Toxoplasma gondii-Induced Long-Term Changes in the Upper Intestinal Microflora during the Chronic Stage of Infection

Toxoplasma gondii is an obligate intracellular parasite with worldwide distribution. Felines are the definitive hosts supporting the complete life cycle of T. gondii. However, other warm-blooded animals such as rodents and humans can also be infected. Infection of such secondary hosts results in long-term infection characterized by the presence of tissue cysts in the brain and other organs. While it is known that T. gondii infection in rodents is associated with behavioral changes, the mechanisms behind these changes remain unclear. Alterations of the host intestinal microflora are recognized as a prominent role player in shaping host behavior and cognition. It has been shown that acute T. gondii infection of mice results in microflora changes as a result of gastrointestinal inflammation in inbred mouse models. The long-term effects of chronic T. gondii infection on microbial communities, however, are unknown. In this study, after we verified using our model in terms of measuring microflora changes during an acute episode of toxoplasmosis, we assessed the microbiome changes that occur during a long-term infection; then we further investigated these changes in a follow-up study of chronic infection. These analyses were performed by constructing and sequencing 16S rRNA amplicon DNA libraries from small intestine fecal specimens. We found that acute infection with the GT1 strain of T. gondii caused an enrichment of Bacteroidetes compared with controls in CD1 mice. Strikingly, this enrichment upheld throughout long-term chronic infection. The potential biological consequences of this alteration in rodents and humans should be subjected to further exploration.

Pathogen-mediated NMDA receptor autoimmunity and cellular barrier dysfunction in schizophrenia

Autoantibodies that bind the N-methyl-D-aspartate receptor (NMDAR) may underlie glutamate receptor hypofunction and related cognitive impairment found in schizophrenia. Exposure to neurotropic pathogens can foster an autoimmune-prone environment and drive systemic inflammation leading to endothelial barrier defects. In mouse model cohorts, we demonstrate that infection with the protozoan parasite, Toxoplasma gondii, caused sustained elevations of IgG class antibodies to the NMDAR in conjunction with compromised blood-gut and blood-brain barriers. In human cohorts, NMDAR IgG and markers of barrier permeability were significantly associated with T. gondii exposure in schizophrenia compared with controls and independently of antipsychotic medication. Combined T. gondii and NMDAR antibody seropositivity in schizophrenia resulted in higher degrees of cognitive impairment as measured by tests of delayed memory. These data underscore the necessity of disentangling the heterogeneous pathophysiology of schizophrenia so that relevant subsets eligible for NMDAR-related treatment can be identified. Our data aid to reconcile conflicting reports regarding a role of pathological NMDAR autoantibodies in this disorder.

Probiotic normalization of Candida albicans in schizophrenia: A randomized, placebo-controlled, longitudinal pilot study

The molecules and pathways of the gut-brain axis represent new targets for developing methods to diagnose and treat psychiatric disorders. Manipulation of the gut microbiome with probiotics may be a therapeutic strategy with the potential to relieve gastrointestinal (GI) comorbidities and improve psychiatric symptoms. Candida albicans and Saccharomyces cerevisiae, commensal yeast species, can be imbalanced in the unhealthy human microbiome, and these fungal exposures were previously found elevated in schizophrenia. In a longitudinal, double-blind, placebo-controlled, pilot investigation of 56 outpatients with schizophrenia, we examined the impact of probiotic treatment on yeast antibody levels, and the relationship between treatment and antibody levels on bowel discomfort and psychiatric symptoms. We found that probiotic treatment significantly reduced C. albicans antibodies over the 14-week study period in males, but not in females. Antibody levels of S. cerevisiae were not altered in either treatment group. The highest levels of bowel discomfort over time occurred in C. albicans-seropositive males receiving the placebo. We observed trends towards improvement in positive psychiatric symptoms in males treated with probiotics who were seronegative for C. albicans. Results from this pilot study hint at an association of C. albicans seropositivity with worse positive psychiatric symptoms, which was confirmed in a larger cohort of 384 males with schizophrenia. In conclusion, the administration of probiotics may help normalize C. albicans antibody levels and C. albicans-associated gut discomfort in many male individuals. Studies with larger sample sizes are warranted to address the role of probiotics in correcting C. albicans-associated psychiatric symptoms.

