The Neurotropic Parasite Toxoplasma gondii Induces Sustained Neuroinflammation with Microvascular Dysfunction in Infected Mice

Contrasting Disease Progression, Microglia Reactivity, Tolerance, and Resistance to Toxoplasma gondii Infection in Two Mouse Strains

Our study investigated the innate immune response to Toxoplasma gondii infection by assessing microglial phenotypic changes and sickness behavior as inflammatory response markers post-ocular tachyzoite instillation. Disease progression in Swiss albino mice was compared with the previously documented outcomes in BALB/c mice using an identical ocular route and parasite burden (2 × 105 tachyzoites), with saline as the control. Contrary to expectations, the Swiss albino mice displayed rapid, lethal disease progression, marked by pronounced sickness behaviors and mortality within 11-12 days post-infection, while the survivors exhibited no apparent signs of infection. Comparative analysis revealed the T. gondii-infected BALB/c mice exhibited reduced avoidance of feline odors, while the infected Swiss albino mice showed enhanced avoidance responses. There was an important increase in microglial cells in the dentate gyrus molecular layer of the infected Swiss albino mice compared to the BALB/c mice and their respective controls. Hierarchical cluster and discriminant analyses identified three microglial morphological clusters, differentially affected by T. gondii infection across strains. The BALB/c mice exhibited increased microglial branching and complexity, while the Swiss albino mice showed reduced shrunken microglial arbors, diminishing their morphological complexity. These findings highlight strain-specific differences in disease progression and inflammatory regulation, indicating lineage-specific mechanisms in inflammatory responses, tolerance, and resistance. Understanding these elements is critical in devising control measures for toxoplasmosis.

Vascular Endothelial Growth Factor-C Treatment Enhances Cerebrospinal Fluid Outflow during Toxoplasma gondii Brain Infection but Does Not Improve Cerebral Edema

Cerebral edema frequently develops in the setting of brain infection and can contribute to elevated intracranial pressure, a medical emergency. How excess fluid is cleared from the brain is not well understood. Previous studies have shown that interstitial fluid is transported out of the brain along perivascular channels that collect into the cerebrospinal fluid (CSF)-filled subarachnoid space. CSF is then removed from the central nervous system through venous and lymphatic routes. The current study tested the hypothesis that increasing lymphatic drainage of CSF would promote clearance of cerebral edema fluid during infection with the neurotropic parasite Toxoplasma gondii. Fluorescent microscopy and magnetic resonance imaging was used to show that C57BL/6 mice develop vasogenic edema 4 to 5 weeks after infection with T. gondii. Tracer experiments were used to evaluate how brain infection affects meningeal lymphatic function, which demonstrated a decreased rate in CSF outflow in T. gondii-infected mice. Next, mice were treated with a vascular endothelial growth factor (VEGF)-C-expressing viral vector, which induced meningeal lymphangiogenesis and improved CSF outflow in chronically infected mice. No difference in cerebral edema was observed between mice that received VEGF-C and those that rececived sham treatment. Therefore, although VEGF-C treatment can improve lymphatic outflow in mice infected with T. gondii, this effect does not lead to increased clearance of edema fluid from the brains of these mice.

Understanding the mechanisms underlying the disruption of the blood-brain barrier in parasitic infections

Parasites have a significant impact on the neurological, cognitive, and mental well-being of humans, with a global population of over 1 billion individuals affected. The pathogenesis of central nervous system (CNS) injury in parasitic diseases remains limited, and prevention and control of parasitic CNS infections remain significant areas of research. Parasites, encompassing both unicellular and multicellular organisms, have intricate life cycles and possess the ability to infect a diverse range of hosts, including the human population. Parasitic illnesses that impact the central and peripheral nervous systems are a significant contributor to morbidity and mortality in low- to middle-income nations. The precise pathways through which neurotropic parasites infiltrate the CNS by crossing the blood-brain barrier (BBB) and cause neurological harm remain incompletely understood. Investigating brain infections caused by parasites is closely linked to studying neuroinflammation and cerebral impairment. The exact molecular and cellular mechanisms involved in this process remain incomplete, but understanding the exact mechanisms could provide insight into their pathogenesis and potentially reveal novel therapeutic targets. This review paper explores the underlying mechanisms involved in the development of neurological disorders caused by parasites, including parasite-derived elements, host immune responses, and modifications in tight junctions (TJs) proteins.

A multimodality therapeutic application on Toxoplasma gondii encephalitis utilizing Spiramycin and 'de novo' Ferula asafetida in immunodeficient mice

This study investigated a 'de Novo' medicinal herb, Ferula asafetida (FA), against toxoplasma encephalitis either alone or combined with spiramycin (SP). Female Swiss-Webster mice (n = 72) were divided into three batches. Batch-I received no DMS to serve as an immunocompetent control, batch-II was immune-suppressed with the DMS (0.25 mg/g/day) for 14 days pre-infection, whilst batch-III was immune-suppressed with the DMS on the same day of infection. All experimental mice were inoculated with Toxoplasma gondii ME49 cysts (n = 75). Each batch was split into four subgroups: Mono-SP, mono-FA, combined drug (SP + FA), or neither. Therapies were administered on day zero of infection in batches (I and II) and 35 days post-infection in batch (III). Treatments lasted for 14 days, and mice were sacrificed 60 days post-infection. Histopathological changes, cysts load, and CD4 and CD8 T-cells were counted in brain tissues. The cyst-load count in mice receiving SP + FA was significantly (p < .0001) the least compared to the mono treatments in all protocols. Interestingly, the combined therapy demolished the T-cell subsets to zero in immunocompetent and immunocompromised infected mice. In conclusion, F. asafetida might be a powerfully natural, safe vehicle of SP in the digestive system and/or across the brain-blood barrier to control toxoplasmosis even through immunodeficient conditions.

