Cytokine responses induced by Toxoplasma gondii in astrocytes and microglial cells

Inflammatory pathways of Toxoplasmagondii infection in pregnancy

Toxoplasma gondii (T. gondii), an obligate intracellular parasite, is considered as an opportunistic infection and causes toxoplasmosis in humans and animals. Congenital toxoplasmosis can influence pregnancy and cause mild to severe consequences for the fetal and neonatal. During early T. gondii infection, neutrophils as the most abundant white blood cells provide a front line of defense mechanism against infection. The activated dendritic cells are then responsible for initiating an inflammatory response via T-helper 1 (Th1) cells. As part of its robust immune response, the infected host cells produce interferon (IFN-γ). IFN-γ inhibits T. gondii replication and promotes its transformation from an active form to tissue cysts. Although anti- T. gondii antibodies play an important role in infection control, T-helper 2 (Th2) immune response, can facilitate the growth and proliferation of T. gondii in the host cell. In pregnant women infected with T. gondii, the expression of cytokines may vary and in response diverse outcomes are expected. Cytokine profiles serve as valuable indicators for estimating the patho-immunological effects of T. gondii infection. This demonstrates the intricate relationship between pro-inflammatory and anti-inflammatory cytokines, as well as their influence on the various pregnancy outcomes in T. gondii infection.

The neuropeptide PACAP alleviates T. gondii infection-induced neuroinflammation and neuronal impairment

Background

Cerebral infection with the protozoan Toxoplasma gondii (T. gondii) is responsible for inflammation of the central nervous system (CNS) contributing to subtle neuronal alterations. Albeit essential for brain parasite control, continuous microglia activation and recruitment of peripheral immune cells entail distinct neuronal impairment upon infection-induced neuroinflammation. PACAP is an endogenous neuropeptide known to inhibit inflammation and promote neuronal survival. Since PACAP is actively transported into the CNS, we aimed to assess the impact of PACAP on the T. gondii-induced neuroinflammation and subsequent effects on neuronal homeostasis.

Methods

Exogenous PACAP was administered intraperitoneally in the chronic stage of T. gondii infection, and brains were isolated for histopathological analysis and determination of pathogen levels. Immune cells from the brain, blood, and spleen were analyzed by flow cytometry, and the further production of inflammatory mediators was investigated by intracellular protein staining as well as expression levels by RT-qPCR. Neuronal and synaptic alterations were assessed on the transcriptional and protein level, focusing on neurotrophins, neurotrophin-receptors and signature synaptic markers.

Results

Here, we reveal that PACAP administration reduced the inflammatory foci and the number of apoptotic cells in the brain parenchyma and restrained the activation of microglia and recruitment of monocytes. The neuropeptide reduced the expression of inflammatory mediators such as IFN-γ, IL-6, iNOS, and IL-1β. Moreover, PACAP diminished IFN-γ production by recruited CD4⁺ T cells in the CNS. Importantly, PACAP promoted neuronal health via increased expression of the neurotrophin BDNF and reduction of p75^NTR, a receptor related to neuronal cell death. In addition, PACAP administration was associated with increased expression of transporters involved in glutamatergic and GABAergic signaling that are particularly affected during cerebral toxoplasmosis.

Conclusions

Together, our findings unravel the beneficial effects of exogenous PACAP treatment upon infection-induced neuroinflammation, highlighting the potential implication of neuropeptides to promote neuronal survival and minimize synaptic prejudice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02639-z.

Neuroimmunology of Common Parasitic Infections in Africa

Parasitic infections of the central nervous system are an important cause of morbidity and mortality in Africa. The neurological, cognitive, and psychiatric sequelae of these infections result from a complex interplay between the parasites and the host inflammatory response. Here we review some of the diseases caused by selected parasitic organisms known to infect the nervous system including Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei spp., and Taenia solium species. For each parasite, we describe the geographical distribution, prevalence, life cycle, and typical clinical symptoms of infection and pathogenesis. We pay particular attention to how the parasites infect the brain and the interaction between each organism and the host immune system. We describe how an understanding of these processes may guide optimal diagnostic and therapeutic strategies to treat these disorders. Finally, we highlight current gaps in our understanding of disease pathophysiology and call for increased interrogation of these often-neglected disorders of the nervous system.

Morphological and biochemical repercussions of Toxoplasma gondii infection in a 3D human brain neurospheres model

Background

Toxoplasmosis is caused by the parasite Toxoplasma gondii that can infect the central nervous system (CNS), promoting neuroinflammation, neuronal loss, neurotransmitter imbalance and behavioral alterations. T. gondii infection is also related to neuropsychiatric disorders such as schizophrenia. The pathogenicity and inflammatory response in rodents are different to the case of humans, compromising the correlation between the behavioral alterations and physiological modifications observed in the disease. In the present work we used BrainSpheres, a 3D CNS model derived from human pluripotent stem cells (iPSC), to investigate the morphological and biochemical repercussions of T. gondii infection in human neural cells.

Methods

We evaluated T. gondii ME49 strain proliferation and cyst formation in both 2D cultured human neural cells and BrainSpheres. Aspects of cell morphology, ultrastructure, viability, gene expression of neural phenotype markers, as well as secretion of inflammatory mediators were evaluated for 2 and 4 weeks post infection in BrainSpheres.

Results

T. gondii can infect BrainSpheres, proliferating and inducing cysts formation, neural cell death, alteration in neural gene expression and triggering the release of several inflammatory mediators.

Conclusions

BrainSpheres reproduce many aspects of T. gondii infection in human CNS, constituting a useful model to study the neurotoxicity and neuroinflammation mediated by the parasite. In addition, these data could be important for future studies aiming at better understanding possible correlations between psychiatric disorders and human CNS infection with T. gondii.

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T. gondii infects, proliferates and induce cysts formation in neurospheres.

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T. gondii infection induces neural cell death in neurospheres.

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T. gondii infection promotes alteration in neural gene expression in neurospheres.

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T. gondii infection promotes release of inflammatory mediators in neurospheres.

Microglia and astrocyte responses to neuropathogenic protozoan parasites

Cerebral toxoplasmosis and cerebral malaria are two important neurological diseases caused by protozoan parasites. In this review, we discuss recent findings regarding the innate immune responses of microglia and astrocytes to Toxoplasma and Plasmodium infection. In both infections, these tissue-resident glial cells perform a sentinel function mediated by alarmin crosstalk that licenses adaptive type 1 immunity in the central nervous system. Divergent protective or pathogenic effects of type 1 activation of these astrocytes and microglia are revealed depending on the inherent lytic potential of the protozoan parasite.