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.

Anti-NMDA receptor autoantibodies and associated neurobehavioral pathology in mice are dependent on age of first exposure to Toxoplasma gondii

BACKGROUND

Toxoplasma gondii is a pathogen implicated in psychiatric disorders. As elevated antibodies to T. gondii are also present in non-symptomatic individuals, we hypothesized that the age during first exposure to the pathogen may affect symptom manifestation. We tested this hypothesis by evaluating neurobehavioral abnormalities and the immune response in mice following adolescent or adult T. gondii infection.

METHODS

Mice were infected with T. gondii at postnatal day 33 (adolescent/juvenile) or 61 (adult). At 8weeks post-infection (wpi), pre-pulse inhibition of the acoustic startle (PPI) in mice administered MK-801 (0.1 and 0.3mg/kg) and amphetamine (5 and 10mg/kg) was assessed. Peripheral (anti-T. gondii, C1q-associated IgG and anti-GLUN2 antibodies) and central (C1q and Iba1) markers of the immune response were also evaluated. In addition, regional brain expression of N-methyl-d-aspartate receptor (NMDAR) subunits (GLUN1 and GLUN2A), glutamatergic (vGLUT1, PSD95) and GABAergic (GAD67) markers, and monoamines (DA, NE, 5-HT) and their metabolites were measured.

RESULTS

Juvenile and adult infected mice exhibited opposite effects of MK-801 on PPI, with decreased PPI in juveniles and increased PPI in adults. There was a significantly greater elevation of GLUN2 autoantibodies in juvenile-compared to adult-infected mice. In addition, age-dependent differences were found in regional expression of NMDAR subunits and markers of glutamatergic, GABAergic, and monoaminergic systems. Activated microglia and C1q elevations were found in both juvenile- and adult-T. gondii infected mice.

CONCLUSIONS

Our study demonstrates that the age at first exposure to T. gondii is an important factor in shaping distinct behavioral and neurobiological abnormalities. Elevation in GLUN2 autoantibodies or complement protein C1q may be a potential underlying mechanism. A better understanding of these age-related differences may lead to more efficient treatments of behavioral disorders associated with T. gondii infection.

Metagenomic Sequencing Indicates That the Oropharyngeal Phageome of Individuals With Schizophrenia Differs From That of Controls

Mucosal sites such as the oropharynx contain a wide range of microorganisms, collectively designated as the microbiome. The microbiome can affect behavior through a number of neurobiological and immunological mechanisms. Most previous studies have focused on the bacterial components of the microbiome. However, the microbiome also includes viruses such as bacteriophages, which are viruses that infect bacteria and alter their metabolism and replication. We employed metagenomic analysis to characterize bacteriophage genomes in the oral pharynx of 41 individuals with schizophrenia and 33 control individuals without a psychiatric disorder. This analysis was performed by the generation of more than 100,000,000 sequence reads from each sample and the mapping of these reads to databases. We identified 79 distinct bacteriophage sequences in the oropharyngeal samples. Of these, one bacteriophage genome, Lactobacillus phage phiadh, was found to be significantly different in individuals with schizophrenia (P < .00037, q < 0.03 adjusted for multiple comparisons). The differential levels of Lactobacillus phage phiadh remained significant when controlling for age, gender, race, socioeconomic status, or cigarette smoking (P < .006). Within the group of individuals with schizophrenia, the level of Lactobacillus phage phiadh correlated with the prevalence of immunological disorders as well as with the administration of valproate, which has been shown in animal models to alter the microbiome. The bacteriophage composition of the oropharynx in individuals with schizophrenia differs from that of controls. The biological consequences of this difference and the potential effects of altering bacteriophage levels through therapeutic interventions are worthy of further investigation.