How colonization bottlenecks, tissue niches, and transmission strategies shape protozoan infections

Protozoan pathogens such as Plasmodium spp., Leishmania spp., Toxoplasma gondii, and Trypanosoma spp. are often associated with high-mortality, acute and chronic diseases of global health concern. For transmission and immune evasion, protozoans have evolved diverse strategies to interact with a range of host tissue environments. These interactions are linked to disease pathology, yet our understanding of the association between parasite colonization and host homeostatic disruption is limited. Recently developed techniques for cellular barcoding have the potential to uncover the biology regulating parasite transmission, dissemination, and the stability of infection. Understanding bottlenecks to infection and the in vivo tissue niches that facilitate chronic infection and spread has the potential to reveal new aspects of parasite biology.

Serum Biomarker Concentrations upon Admission in Acute Traumatic Brain Injury: Associations with TBI Severity, Toxoplasma gondii Infection, and Outcome in a Referral Hospital Setting in Cameroon

Despite the available literature on traumatic brain injury (TBI) biomarkers elsewhere, data are limited or non-existent in sub-Saharan Africa (SSA). The aim of the study was to analyse associations in acute TBI between the admission serum biomarker concentrations and TBI severity, CT-scan findings, and outcome, as well as to explore the influence of concurrent Toxoplasma gondii infection. The concentrations of serum biomarkers (GFAP, NFL Tau, UCH-L1, and S100B) were measured and Toxoplasma gondii were detected in the samples obtained <24 h post injury. GOSE was used to evaluate the 6-month outcome. All of the biomarker levels increased with the severity of TBI, but this increase was significant only for NFL (p = 0.01). The GFAP values significantly increased (p = 0.026) in those with an unfavourable outcome. The Tau levels were higher in those who died (p = 0.017). GFAP and NFL were sensitive to CT-scan pathology (p values of 0.004 and 0.002, respectively). The S100B levels were higher (p < 0.001) in TBI patients seropositive to Toxoplasma gondii. In conclusion, NFL was found to be sensitive to TBI severity, while NFL and GFAP were predictive of CT intracranial abnormalities. Increased levels of GFAP and Tau were associated with poorer outcomes 6 months after TBI, and the S100B levels were significantly affected by concurrent T. gondii infection in TBI patients compared with the seronegative patients.

Ivermectin modulated cerebral γ-aminobutyric acid (GABA) and reduced the number of chronic Toxoplasma gondii cysts significantly in the brains of immunocompromised mice

Disruption of GABAergic signaling could exaggerate the inflammatory reaction associated with Toxoplasma gondii infection, as well as produce neurophysiological consequences including seizures that occur within the brain tissues. The current study aimed to evaluate the efficacy of ivermectin (IVM) in treating latent cerebral toxoplasmosis and define its role in the neuromodulation of cerebral tissue GABA expression, conducted in an immunocompromised dexamethasone-treated mouse model infected with the ME49 Toxoplasma strain. The control (non-infected non-treated) group showed a mean of 22.1 ± 0.71 for local expression of GABA. Significantly lower expression (3.78 ± 1.38) was recorded in the infected non-treated group (p ≤ 0.05). On the contrary, a significantly higher expression was reported in the group infected and treated with IVM than in the infected non-treated group (19.8 ± 0.8). While the infected spiramycin (SP)-treated group reported a significantly lower level than the control. Non-infected groups that received only IVM or SP recorded 22.3 ± 0.45 and 22 ± 0.89 respectively with no significant difference. IVM is shown in this work, not only to reduce the size and the number of Toxoplasma cystic lesions within the brain significantly with a reduction rate of 68.85% but to also increase the level of GABA local expression significantly in addition to improving cerebral histopathology. Thus, IVM by its ability to modulate GABA expression may improve such clinical situations, if used as a treatment either exclusively or in combination with other medications.

Maternal Toxoplasma gondii infection affects proliferation, differentiation and cell cycle regulation of retinal neural progenitor cells in mouse embryo

Background

Toxoplasmosis affects one third of the world population and has the protozoan Toxoplasma gondii as etiological agent. Congenital toxoplasmosis (CT) can cause severe damage to the fetus, including miscarriages, intracranial calcification, hydrocephalus and retinochoroiditis. Severity of CT depends on the gestational period in which infection occurs, and alterations at the cellular level during retinal development have been reported. In this study, we proposed a mouse CT model to investigate the impact of infection on retinal development.

Methods

Pregnant females of pigmented C57BL/6 strain mice were infected intragastrically with two T. gondii cysts (ME49 strain) at embryonic day 10 (E10), and the offspring were analyzed at E18.

Results

Infected embryos had significantly smaller body sizes and weights than the PBS-treated controls, indicating that embryonic development was affected. In the retina, a significant increase in the number of Ki-67-positive cells (marker of proliferating cells) was found in the apical region of the NBL of infected mice compared to the control. Supporting this, cell cycle proteins Cyclin D3, Cdk6 and pChK2 were significantly altered in infected retinas. Interestingly, the immunohistochemical analysis showed a significant increase in the population of β-III-tubulin-positive cells, one of the earliest markers of neuronal differentiation.

Conclusions

Our data suggests that CT affects cell cycle progression in retinal progenitor cells, possibly inducing the arrest of these cells at G2/M phase. Such alterations could influence the differentiation, anticipating/increasing neuronal maturation, and therefore leading to abnormal retinal formation. Our model mimics important events observed in ocular CT.

