Differential effects of three canonical Toxoplasma strains on gene expression in human neuroepithelial cells

Strain-specific pre-existing immunity: A key to understanding the role of chronic Toxoplasma infection in cognition and Alzheimer's diseases?

Toxoplasma exposure can elicit cellular and humoral immune responses. In the case of chronic Toxoplasma infection, these immune responses are long-lasting. Some studies suggest that pre-existing immunity from Toxoplasma infection can shape immune responses and resistance to other pathogens and brain insults later in life. Much evidence has been generated suggesting Toxoplasma infection may contribute to cognitive impairment in the elderly. However, there have also been studies that disagree with the conclusion. Toxoplasma has many strain types, with virulence being the most notable difference. There is also considerable variation in the outcomes following Toxoplasma exposure ranging from resolved to persistent infection. Therefore, the brain microenvironment, particularly cellular constituents, differs based on the infecting strain (virulent versus hypovirulent) and infection stage (resolved versus persistent). Such difference might play a critical role in determining the outcome of the host on subsequent challengings to the brain. The ability of Toxoplasma strains to set up distinct stages for neurodegenerative pathology through varying degrees of virulence provides unique experimental tools for characterizing these pathways.

New role of sertraline against Toxoplasma gondii-induced depression-like behaviours in mice

Toxoplasma gondii (T. gondii) is a neurotropic protozoan parasite, which can cause mental and behavioural disorders. The present study aimed to elucidate the effects and underlying molecular mechanisms of sertraline (SERT) on T. gondii-induced depression-like behaviours. In the present study, a mouse model and a microglial cell line (BV2 cells) model were established by infecting with the T. gondii RH strain. In in vivo and in vitro experiments, the underlying molecular mechanisms of SERT in inhibiting depression-like behaviours and cellular perturbations caused by T. gondii infection were investigated in the mouse brain and BV2 cells. The administration of SERT significantly ameliorated depression-like behaviours in T. gondii-infected mice. Furthermore, SERT inhibited T. gondii proliferation. Treatment with SERT significantly inhibited the activation of microglia and decreased levels of pro-inflammatory cytokines such as tumour necrosis factor-alpha, and interferon-gamma, by down-regulating tumour necrosis factor receptor 1/nuclear factor-kappa B signalling pathway, thereby ameliorating the depression-like behaviours induced by T. gondii infection. Our study provides insight into the underlying molecular mechanisms of the newly discovered role of SERT against T. gondii-induced depression-like behaviours.

Toxoplasma gondii seropositivity in patients with depressive and anxiety disorders

Introduction

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that is estimated to be carried by one-third of the world population. Latent T. gondii infection has been linked to several neuropsychiatric mood disorders and behaviors. The aim of the present study was to examine whether T. gondii seropositivity is associated with affective disorders, as well as with aggression reactivity and suicidal thoughts.

Methods

In the Netherlands Study of Depression and Anxiety (NESDA), T. gondii antibodies were assessed in patients with current depressive (n ​= ​133), anxiety (n ​= ​188), comorbid depressive and anxiety (n ​= ​148), and remitted disorders (n ​= ​889), as well as in healthy controls (n ​= ​373) based on DSM-IV criteria. Seropositivity was analyzed in relation to disorder status, aggression reactivity and suicidal thoughts using multivariate analyses of covariance and regression analyses.

Results

Participants were on average 51.2 years (SD ​= ​13.2), and 64.4% were female. Seropositivity was found in 673 participants (38.9%). A strong positive association between T. gondii seropositivity and age was observed. No significant associations were found between T. gondii seropositivity and disorder status, aggression reactivity and suicidal thoughts. The adjusted odds ratio (OR) for any remitted disorder versus controls was 1.13 (95% CI: 0.87-1.49), and for any current disorder versus controls was 0.94 (95% CI: 0.69-1.28).

Conclusions

No evidence was found for a relationship between affective disorders and T. gondii infection in the current sample.

Mucosal Administration of Recombinant Baculovirus Displaying Toxoplasma gondii ROP4 Confers Protection Against T. gondii Challenge Infection in Mice

Pathogens require physical contact with the mucosal surface of the host organism to initiate infection and as such, vaccines eliciting both mucosal and systemic immune responses would be promising. Studies involving the use of recombinant baculoviruses (rBVs) as mucosal vaccines are severely lacking despite their inherently safe nature, especially against pathogens of global importance such as Toxoplasma gondii. Here, we generated rBVs displaying T. gondii rhoptry protein 4 (ROP4) and evaluated their protective efficacy in BALB/c mice following immunization via intranasal (IN) and oral routes. IN immunization with the ROP4-expressing rBVs elicited higher levels of parasite-specific IgA antibody responses compared to oral immunization. Upon challenge infection with a lethal dose of T. gondii ME49, IN immunization elicited significantly higher parasite-specific antibody responses in the mucosal tissues such as intestines, feces, vaginal samples, and brain than oral immunization. Marked increases in IgG and IgA antibody-secreting cell (ASC) responses were observed from intranasally immunized mice. IN immunization elicited significantly enhanced induction of CD4+, CD8+ T cells, and germinal center B (GC B) cell responses from secondary lymphoid organs while limiting the production of the inflammatory cytokines IFN-γ and IL-6 in the brain, all of which contributed to protecting mice against T. gondii lethal challenge infection. Our findings suggest that IN delivery of ROP4 rBVs induced better mucosal and systemic immunity against the lethal T. gondii challenge infection compared to oral immunization.

Impact of Toxoplasma gondii infection on TM3 Leydig cells: Alterations in testosterone and cytokines levels

Leydig cells play pivotal roles in eliciting male characteristics by producing testosterone and any damage to these cells can compromise male fertility Toxoplasma gondii (T. gondii) is an intracellular parasite capable to invade any nucleated cell, including cells from male reproductive system. Herein, we evaluated the capacity of RH strain of T. gondii to infect TM3 Leydig cells and the impact of this infection on testosterone and inflammatory mediators production. We first, by performing adherence, infection, and intracellular proliferation assays, we found a significant increase in the number of infected Leydig cells, peaking 48 h after the infection with T. gondii. Supernatants of TM3 infected cells exhibited, in a time-dependent manner, increased levels of testosterone as well as monocyte chemoattractant protein-1 (MCP-1) and interferon-γ (IFN-γ), which is correlated with the robust T. gondii infection. In conclusion, our study provides new insights regarding the harmful effects of T. gondii infection on male reproductive system.