IgG dynamics of dietary antigens point to cerebrospinal fluid barrier or flow dysfunction in first-episode schizophrenia

Schizophrenia is a complex brain disorder that may be accompanied by idiopathic inflammation. Classic central nervous system (CNS) inflammatory disorders such as viral encephalitis or multiple sclerosis can be characterized by incongruent serum and cerebrospinal fluid (CSF) IgG due in part to localized intrathecal synthesis of antibodies. The dietary antigens, wheat gluten and bovine milk casein, can induce a humoral immune response in susceptible individuals with schizophrenia, but the correlation between the food-derived serological and intrathecal IgG response is not known. Here, we measured IgG to wheat gluten and bovine milk casein in matched serum and CSF samples from 105 individuals with first-episode schizophrenia (n=75 antipsychotic-naïve), and 61 controls. We found striking correlations in the levels of IgG response to dietary proteins between serum and CSF of schizophrenia patients, but not controls (schizophrenia, R(2)=0.34-0.55, p⩽0.0001; controls R(2)=0.05-0.06, p>0.33). A gauge of blood-CSF barrier permeability and CSF flow rate, the CSF-to-serum albumin ratio, was significantly elevated in cases compared to controls (p⩽0.001-0.003). Indicators of intrathecal IgG production, the CSF IgG index and the specific Antibody Index, were not significantly altered in schizophrenia compared to controls. Thus, the selective diffusion of bovine milk casein and wheat gluten antibodies between serum and CSF in schizophrenia may be the function of a low-level anatomical barrier dysfunction or altered CSF flow rate, which may be transient in nature.

Chlorovirus ATCV-1 is part of the human oropharyngeal virome and is associated with changes in cognitive functions in humans and mice

Chloroviruses (family Phycodnaviridae) are large DNA viruses known to infect certain eukaryotic green algae and have not been previously shown to infect humans or to be part of the human virome. We unexpectedly found sequences homologous to the chlorovirus Acanthocystis turfacea chlorella virus 1 (ATCV-1) in a metagenomic analysis of DNA extracted from human oropharyngeal samples. These samples were obtained by throat swabs of adults without a psychiatric disorder or serious physical illness who were participating in a study that included measures of cognitive functioning. The presence of ATCV-1 DNA was confirmed by quantitative PCR with ATCV-1 DNA being documented in oropharyngeal samples obtained from 40 (43.5%) of 92 individuals. The presence of ATCV-1 DNA was not associated with demographic variables but was associated with a modest but statistically significant decrease in the performance on cognitive assessments of visual processing and visual motor speed. We further explored the effects of ATCV-1 in a mouse model. The inoculation of ATCV-1 into the intestinal tract of 9-11-wk-old mice resulted in a subsequent decrease in performance in several cognitive domains, including ones involving recognition memory and sensory-motor gating. ATCV-1 exposure in mice also resulted in the altered expression of genes within the hippocampus. These genes comprised pathways related to synaptic plasticity, learning, memory formation, and the immune response to viral exposure.

Maternal complement C1q and increased odds for psychosis in adult offspring

The presence of maternal antibodies to food and infectious antigens may confer an increased risk of developing schizophrenia and psychosis in adult offspring. Complement factor C1q is an immune molecule with multiple functions including clearance of antigen-antibody complexes from circulation and mediation of synaptic pruning during fetal brain development. To determine if maternal C1q was associated with offspring schizophrenia and psychosis, we evaluated 55 matched case-control maternal serum pairs from the National Collaborative Perinatal Project. Sample pairs were composed of mothers whose offspring developed psychoses as adults and those whose offspring were free from psychiatric disease. Matching criteria for offspring included birth date, delivery hospital, race, and gender, with further matching based on mother's age. IgG markers of C1q, bovine milk casein, egg ovalbumin, and wheat gluten were measured with enzyme-linked immunosorbent assays. C1q levels were compared to food antigen IgG and to previously generated data for C-reactive protein, adenovirus, herpes simplex viruses, influenza viruses, measles virus, and Toxoplasma gondii. C1q was significantly elevated in case mothers with odds ratios of 2.66-6.31 (conditional logistic regressions, p ≤ 0.008-0.05). In case mothers only, C1q was significantly correlated with antibodies to both food and infectious antigens: gluten (R(2)=0.26, p ≤ 0.004), herpes simplex virus type 2 (R(2)=0.21, p ≤ 0.02), and adenovirus (R(2)=0.25, p ≤ 0.006). In conclusion, exposure to maternal C1q activity during pregnancy may be a risk factor for the development of schizophrenia and psychosis in offspring. Prenatal measurement of maternal C1q may be an important and convergent screening tool to identify potentially deleterious immune activation from multiple sources.