Human Brain Microvascular Endothelial Cells Exposure to SARS-CoV-2 Leads to Inflammatory Activation through NF-κB Non-Canonical Pathway and Mitochondrial Remodeling

Neurological effects of COVID-19 and long-COVID-19, as well as neuroinvasion by SARS-CoV-2, still pose several questions and are of both clinical and scientific relevance. We described the cellular and molecular effects of the human brain microvascular endothelial cells (HBMECs) in vitro exposure by SARS-CoV-2 to understand the underlying mechanisms of viral transmigration through the blood-brain barrier. Despite the low to non-productive viral replication, SARS-CoV-2-exposed cultures displayed increased immunoreactivity for cleaved caspase-3, an indicator of apoptotic cell death, tight junction protein expression, and immunolocalization. Transcriptomic profiling of SARS-CoV-2-challenged cultures revealed endothelial activation via NF-κB non-canonical pathway, including RELB overexpression and mitochondrial dysfunction. Additionally, SARS-CoV-2 led to altered secretion of key angiogenic factors and to significant changes in mitochondrial dynamics, with increased mitofusin-2 expression and increased mitochondrial networks. Endothelial activation and remodeling can further contribute to neuroinflammatory processes and lead to further BBB permeability in COVID-19.

Chronic Toxoplasma gondii infection contributes to perineuronal nets impairment in the primary somatosensory cortex

Toxoplasma gondii is able to manipulate the host immune system to establish a persistent and efficient infection, contributing to the development of brain abnormalities with behavioral repercussions. In this context, this work aimed to evaluate the effects of T. gondii infection on the systemic inflammatory response and structure of the primary somatosensory cortex (PSC). C57BL/6 and BALB/c mice were infected with T. gondii ME49 strain tissue cysts and accompanied for 30 days. After this period, levels of cytokines IFN-γ, IL-12, TNF-α and TGF-β were measured. After blood collection, mice were perfused and the brains were submitted to immunohistochemistry for perineuronal net (PNN) evaluation and cyst quantification. The results showed that C57BL/6 mice presented higher levels of TNF-α and IL-12, while the levels of TGF-β were similar between the two mouse lineages, associated with the elevated number of tissue cysts, with a higher occurrence of cysts in the posterior area of the PSC when compared to BALB/c mice, which presented a more homogeneous cyst distribution. Immunohistochemistry analysis revealed a greater loss of PNN labeling in C57BL/6 animals compared to BALB/c. These data raised a discussion about the ability of T. gondii to stimulate a systemic inflammatory response capable of indirectly interfering in the brain structure and function.

Study on the effect of koumiss on reactivation of Toxoplasma gondii infection

Toxoplasma gondii is an obligate intracellular parasite that infects nucleated cells of all warm-blooded animals, and most patients have latent infections. The latent infection will be reactivated in the immunocompromised or immunocompromised individuals, which will lead to severe toxoplasmosis. At present, less research has been focused on the reactivation of T. gondii infection. Koumiss is a kind of fermented milk made from fresh mare’s milk through natural fermentation that can be applied to clinical and rehabilitation medicine to mitigate the development of various diseases due to its unique functional characteristics. In this study, we explored the antagonistic effect of koumiss on reactivation of T. gondii infection. Mice were treated with dexamethasone to establish a reactivation model after infection with T. gondii and then treated with koumiss. The survival rate, SHIRPA test, serum cytokine levels, organ parasite burden and intestinal microbiota were measured, respectively. Our results showed that koumiss treatment improved the clinical symptoms of mice, significantly reduced the organ parasite burden of mice, and improved the composition and structure of intestinal flora. This study provides new evidence for the alleviation and treatment of toxoplasmosis and provides a novel idea for the development and utilization of koumiss.

Study on the antagonistic effects of koumiss on Toxoplasma gondii infection in mice

Toxoplasma gondii is an important food-borne zoonotic parasite, and approximately one-third of people worldwide are positive for T. gondii antibodies. To date, there are no specific drugs or vaccines against T. gondii. Therefore, developing a new safe and effective method has become a new trend in treating toxoplasmosis. Koumiss is rich in probiotics and many components that can alleviate the clinical symptoms of many diseases via the functional characteristics of koumiss and its regulation of intestinal flora. To investigate the antagonistic effect of koumiss on T. gondii infection, the model of acute and chronic T. gondii infection was established in this study. The survival rate, SHIRPA score, serum cytokine levels, brain cyst counts, β-amyloid deposition and intestinal flora changes were measured after koumiss feeding. The results showed that the clinical symptoms of mice were improved at 6 dpi and that the SHIRPA score decreased after koumiss feeding (P &lt; 0.05). At the same time, the levels of IL-4, IFN-γ and TNF-α decreased (P &lt; 0.001, P &lt; 0.001, P &lt; 0.01). There was no significant difference of survival rate between koumiss treatment and the other groups. Surprisingly, the results of chronic infection models showed that koumiss could significantly reduce the number of brain cysts in mice (P &lt; 0.05), improve β-amyloid deposition in the hippocampus (P &lt; 0.01) and decrease the levels of IFN-γ and TNF-α (P &lt; 0.01, P &lt; 0.05). Moreover, koumiss could influence the gut microbiota function in resisting T. gondii infection. In conclusion, koumiss had a significant effect on chronic T. gondii infection in mice and could improve the relevant indicators of acute T. gondii infection in mice. The research provides new evidence for the development of safe and effective anti-T. gondii methods, as well as a theoretical basis and data support for the use of probiotics against T. gondii infection and broadened thoughts for the development and utilization of koumiss.