Toxoplasmosis and Psychiatric and Neurological Disorders: A Step toward Understanding Parasite Pathogenesis

Toxoplasmosis, a disease that disrupts fetal brain development and severely affects the host's brain, has been linked to many behavioral and neurological disorders. There is growing interest in how a single-celled neurotropic parasite, Toxoplasma gondii, can control or change the behavior of the host as well as how it dominates the host's neurons. Secrets beyond these could be answered by decoding the Toxoplasma gondii genome, unravelling the function of genomic sequences, and exploring epigenetics and mRNAs alterations, as well as the postulated mechanisms contributing to various neurological and psychiatric symptoms caused by this parasite. Substantial efforts have been made to elucidate the action of T. gondii on host immunity and the biology of its infection. However, the available studies on the molecular aspects of toxoplasmosis that affect central nervous system (CNS) circuits remain limited, and much research is still needed on this interesting topic. In my opinion, this parasite is a gift for studying the biology of the nervous system and related diseases. We should utilize the unique features of Toxoplasma, such as its abilities to modulate brain physiology, for neurological studies or as a possible tool or approach to cure neurological disease.

Toxoplasmosis in a Cohort of Italian Patients With Bipolar and Psychotic Disorders: How Infection May Affect Clinical Features?

This study investigated the seroprevalence of Toxoplasma gondii in a cohort of 101 Italian inpatients affected by mood or schizophrenia-spectrum disorders and compared clinical features between seronegative and seropositive subjects. Patients diagnosed according to DSM-5 criteria underwent clinical assessments and blood collection to test parasite-specific IgG/IgM serum levels. Twenty-eight patients (27.7%) had IgG anti-T. gondii, and none had IgM antibodies. We found higher prevalence rate in patients aged 40 years or older, as compared with younger. No significant association was detected between T. gondii and a specific diagnostic category; however, bipolar disorder (BD)-II showed the highest positivity rate (40.9%). The seropositive status was significantly associated with a lower presence of psychotic symptoms, higher number of total episodes of predominant excitatory polarity, longer illness duration, and lower severity of current episode, particularly anxiety, depressive, and withdrawal/retardation symptoms. These preliminary results seem to point out an association between chronic toxoplasmosis and a specific subtype of BD.

Persistent Toxoplasma Infection of the Brain Induced Neurodegeneration Associated with Activation of Complement and Microglia

Toxoplasma gondii, a common neurotropic parasite, is increasingly being linked to neuropsychiatric disorders, including schizophrenia, Alzheimer's disease, and Parkinson's disease. However, the pathogenic mechanisms underlying these associations are not clear. Toxoplasma can reside in the brain for extensive periods in the form of tissue cysts, and this process requires a continuous immune response to prevent the parasite's reactivation. Because neuroinflammation may promote the onset and progression of neurodegenerative diseases, we investigated neurodegeneration-associated pathological changes in a mouse model of chronic Toxoplasma infection. Under conditions of high-grade chronic infection, we documented the presence of neurodegeneration in specific regions of the prefrontal cortex, namely, the anterior cingulate cortex (ACC) and somatomotor cortex (SC). Neurodegeneration occurred in both glutamatergic and GABAergic neurons. Neurons that showed signs of degeneration expressed high levels of CX3CL1, were marked by profoundly upregulated complement proteins (e.g., C1q and C3), and were surrounded by activated microglia. Our findings suggest that chronic Toxoplasma infection leads to cortical neurodegeneration and results in CX3CL1, complement, and microglial interactions, which are known to mediate the phagocytic clearance of degenerating neurons. Our study provides a mechanistic explanation for the link between Toxoplasma infection and psychiatric disorders.

Mechanisms of Human Innate Immune Evasion by Toxoplasma gondii

Toxoplasma gondii is an intracellular protozoan parasite of global importance that can remarkably infect, survive, and replicate in nearly all mammalian cells. Notably, 110 years after its discovery, Toxoplasmosis is still a neglected parasitic infection. Although most human infections with T. gondii are mild or asymptomatic, T. gondii infection can result in life-threatening disease in immunocompromised individuals and in the developing fetus due to congenital infection, underscoring the role of the host immune system in controlling the parasite. Recent evidence indicates that T. gondii elicits a robust innate immune response during infection. Interestingly, however, T. gondii has evolved strategies to successfully bypass or manipulate the immune system and establish a life-long infection in infected hosts. In particular, T. gondii manipulates host immunity through the control of host gene transcription and dysregulation of signaling pathways that result in modulation of cell adhesion and migration, secretion of immunoregulatory cytokines, production of microbicidal molecules, and apoptosis. Many of these host-pathogen interactions are governed by parasite effector proteins secreted from the apical secretory organelles, including the rhoptries and dense granules. Here, we review recent findings on mechanisms by which T. gondii evades host innate immunity, with a focus on parasite evasion of the human innate immune system.

Lack of circulating toxoplasma gondii DNA in seropositive patients with bipolar or schizophrenia spectrum disorders

Toxoplasmosis has been previously associated with an increased risk of having Schizophrenia or Bipolar disorder in several epidemiological studies. The aim of this observational, cross-sectional study was to examine the seroprevalence of Toxoplasma infection in a cohort of Italian psychiatric inpatients and to verify the presence of circulating Toxoplasma gondii DNA in the seropositive subjects. Sixty-three patients affected by bipolar or schizoaffective disorders according to DSM-5 criteria were enrolled. The presence of Toxoplasma infection was firstly examined using an indirect serological method (ELFA), and three different direct PCR-based methods were performed to detect circulating DNA in the seropositive patients. The seroprevalence of infection was 28.6%, with a significant association between higher age and the infection status. PCR, nested-PCR and Real-Time PCR revealed no positive samples for Toxoplasma gondii. This result is in contrast with recent data from case-control studies that detected parasite genome in patients with different neuropsychiatric diagnosis without clinical evidence of acute toxoplasmosis. Our findings are to be interpreted with caution, because of the small sample size, the heterogeneity of enrolled patients and the observational nature of the study. Further studies are needed to better define the clinical features correlated to the seropositive status in neuropsychiatric patients.