Hypericum perforatum extract and hyperforin inhibit the growth of neurotropic parasite Toxoplasma gondii and infection-induced inflammatory responses of glial cells in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Hypericum perforatum L. has been widely used as a natural antidepressant. However, it is unknown whether it is effective in treating infection-induced neuropsychiatric disorders.

AIM OF THE STUDY

In order to evaluate the effectiveness of H. perforatum against infection with neurotropic parasite Toxoplasma gondii, which has been linked to neuropsychiatric disorders, this study investigated the anti-Toxoplasma activity using in vitro models.

MATERIALS AND METHODS

Dried alcoholic extracts were prepared from three Hypericum species: H. perforatum, H. erectum, and H. ascyron. H. perforatum extract was further separated by solvent-partitioning. Hyperforin and hypericin levels in the extracts and fractions were analyzed by high resolution LC-MS. Anti-Toxoplasma activities were tested in vitro, using cell lines (Vero and Raw264), murine primary mixed glia, and primary neuron-glia. Toxoplasma proliferation and stage conversion were analyzed by qPCR. Infection-induced damages to the host cells were analyzed by Sulforhodamine B cytotoxicity assay (Vero) and immunofluorescent microscopy (neurons). Infection-induced inflammatory responses in glial cells were analysed by qPCR and immunofluorescent microscopy.

RESULTS

Hyperforin was identified only in H. perforatum among the three tested species, whereas hypericin was present in H. perforatum and H. erectum. H. perforatum extract and hyperforin-enriched fraction, as well as hyperforin, exhibited significant anti-Toxoplasma property as well as inhibitory activity against infection-induced inflammatory responses in glial cells. In addition, H. perforatum-derived hyperforin-enriched fraction restored neuro-supportive environment in mixed neuron-glia culture.

CONCLUSIONS

H. perforatum and its major constituent hyperforin are promising anti-Toxoplasma agents that could potentially protect neurons and glial cells against infection-induced damages. Further study is warranted to establish in vivo efficacy.

The Parasites Caught In-Action: Imaging at the Host-Parasite Interface

For many decades, scientists were unable to expose the invisible existence of the parasites in their living hosts, except by scarification and then dissection of the animal model. This process just demonstrates a dead parasite in a dead host. Using this approach, very limited information can be obtained concerning the dynamics of infection and the pathways utilized by the parasite to survive within a hostile host's environment. Introduction of ultra-high-speed imaging techniques, with a time domain of barely few microseconds or even less, has revolutionized the "in vivo dissection" of the parasites. Such methods provide platforms for imaging host-parasite interactions at diverse scales, down to the molecular level. These have complementary advantages and relative assets in investigating host-parasite interactions. Therefore, better elucidation of such interaction may require the usage of more than one approach. Precise in vivo quantification, of the parasite load within the host, and better insight into the kinetics of infection are the two main advantages of the novel imaging procedures. However, imaging parasite-host interplay is still a challenging approach due to many constraints related to the parasite biology, the tissue environment within which the parasites exist, and the logistic technical limitations. This review was planned to assist better understanding of how much the new imaging techniques impacted the recent advances in parasite biology, especially the immunobiology of protozoan parasites.

Human Neural Stem Cell Systems to Explore Pathogen-Related Neurodevelopmental and Neurodegenerative Disorders

Building and functioning of the human brain requires the precise orchestration and execution of myriad molecular and cellular processes, across a multitude of cell types and over an extended period of time. Dysregulation of these processes affects structure and function of the brain and can lead to neurodevelopmental, neurological, or psychiatric disorders. Multiple environmental stimuli affect neural stem cells (NSCs) at several levels, thus impairing the normal human neurodevelopmental program. In this review article, we will delineate the main mechanisms of infection adopted by several neurotropic pathogens, and the selective NSC vulnerability. In particular, TORCH agents, i.e., Toxoplasma gondii, others (including Zika virus and Coxsackie virus), Rubella virus, Cytomegalovirus, and Herpes simplex virus, will be considered for their devastating effects on NSC self-renewal with the consequent neural progenitor depletion, the cellular substrate of microcephaly. Moreover, new evidence suggests that some of these agents may also affect the NSC progeny, producing long-term effects in the neuronal lineage. This is evident in the paradigmatic example of the neurodegeneration occurring in Alzheimer's disease.

Gasdermin-D-dependent IL-1α release from microglia promotes protective immunity during chronic Toxoplasma gondii infection

Microglia, resident immune cells of the CNS, are thought to defend against infections. Toxoplasma gondii is an opportunistic infection that can cause severe neurological disease. Here we report that during T. gondii infection a strong NF-κB and inflammatory cytokine transcriptional signature is overrepresented in blood-derived macrophages versus microglia. Interestingly, IL-1α is enriched in microglia and IL-1β in macrophages. We find that mice lacking IL-1R1 or IL-1α, but not IL-1β, have impaired parasite control and immune cell infiltration within the brain. Further, we show that microglia, not peripheral myeloid cells, release IL-1α ex vivo. Finally, we show that ex vivo IL-1α release is gasdermin-D dependent, and that gasdermin-D and caspase-1/11 deficient mice show deficits in brain inflammation and parasite control. These results demonstrate that microglia and macrophages are differently equipped to propagate inflammation, and that in chronic T. gondii infection, microglia can release the alarmin IL-1α, promoting neuroinflammation and parasite control.

Control over T. gondii infection in the brain involves microglial cells, but how these cells execute this control is not clear. Here the authors show that unlike IL-1β dominant macrophages, microglia are primed for gasdermin-D-dependent IL-1α production that is critical for protection against T. gondii infection.

