to a Fab derived from a monoclonal antibody raised against tachyzoite particles. This antibody competes strongly with human Toxoplasma-specific sera, suggesting that its epitope is part of an immunodominant region present on the surface of SAG1. The structure reveals that this conformational epitope, located within the SAG1 N-terminal domain, does not overlap with the proposed ligand-binding pocket. This study provides the first structural description of the monomeric form of SAG1, and significant insights into its dual role of adhesin and immune target during parasite infection.

Role of gamma interferon and T cells in congenital Toxoplasma transmission

In the BALB/c mouse model, primary infection with Toxoplasma gondii during the second third of gestation leads to a high percentage of infected foetuses. However, immunity induced by infection contracted before pregnancy prevents parasites from crossing the placenta and completely protects the foetuses, as well as the pregnant women. In order to clarify the roles of CD4+, CD8+ T lymphocytes and IFN-gamma in this protection, pregnant BALB/c mice were treated with depleting monoclonal antibodies against CD4, CD8, IFN-gamma, or control antibody. Only the foetuses of the groups treated with anti-CD8 and anti-IFN-gamma antibodies developed congenital toxoplasmosis. The maternal production of IFN-gamma was depressed in the mice depleted of CD4 and CD8 cells (P < 0.001). Determination of the blood parasite load demonstrated that materno-foetal transmission of T. gondii correlates with maternal parasitaemia. Together, these results show that CD8+ T lymphocytes and IFN-gamma play an important role in protection against congenital toxoplasmosis during reinfection.

Effects of iNOS inhibitor on IFN-gamma production and apoptosis of splenocytes in genetically different strains of mice infected with Toxoplasma gondii

To evaluate the role of nitric oxide (NO) in IFN-gamma production and apoptosis of splenocytes in genetically different strains of mice with toxoplasmosis, BALB/c (a toxoplasmosis resistant strain) and C57BL/6 (a toxoplasmosis susceptible strain) mice were infected with Toxoplasma gondii cysts orally and subsequently injected intraperitoneally with aminoguanidine, an iNOS inhibitor (AG; 35 mg/kg per mouse daily for 14 days). When BALB/c or C57BL/6 mice were infected with T. gondii without AG treatment, number of brain cysts, NO and IFN-gamma production by splenocytes, and percentages of apoptotic splenocytes were increased compared to uninfected control mice without AG treatment. AG treatment increased the number of brain cysts, and reduced NO and IFN-gamma production in T. gondii-infected C57BL/6 mice. In contrast, in T. gondii-infected BABL/c mice, the number of brain cysts, and NO and IFN-gamma production of splenocytes was not altered by treatment with AG. However, the percentages of apoptotic splenocytes in T. gondii-infected BALB/c or C57BL/6 mice were not affected by AG treatment. These results suggest that NO modulates IFN-gamma production in T. gondii-infected C57BL/6 mice, and that NO is involved in mediating a protective response in toxoplasmosis susceptible, but not resistant, mice strain during acute infection.

Stage conversion of Toxoplasma gondii RH parasites in mice by treatment with atovaquone and pyrrolidine dithiocarbamate

The mouse-virulent RH strain of Toxoplasma gondii is generally considered to have lost its cyst-forming capacity, and conversion of RH tachyzoites into cysts in non-immune mice has previously been shown exclusively following early treatment with sulfadiazine (SDZ). We here describe the development of tissue cysts in mice infected with RH strain parasites and treated with atovaquone (ATO) combined with pyrrolidine dithiocarbamate (PDTC). Groups of Swiss-Webster mice infected intraperitoneally (i.p.) with 10(2) RH tachyzoites were treated with 5, 25 and 100 mg of ATO/kg per day alone or combined with PDTC at 250 mg/kg per day from day 1 postinfection (p.i.) for 14 days. A total of 19 mice survived the 6-week observation period. Of these, brain cysts were recovered in nine (47%), with burdens ranging from 50 to 3120 (mean +/- S.D. = 622 +/- 963). All cyst-harboring mice had high specific IgG antibody levels (1:10,240-1:40,960, corresponding to 500-2000 IU/ml), as did one mouse in which cysts were not demonstrated, which was therefore included in the group of mice with residual infection. Bioassay performed to test the infectivity of these cysts produced acute lethal toxoplasmosis following i.p. inoculation in all instances (100%), and importantly, following peroral inoculation in four (29%). The recovered tachyzoites were highly infectious. In addition, significantly elevated interferon gamma (IFN-gamma) in the treated mice which developed residual infection compared with any group of infection-free (treated or subinoculated) mice, indicates immunological control of the parasite in the latent form. In conclusion, early treatment of mice infected with T. gondii RH tachyzoites with ATO and PDTC induces conversion into tissue cysts, thus providing a new model for studying the mechanism(s) of T. gondii stage conversion.