Brazilian strains of Toxoplasma gondii are controlled by azithromycin and modulate cytokine production in human placental explants

BACKGROUND

Toxoplasma gondii is a protozoan parasite that causes congenital toxoplasmosis by transplacental transmission. Parasite strains are genetically diverse and disease severity is related to the genotype. In Uberlândia city, Brazil, two virulent strains were isolated: TgChBrUD1 and TgChBrUD2. Congenital toxoplasmosis is more prevalent in South America compared to Europe, and more often associated with severe symptoms, usually as a result of infection with atypical strains.

METHODS

Considering that T. gondii has shown high genetic diversity in Brazil, the effectiveness of traditional treatment may not be the same, as more virulent strains of atypical genotypes may predominate. Thus, the aim of this study were to evaluate the Brazilian strain infection rate in human villous explants and the azithromycin efficacy with regard to the control of these strains compared to traditional therapy. Villi were infected with RH, ME49, TgChBrUD1 or TgChBrUD2 strains and treated with azithromycin, spiramycin or a combination of pyrimethamine plus sulfadiazine. The villous viability was analyzed by LDH assay and morphological analysis. Parasite proliferation, as well as production of cytokines was analyzed by qPCR and ELISA, respectively. Statistical analysis was performed using the GraphPad Prism 5.0.

RESULTS

The treatments were not toxic and TgChBrUD1 infected villi showed a higher parasite burden compared with others strains. Treatments significantly reduced the intracellular proliferation of T. gondii, regardless of the strain. TgChBrUD1-infected villi produced a larger amount of MIF, IL-6 and TGF-β1 compared with other infected villi. Azithromycin treatment increased MIF production by RH- or TgChBrUD2-infected villi, but in ME49- or TgChBrUD1-infected villi, the MIF production was not altered by treatment. On the other hand, azithromycin treatment induced lower IL-6 production by ME49- or TgChBrUD1-infected villi.

CONCLUSIONS

Azithromycin treatment was effective against T. gondii Brazilian strains compared with conventional treatment. Also, the TgChBrUD1 strain replicated more in villi and modulated important cytokines involved in parasite control, showing that different strains use different strategies to evade the host immune response and ensure their survival.

A New T. gondii Mouse Model of Gene-Environment Interaction Relevant to Psychiatric Disease

Infection with the protozoan parasite, Toxoplasma gondii (T. gondii), was linked to several psychiatric disorders. The exact mechanisms of a hypothesized contribution of T. gondii infection are poorly understood, and it appears that only a subset of seropositive individuals go on to develop a mental illness, suggesting genetic vulnerability. In order to stimulate mechanistic studies of how exposure to T. gondii could interact with genetic predisposition to psychiatric disorders, we have generated and characterized a mouse model of chronic T. gondii infection in BALB/c mice with inducible forebrain neuronal expression of a C-terminus truncated dominant-negative form of disrupted-in-schizophrenia 1 (DN-DISC1). In this gene-environment interaction (GxE) model, exposing control and DN-DISC1 male and female mice to T. gondii produced sex-dependent abnormalities in locomotor activity and prepulse inhibition of the acoustic startle. No genotype- or sex-dependent effects were found on levels of anti-Toxoplasma IgG antibodies or anti-NMDAR or C1q antibodies. Our work demonstrates that a psychiatric genetic risk factor, DN-DISC1, modulates the neurobehavioral effects of chronic T. gondii infection in a sex-dependent manner. The present T. gondii model of GxE provides a valuable experimental system for future mechanistic studies and evaluation of new treatments.

Prevalence of toxoplasmosis and its association with dementia in older adults in Central Africa: a result from the EPIDEMCA programme

OBJECTIVE

We aimed at estimating the seroprevalence of Toxoplasma gondii (T. gondii) infection in older adults living in Central Africa and investigating its association with dementia using data from the Epidemiology of Dementia in Central Africa (EPIDEMCA) programme.

METHODS

A cross-sectional multicentre population-based study was carried out among participants aged 73 (±7) years on average, living in rural and urban areas of the Central African Republic and the Republic of Congo between November 2011 and December 2012. Blood samples were collected from each consenting participant. The detection of anti-T. gondii immunoglobulin G antibodies was performed in 2014 in France using a commercially available ELISA kit. Participants were interviewed using a standardised questionnaire including sociodemographic characteristics. DSM-IV criteria were required for a diagnosis of dementia. Multivariate binary logistic regression models were used to assess the association between toxoplasmosis infection and dementia.

RESULTS

Among 1662 participants, the seroprevalence of toxoplasmosis was 63.0% (95% confidence interval (CI): 60.7-65.3) overall, 66.6% (95%CI: 63.4-69.8) in Central African Republic and 59.4% (95%CI: 56.1-62.7) in the Republic of Congo. In multivariate analyses, toxoplasmosis status was significantly associated with increasing age (P = 0.006), Republic of Congo (P = 0.002), urban area (P = 0.001) and previous occupation (P = 0.002). No associations between dementia and toxoplasmosis status or anti-T. gondii IgG titres were found.

CONCLUSION

Toxoplasma gondii infection was not associated with dementia among older adults in Central Africa. Our findings are consistent with previous studies and add to the knowledge on the relationship between T. gondii infection and neurological disorders.

Toxoplasma gondii: Biological Parameters of the Connection to Schizophrenia

It is increasingly evident that the brain is not truly an immune privileged site and that cells of the central nervous system are sensitive to the inflammation generated when the brain is fighting off infection. Among the many microorganisms that have access to the brain, the apicomplexan protozoan Toxoplasma gondii has been one of the most studied. This parasite has been associated with many neuropsychiatric disorders including schizophrenia. This article provides a comprehensive review of the status of Toxoplasma research in schizophrenia. Areas of interest include (1) the limitations and improvements of immune-based assays to detect these infections in humans, (2) recent discoveries concerning the schizophrenia-Toxoplasma association, (3) findings of Toxoplasma neuropathology in animal models related to schizophrenia pathogenesis, (4) interactions of Toxoplasma with the host genome, (5) gastrointestinal effects of Toxoplasma infections, and (6) therapeutic intervention of Toxoplasma infections.