Inflammatory molecular signature associated with infectious agents in psychosis

Schizophrenia (SZ) is a devastating mental condition with onset in young adulthood. The identification of molecular biomarkers that reflect illness pathology is crucial. Recent evidence suggested immune and inflammatory cascades in conjunction with infection may play a role in the pathology. To address this question, we investigated molecular changes in cerebrospinal fluid (CSF) from antipsychotic-naïve patients with SZ and at risk mental status for psychosis (ARMS), in comparison with healthy controls (HCs). We measured 90 analytes using a broad multiplex platform focusing on immune and inflammatory cascades then selected 35 with our quality reporting criteria for further analysis. We also examined Toxoplasma gondii (TG) and herpes simplex virus 1 antibody levels in CSF. We report that expression of 15 molecules was significantly altered in the patient groups (SZ and ARMS) compared with HCs. The majority of these molecular changes (alpha-2-macroglobulin [α2M], fibrinogen, interleukin-6 receptor [IL-6R], stem cell factor [SCF], transforming growth factor alpha [TGFα], tumor necrosis factor receptor 2 [TNFR2], IL-8, monocyte chemotactic protein 2 [MCP-2/CCL8], testosterone [for males], angiotensin converting enzyme [ACE], and epidermal growth factor receptor) were consistent between SZ and ARMS patients, suggesting these may represent trait changes associated with psychotic conditions in general. Interestingly, many of these analytes (α2M, fibrinogen, IL-6R, SCF, TGFα, TNFR2, IL-8, MCP-2/CCL8, and testosterone [for males]) were exacerbated in subjects with ARMS compared with subjects with SZ. Although further studies are needed, we optimistically propose that these molecules may be good candidates for predictive markers for psychosis from an early stage. Lastly, reduction of IL-6R, TGFα, and ACE was correlated with positivity of TG antibody in the CSF, suggesting possible involvement of TG infection in the pathology.

One minute ultraviolet exposure inhibits Toxoplasma gondii tachyzoite replication and cyst conversion without diminishing host humoral-mediated immune response

We developed a protocol to inactivate Toxoplasma gondii (T. gondii) tachyzoites employing 1 min of ultraviolet (UV) exposure. We show that this treatment completely inhibited parasite replication and cyst formation in vitro and in vivo but did not affect the induction of a robust IgG response in mice. We propose that our protocol can be used to study the contribution of the humoral immune response to rodent behavioral alterations following T. gondii infection.

Seroreactive marker for inflammatory bowel disease and associations with antibodies to dietary proteins in bipolar disorder

OBJECTIVES

Immune sensitivity to wheat glutens and bovine milk caseins may affect a subset of individuals with bipolar disorder. Digested byproducts of these foods are exorphins that have the potential to impact brain physiology through action at opioid receptors. Inflammation in the gastrointestinal (GI) tract might accelerate exposure of food antigens to systemic circulation and help explain elevated gluten and casein antibody levels in individuals with bipolar disorder.

METHODS

We measured a marker of GI inflammation, anti-Saccharomyces cerevisiae antibodies (ASCA), in non-psychiatric controls (n = 207), in patients with bipolar disorder without a recent onset of psychosis (n = 226), and in patients with bipolar disorder with a recent onset of psychosis (n = 38). We compared ASCA levels to antibodies against gluten, casein, Epstein-Barr virus (EBV), herpes simplex virus 1 (HSV-1), influenza A, influenza B, measles, and Toxoplasma gondii.