Characterisation of Toxoplasma gondii engineered to express mouse interferon-gamma

Recent studies have shown the feasibility of using Toxoplasma gondii as an expression system for heterologous protein. For better understanding of the mechanism of interferon-gamma (IFN-gamma) dependent immunity to T. gondii, the parasites were stably transfected with IFN-gamma gene, under control of the GRA1 promoter. Immunofluorescence analyses showed that recombinant mouse IFN-gamma localised to discrete punctuate structures consistent with dense granules and secreted into the vacuolar space. The production of IFN-gamma was detectable in both extracellular parasites and the parasite-infected cells. Growth of the recombinant parasites was inhibited in the mouse macrophage cell line (J774A.1 cells), but not in monkey kidney adherent fibroblasts (Vero cells), demonstrating the species-specificity of IFN-gamma. Addition of anti-mouse IFN-gamma antibody resulted in growth recovery of the recombinant parasites, suggesting that IFN-gamma, secreted from the parasitised host cells across the parasitophorous vacuole membrane, acted in a paracrine manner. Reverse transcription (RT)-PCR analysis revealed significant expression of inducible nitric oxide synthase mRNA and high levels of nitric oxide production in recombinant parasite-infected J774A.1 cells. A competitive inhibitor of the L-arginine-dependent effector pathway, N(G)-monomethyl-L-arginine, inhibited the reduction of recombinant parasite growth in J774A.1 cells. Taken together, our data suggest that the T. gondii expression system may provide a new tool for cytokine gene expression and that parasites engineered to express a cytokine gene may be rationally designed for use in studies on immune responses to T. gondii.

Generation of Toxoplasma gondii GRA1 protein and DNA vaccine loaded chitosan particles: preparation, characterization, and preliminary in vivo studies

Chitosan microparticles as carriers for GRA-1 protein vaccine were prepared and characterized with respect to loading efficiency and GRA-1 stability after short-term storage. Chitosan nanoparticles as carriers for GRA-1 pDNA vaccine were prepared and characterized with respect to size, zeta potential, and protection of the pDNA vaccine against degradation by DNase I. Both protein and pDNA vaccine preparations were tested with regard to their potential to elicit GRA-1-specific immune response after intragastric administration using different prime/boost regimen. The immune response was measured by determination of IgG2a and IgG1 antibody titers. It was shown that priming with GRA1 protein vaccine loaded chitosan particles and boosting with GRA1 pDNA vaccine resulted in high anti-GRA1 antibodies, characterized by a mixed IgG2a/IgG1 ratio. These results showed that oral delivery of vaccines using chitosan as a carrier material appears to be beneficial for inducing an immune response against Toxoplasma gondii. The type of immune response, however, will largely depend on the prime/boost regimen and the type of vaccine used.

Molecular dissection of the human B-cell response against Toxoplasma gondii infection by lambda display of cDNA libraries

The disorders generated by Toxoplasma gondii infection are closely associated with the competence of the host immune system and both humoral and cell mediated immunity are involved in response to parasite invasion. To identify antigens implicated in human B-cell responses, we screened a phage-display library of T. gondii cDNA fragments with sera of infected individuals. This approach identified a panel of recombinant phage clones carrying B-cell epitopes. All the peptide sequences selected by this procedure are regions of T. gondii gene products. These regions contain epitopes of the T. gondii antigens SAG1, GRA1, GRA7, GRA8 and MIC5, which are recognised by human immunoglobulins. Moreover, we report the isolation and characterisation of two additional immunodominant regions encoded by GRA3 and MIC3 genes, whose products have never been described as antigens of the human B-cell response against T. gondii infection. These results demonstrate potential of lambda-display technology for antigen discovery and for the study of the human antibody response against infectious agents.