PD-1 immune checkpoint blockade promotes brain leukocyte infiltration and diminishes cyst burden in a mouse model of Toxoplasma infection

Tissue cysts, the hallmark of chronic Toxoplasma gondii infection, are predominantly located in the brain making clearance of the parasite difficult. Currently available anti-T. gondii drugs are ineffective on cysts and fail to prevent reactivation of latent toxoplasmosis. We examined whether abrogation of inhibitory signaling pathways that maintain T cells in an exhausted state can be exploited for treating T. gondii tissue cysts. By using a mouse model of chronic toxoplasmosis, we showed immune checkpoint blockade directed against the programmed death-1 (PD-1) pathway results in a significant reduction in brain cyst number (77% lower). We showed leukocyte infiltration (CD3+ T cells, CD8+ T cells, and CD11b + cells) in the leptomeninges, choroid plexus, and subependymal tissue, which are known routes of entry of immune cells into the brain, and in proximal brain parenchyma. Our study provides proof of concept for blockade of immune checkpoint inhibitors as a therapy for chronic toxoplasmosis and potentially for other brain pathogens.

Toxoplasma genotyping in congenital toxoplasmosis in Upper Egypt: evidence of type I strain

Toxoplasma gondii has subpopulation structures in different geographical regions caused by less frequent sexual recombination, population sweeps, and biogeography. The majority of strains isolated in North America and Europe fall into one of three clonal lineages, referred to as types I, II, and III. So far, little is known about genetics of Toxoplasma strains in Africa. The present study aimed to determine the genotype of Toxoplasma strains obtained directly from trophoblastic/placental tissues of 29 complicated pregnant women using multilocus nested-PCR-RFLP technique depending on four independent genetic loci (5' SAG2 and 3' SAG2), SAG3, GRA6, and BTUB genes. All samples gave positive amplicons at 5'-3' SAG2 and SAG3 genes. Meanwhile, no amplification products were observed in 12 (41.37%) and 10 (34.48%) samples with GRA6 and BTUB genes, respectively. The restriction pattern revealed the presence of genotype I in all samples, except one sample, which revealed atypical genotype with unusual restriction pattern at 3' SAG2 gene. The negative amplifications in some samples could be due to presence of mutations or polymorphisms in the primer binding sites of these isolates, raising the possibility of mixed or recombinant genotypes. To the best of our knowledge, this is the first time to perform genotype analysis study based on Multiplex nPCR-RFLP technique for genetic characterization of T. gondii in Egypt. Besides, it is the first time to prove that the most prevalent strain of T. gondii, responsible for congenital toxoplasmosis in Upper Egypt, is the highly virulent type I. Atypical genotype was detected as well.

Toxoplasma gondii infection in schizophrenia and associated clinical features

The belief that latent toxoplasmosis is asymptomatic has been questioned, in particular due to the repeated highlighted link between the Toxoplasma gondii infection and an increased incidence of schizophrenia. However, to understand this relationship, the effect of infection with Toxoplasma gondii on the severity of schizophrenia has been poorly studied. Our work focused on comparing the prevalence of Toxoplasma infection between schizophrenic patients and healthy controls, as well as comparing the clinical features and the demographic characteristics between Toxoplasma-seronegative and Toxoplasma-seropositive patients with schizophrenia. The rate of IgG antibody in the schizophrenia patients was 74.8% compared 53.8% in controls. Patients with schizophrenia had a significantly higher mean of serum IgG antibodies to T. gondii compared to controls. The seropositive male patients had a higher age of disease onset, a higher BPRS score, a greater negative PANSS score and a lower GAF score than the seronegative male patients. These results suggest a higher severity of clinical symptoms in the male patients with schizophrenia. This study provides further evidence to the hypothesis that exposure to Toxoplasma may be a risk factor for schizophrenia. Moreover, toxoplasmosis in men with schizophrenia may lead to more severe negative and cognitive symptoms and a less favorable course of schizophrenia.

Cerebral complement C1q activation in chronic Toxoplasma infection

Exposure to the neurotropic parasite, Toxoplasma gondii, causes significant brain and behavioral anomalies in humans and other mammals. Understanding the cellular mechanisms of T. gondii-generated brain pathologies would aid the advancement of novel strategies to reduce disease. Complement factor C1q is part of a classic immune pathway that functions peripherally to tag and remove infectious agents and cellular debris from circulation. In the developing and adult brain, C1q modifies neuronal architecture through synapse marking and pruning. T. gondii exposure and complement activation have both been implicated in the development of complex brain disorders such as schizophrenia. Thus, it seems logical that mechanistically, the physiological pathways associated with these two factors are connected. We employed a rodent model of chronic infection to investigate the extent to which cyst presence in the brain triggers activation of cerebral C1q. Compared to uninfected mice, cortical C1q was highly expressed at both the RNA and protein levels in infected animals bearing a high cyst burden. In these mice, C1q protein localized to cytoplasm, adjacent to GFAP-labeled astrocytes, near degenerating cysts, and in punctate patterns along processes. In summary, our results demonstrated an upregulation of cerebral C1q in response to latent T. gondii infection. Our data preliminarily suggest that this complement activity may aid in the clearance of this parasite from the CNS and in so doing, have consequences for the connectivity of neighboring cells and synapses.

Autoimmune diseases, gastrointestinal disorders and the microbiome in schizophrenia: more than a gut feeling

Autoimmunity, gastrointestinal (GI) disorders and schizophrenia have been associated with one another for a long time. This paper reviews these connections and provides a context by which multiple risk factors for schizophrenia may be related. Epidemiological studies strongly link schizophrenia with autoimmune disorders including enteropathic celiac disease. Exposure to wheat gluten and bovine milk casein also contribute to non-celiac food sensitivities in susceptible individuals. Co-morbid GI inflammation accompanies humoral immunity to food antigens, occurs early during the course of schizophrenia and appears to be independent from antipsychotic-generated motility effects. This inflammation impacts endothelial barrier permeability and can precipitate translocation of gut bacteria into systemic circulation. Infection by the neurotropic gut pathogen, Toxoplasma gondii, will elicit an inflammatory GI environment. Such processes trigger innate immunity, including activation of complement C1q, which also functions at synapses in the brain. The emerging field of microbiome research lies at the center of these interactions with evidence that the abundance and diversity of resident gut microbiota contribute to digestion, inflammation, gut permeability and behavior. Dietary modifications of core bacterial compositions may explain inefficient gluten digestion and how immigrant status in certain situations is a risk factor for schizophrenia. Gut microbiome research in schizophrenia is in its infancy, but data in related fields suggest disease-associated altered phylogenetic compositions. In summary, this review surveys associative and experimental data linking autoimmunity, GI activity and schizophrenia, and proposes that understanding of disrupted biological pathways outside of the brain can lend valuable information regarding pathogeneses of complex, polygenic brain disorders.