Laminin as a Biomarker of Blood-Brain Barrier Disruption under Neuroinflammation: A Systematic Review

Laminin, a non-collagenous glycoprotein present in the brain extracellular matrix, helps to maintain blood–brain barrier (BBB) integrity and regulation. Neuroinflammation can compromise laminin structure and function, increasing BBB permeability. The aim of this paper is to determine if neuroinflammation-induced laminin functional changes may serve as a potential biomarker of alterations in the BBB. The 38 publications included evaluated neuroinflammation, BBB disruption, and laminin, and were assessed for quality and risk of bias (protocol registered in PROSPERO; CRD42020212547). We found that laminin may be a good indicator of BBB overall structural integrity, although changes in expression are dependent on the pathologic or experimental model used. In ischemic stroke, permanent vascular damage correlates with increased laminin expression (β and γ subunits), while transient damage correlates with reduced laminin expression (α subunits). Laminin was reduced in traumatic brain injury and cerebral hemorrhage studies but increased in multiple sclerosis and status epilepticus studies. Despite these observations, there is limited knowledge about the role played by different subunits or isoforms (such as 411 or 511) of laminin in maintaining structural architecture of the BBB under neuroinflammation. Further studies may clarify this aspect and the possibility of using laminin as a biomarker in different pathologies, which have alterations in BBB function in common.

SARS-CoV-2 infection of human brain microvascular endothelial cells leads to inflammatory activation through NF-κB non-canonical pathway and mitochondrial remodeling

Neurological effects of COVID-19 and long-COVID-19 as well as neuroinvasion by SARS-CoV-2 still pose several questions and are of both clinical and scientific relevance. We described the cellular and molecular effects of the human brain microvascular endothelial cells (HBMECs) in vitro infection by SARS-CoV-2 to understand the underlying mechanisms of viral transmigration through the Blood-Brain Barrier. Despite the low to non-productive viral replication, SARS-CoV-2-infected cultures displayed increased apoptotic cell death and tight junction protein expression and immunolocalization. Transcriptomic profiling of infected cultures revealed endothelial activation via NF-κB non-canonical pathway, including RELB overexpression, and mitochondrial dysfunction. Additionally, SARS-CoV-2 led to altered secretion of key angiogenic factors and to significant changes in mitochondrial dynamics, with increased mitofusin-2 expression and increased mitochondrial networks. Endothelial activation and remodeling can further contribute to neuroinflammatory processes and lead to further BBB permeability in COVID-19.

Sulfadiazine Plus Pyrimethamine Therapy Reversed Multiple Behavioral and Neurocognitive Changes in Long-Term Chronic Toxoplasmosis by Reducing Brain Cyst Load and Inflammation-Related Alterations

Toxoplasma gondii infects one-third of the world population. For decades, it has been considered a silent lifelong infection. However, chronically T. gondii-infected persons may present psychiatric and neurocognitive changes as anxiety, depression, and memory loss. In a model of long-term chronic infection, behavioral alterations parallel neuroinflammation and systemic high cytokine levels, and may reflect brain cyst load. Recent findings support that in chronic infection an active parasite-host interplay involves an immune-mediated control of tissue cysts. Here, we tested the idea that etiological treatment in chronic phase may add advantage to intrinsic immune-mediated cyst control and impact behavioral changes. Thus, we combined sulfadiazine-plus-pyrimethamine (S+P), the first-choice therapy for toxoplasmosis, to study the association of brain cyst load and biological processes related to the immune response (neuroinflammation, blood-brain barrier -BBB- disruption and serum cytokine levels), with behavioral and neurocognitive changes of long-term chronic infection. Female C57BL/6 mice (H-2^b) were infected (5 cysts, ME-49 strain) and treated with S+P from 30 to 60 days postinfection (dpi), compared with vehicle (Veh)-treated and noninfected controls. At endpoints (pre-therapy, 30 dpi; S+P therapy, 60 dpi; after ceased therapy, 90 dpi), independent groups were subjected to behavioral tests, and brain tissues and sera were collected. Multiple behavioral and neurocognitive changes were detected in the early (30 dpi) and long-term (60 and 90 dpi) chronic infection. S+P therapy resolved locomotor alterations, anxiety, and depressive-like behavior, partially or transiently ameliorated hyperactivity and habituation memory loss. Analysis after therapy cessation showed that S+P therapy reduced the number of stimuli required for aversive memory consolidation. S+P therapy resulted in reduced brain cyst load, neuroinflammation and BBB disruption, and lowered systemic Th1-cytokine levels. Correlation analysis revealed association between IFNγ, TNF and MCP-1/CCL2 serum levels, brain cyst load and behavioral and neurocognitive alterations. Moreover, principal-component analysis (PCA-2D and 3D projections) highlighted distinction between clusters (noninfected; Veh-treated and S+P-treated infected). Thus, our data suggest that S+P therapy added gain to intrinsic brain cyst control and, direct or indirectly, ameliorated inflammation-related alterations, traits associated with behavioral and neurocognitive alterations.

Blood-brain barrier-restricted translocation of Toxoplasma gondii from cortical capillaries

The cellular barriers of the central nervous system proficiently protect the brain parenchyma from infectious insults. Yet, the single-celled parasite Toxoplasma gondii commonly causes latent cerebral infection in humans and other vertebrates. Here, we addressed the role of the cerebral vasculature in the passage of T. gondii to the brain parenchyma. Shortly after inoculation in mice, parasites mainly localized to cortical capillaries, in preference over post-capillary venules, cortical arterioles or meningeal and choroidal vessels. Early invasion to the parenchyma (days 1-5) occurred in absence of a measurable increase in blood-brain barrier (BBB) permeability, perivascular leukocyte cuffs or hemorrhage. However, sparse focalized permeability elevations were detected adjacently to replicative parasite foci. Further, T. gondii triggered inflammatory responses in cortical microvessels and endothelium. Pro- and anti-inflammatory treatments of mice with LPS and hydrocortisone, respectively, impacted BBB permeability and parasite loads in the brain parenchyma. Finally, pharmacological inhibition or Cre/loxP conditional knockout of endothelial focal adhesion kinase (FAK), a BBB intercellular junction regulator, facilitated parasite translocation to the brain parenchyma. The data reveal that the initial passage of T. gondii to the central nervous system occurs principally across cortical capillaries. The integrity of the microvascular BBB restricts parasite transit, which conversely is exacerbated by the inflammatory response.