Besnoitia besnoiti-driven endothelial host cell cycle alteration

Besnoitia besnoiti is an important obligate intracellular parasite of cattle which primarily infects host endothelial cells of blood vessels during the acute phase of infection. Similar to the closely related parasite Toxoplasma gondii, B. besnoiti has fast proliferating properties leading to rapid host cell lysis within 24–30 h p.i. in vitro. Some apicomplexan parasites were demonstrated to modulate the host cellular cell cycle to successfully perform their intracellular development. As such, we recently demonstrated that T. gondii tachyzoites induce G2/M arrest accompanied by chromosome missegregation, cell spindle alteration, formation of supernumerary centrosomes, and cytokinesis impairment when infecting primary bovine umbilical vein endothelial cells (BUVEC). Here, we follow a comparative approach by using the same host endothelial cell system for B. besnoiti infections. The current data showed that—in terms of host cell cycle modulation—infections of BUVEC by B. besnoiti tachyzoites indeed differ significantly from those by T. gondii. As such, cyclin expression patterns demonstrated a significant upregulation of cyclin E1 in B. besnoiti–infected BUVEC, thereby indicating parasite-driven host cell stasis at G1-to-S phase transition. In line, the mitotic phase of host cell cycle was not influenced since alterations of chromosome segregation, mitotic spindle formation, and cytokinesis were not observed. In contrast to respective T. gondii–related data, we furthermore found a significant upregulation of histone H3 (S10) phosphorylation in B. besnoiti–infected BUVEC, thereby indicating enhanced chromosome condensation to occur in these cells. In line to altered G1/S-transition, we here additionally showed that subcellular abundance of proliferating cell nuclear antigen (PCNA), a marker for G1 and S phase sub-stages, was affected by B. besnoiti since infected cells showed increased nuclear PCNA levels when compared with that of control cells.

Latent toxoplasmosis and psychiatric symptoms - A role of tryptophan metabolism?

Toxoplasma gondii (TOX) is a common parasite which infects approximately one third of the human population. In recent years, it has been suggested that latent toxoplasmosis may be a risk factor for the development of mental disorders, particularly schizophrenia and anxiety. With regards to depression the results have been varied. The main objective of this study was to examine subpopulations from the Danish PRISME and GENDEP populations for TOX IgG antibodies. These consisted of: a group with symptoms of anxiety, a group suffering from burnout syndrome, as well as two different subpopulations with depression of differing severity. The secondary objective of this study was to examine whether tryptophan metabolism was altered in TOX-positive subjects within each subpopulation. Our results show that the anxiety and burnout populations were more likely to be TOX IgG seropositive. Furthermore, we find that the moderate-severe but not mild-moderate depressive subpopulation were associated with TOX seropositivety, suggesting a possible role of symptom severity. Additionally, we found that TOX positive subjects in the anxiety and burnout subpopulations had altered tryptophan metabolism. This relationship did not exist in the mild-moderate depressive subpopulation. These results suggest that TOX seropositivity may be related to anxiety, burnout and potentially to severity of depression. We furthermore show that the psychiatric symptoms could be associated with an altered tryptophan metabolism.

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.

Latent toxoplasmosis aggravates anxiety- and depressive-like behaviour and suggest a role of gene-environment interactions in the behavioural response to the parasite

Toxoplasma gondii (TOX) is an intracellular parasite which infects warm-blooded animals including humans. An increasing number of clinical studies now hypothesize that latent toxoplasmosis may be a risk factor for the development of psychiatric disease. For depression, the results have been varied and we speculate that genetic background is important for the response to latent toxoplasmosis. The main objective of this study was to elucidate gene - environment interactions in the behavioural response to TOX infection by use of genetically vulnerable animals (Flinders sensitive line, FSL) compared to control animals (Flinders resistant line, FRL). Our results show that all infected animals displayed increased anxiety-like behaviour whereas only genetically vulnerable animals (FSL rats) showed depressive-like behaviour as a consequence of the TOX infection. Furthermore, peripheral cytokine expression was increased following the infection, primarily independent of strain. In the given study 14 cytokines, chemokines, metabolic hormones, and growth factors were quantified with the bead-based Luminex200 system, however, only IL-1α expression was affected differently in FSL animals compared to FRL rats. These results suggest that latent TOX infection can induce anxiety-like behaviour independent of genetic background. Intriguingly, we also report that for depressive-like behaviour only the vulnerable rat strain is affected. This could explain the discrepancy in the literature as to whether TOX infection is a risk factor for depressive symptomatology. We propose that the low grade inflammation caused by the chronic infection is related to the development of behavioural symptoms.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Galectin-3 and Galectin-9 May Differently Regulate the Expressions of Microglial M1/M2 Markers and T Helper 1/Th2 Cytokines in the Brains of Genetically Susceptible C57BL/6 and Resistant BALB/c Mice Following Peroral Infection With Toxoplasma gondii

Toxoplasmic encephalitis (TE), an opportunistic infection, is a severe health problem in immunocompromised patients. Previous studies have revealed that C57BL/6 mice are susceptible and BALB/c mice are resistant to TE. To investigate the mechanisms involved in the immunopathogenesis of TE in susceptible C57BL/6 and resistant BALB/c mice, both strains of mice were perorally infected with the Prugniuad (Pru) strain of Toxoplasma gondii. Our results showed that compared with BALB/c mice, C57BL/6 mice infected with T. gondii Pru strain had more severe brain histopathological damage, and higher mRNA expression levels of tachyzoite-specific surface antigen 1, bradyzoite-specific antigen 1, interferon gamma (IFNγ), interleukin (IL)-10, arginase1 (Arg1) (M2 marker), galectin (Gal)-3, Gal-9, T. gondii microneme protein 1 (TgMIC1), TgMIC4, and TgMIC6 during the course of infection by using quantitative real-time reverse transcription-polymerase chain reaction. Further analysis displayed that BALB/c mice showed higher numbers of microglial cells and higher levels of IL-1β, inducible nitric oxide synthase (iNOS) (M1 marker), and chitinase-3-like protein 3 (Ym1) (M2 marker) in the early infective stage [at day 14 or 35 post infection (p.i.)] compared with C57BL/6 mice, whereas C57BL/6 mice showed higher numbers of microglial cells and higher levels of IL-10, iNOS (M1 marker), and Ym1 (M2 marker) at days 35, 50, or 70 p.i. compared with BALB/c mice. Correlation analysis showed that significant positive correlations existed between Gal-3 and IL-4/IL-10/iNOS/Ym1 and between Gal-9 and IL-4/Ym1 in C57BL/6 mice; between Gal-3 and IFNγ/Arg1 and between Gal-9 and IFNγ/Arg1 in BALB/c mice. Together, our data demonstrated that different Gal-3 and Gal-9 expressions as well as different positive correlations were found between Gal-3 and T helper 1 (Th1)/Th2/M1/M2 cytokines or between Gal-9 and Th1/Th2/M2 cytokines in the brains of T. gondii Pru strain-infected C57BL/6 and BALB/c mice.