Genome-wide expression analysis comparing hypertrophic changes in normal and dysferlinopathy mice

Because myostatin normally limits skeletal muscle growth, there are extensive efforts to develop myostatin inhibitors for clinical use. One potential concern is that in muscle degenerative diseases, inducing hypertrophy may increase stress on dystrophic fibers. Our study shows that blocking this pathway in dysferlin deficient mice results in early improvement in histopathology but ultimately accelerates muscle degeneration. Hence, benefits of this approach should be weighed against these potential detrimental effects. Here, we present detailed experimental methods and analysis for the gene expression profiling described in our recently published study in Human Molecular Genetics (Lee et al., 2015). Our data sets have been deposited in the Gene Expression Omnibus (GEO) database (GSE62945) and are available at http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE62945. Our data provide a resource for exploring molecular mechanisms that are related to hypertrophy-induced, accelerated muscular degeneration in dysferlinopathy.

Patterns of Hydrocephalus Caused by Congenital Toxoplasma gondii Infection Associate With Parasite Genetics

Four anatomical patterns of hydrocephalus secondary to congenital Toxoplasma gondii infection were identified and characterized for infants enrolled in the National Collaborative Chicago-based Congenital Toxoplasmosis Study. Analysis of parasite serotype revealed that different anatomical patterns associate with Type-II vs Not-Exclusively Type-II strains (NE-II) (P = .035).

Muscle hypertrophy induced by myostatin inhibition accelerates degeneration in dysferlinopathy

Myostatin is a secreted signaling molecule that normally acts to limit muscle growth. As a result, there is extensive effort directed at developing drugs capable of targeting myostatin to treat patients with muscle loss. One potential concern with this therapeutic approach in patients with muscle degenerative diseases like muscular dystrophy is that inducing hypertrophy may increase stress on dystrophic fibers, thereby accelerating disease progression. To investigate this possibility, we examined the effect of blocking the myostatin pathway in dysferlin-deficient (Dysf^−/−) mice, in which membrane repair is compromised, either by transgenic expression of follistatin in skeletal muscle or by systemic administration of the soluble form of the activin type IIB receptor (ACVR2B/Fc). Here, we show that myostatin inhibition by follistatin transgene expression in Dysf^−/− mice results in early improvement in histopathology but ultimately exacerbates muscle degeneration; this effect was not observed in dystrophin-deficient (mdx) mice, suggesting that accelerated degeneration induced by follistatin transgene expression is specific to mice lacking dysferlin. Dysf^−/− mice injected with ACVR2B/Fc showed significant increases in muscle mass and amelioration of fibrotic changes normally seen in 8-month-old Dysf^−/− mice. Despite these potentially beneficial effects, ACVR2B/Fc treatment caused increases in serum CK levels in some Dysf^−/− mice, indicating possible muscle damage induced by hypertrophy. These findings suggest that depending on the disease context, inducing muscle hypertrophy by myostatin blockade may have detrimental effects, which need to be weighed against the potential gains in muscle growth and decreased fibrosis.

Strain hypothesis of Toxoplasma gondii infection on the outcome of human diseases

The intracellular protozoan Toxoplasma gondii is an exceptionally successful food and waterborne parasite that infects approximately 1 billion people worldwide. Genotyping of T. gondii isolates from all continents revealed a complex population structure. Recent research supports the notion that T. gondii genotype may be associated with disease severity. Here, we (1) discuss molecular and serological approaches for designation of T. gondii strain type, (2) overview the literatures on the association of T. gondii strain type and the outcome of human disease and (3) explore possible mechanisms underlying these strain-specific pathology and severity of human toxoplasmosis. Although no final conclusions can be drawn, it is clear that virulent strains (e.g. strains containing type I or atypical alleles) are significantly more often associated with increased frequency and severity of human toxoplasmosis. The significance of highly virulent strains can cause severe diseases in immunocompetent patients and might implicated in brain disorders such as schizophrenia should led to reconsideration of toxoplasmosis. Further studies that combine parasite strain typing and human factor analysis (e.g. immune status and genetic background) are required for better understanding of human susceptibility or resistance to toxoplasmosis.

Toxoplasma gondii prevalent in China induce weaker apoptosis of neural stem cells C17.2 via endoplasmic reticulum stress (ERS) signaling pathways

Background

Toxoplasma gondii, an obligate intracellular pathogen, has a strong affinity for the nervous system. TgCtwh3, a representative Chinese 1 Toxoplasma strain prevalent in China, has the polymorphic features of the effectors ROP16_I/III with type I and GRA15_II with type II Toxoplasma strains. The interaction of this atypical strain with host cells remains extremely elusive.

Methods

Using a transwell system, neural stem cells C17.2 were co-cultured with the tachyzoites of TgCtwh3 or standard type I RH strain. The apoptosis levels of C17.2 cells and the expression levels of related proteins in the endoplasmic reticulum stress (ERS)-mediated pathway were detected by flow cytometry and Western blotting.

Results

The apoptosis level of C17.2 cells co-cultured with TgCtwh3 had a significant increase compared to the negative control group; however, the apoptosis level in the TgCtwh3 group was significantly lower than that in the RH co-culture group. Western blotting analyses reveal that, after the C17.2 cells were co-cultured with TgCtwh3 and RH tachyzoites, the expression levels of caspase-12, CHOP and p-JNK in the cells increased significantly when compared to the control groups. After the pretreatment of Z-ATAD-FMK, an inhibitor of caspase-12, the apoptosis level of the C17.2 cells co-cultured with TgCtwh3 or RH tachyzoites had an apparent decline, and correspondingly, the expression levels of those related proteins were notably decreased.

Conclusions

Our findings suggest that TgCtwh3 may induce the apoptosis of the C17.2 cells by up-regulation of caspase-12, CHOP, and p-JNK, which are associated with ERS signaling pathways. This work contributes to better understanding the possible mechanism of brain pathology induced by T. gondii Chinese 1 isolates prevalent in China, and also reveals the potential value of ERS inhibitors to treat such related diseases in the future.

The urban risk and migration risk factors for schizophrenia: are cats the answer?

Being born in and/or raised in an urban area is a proven risk factor for developing schizophrenia. Migrating from countries such as Jamaica or Morocco to countries such as England or the Netherlands is also a proven risk factor for developing schizophrenia. The transmission of Toxoplasma gondii oocysts to children is reviewed and proposed as a partial explanation for both of these risk factors.