RESULTS

Elevated ASCA conferred a 3.5-4.4-fold increased odds ratio of disease association (age-, race-, and gender-corrected multinomial logistic regressions, p ≤ 0.00001) that was independent of type of medication received. ASCA correlated with food antibodies in both bipolar disorder groups (R(2)  = 0.29-0.59, p ≤ 0.0005), and with measles and T. gondii immunoglobulin G (IgG) in the recent onset psychosis bipolar disorder group (R(2)  = 0.31-0.36, p ≤ 0.004-0.01).

CONCLUSIONS

Elevated seropositivity of a GI-related marker and its association with antibodies to food-derived proteins and self-reported GI symptoms suggest a GI comorbidity in at least a subgroup of individuals with bipolar disorder. Marker seroreactivity may also represent part of an overall heightened activated immune state inherent to this mood disorder.

Anti-gluten immune response following Toxoplasma gondii infection in mice

Gluten sensitivity may affect disease pathogenesis in a subset of individuals who have schizophrenia, bipolar disorder or autism. Exposure to Toxoplasma gondii is a known risk factor for the development of schizophrenia, presumably through a direct pathological effect of the parasite on brain and behavior. A co-association of antibodies to wheat gluten and to T. gondii in individuals with schizophrenia was recently uncovered, suggesting a coordinated gastrointestinal means by which T. gondii and dietary gluten might generate an immune response. Here, we evaluated the connection between these infectious- and food-based antigens in mouse models. BALB/c mice receiving a standard wheat-based rodent chow were infected with T. gondii via intraperitoneal, peroral and prenatal exposure methods. Significant increases in the levels of anti-gluten IgG were documented in all infected mice and in offspring from chronically infected dams compared to uninfected controls (repetitive measures ANOVAs, two-tailed t-tests, all p≤0.00001). Activation of the complement system accompanied this immune response (p≤0.002–0.00001). Perorally-infected females showed higher levels of anti-gluten IgG than males (p≤0.009) indicating that T. gondii-generated gastrointestinal infection led to a significant anti-gluten immune response in a sex-dependent manner. These findings support a gastrointestinal basis by which two risk factors for schizophrenia, T. gondii infection and sensitivity to dietary gluten, might be connected to produce the immune activation that is becoming an increasingly recognized pathology of psychiatric disorders.

Complement C1q formation of immune complexes with milk caseins and wheat glutens in schizophrenia

Immune system factors including complement pathway activation are increasingly linked to the etiology and pathophysiology of schizophrenia. Complement protein, C1q, binds to and helps to clear immune complexes composed of immunoglobulins coupled to antigens. The antigenic stimuli for C1q activation in schizophrenia are not known. Food sensitivities characterized by elevated IgG antibodies to bovine milk caseins and wheat glutens have been reported in individuals with schizophrenia. Here, we examined the extent to which these food products might comprise the antigen component of complement C1q immune complexes in individuals with recent onset schizophrenia (n=38), non-recent onset schizophrenia (n=61) and non-psychiatric controls (n=63). C1q seropositivity was significantly associated with both schizophrenia groups (recent onset, odds ratio (OR)=8.02, p≤0.008; non-recent onset, OR=3.15, p≤0.03) compared to controls (logistic regression models corrected for age, sex, race and smoking status). Casein- and/or gluten-IgG binding to C1q was significantly elevated in the non-recent onset group compared to controls (OR=4.36, p≤0.01). Significant amounts of C1q-casein/gluten-related immune complexes and C1q correlations with a marker for gastrointestinal inflammation in non-recent onset schizophrenia suggests a heightened rate of food antigens in the systemic circulation, perhaps via a disease-associated altered intestinal permeability. In individuals who are in the early stages of disease onset, C1q activation may reflect the formation of immune complexes with non-casein- or non-gluten-related antigens, the presence of C1q autoantibodies, and/or a dissociated state of immune complex components. In conclusion, complement activation may be a useful biomarker to diagnose schizophrenia early during the course of the disease. Future prospective studies should evaluate the impacts of casein- and gluten-free diets on C1q activation in schizophrenia.

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.