Stimulation of IL-1β and IL-6 through NF-κB and sonic hedgehog-dependent pathways in mouse astrocytes by excretory/secretory products of fifth-stage larval Angiostrongylus cantonensis

BACKGROUND

Angiostrongylus cantonensis is an important causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. Previous studies have shown that the Sonic hedgehog (Shh) signaling pathway may reduce cell apoptosis by inhibiting oxidative stress in A. cantonensis infection. In this study, we investigated the relationship between cytokine secretion and Shh pathway activation after treatment with excretory/secretory products (ESP) of fifth-stage larval A. cantonensis (L5).

RESULTS

The results showed that IL-1β and IL-6 levels in mouse astrocytes were increased. Moreover, ESP stimulated the protein expression of Shh pathway molecules, including Shh, Ptch, Smo and Gli-1, and induced IL-1β and IL-6 secretion. The transcription factor nuclear factor-κB (NF-κB) plays an important role in inflammation, and it regulates the expression of proinflammatory genes, including cytokines and chemokines, such as IL-1β and TNF-α. After ESP treatment, NF-κB induced IL-1β and IL-6 secretion in astrocytes by activating the Shh signaling pathway.

CONCLUSIONS

Overall, the data presented in this study showed that ESP of fifth-stage larval A. cantonensis stimulates astrocyte activation and cytokine generation through NF-κB and the Shh signaling pathway.

Using blood cytokine measures to define high inflammatory biotype of schizophrenia and schizoaffective disorder

Background

Increases in pro-inflammatory cytokines are found in the brain and blood of people with schizophrenia. However, increased cytokines are not evident in all people with schizophrenia, but are found in a subset. The cytokine changes that best define this subset, termed the “elevated inflammatory biotype”, are still being identified.

Methods

Using quantitative RT-PCR, we measured five cytokine mRNAs (IL-1β, IL-2 IL-6, IL-8 and IL-18) from peripheral blood of healthy controls and of people with schizophrenia or schizoaffective disorder (n = 165). We used a cluster analysis of the transcript levels to define those with low and those with elevated levels of cytokine expression. From the same cohort, eight cytokine proteins (IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12, IFNγ and TNFα) were measured in serum and plasma using a Luminex Magpix-based assay. We compared peripheral mRNA and protein levels across diagnostic groups and between those with low and elevated levels of cytokine expression according to our transcription-based cluster analysis.

Results

We found an overall decrease in the anti-inflammatory IL-2 mRNA (p = 0.006) and an increase in three serum cytokines, IL-6 (p = 0.010), IL-8 (p = 0.024) and TNFα (p < 0.001) in people with schizophrenia compared to healthy controls. A greater percentage of people with schizophrenia (48%) were categorised into the elevated inflammatory biotype compared to healthy controls (33%). The magnitude of increase in IL-1β, IL-6, IL-8 and IL-10 mRNAs in people in the elevated inflammation biotype ranged from 100 to 220% of those in the non-elevated inflammatory biotype and was comparable between control and schizophrenia groups. Blood cytokine protein levels did not correlate with cytokine mRNA levels, and plasma levels of only two cytokines distinguished the elevated and low inflammatory biotypes, with IL-1β significantly increased in the elevated cytokine control group and IL-8 significantly increased in the elevated cytokine schizophrenia group.

Conclusions

Our results confirm that individuals with schizophrenia are more likely to have elevated levels of inflammation compared to controls. We suggest that efforts to define inflammatory status based on peripheral measures need to consider both mRNA and protein measures as each have distinct advantages and disadvantages and can yield different results.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0962-y) contains supplementary material, which is available to authorized users.

Nitric oxide and cytokine production by glial cells exposed in vitro to neuropathogenic schistosome Trichobilharzia regenti

Background

Helminth neuroinfections represent a serious health problem, but host immune mechanisms in the nervous tissue often remain undiscovered. This study aims at in vitro characterization of the response of murine astrocytes and microglia exposed to Trichobilharzia regenti which is a neuropathogenic schistosome migrating through the central nervous system of vertebrate hosts. Trichobilharzia regenti infects birds and mammals in which it may cause severe neuromotor impairment. This study was focused on astrocytes and microglia as these are immunocompetent cells of the nervous tissue and their activation was recently observed in T. regenti-infected mice.

Results

Primary astrocytes and microglia were exposed to several stimulants of T. regenti origin. Living schistosomulum-like stages caused increased secretion of IL-6 in astrocyte cultures, but no changes in nitric oxide (NO) production were noticed. Nevertheless, elevated parasite mortality was observed in these cultures. Soluble fraction of the homogenate from schistosomulum-like stages stimulated NO production by both astrocytes and microglia, and IL-6 and TNF-α secretion in astrocyte cultures. Similarly, recombinant cathepsins B1.1 and B2 triggered IL-6 and TNF-α release in astrocyte and microglia cultures, and NO production in astrocyte cultures. Stimulants had no effect on production of anti-inflammatory cytokines IL-10 or TGF-β1.

Conclusions

Both astrocytes and microglia are capable of production of NO and proinflammatory cytokines IL-6 and TNF-α following in vitro exposure to various stimulants of T. regenti origin. Astrocytes might be involved in triggering the tissue inflammation in the early phase of T. regenti infection and are proposed to participate in destruction of migrating schistosomula. However, NO is not the major factor responsible for parasite damage. Both astrocytes and microglia can be responsible for the nervous tissue pathology and maintaining the ongoing inflammation since they are a source of NO and proinflammatory cytokines which are released after exposure to parasite antigens.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1869-7) contains supplementary material, which is available to authorized users.

Besnoitia besnoiti infections activate primary bovine endothelial cells and promote PMN adhesion and NET formation under physiological flow condition

Besnoitia besnoiti is an obligate intracellular and emerging coccidian parasite of cattle that mainly infects host endothelial cells during acute infection. We here analyzed early innate immune reactions of B. besnoiti-infected primary bovine umbilical vein endothelial cells (BUVEC). B. besnoiti infections significantly activated BUVEC since the gene transcripts of several adhesion molecules (P-selectin, intercellular adhesion molecule 1(ICAM-1)), chemokines (CXCL1, CXCL8, CCL5), and of COX-2 were significantly upregulated during in vitro infection. Overall, the highest upregulation of most transcripts was observed at 24 or 48 h post infection (p.i.). Enhanced adhesion molecule expression in infected host cells was confirmed by PMN adhesion assays being performed under physiological flow conditions revealing a significantly increased PMN adhesion on B. besnoiti-infected BUVEC layers at 24 h p.i. Furthermore, we were able to illustrate neutrophil extracellular traps (NETs) being released by PMN under physiological flow conditions after adhesion to B. besnoiti-infected BUVEC layers. The present study shows that B. besnoiti infections of primary BUVEC induce a cascade of pro-inflammatory reactions and triggers early innate immune responses.