Chronic infection of Toxoplasma gondii downregulates miR-132 expression in multiple brain regions in a sex-dependent manner

MicroRNA-132 (miR-132) has been demonstrated to affect multiple neuronal functions and its dysregulation is linked to several neurological disorders. We previously showed that acute Toxoplasma gondii infection induces miR-132 expression both in vitro and in vivo. To investigate the impact of chronic infection on miR-132, we infected mice with T. gondii PRU strain and performed assessment 5 months later in six brain regions (cortex, hypothalamus, striatum, cerebellum, olfactory bulb and hippocampus) by qPCR. We found that while acute infection of T. gondii increases the expression of miR-132, chronic infection has the opposite effect. The effect varied amongst different regions of the brain and presented in a sex-dependent manner, with females exhibiting more susceptibility than males. MiR-132 and brain-derived neurotrophic factor (BDNF, an inducer of miR-132) were not co-varies in the brain areas of infected mice. T. gondii DNA/RNA was found in all tested brain regions and a selective tropism towards the hippocampus, based on bradyzoite density, was observed in both males and females. However, the expressions of miR-132 or BDNF were poorly reflected by the density of T. gondii in brain areas. Our findings highlight the importance of investigating the miR-132-mediated neuronal function in mice infected with T. gondii.

In vitro infection of human nervous cells by two strains of Toxoplasma gondii: a kinetic analysis of immune mediators and parasite multiplication

The severity of toxoplasmic infection depends mainly on the immune status of the host, but also on the Toxoplasma gondii strains, which differ by their virulence profile. The relationship between the human host and T. gondii has not yet been elucidated because few studies have been conducted on human models. The immune mechanisms involved in the persistence of T. gondii in the brains of immunocompetent subjects and during the reactivation of latent infections are still unclear. In this study, we analyzed the kinetics of immune mediators in human nervous cells in vitro, infected with two strains of T. gondii. Human neuroblast cell line (SH SY5Y), microglial (CMH5) and endothelial cells (Hbmec) were infected separately by RH (type I) or PRU (type II) strains for 8 h, 14 h, 24 h and 48 h (ratio 1 cell: 2 tachyzoites). Pro-inflammatory protein expression was different between the two strains and among different human nervous cells. The cytokines IL-6, IL-8 and the chemokines MCP-1 and GROα, and SERPIN E1 were significantly increased in CMH5 and SH SY5Y at 24 h pi. At this point of infection, the parasite burden declined in microglial cells and neurons, but remained high in endothelial cells. This differential effect on the early parasite multiplication may be correlated with a higher production of immune mediators by neurons and microglial cells compared to endothelial cells. Regarding strain differences, PRU strain, but not RH strain, stimulates all cells to produce pro-inflammatory growth factors, G-CSF and GM-CSF. These proteins could increase the inflammatory effect of this type II strain. These results suggest that the different protein expression profiles depend on the parasitic strain and on the human nervous cell type, and that this could be at the origin of diverse brain lesions caused by T. gondii.

MicroRNA-132 dysregulation in Toxoplasma gondii infection has implications for dopamine signaling pathway

Congenital toxoplasmosis and toxoplasmic encephalitis can be associated with severe neuropsychiatric symptoms. However, which host cell processes are regulated and how Toxoplasma gondii affects these changes remain unclear. MicroRNAs (miRNAs) are small noncoding RNA sequences critical to neurodevelopment and adult neuronal processes by coordinating the activity of multiple genes within biological networks. We examined the expression of over 1000 miRNAs in human neuroepithelioma cells in response to infection with Toxoplasma. MiR-132, a cyclic AMP-responsive element binding (CREB)-regulated miRNA, was the only miRNA that was substantially upregulated by all three prototype Toxoplasma strains. The increased expression of miR-132 was also documented in mice following infection with Toxoplasma. To identify cellular pathways regulated by miR-132, we performed target prediction followed by pathway enrichment analysis in the transcriptome of Toxoplasma-infected mice. This led us to identify 20 genes and dopamine receptor signaling was their strongest associated pathway. We then examined myriad aspects of the dopamine pathway in the striatum of Toxoplasma-infected mice 5days after infection. Here we report decreased expression of D1-like dopamine receptors (DRD1, DRD5), metabolizing enzyme (MAOA) and intracellular proteins associated with the transduction of dopamine-mediated signaling (DARPP-32 phosphorylation at Thr34 and Ser97). Increased concentrations of dopamine and its metabolites, serotonin (5-HT) and 5-hydroxyindoleacetic acid were documented by HPLC analysis; however, the metabolism of dopamine was decreased and 5-HT metabolism was unchanged. Our data show that miR-132 is upregulated following infection with Toxoplasma and is associated with changes in dopamine receptor signaling. Our findings provide a possible mechanism for how the parasite contributes to the neuropathology of infection.

Do the placental barrier, parasite genotype and Toll-like receptor polymorphisms contribute to the course of primary infection with various Toxoplasma gondii genotypes in pregnant women?

Toxoplasma gondii has a highly clonal genetic structure classified into three major genetic types, I, II, and III, plus additional recombinant and atypical strains. In humans, type I and atypical strains usually associate with severe toxoplasmosis. Type II strains, predominantly identified in European countries and the United States, correlate with a differential course of toxoplasmosis. During pregnancy, the important protective role of the placenta against maternal–fetal T. gondii transmission has been reported. T. gondii preferentially colonizes extravillous trophoblasts as compared to syncytiotrophoblasts. The latter compartment was suggested to act as the real barrier to the fetal dissemination of T. gondii. Alterations in immune response to particular T. gondii strains were observed. Higher transcription levels of IP-10, IL-1β, IL-6, IL-10, IL-12 cytokines, and NF-κB translocation to the nucleus were more often documented for type II strains than type I strains. Since the induction of IL-12 during type II infection was Myd88-dependent, the involvement of Toll-like receptors (TLRs) in the immunity against these strains was suggested. Differential expression of TLRs depends on placental cell types and gestational age. The expression of TLR2 and TLR4 in the first trimester of pregnancy was reported only for villous cytotrophoblasts and extravillous trophoblasts, but not for syncytiotrophoblasts. The involvement of single-nucleotide polymorphisms (SNPs) in the TLR genes in infectious pathogenicity, including toxoplasmic retinochoroiditis, points at a possible involvement of TLR alterations in immunity against T. gondii. We conclude that studies on TLR contributions in the maternal–fetal transmission of particular parasite strains and congenital toxoplasmosis are warranted.