CD154 plays a central role in regulating dendritic cell activation during infections that induce Th1 or Th2 responses

We compared splenic DC activation during infection with either the Th2 response-inducing parasite Schistosoma mansoni or with the Th1 response-inducing parasite Toxoplasma gondii. CD8alpha(+) DC from schistosome-infected mice exhibited a 2- to 3-fold increase in the expression of MHC class II, CD80, and CD40 (but not CD86) compared with DC from uninfected control animals, while CD8alpha(-) DC exhibited a 2- to 3-fold increase in the expression of MHC class II and CD80 and no alteration, compared with DC from uninfected mice, in the expression of CD86 or CD40. Intracellular staining revealed that DC did not produce IL-12 during infection with S. mansoni. In contrast, infection with T. gondii resulted in a more pronounced increase in the expression of activation-associated molecules (MHC class II, CD80, CD86, and CD40) on both CD8alpha(-) and CD8alpha(+) splenic DC and promoted elevated IL-12 production by DC. Analysis of MHC class I and of additional costimulatory molecules (ICOSL, ICAM-1, OX40L, 4-1BBL, and B7-DC) revealed a generally similar pattern, with greater indication of activation in T. gondii-infected mice compared with S. mansoni-infected animals. Strikingly, the activation of DC observed during infection with either parasite was not apparent in DC from infected CD154(-/-) mice, indicating that CD40/CD154 interactions are essential for maintaining DC activation during infection regardless of whether the outcome is a Th1 or a Th2 response. However, the ability of this activation pathway to induce IL-12 production by DC is restrained in S. mansoni-infected, but not T. gondii-infected, mice by Ag-responsive CD11c(-) cells.

A GRA1 DNA vaccine primes cytolytic CD8(+) T cells to control acute Toxoplasma gondii infection

Protective immunity against Toxoplasma gondii is known to be mediated mainly by T lymphocytes and gamma interferon (IFN-gamma). The contribution of CD4(+) and CD8(+) T-lymphocyte subsets to protective immune responses against T. gondii infection, triggered by a GRA1 (p24) DNA vaccine, was assessed in this study. In vitro T-cell depletion experiments indicated that both CD4(+) and CD8(+) T-cell subsets produced IFN-gamma upon restimulation with a T. gondii lysate. In addition, the GRA1 DNA vaccine elicited CD8(+) T cells that were shown to have cytolytic activity against parasite-infected target cells and a GRA1-transfected cell line. C3H mice immunized with the GRA1 DNA vaccine showed 75 to 100% protection, while 0 to 25% of the mice immunized with the empty control vector survived challenge with T. gondii cysts. In vivo T-cell depletion experiments indicated that CD8(+) T cells were essential for the survival of GRA1-vaccinated C3H mice during the acute phase of T. gondii infection, while depletion of CD4(+) T cells led to an increase in brain cyst burden during the chronic phase of infection.

T cell phenotype and intracellular IFN-gamma production in peritoneal exudate cells and gut intraepithelial lymphocytes during acute Toxoplasma gondii infection in mice

Although there are many reports on the splenic (systemic) T cell response after Toxoplasma gondii infection, little information is available regarding the local T cell responses of peritoneal exudate cells (PEC) and gut intraepithelial lymphocytes (IEL) following peroral infection with bradyzoites. Mice were infected with 40 cysts of the 76K strain of T. gondii, and then sacrificed at days 0, 1, 4, 7 and 10 postinfection (PI). The cellular composition and T cell responses of PEC and IEL were analyzed. The total number of PEC and IEL per mouse increased after infection, but the ratio of increase was higher in IEL. Lymphocytes were the major component of both PEC and IEL. The relative percentages of PEC macrophages and neutrophils/eosinophils increased significantly at day 1 and 4 PI, whereas those of IEL did not change significantly. The percentage of PEC NK1.1 and gamma delta T cells peaked at day 4 PI (p < 0.0001), and CD4 and CD8 alpha T cells increased continuously after infection. The percentages of IEL CD8 alpha and gamma delta T cells decreased slightly at first, and then increased. CD4 and NK1.1 T cells of IEL did not change significantly after infection. IFN-gamma-producing PEC NK1.1 T cells increased significantly from day 1 PI, but the other T cell subsets produced IFN-gamma abundantly thereafter. The proportion of IEL IFN-gamma-producing CD8 alpha and gamma delta T cells increased significantly after infection, while IEL NK1.1 T cells had similar IFN-gamma production patterns. Taken together, CD4 T cells were the major phenotype and the important IFN-gamma-producing T cell subsets in PEC after oral infection with T. gondii, whereas CD8 alpha T cells had these roles in IEL. These results suggest that PEC and IEL comprise different cell differentials and T cell responses, and according to infection route these factors may contribute to the different cellular immune responses.