An aspartyl protease defines a novel pathway for export of Toxoplasma proteins into the host cell

Infection by Toxoplasma gondii leads to massive changes to the host cell. Here, we identify a novel host cell effector export pathway that requires the Golgi-resident aspartyl protease 5 (ASP5). We demonstrate that ASP5 cleaves a highly constrained amino acid motif that has similarity to the PEXEL-motif of Plasmodium parasites. We show that ASP5 matures substrates at both the N- and C-terminal ends of proteins and also controls trafficking of effectors without this motif. Furthermore, ASP5 controls establishment of the nanotubular network and is required for the efficient recruitment of host mitochondria to the vacuole. Assessment of host gene expression reveals that the ASP5-dependent pathway influences thousands of the transcriptional changes that Toxoplasma imparts on its host cell. All these changes result in attenuation of virulence of Δasp5 tachyzoites in vivo. This work characterizes the first identified machinery required for export of Toxoplasma effectors into the infected host cell.

Transcriptomic analysis of global changes in cytokine expression in mouse spleens following acute Toxoplasma gondii infection

Toxoplasma gondii is a global pathogen that infects a wide range of animals and humans. During T. gondii infection, the spleen plays an important role in coordinating the adaptive and innate immune responses. However, there is little information regarding the changes in global gene expression within the spleen following T. gondii infection. To address this gap in knowledge, we examined the transcriptome of the mouse spleen following T. gondii infection. We observed differential expression of 2310 transcripts under these conditions. Analysis of KEGG and GO enrichment indicated that T. gondii alters multiple immune signaling cascades. Most of differentially expressed GO terms and pathways were downregulated, while immune-related GO terms and pathways were upregulated with response to T. gondii infection in mouse spleen. Most cytokines were upregulated in infected spleens, and all differentially expressed chemokines were upregulated which enhanced the immune cells chemotaxis to promote recruitment of immune cells, such as neutrophils, eosinophils, monocytes, dendritic cells, macrophages, NK cells, basophils, B cells, and T cells. Although IFN-γ-induced IDO (Ido1) was upregulated in the present study, it may not contribute a lot to the control of T. gondii because most differentially expressed genes involved in tryptophan metabolism pathway were downregulated. Innate immunity pathways, including cytosolic nucleic acid sensing pathway and C-type lectins-Syk-Card9 signaling pathways, were upregulated. We believe our study is the first comprehensive attempt to define the host transcriptional response to T. gondii infection in the mouse spleen.

Global Metabolomic Profiling of Mice Brains following Experimental Infection with the Cyst-Forming Toxoplasma gondii

The interplay between the Apicomplexan parasite Toxoplasma gondii and its host has been largely studied. However, molecular changes at the metabolic level in the host central nervous system and pathogenesis-associated metabolites during brain infection are largely unexplored. We used a global metabolomics strategy to identify differentially regulated metabolites and affected metabolic pathways in BALB/c mice during infection with T. gondii Pru strain at 7, 14 and 21 days post-infection (DPI). The non-targeted Liquid Chromatography-Mass Spectrometry (LC-MS) metabolomics analysis detected approximately 2,755 retention time-exact mass pairs, of which more than 60 had significantly differential profiles at different stages of infection. These include amino acids, organic acids, carbohydrates, fatty acids, and vitamins. The biological significance of these metabolites is discussed. Principal Component Analysis and Orthogonal Partial Least Square-Discriminant Analysis showed the metabolites' profile to change over time with the most significant changes occurring at 14 DPI. Correlated metabolic pathway imbalances were observed in carbohydrate metabolism, lipid metabolism, energetic metabolism and fatty acid oxidation. Eight metabolites correlated with the physical recovery from infection-caused illness were identified. These findings indicate that global metabolomics adopted in this study is a sensitive approach for detecting metabolic alterations in T. gondii-infected mice and generated a comparative metabolic profile of brain tissue distinguishing infected from non-infected host.

Nitric oxide production increases during Toxoplasma gondii encephalitis in mice

Toxoplasma gondii is an intracellular parasite with the potential of causing severe encephalitis among immunocompromised human and animals. The aim of this experimental study was to investigate the immunomodulatory and immunopathological role of nitric oxide (NO) in central nervous systems and to identify any correlation between toxoplasmosis neuropathology and investigate the consequences of the cellular responses protect against T. gondii. Mice were infected with ME49 strain T. gondii and levels of endothelial, neuronal and inducible nitric oxide synthase (eNOS, nNOS, iNOS), glial fibrillary acidic protein (GFAP) and neurofilament (NF) were examined in brain tissues by immunohistochemistry, during the development and establishment of a chronic infection at 10 30 and 60 days post infection. Results of the study revealed that the levels of eNOS (p < 0.05), nNOS (p < 0.05), iNOS (p < 0.005), GFAP (p < 0.005) and NF (p < 0.005) were remarkably higher in T. gondii-infected mice than in uninfected control. The most prominent finding from our study was 10 and 30 days after inoculation data indicating that increased levels of NO not only a potential neuroprotective role for immunoregulatory and immunopathological but also might be a molecular trigger of bradyzoite development. Furthermore, this findings were shown that high expressed NO origin was not only inducible nitric oxide synthase but also endothelial and neuronal. We demonstrated that activation of astrocytes and microglia/macrophages is a significant event in toxoplasma encephalitis (TE). The results also clearly indicated that increased levels of NO might contribute to neuropathology related with TE. Furthermore, expression of NF might gives an idea of the progress and critical for diagnostic significance of this disease.