Neuropsychiatric manifestations of latent toxoplasmosis on mothers and their offspring

Toxoplasmosis is one of the most common parasitic diseases worldwide. It is estimated that approximately one-third of the world's population is latently infected. Infection generally occurs via oral the route and maternal transmission. Damage of the central nervous system is one of the most serious consequences of congenital toxoplasmosis. Moreover, recent investigations proposed that acute and sub-acute congenital toxoplasmosis as well as latent toxoplasmosis during pregnancy; play various roles in the etiology of different neuropsychiatric disorders in mothers and their offspring. This paper reviews new findings about the role of latent toxoplasmosis in the etiology of various neuropsychiatric disorders in mothers and their offspring.

Abnormalities of neurotransmitter and neuropeptide systems in human neuroepithelioma cells infected by three Toxoplasma strains

Since Toxoplasma gondii can establish a persistent infection in the central nervous system in humans, we studied its effects on a host's neurotransmitter and neuropeptide systems (NNS). Using microarray technology, we have screened the expression of genes coding for NNS in human neuroepithelioma cells in response to representative strains of Toxoplasma to identify potential target genes. Transcripts that displayed expression levels distinct from uninfected controls were examined by RT-PCR and Western blot. Our results indicate the presence of disturbed NNS upon Toxoplasma infection and the extent of this disturbance varies considerably among the three strains. In cells infected by type I strain, three neurotransmitter systems (dopamine, glutamate and serotonin) and two neuropeptides (PROK2 and TAC1) displayed abnormalities relative to controls. Type III infection led to the change of a critical enzyme, TDO2, in the kynurenine pathway. No significant effects of type II infection were found in the NNS. These data may have implications for understanding the pathogenesis and heterogeneity of neurologic disturbances in toxoplasmosis.

A genome-wide siRNA screen to identify host factors necessary for growth of the parasite Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that is able to infect virtually any nucleated cell of all warm-blooded animals. The host cell factors important for parasite attachment, invasion, and replication are poorly understood. We screened a siRNA library targeting 18,200 individual human genes in order to identify host proteins with a role in T. gondii growth. Our screen identified 19 genes whose inhibition by siRNA consistently and significantly lowered parasite replication. The gene ontology categories for those 19 genes represented a wide variety of functions with several genes implicated in regulation of the cell cycle, ion channels and receptors, G-protein coupled receptors, and cytoskeletal structure as well as genes involved in transcription, translation and protein degradation. Further investigation of 5 of the 19 genes demonstrated that the primary reason for the reduction in parasite growth was death of the host cell. Our results suggest that once T. gondii has invaded and established an infection, global changes in the host cell may be necessary to reduce parasite replication. While siRNA screens have been used, albeit rarely, in other parasite systems, this is the first report to describe a high-throughput siRNA screen for host proteins that affect T. gondii replication.

Genome-wide comparative analysis revealed significant transcriptome changes in mice after Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii is an intracellular parasite that can modulate host responses and presumably host behavior. Host responses as well as pathogenesis vary depending on the parasite strains that are responsible for infection. In immune competent individuals, T. gondii preferentially infects tissues of the central nervous systems (CNS), which might be an additional factor in certain psychiatric disorders. While in immune-compromised individuals and pregnant women, the parasite can cause life-threatening infections. With the availability of the genome-wide investigation platform, the global responses in gene expression of the host after T. gondii infection can be systematically investigated.

METHODS

Total RNA of brain tissues and peripheral lymphocytes of BALB/C mice infected with RH and ME 49 strain T. gondii as well as that of healthy mice were purified and converted to cRNA with incorporated Cy5-CTP (experimental samples), or Cy3-CTP (control samples). The labeled cRNA probes were hybridized to the Whole Mouse Genome Microarray. The impact of parasite infection on gene expression in both brain tissues and peripheral lymphocytes were analyzed. Differentially expressed genes were revalidated with real-time quantitative reverse transcriptase-polymerase chain reaction (Q-PCR).

RESULTS

Data indicated that the genes associated with immunity were up-regulated after infection by the two parasite strains, but significant up-regulation was observed in both brain tissues and peripheral lymphocytes of mice infected with ME49 strain compared to that infected by RH strain. The pathways related to pathogenesis of the nervous system were more significantly up-regulated in mice infected with RH strain.

CONCLUSIONS

Genetically distinct T. gondii strains showed clear differences in modulation of host pathophysiological and immunological responses in both brain tissue and peripheral lymphocytes. It was likely that some of the host responses to T. gondii infection were universal, but the immune response and CNS reaction were in a strain-specific manner.

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 infection, from predation to schizophrenia: can animal behaviour help us understand human behaviour?

We examine the role of the protozoan Toxoplasma gondii as a manipulatory parasite and question what role study of infections in its natural intermediate rodent hosts and other secondary hosts, including humans, may elucidate in terms of the epidemiology, evolution and clinical applications of infection. In particular, we focus on the potential association between T. gondii and schizophrenia. We introduce the novel term 'T. gondii-rat manipulation-schizophrenia model' and propose how future behavioural research on this model should be performed from a biological, clinical and ethically appropriate perspective.

A review of the infection, genetics, and evolution of Neospora caninum: from the past to the present

This paper is a review of current knowledge on Neospora caninum in the context of other apicomplexan parasites and with an emphasis on: life cycle, disease, epidemiology, immunity, control and treatment, evolution, genomes, and biological databases and web resources. N. caninum is an obligate, intracellular, coccidian, protozoan parasite of the phylum Apicomplexa. Infection can cause the clinical disease neosporosis, which most notably is associated with abortion in cattle. These abortions are a major root cause of economic loss to both the dairy and beef industries worldwide. N. caninum has been detected in every country in which a study has been specifically conducted to detect this parasite in cattle. The major mode of transmission in cattle is transplacental (or vertical) transmission and several elements of the N. caninum life cycle are yet to be studied in detail. The outcome of an infection is inextricably linked to the precise timing of the infection coupled with the status of the immune system of the dam and foetus. There is no community consensus as to whether it is the dam's pro-inflammatory cytotoxic response to tachyzoites that kills the foetus or the tachyzoites themselves. From economic analysis the most cost-effective approach to control neosporosis is a vaccine. The perfect vaccine would protect against both infection and the clinical disease, and this implies a vaccine is needed that can induce a non-foetopathic cell mediated immunity response. Researchers are beginning to capitalise on the vast potential of -omics data (e.g. genomes, transcriptomes, and proteomes) to further our understanding of pathogens but especially to identify vaccine and drug targets. The recent publication of a genome for N. caninum offers vast opportunities in these areas.