Behavioral alterations in long-term Toxoplasma gondii infection of C57BL/6 mice are associated with neuroinflammation and disruption of the blood brain barrier

The Apicomplexa protozoan Toxoplasma gondii is a mandatory intracellular parasite and the causative agent of toxoplasmosis. This illness is of medical importance due to its high prevalence worldwide and may cause neurological alterations in immunocompromised persons. In chronically infected immunocompetent individuals, this parasite forms tissue cysts mainly in the brain. In addition, T. gondii infection has been related to mental illnesses such as schizophrenia, bipolar disorder, depression, obsessive-compulsive disorder, as well as mood, personality, and other behavioral changes. In the present study, we evaluated the kinetics of behavioral alterations in a model of chronic infection, assessing anxiety, depression and exploratory behavior, and their relationship with neuroinflammation and parasite cysts in brain tissue areas, blood-brain-barrier (BBB) integrity, and cytokine status in the brain and serum. Adult female C57BL/6 mice were infected by gavage with 5 cysts of the ME-49 type II T. gondii strain, and analyzed as independent groups at 30, 60 and 90 days postinfection (dpi). Anxiety, depressive-like behavior, and hyperactivity were detected in the early (30 dpi) and long-term (60 and 90 dpi) chronic T. gondii infection, in a direct association with the presence of parasite cysts and neuroinflammation, independently of the brain tissue areas, and linked to BBB disruption. These behavioral alterations paralleled the upregulation of expression of tumor necrosis factor (TNF) and CC-chemokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES) in the brain tissue. In addition, increased levels of interferon-gamma (IFNγ), TNF and CCL2/MCP-1 were detected in the peripheral blood, at 30 and 60 dpi. Our data suggest that the persistence of parasite cysts induces sustained neuroinflammation, and BBB disruption, thus allowing leakage of cytokines of circulating plasma into the brain tissue. Therefore, all these factors may contribute to behavioral changes (anxiety, depressive-like behavior, and hyperactivity) in chronic T. gondii infection.

Association of Toxoplasma gondii Seropositivity With Cognitive Function in Healthy People: A Systematic Review and Meta-analysis

IMPORTANCE

The parasite Toxoplasma gondii has been associated with behavioral alterations and psychiatric disorders. Studies investigating neurocognition in people with T gondii infection have reported varying results. To systematically analyze these findings, a meta-analysis evaluating cognitive function in healthy people with and without T gondii seropositivity is needed.

OBJECTIVE

To assess whether and to what extent T gondii seropositivity is associated with cognitive function in otherwise healthy people.

DATA SOURCES

A systematic search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. A systematic search of PubMed, MEDLINE, Web of Science, PsycInfo, and Embase was performed to identify studies from database inception to June 7, 2019, that analyzed cognitive function among healthy participants with available data on T gondii seropositivity. Search terms included toxoplasmosis, neurotoxoplasmosis, Toxoplasma gondii, cognition disorder, neuropsychological, and psychomotor performance.

STUDY SELECTION

Studies that performed cognitive assessment and analyzed T gondii seroprevalence among otherwise healthy participants were included.

DATA EXTRACTION AND SYNTHESIS

Two researchers independently extracted data from published articles; if needed, authors were contacted to provide additional data. Quantitative syntheses were performed in predefined cognitive domains when 4 independent data sets per domain were available. Study quality, heterogeneity, and publication bias were assessed.

MAIN OUTCOMES AND MEASURES

Performance on neuropsychological tests measuring cognitive function.

RESULTS

The systematic search yielded 1954 records. After removal of 533 duplicates, an additional 1363 records were excluded based on a review of titles and abstracts. A total of 58 full-text articles were assessed for eligibility (including reference list screening); 45 articles were excluded because they lacked important data or did not meet study inclusion or reference list criteria. The remaining 13 studies comprising 13 289 healthy participants (mean [SD] age, 46.7 [16.0] years; 6586 men [49.6%]) with and without T gondii seropositivity were included in the meta-analysis. Participants without T gondii seropositivity had favorable functioning in 4 cognitive domains: processing speed (standardized mean difference [SMD], 0.12; 95% CI, 0.05-0.19; P = .001), working memory (SMD, 0.16; 95% CI, 0.06-0.26; P = .002), short-term verbal memory (SMD, 0.18; 95% CI, 0.09-0.27; P < .001), and executive functioning (SMD, 0.15; 95% CI, 0.01-0.28; P = .03). A meta-regression analysis found a significant association between older age and executive functioning (Q = 6.17; P = .01). Little suggestion of publication bias was detected.

CONCLUSIONS AND RELEVANCE

The study's findings suggested that T gondii seropositivity was associated with mild cognitive impairment in several cognitive domains. Although effect sizes were small, given the ubiquitous prevalence of this infection globally, the association with cognitive impairment could imply a considerable adverse effect at the population level. Further research is warranted to investigate the underlying mechanisms of this association.