Suitable in vitro culture of Eimeria bovis meront II stages in bovine colonic epithelial cells and parasite-induced upregulation of CXCL10 and GM-CSF gene transcription

We here established a suitable in vitro cell culture system based on bovine colonic epithelial cells (BCEC) for the development of Eimeria bovis merozoites I and the characterization of early parasite-induced innate epithelial host cell reactions as gene transcription of proinflammatory molecules. Both primary and permanent BCEC (BCEC (rim) and BCEC(perm)) were suitable for E. bovis merozoite I invasion and subsequent development of meronts II leading to the release of viable merozoites II. E. bovis merozoite II failed to develop any further neither into gamont nor oocyst stages in BCEC in vitro. E. bovis merozoite I induced innate epithelial host cell reactions at the level of CXC/CCL chemokines (CXCL1, CXCL8, CXCL10, CCL2), IL-6, and GM-CSF gene transcription. Overall, both BCEC types were activated by merozoite I infections since they showed significantly enhanced gene transcript levels of the immunomodulatory molecules CXCL10 and GM-CSF. However, gene transcription profiles of BCEC(prim) and BCEC(perm) revealed different reaction patterns in response to merozoite I infection with regard to quality and kinetics of chemokine/cytokine gene transcription. Although both BCEC types equally showed most prominent responses for CXCL10 and GM-CSF, the induction of CXCL1, CXCL8, CCL2, and IL-6 gene transcripts varied qualitatively and quantitatively. Our results demonstrate that BCEC seem capable to respond to E. bovis merozoite I infection by the upregulation of CXCL10 and GM-CSF gene transcription and therefore probably contribute to host innate effector mechanisms against E. bovis.

Toxoplasma gondii-induced neuronal alterations

The zoonotic pathogen Toxoplasma gondii infects over 30% of the human population. The intracellular parasite can persist lifelong in the CNS within neurons modifying their function and structure, thus leading to specific behavioural changes of the host. In recent years, several in vitro studies and murine models have focused on the elucidation of these modifications. Furthermore, investigations of the human population have correlated Toxoplasma seropositivity with changes in neurological functions; however, the complex underlying mechanisms of the subtle behavioural alteration are still not fully understood. The parasites are able to induce direct modifications in the infected cells, for example by altering dopamine metabolism, by functionally silencing neurons as well as by hindering apoptosis. Moreover, indirect effects of the peripheral immune system and alterations of the immune status of the CNS, observed during chronic infection, might also contribute to changes in neuronal connectivity and synaptic plasticity. In this review, we will provide an overview and highlight recent advances, which describe changes in the neuronal function and morphology upon T. gondii infection.

Persistence of Toxoplasma gondii in the central nervous system: a fine-tuned balance between the parasite, the brain and the immune system

Upon infection of humans and animals with Toxoplasma gondii, the parasites persist as intraneuronal cysts that are controlled, but not eliminated by the immune system. In particular, intracerebral T cells are crucial in the control of T. gondii infection and are supported by essential functions from other leukocyte populations. Additionally, brain-resident cells including astrocytes, microglia and neurons contribute to the intracerebral immune response by the production of cytokines, chemokines and expression of immunoregulatory cell surface molecules, such as major histocompatibility (MHC) antigens. However, the in vivo behaviour of these individual cell populations, specifically their interaction during cerebral toxoplasmosis, remains to be elucidated. We discuss here what is known about the function of T cells, recruited myeloid cells and brain-resident cells, with particular emphasis on the potential cross-regulation of these cell populations, in governing cerebral toxoplasmosis.

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.

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.

Possible link between Toxoplasma gondii and the anosmia associated with neurodegenerative diseases

Toxoplasma gondii is an intracellular protozoan infecting 30% to 50% of global human population. Recently, it was suggested that chronic latent neuroinflammation caused by the parasite may be responsible for the development of several neurodegenerative diseases manifesting with the loss of smell. Studies in animals inoculated with the parasite revealed cysts in various regions of the brain, including olfactory bulb. Development of behavioral changes was paralleled by the preferential persistence of cysts in defined anatomic structures of the brain, depending on the host, strain of the parasite, its virulence, and route of inoculation. Olfactory dysfunction reported in Alzheimer's disease, multiple sclerosis, and schizophrenia was frequently associated with the significantly increased serum anti-T gondii immunoglobulin G antibody levels. Damage of the olfactory system may be also at least in part responsible for the development of depression because T gondii infection worsened mood in such patients, and the olfactory bulbectomized rat serves as a model of depression.

Astrocytes, microglia/macrophages, and neurons expressing Toll-like receptor 11 contribute to innate immunity against encephalitic Toxoplasma gondii infection

Toll-like receptor 11 (TLR11) is a specific receptor for Toxoplasma gondii and uropathogenic Escherichia coli and has recently been identified in the mouse brain. In the present study, TLR11 gene expression was measured in the mouse brain by Real-time quantitative polymerase chain reaction (RT-PCR). Furthermore, the TLR11 protein expression profile was evaluated in neuroglia and neurons throughout the encephalitic period (10, 20, and 30days after inoculation) in mice with experimentally induced T. gondii infection. In the brains of experimental (n=21) and control (n=7) mice, TLR11, glial fibrillary acidic protein (GFAP), cd11b, NeuN, TLR11/GFAP+, TLR11/cd11b+, and TLR11/NeuN+ cells were investigated using either indirect single- or double-labeling immunoperoxidase staining. The results indicated that TLR11 gene expression increased during chronic toxoplasmic encephalitis, and there was a variable degree of TLR11 immunopositivity among cd11b+, GFAP+, and NeuN+ cells in the brain. On the tenth day of infection, there was a significant increase in TLR11 protein and gene expression, which remained stable during the later stages of infection. In this experimental model, TLR11 expression was induced in astrocytes, neurons, and microglia/macrophages during the immune response to T. gondii infection.

Inflammation and the two-hit hypothesis of schizophrenia

The high societal and individual cost of schizophrenia necessitates finding better, more effective treatment, diagnosis, and prevention strategies. One of the obstacles in this endeavor is the diverse set of etiologies that comprises schizophrenia. A substantial body of evidence has grown over the last few decades to suggest that schizophrenia is a heterogeneous syndrome with overlapping symptoms and etiologies. At the same time, an increasing number of clinical, epidemiological, and experimental studies have shown links between schizophrenia and inflammatory conditions. In this review, we analyze the literature on inflammation and schizophrenia, with a particular focus on comorbidity, biomarkers, and environmental insults. We then identify several mechanisms by which inflammation could influence the development of schizophrenia via the two-hit hypothesis. Lastly, we note the relevance of these findings to clinical applications in the diagnosis, prevention, and treatment of schizophrenia.

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.

Dark side illuminated: imaging of Toxoplasma gondii through the decades

In the more than 100 years since its discovery, our knowledge of Toxoplasma biology has improved enormously. The evolution of molecular biology, immunology and genomics has had profound influences on our understanding of this ubiquitous bug. However, it could be argued that in science today the adage "seeing is believing" has never been truer. Images are highly influential and in the time since the first description of T. gondii, advances in microscopy and imaging technology have been and continue to be dramatic. In this review we recount the discovery of T. gondii and the contribution of imaging techniques to elucidating its life cycle, biology and the immune response of its host.