Gastrointestinal inflammation and associated immune activation in schizophrenia

Immune factors are implicated in normal brain development and in brain disorder pathogenesis. Pathogen infection and food antigen penetration across gastrointestinal barriers are means by which environmental factors might affect immune-related neurodevelopment. Here, we test if gastrointestinal inflammation is associated with schizophrenia and therefore, might contribute to bloodstream entry of potentially neurotropic milk and gluten exorphins and/or immune activation by food antigens. IgG antibodies to Saccharomyces cerevisiae (ASCA, a marker of intestinal inflammation), bovine milk casein, wheat-derived gluten, and 6 infectious agents were assayed. Cohort 1 included 193 with non-recent onset schizophrenia, 67 with recent onset schizophrenia and 207 non-psychiatric controls. Cohort 2 included 103 with first episode schizophrenia, 40 of whom were antipsychotic-naïve. ASCA markers were significantly elevated and correlated with food antigen antibodies in recent onset and non-recent onset schizophrenia compared to controls (p≤0.00001-0.004) and in unmedicated individuals with first episode schizophrenia compared to those receiving antipsychotics (p≤0.05-0.01). Elevated ASCA levels were especially evident in non-recent onset females (p≤0.009), recent onset males (p≤0.01) and in antipsychotic-naïve males (p≤0.03). Anti-food antigen antibodies were correlated to antibodies against Toxoplasma gondii, an intestinally-infectious pathogen, particularly in males with recent onset schizophrenia (p≤0.002). In conclusion, gastrointestinal inflammation is a relevant pathology in schizophrenia, appears to occur in the absence of but may be modified by antipsychotics, and may link food antigen sensitivity and microbial infection as sources of immune activation in mental illness.

Prematurity and severity are associated with Toxoplasma gondii alleles (NCCCTS, 1981-2009)

BACKGROUND

Congenital toxoplasmosis is a severe, life-altering disease in the United States. A recently developed enzyme-linked immunosorbent assay (ELISA) distinguishes Toxoplasma gondii parasite types (II and not exclusively II [NE-II]) by detecting antibodies in human sera that recognize allelic peptide motifs of distinct parasite types.

METHODS

ELISA determined parasite serotype for 193 congenitally infected infants and their mothers in the National Collaborative Chicago-based Congenital Toxoplasmosis Study (NCCCTS), 1981-2009. Associations of parasite serotype with demographics, manifestations at birth, and effects of treatment were determined.

RESULTS

Serotypes II and NE-II occurred in the United States with similar proportions during 3 decades. For persons diagnosed before or at birth and treated in infancy, and persons diagnosed after 1 year of age who missed treatment in infancy, proportions were similar (P = .91). NE-II serotype was more common in hot, humid regions (P = .02) but was also present in other regions. NE-II serotype was associated with rural residence (P < .01), lower socioeconomic status (P < .001), and Hispanic ethnicity (P < .001). Prematurity (P = .03) and severe disease at birth (P < .01) were associated with NE-II serotype. Treatment with lower and higher doses of pyrimethamine with sulfadizine improved outcomes relative to those outcomes of persons in the literature who did not receive such treatment.

CONCLUSIONS

Type II and NE-II parasites cause congenital toxoplasmosis in North America. NE-II serotype was more prevalent in certain demographics and associated with prematurity and severe disease at birth. Both type II and NE-II infections improved with treatment.

CLINICAL TRIALS REGISTRATION

NCT00004317.

Latent toxoplasmosis and human

Toxoplasmosis is one of the most common parasitic diseases worldwide. Although estimated that one third of the world's population are infected with Toxoplasma gondii, but the most common form of the disease is latent (asymptomatic). On the other hand, recent findings indicated that latent toxoplasmosis is not only unsafe for human, but also may play various roles in the etiology of different mental disorders. This paper reviews new findings about importance of latent toxoplasmosis (except in immunocompromised patients) in alterations of behavioral parameters and also its role in the etiology of schizophrenia and depressive disorders, obsessive-compulsive disorder, Alzheimer's diseases and Parkinson's disease, epilepsy, headache and or migraine, mental retardation and intelligence quotients, suicide attempt, risk of traffic accidents, sex ratio and some possible mechanisms of T. gondii that could contribute in the etiology of these alterations.

Differential gene expression in mice infected with distinct Toxoplasma strains

Toxoplasma gondii is the causative agent of toxoplasmosis in human and animals. In a mouse model, T. gondii strains can be divided into three groups, including the virulent, intermediately virulent, and nonvirulent. The clonal type I, II, and III T. gondii strains belong to these three groups, respectively. To better understand the basis of virulence phenotypes, we investigated mouse gene expression responses to the infection of different T. gondii strains at day 5 after intraperitoneal inoculation with 500 tachyzoites. The transcriptomes of mouse peritoneal cells showed that 1,927, 1,573, and 1,009 transcripts were altered more than 2-fold by type I, II, and III infections, respectively, and that the majority of altered transcripts were shared. Overall transcription patterns were similar in type I and type II infections, and both had greater changes than infection with type III. Quantification of parasite burden in mouse spleens showed that the burden with type I infection was 1,000 times higher than that of type II and that the type II burden was 20 times higher than that of type III. Fluorescence-activated cell sorting revealed that type I and II infections had comparable macrophage populations, and both were higher than the population with type III infection. In addition, type I infection had a higher percentage of neutrophils than type II and III infections. Taken together, these results suggested that there is a common gene expression response to T. gondii infection in mice. This response is further modified by parasite strain-specific factors that determine their distinct virulence phenotypes.

Apicomplexan parasites and subversion of the host cell microRNA pathway

RNA silencing plays a major role in innate antiviral and antibacterial defenses in plants, insects, and animals through the action of microRNAs (miRNAs). miRNAs can act in favor of the microorganism, either when it is pathogen-encoded or when the microorganism subverts host miRNAs to its benefit. Recent data point to the possibility that apicomplexan parasites have developed tactics to interfere with host miRNA populations in a parasite-specific manner, thereby identifying the RNA-silencing pathway as a new means to reshape their cellular environment. This review highlights the current understanding and new insights concerning the mechanisms that could be involved and the potential roles of the host microRNome (miRNome) in apicomplexan infection.