Ethanol Gestational Exposure Impairs Vascular Development and Endothelial Potential to Control BBB-Associated Astrocyte Function in the Developing Cerebral Cortex

Ethanol consumption during pregnancy or lactation period can induce permanent damage to the development of the central nervous system (CNS), resulting in fetal alcohol spectrum disorders (FASD). CNS development depends on proper neural cells and blood vessel (BV) development and blood-brain barrier (BBB) establishment; however, little is known about how ethanol affects these events. Here, we investigated the impact of ethanol exposure to endothelial cells (ECs) function and to ECs interaction with astrocytes in the context of BBB establishment. Cerebral cortex of newborn mice exposed in utero to ethanol (FASD model) presented a hypervascularized phenotype, revealed by augmented vessel density, length, and branch points. Further, aberrant distribution of the tight junction ZO-1 protein along BVs and increased rates of perivascular astrocytic endfeet around BVs were observed. In vitro exposure of human brain microcapillary ECs (HBMEC) to ethanol significantly disrupted ZO-1 distribution, decreased Claudin-5 and GLUT-1 expression and impaired glucose uptake, and increased nitric oxide secretion. These events were accompanied by upregulation of angiogenesis-related secreted proteins by ECs in response to ethanol exposure. Treatment of cortical astrocytes with conditioned medium (CM) from ethanol exposed ECs, upregulated astrocyte's expression of GFAP, Cx43, and Lipocalin-2 genes, as well as the pro-inflammatory genes, IL-1beta, IL-6, and TNF-alpha, which was accompanied by NF-kappa B protein nuclear accumulation. Our findings suggest that ethanol triggers a dysfunctional phenotype in brain ECs, leading to impairment of cortical vascular network formation, and promotes ECs-induced astrocyte dysfunction, which could dramatically affect BBB establishment in the developing brain.

Toxoplasmosis: Recent Advances in Understanding the Link Between Infection and Host Behavior

Humans, wildlife, and domestic animals are intimately linked through shared infections. Many parasites and pathogens use multiple host species, either opportunistically or sequentially, such that managing disease risk frequently requires a broader understanding of the ecological community. The coccidian protozoan Toxoplasma gondii infects more than one hundred species of vertebrates, ranging from bats to beluga whales. In humans, acute toxoplasmosis can have serious health consequences for immunocompromised individuals. Even amongst asymptomatic patients, however, toxoplasmosis has been linked to a range of behavioral alterations and conditions, such as changes in risk tolerance, neuroticism, mental illness, suicide, and accident proneness. Whether such links are causal or simply correlational has been the subject of intense study and debate; from an evolutionary standpoint, selection may favor parasite-induced alterations in host behavior that increase the likelihood a host is consumed by the definitive host-in this case a domestic or wild felid. Here, we examine current evidence for parasite-induced manipulations of host behavior, in both humans and other animals. We critically evaluate proposed mechanisms through which infection might influence host behavior, which range from inflammation in the brain to changes in hormones or neurotransmitters. Considering estimates that T. gondii may infect up to one-third of the global human population, we conclude by examining the implications of these changes for human behavior, individual fitness, and emergent cultural properties.

Evaluation of CpG-ODN-Adjuvanted Toxoplasma Gondii Virus-Like Particle Vaccine upon One, Two, and Three Immunizations

Successful vaccines against specific pathogens often require multiple immunizations and adjuvant usage. Yet, assessing the protective efficacy of different immunization regimens with adjuvanted Toxoplasma gondii vaccines remains elusive. In this study, we investigated the vaccine efficacy induced by CpG-ODN-adjuvanted T. gondii virus-like particles (VLPs) after challenge infection with T. gondii (ME49) in mice (BALB/c) upon one, two, and three immunizations. Immunization with adjuvanted T. gondii VLPs induced higher levels of T. gondii-specific IgG and/or IgA antibody responses, germinal center (GC) B cells, total B cells, and CD4⁺ and CD8⁺ T cells compared with unadjuvanted VLPs. Increasing the number of immunizations was strongly correlated with enhanced protective immunity against T. gondii in mice, with the highest protection being demonstrated in mice thrice-immunized with either adjuvanted T. gondii VLPs or VLPs alone. Notably, lesser bodyweight reductions and cerebral cyst counts were observed in mice receiving multiple immunizations with the adjuvanted VLPs, thereby confirming the effectiveness of adjuvanted boost immunizations. These results demonstrated that multiple immunizations with T. gondii VLPs is an effective approach, and the CpG-ODN can be developed as an effective adjuvant for T. gondii VLP vaccines.

Structural, Functional, and Metabolic Alterations in Human Cerebrovascular Endothelial Cells during Toxoplasma gondii Infection and Amelioration by Verapamil In Vitro

Toxoplasma gondii (T. gondii), the causative agent of toxoplasmosis, is a frequent cause of brain infection. Despite its known ability to invade the brain, there is still a dire need to better understand the mechanisms by which this parasite interacts with and crosses the blood–brain barrier (BBB). The present study revealed structural and functional changes associated with infection and replication of T. gondii within human brain microvascular endothelial cells (BMECs) in vitro. T. gondii proliferated within the BMECs and disrupted the integrity of the cerebrovascular barrier through diminishing the cellular viability, disruption of the intercellular junctions and increasing permeability of the BMEC monolayer, as well as altering lipid homeostasis. Proton nuclear magnetic resonance (¹H NMR)-based metabolomics combined with multivariate data analysis revealed profiles that can be attributed to infection and variations in the amounts of certain metabolites (e.g., amino acids, fatty acids) in the extracts of infected compared to control cells. Notably, treatment with the Ca²⁺ channel blocker verapamil rescued BMEC barrier integrity and restricted intracellular replication of the tachyzoites regardless of the time of treatment application (i.e., prior to infection, early- and late-infection). This study provides new insights into the structural and functional changes that accompany T. gondii infection of the BMECs, and sheds light upon the ability of verapamil to inhibit the parasite proliferation and to ameliorate the adverse effects caused by T. gondii infection.