Pro-inflammatory cytokines predominate in the brains of dogs with visceral leishmaniasis: a natural model of neuroinflammation during systemic parasitic infection

Visceral leishmaniasis is a multisystemic zoonotic disease that can manifest with several symptoms, including neurological disorders. To investigate the pathogenesis of brain alterations occurring during visceral leishmaniasis infection, the expression of the cytokines IL-1β, IL-6, IL-10, IL-12p40, IFN-γ, TGF-β and TNF-α and their correlations with peripheral parasite load were evaluated in the brains of dogs naturally infected with Leishmania infantum. IL-1β, IFN-γ and TNF-α were noticeably up-regulated, and IL-10, TGF-β and IL-12p40 were down-regulated in the brains of infected dogs. Expression levels did not correlate with parasite load suggestive that the brain alterations are due to the host's immune response regardless of the phase of the disease. These data indicate the presence of a pro-inflammatory status in the nervous milieu of dogs with visceral leishmaniasis especially because IL-1β and TNF-α are considered key factors for the initiation, maintenance and persistence of inflammation.

Immune response and immunopathology during toxoplasmosis

Toxoplasma gondii is a protozoan parasite of medical and veterinary significance that is able to infect any warm-blooded vertebrate host. In addition to its importance to public health, several inherent features of the biology of T. gondii have made it an important model organism to study host-pathogen interactions. One factor is the genetic tractability of the parasite, which allows studies on the microbial factors that affect virulence and allows the development of tools that facilitate immune studies. Additionally, mice are natural hosts for T. gondii, and the availability of numerous reagents to study the murine immune system makes this an ideal experimental system to understand the functions of cytokines and effector mechanisms involved in immunity to intracellular microorganisms. In this article, we will review current knowledge of the innate and adaptive immune responses required for resistance to toxoplasmosis, the events that lead to the development of immunopathology, and the natural regulatory mechanisms that limit excessive inflammation during this infection.

Toxoplasma gondii invasion and replication in astrocyte primary cultures and astrocytoma cell lines: systematic review of the literature

Toxoplasma gondii is a cosmopolitan protozoan which infects all homoeothermic species, including humans. This parasite may cause severe neurological problems in congenitally infected newborns or immunocompromised individuals, but it also provokes psychiatric and neurological disorders as well as behavioural and sensory deficit. There is controversy regarding the effect of T. gondii upon astrocytes, which may serve as parasite proliferation recipients or protective immune response activators within the central nervous system. This apparent contradiction could partially be due to the infection degree obtained in the different experiments reported. Thus, we decided to systematically review the in vitro models used to study these phenomena. Fifteen articles from which direct invasion and replication data could be gathered were found. Very heterogeneous results emerged, mainly due to diversity of models in relation to parasite strain (virulence), host species, parasite dose and evaluation times after infection. Also, the results were measured in diverse ways, i.e. some reported percent infected cells, while others informed parasites pervacuole or cell, or parasitic vacuoles per cell. Very few conclusions could be drawn, among them that human astrocytoma cell lines and mouse astrocytes seem more susceptible to infection and less resistant to tachyzoite proliferation than human primary culture astrocytes. The present study supports the need to reanalyse T. gondii astrocyte invasion and replication processes, especially with the use of actual technology, which allows detailed mechanistic studies.

Trimethoprim as adjuvant treatment in schizophrenia: a double-blind, randomized, placebo-controlled clinical trial

Various infectious agents, such as Toxoplasma gondii, have been hypothesized to be potentially relevant etiological factors in the onset of some cases of schizophrenia. We conducted a randomized, double-blind, placebo-controlled treatment trial in an attempt to explore the hypothesis that the symptoms of schizophrenia may be related to infection of the central nervous system with toxoplasma gondii. Systematically selected patients with ongoing and at least moderately severe schizophrenia from Butajira, in rural Ethiopia, were randomly allocated to trimethoprim or placebo, which were added on to participants' regular antipsychotic treatments. Trial treatments were given for 6 months. The Positive and Negative Syndrome Scale (PANSS) was used to assess outcome. Ninety-one patients were included in the study, with 80 cases (87.9%) positive for T. gondii immunoglobulin G antibody. Seventy-nine subjects (87.0%) completed the trial. The mean age of subjects was 35.3 (SD = 8.0) years, with a mean duration of illness of 13.2 (SD = 6.7) years. Both treatment groups showed significant reduction in the overall PANSS score with no significant between-group difference. In this sample of patients with chronic schizophrenia, trimethoprim used as adjuvant treatment is not superior to placebo. However, it is not possible to draw firm conclusion regarding the etiological role of toxoplasmosis on schizophrenia based on this study because the timing and the postulated mechanisms through which toxoplasmosis produces schizophrenia are variable.

Host Cell Preference of Toxoplasma gondii Cysts in Murine Brain: A Confocal Study

Toxoplasma gondii is a protozoan parasite that is widely prevalent in humans and typically results in a chronic infection characterized by cysts located predominantly in the central nervous system. In immunosuppressed hosts, such as patients with HIV infection, the infection can be reactivated from the cysts in the brain resulting in a severe and potentially fatal encephalitis. Studies suggest that the chronic infection may also have neuropathological and behavioral effects in immune competent hosts. An improved understanding of tissue cyst behavior is of importance for understanding both the reactivation as well as the neurophysiological consequences of chronic infection. In vivo studies have identified neurons as host cells for cysts but in vitro studies have found that astrocytes can also foster development of the cysts. In this study we have addressed the question of which neural cell tissue cysts of T. gondii reside during chronic infection using a mouse model. Mice were infected with Me49 Strain T. gondii and the intracellular localization of the cysts analyzed during the development and establishment of a chronic infection at 1, 2, and 6 months post infection. Brains were fixed, cryosectioned, and stained with FITC-Dolichos biflorans to identify the Toxoplasma cysts and they were labeled with cell specific antibodies to neurons or astrocytes and then analyzed using confocal fluorescence microscopy. Cysts were found to occur almost exclusively in neurons throughout chronic infection. No cysts were identified in astrocytes, using the astrocyte marker, GFAP. Astrocyte interactions with neuronal-cysts, however, were frequently observed.