Catastrophic consequences: can the feline parasite Toxoplasma gondii prompt the purrfect neuroinflammatory storm following traumatic brain injury?

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide; however, treatment development is hindered by the heterogenous nature of TBI presentation and pathophysiology. In particular, the degree of neuroinflammation after TBI varies between individuals and may be modified by other factors such as infection. Toxoplasma gondii, a parasite that infects approximately one-third of the world’s population, has a tropism for brain tissue and can persist as a life-long infection. Importantly, there is notable overlap in the pathophysiology between TBI and T. gondii infection, including neuroinflammation. This paper will review current understandings of the clinical problems, pathophysiological mechanisms, and functional outcomes of TBI and T. gondii, before considering the potential synergy between the two conditions. In particular, the discussion will focus on neuroinflammatory processes such as microglial activation, inflammatory cytokines, and peripheral immune cell recruitment that occur during T. gondii infection and after TBI. We will present the notion that these overlapping pathologies in TBI individuals with a chronic T. gondii infection have the strong potential to exacerbate neuroinflammation and related brain damage, leading to amplified functional deficits. The impact of chronic T. gondii infection on TBI should therefore be investigated in both preclinical and clinical studies as the possible interplay could influence treatment strategies.

The molecular biology and immune control of chronic Toxoplasma gondii infection

Toxoplasma gondii is an incredibly successful parasite owing in part to its ability to persist within cells for the life of the host. Remarkably, at least 350 host species of T. gondii have been described to date, and it is estimated that 30% of the global human population is chronically infected. The importance of T. gondii in human health was made clear with the first reports of congenital toxoplasmosis in the 1940s. However, the AIDS crisis in the 1980s revealed the prevalence of chronic infection, as patients presented with reactivated chronic toxoplasmosis, underscoring the importance of an intact immune system for parasite control. In the last 40 years, there has been tremendous progress toward understanding the biology of T. gondii infection using rodent models, human cell experimental systems, and clinical data. However, there are still major holes in our understanding of T. gondii biology, including the genes controlling parasite development, the mechanisms of cell-intrinsic immunity to T. gondii in the brain and muscle, and the long-term effects of infection on host homeostasis. The need to better understand the biology of chronic infection is underscored by the recent rise in ocular disease associated with emerging haplotypes of T. gondii and our lack of effective treatments to sterilize chronic infection. This Review discusses the cell types and molecular mediators, both host and parasite, that facilitate persistent T. gondii infection. We highlight the consequences of chronic infection for tissue-specific pathology and identify open questions in this area of host-Toxoplasma interactions.

Toxoplasma gondii infection impairs radial glia differentiation and its potential to modulate brain microvascular endothelial cell function in the cerebral cortex

Congenital toxoplasmosis is a parasitic disease that occurs due vertical transmission of the protozoan Toxoplasma gondii (T. gondii) during pregnancy. The parasite crosses the placental barrier and reaches the developing brain, infecting progenitor, glial, neuronal and vascular cell types. Although the role of Radial glia (RG) neural stem cells in the development of the brain vasculature has been recently investigated, the impact of T. gondii infection in these events is not yet understood. Herein, we studied the role of T. gondii infection on RG cell function and its interaction with endothelial cells. By infecting isolated RG cultures with T. gondii tachyzoites, we observed a cytotoxic effect with reduced numbers of RG populations together with decrease neuronal and oligodendrocyte progenitor populations. Conditioned medium (CM) from RG control cultures increased ZO-1 protein levels and organization on endothelial bEnd.3 cells membranes, which was impaired by CM from infected RG, accompanied by decreased trans-endothelial electrical resistance (TEER). ELISA assays revealed reduced levels of anti-inflammatory cytokine TGF-β1 in CM from T. gondii-infected RG cells. Treatment with recombinant TGF-β1 concomitantly with CM from infected RG cultures led to restoration of ZO-1 staining in bEnd.3 cells. Congenital infection in Swiss Webster mice led to abnormalities in the cortical microvasculature in comparison to uninfected embryos. Our results suggest that infection of RG cells by T. gondii negatively modulates cytokine secretion, which might contribute to endothelial loss of barrier properties, thus leading to impairment of neurovascular interaction establishment.

Downregulation of lncRNA-11496 in the Brain Contributes to Microglia Apoptosis via Regulation of Mef2c in Chronic T. gondii Infection Mice

Though it is well known that chronic infections of Toxoplasma gondii (T. gondii) can induce mental and behavioral disorders in the host, little is known about the role of long non-coding RNAs (lncRNAs) in this pathological process. In this study, we employed an advanced lncRNAs and mRNAs integration chip (Affymetrix HTA 2.0) to detect the expression of both lncRNAs and mRNAs in T. gondii Chinese 1 strain infected mouse brain. As a result, for the first time, the downregulation of lncRNA-11496 (NONMMUGO11496) was identified as the responsible factor for this pathological process. We showed that dysregulation of lncRNA-11496 affected proliferation, differentiation and apoptosis of mouse microglia. Furthermore, we proved that Mef2c (Myocyte-specific enhancer factor 2C), a member of the MEF2 subfamily, is the target gene of lncRNA-11496. In a more detailed study, we confirmed that lncRNA-11496 positively regulated the expression of Mef2c by binding to histone deacetylase 2 (HDAC2). Importantly, Mef2c itself could coordinate neuronal differentiation, survival, as well as synapse formation. Thus, our current study provides the first evidence in terms of the modulatory action of lncRNAs in chronic toxoplasmosis in T. gondii infected mouse brain, providing a solid scientific basis for using lncRNA-11496 as a therapeutic target to treat T. gondii induced neurological disorder.

Chronic Toxoplasma gondii infection contributes to decreasing of perineuronal nets surrounding neurons in the Corpus striatum of mice

Recent advances in chronic toxoplasmosis understanding became the focus of discussion about behavioral abnormalities, which could be explained by cyst location and neuronal impairment in specific brain areas. Perineuronal nets (PNNs) are specialized extracellular matrices that surround the neuronal body and proximal dendrites and play key roles in neuronal circuitry maintenance and stabilization. Its impairment can lead to abnormal synaptic functioning with behavioral repercussions. In this context, we analyzed the impact of Toxoplasma gondii infection on neuronal integrity in the Corpus striatum of chronically infected mice. C57BL/6 and Balb/c female mice were infected with T. gondii ME49 cysts. Brain sections were submitted to immunohistochemistry with Wisteria floribunda agglutinin (WFA) for PNN labeling followed by quantification of tissue cyst and labeled neuronal cells 30 days after infection. Our results revealed that C57BL/6 exhibited a significant decrease in PNN-positive (WFA+) labeled neurons and an expressively higher number of tissue cysts than Balb/c mice. It was also possible to observe that the number of T. gondii tissue cysts and the number of WFA+ neurons were inversely correlated for C57BL/6-infected mice. However, no correlation was observed for Balb/c mice. These data suggest how the impact of parasite dissemination in the brain and host characteristics can influence neuronal integrity impairment during infection by decreasing WFA+ neurons. This might be a plausible pathway in which the presence of T. gondii contributes to behavioral changes in the infected host.

Disruption of the Blood-Brain Barrier During Neuroinflammatory and Neuroinfectious Diseases

As the organ of highest metabolic demand, utilizing over 25% of total body glucose utilization via an enormous vasculature with one capillary every 73 μm, the brain evolves a barrier at the capillary and postcapillary venules to prevent toxicity during serum fluctuations in metabolites and hormones, to limit brain swelling during inflammation, and to prevent pathogen invasion. Understanding of neuroprotective barriers has since evolved to incorporate the neurovascular unit (NVU), the blood-cerebrospinal fluid (CSF) barrier, and the presence of CNS lymphatics that allow leukocyte egress. Identification of the cellular and molecular participants in BBB function at the NVU has allowed detailed analyses of mechanisms that contribute to BBB dysfunction in various disease states, which include both autoimmune and infectious etiologies. This chapter will introduce some of the cellular and molecular components that promote barrier function but may be manipulated by inflammatory mediators or pathogens during neuroinflammation or neuroinfectious diseases.

Intravital microscopy: Imaging host-parasite interactions in the brain

Intravital fluorescence microscopy (IVM) is a powerful technique for imaging multiple organs, including the brain of living mice and rats. It enables the direct visualisation of cells in situ providing a real-life view of biological processes that in vitro systems cannot. In addition, to the technological advances in microscopy over the last decade, there have been supporting innovations in data storage and analytical packages that enable the visualisation and analysis of large data sets. Here, we review the advantages and limitations of techniques predominantly used for brain IVM, including thinned skull windows, open skull cortical windows, and a miniaturised optical system based on microendoscopic probes that can be inserted into deep tissues. Further, we explore the relevance of these techniques for the field of parasitology. Several protozoan infections are associated with neurological symptoms including Plasmodium spp., Toxoplasma spp., and Trypanosoma spp. IVM has led to crucial findings on these parasite species, which are discussed in detail in this review.

Advances and Challenges in Understanding Cerebral Toxoplasmosis

Toxoplasma gondii is a widespread parasitic pathogen that infects over one third of the global human population. The parasite invades and chronically persists in the central nervous system (CNS) of the infected host. Parasite spread and persistence is intimately linked to an ensuing immune response, which does not only limit parasite-induced damage but also may facilitate dissemination and induce parasite-associated immunopathology. Here, we discuss various aspects of toxoplasmosis where knowledge is scarce or controversial and, the recent advances in the understanding of the delicate interplay of T. gondii with the immune system in experimental and clinical settings. This includes mechanisms for parasite passage from the circulation into the brain parenchyma across the blood-brain barrier during primary acute infection. Later, as chronic latent infection sets in with control of the parasite in the brain parenchyma, the roles of the inflammatory response and of immune cell responses in this phase of the disease are discussed. Additionally, the function of brain resident cell populations is delineated, i.e., how neurons, astrocytes and microglia serve both as target cells for the parasite but also actively contribute to the immune response. As the infection can reactivate in the CNS of immune-compromised individuals, we bring up the immunopathogenesis of reactivated toxoplasmosis, including the special case of congenital CNS manifestations. The relevance, advantages and limitations of rodent infection models for the understanding of human cerebral toxoplasmosis are discussed. Finally, this review pinpoints questions that may represent challenges to experimental and clinical science with respect to improved diagnostics, pharmacological treatments and immunotherapies.

Toolbox for In Vivo Imaging of Host-Parasite Interactions at Multiple Scales

Animal models have for long been pivotal for parasitology research. Over the last few years, techniques such as intravital, optoacoustic and magnetic resonance imaging, optical projection tomography, and selective plane illumination microscopy developed promising potential for gaining insights into host-pathogen interactions by allowing different visualization forms in vivo and ex vivo. Advances including increased resolution, penetration depth, and acquisition speed, together with more complex image analysis methods, facilitate tackling biological problems previously impossible to study and/or quantify. Here we discuss advances and challenges in the in vivo imaging toolbox, which hold promising potential for the field of parasitology.