Astrocyte gp130 expression is critical for the control of Toxoplasma encephalitis

Toxoplasma gondii infects astrocytes, neurons and microglia cells in the CNS and, after acute encephalitis, persists within neurons. Robust astrocyte activation is a hallmark of Toxoplasma encephalitis (TE); however, the in vivo function of astrocytes is largely unknown. To study their role in TE we generated C57BL/6 GFAP-Cre gp130(fl/fl) mice (where GFAP is glial fibrillary acid protein), which lack gp130, the signal-transducing receptor for IL-6 family cytokines, in their astrocytes. In the TE of wild-type mice, the gp130 ligands IL-6, IL-11, IL-27, LIF, oncostatin M, ciliary neurotrophic factor, B cell stimulating factor, and cardiotrophin-1 were up-regulated. In addition, GFAP(+) astrocytes of gp130(fl/fl) control mice were activated, increased in number, and efficiently restricted inflammatory lesions and parasites, thereby contributing to survival from TE. In contrast, T. gondii- infected GFAP-Cre gp130(fl/fl) mice lost GFAP(+) astrocytes in inflammatory lesions resulting in an inefficient containment of inflammatory lesions, impaired parasite control, and, ultimately, a lethal necrotizing TE. Production of IFN-gamma and the IFN-gamma-induced GTPase (IGTP), which mediate parasite control in astrocytes, was even increased in GFAP-Cre gp130(fl/fl) mice, indicating that instead of the direct antiparasitic effect the immunoregulatory function of GFAP-Cre gp130(fl/fl) astrocytes was disturbed. Correspondingly, in vitro infected GFAP-Cre gp130(fl/fl) astrocytes inhibited the growth of T. gondii efficiently after stimulation with IFN-gamma, whereas neighboring noninfected and TNF-stimulated GFAP-Cre gp130(fl/fl) astrocytes became apoptotic. Collectively, these are the first experiments demonstrating a crucial function of astrocytes in CNS infection.

Effects of Toxoplasma gondii infection on the brain

Toxoplasma gondii, an intracellular protozoan parasite, can infect humans in 3 different ways: ingestion of tissue cysts, ingestion of oocysts, or congenital infection with tachyzoites. After proliferation of tachyzoites in various organs during the acute stage, the parasite forms cysts preferentially in the brain and establishes a chronic infection, which is a balance between host immunity and the parasite's evasion of the immune response. A variety of brain cells, including astrocytes and neurons, can be infected. In vitro studies using non-brain cells have demonstrated profound effects of the infection on gene expression of host cells, including molecules that promote the immune response and those involved in signal transduction pathways, suggesting that similar effects could occur in infected brain cells. Interferon-gamma is the essential mediator of the immune response to control T. gondii in the brain and to maintain the latency of chronic infection. Infection also induces the production of a variety of cytokines by microglia, astrocytes, and neurons, which promote or suppress inflammatory responses. The strain (genotype) of T. gondii, genetic factors of the host, and probably the route of infection and the stage (tachyzoite, cyst, or oocyst) of the parasite initiating infection all contribute to the establishment of a balance between the host and the parasite and affect the outcome of the infection.

Effects of low dose GM-CSF on microglial inflammatory profiles to diverse pathogen-associated molecular patterns (PAMPs)

Background

It is well appreciated that obtaining sufficient numbers of primary microglia for in vitro experiments has always been a challenge for scientists studying the biological properties of these cells. Supplementing culture medium with granulocyte-macrophage colony-stimulating factor (GM-CSF) partially alleviates this problem by increasing microglial yield. However, GM-CSF has also been reported to transition microglia into a dendritic cell (DC)-like phenotype and consequently, affect their immune properties.

Methods

Although the concentration of GM-CSF used in our protocol for mouse microglial expansion (0.5 ng/ml) is at least 10-fold less compared to doses reported to affect microglial maturation and function (≥ 5 ng/ml), in this study we compared the responses of microglia derived from mixed glial cultures propagated in the presence/absence of low dose GM-CSF to establish whether this growth factor significantly altered the immune properties of microglia to diverse bacterial stimuli. These stimuli included the gram-positive pathogen Staphylococcus aureus (S. aureus) and its cell wall product peptidoglycan (PGN), a Toll-like receptor 2 (TLR2) agonist; the TLR3 ligand polyinosine-polycytidylic acid (polyI:C), a synthetic mimic of viral double-stranded RNA; lipopolysaccharide (LPS) a TLR4 agonist; and the TLR9 ligand CpG oligonucleotide (CpG-ODN), a synthetic form of bacteria/viral DNA.

Results

Interestingly, the relative numbers of microglia recovered from mixed glial cultures following the initial harvest were not influenced by GM-CSF. However, following the second and third collections of the same mixed cultures, the yield of microglia from GM-CSF-supplemented flasks was increased two-fold. Despite the ability of GM-CSF to expand microglial numbers, cells propagated in the presence/absence of GM-CSF demonstrated roughly equivalent responses following S. aureus and PGN stimulation. Specifically, the induction of tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2/CXCL2), and major histocompatibility complex (MHC) class II, CD80, CD86 expression by microglia in response to S. aureus were similar regardless of whether cells had been exposed to GM-CSF during the mixed culture period. In addition, microglial phagocytosis of intact bacteria was unaffected by GM-CSF. In contrast, upon S. aureus stimulation, CD40 expression was induced more prominently in microglia expanded in GM-CSF. Analysis of microglial responses to additional pathogen-associate molecular patterns (PAMPs) revealed that low dose GM-CSF did not significantly alter TNF-α or MIP-2 production in response to the TLR3 and TLR4 agonists polyI:C or LPS, respectively; however, cells expanded in the presence of GM-CSF produced lower levels of both mediators following CpG-ODN stimulation.

Conclusion

We demonstrate that low levels of GM-CSF are sufficient to expand microglial numbers without significantly affecting their immunological responses following activation of TLR2, TLR4 or TLR3 signaling. Therefore, low dose GM-CSF can be considered as a reliable method to achieve higher microglial yields without introducing dramatic activation artifacts.

Comparative analysis of cytokine gene expression in cerebrospinal fluid of horses without neurologic signs or with selected neurologic disorders

OBJECTIVE

To determine gene transcription for cytokines in nucleated cells in CSF of horses without neurologic signs or with cervical stenotic myelopathy (CSM), West Nile virus (WNV) encephalitis, equine protozoal myeloencephalitis (EPM), or spinal cord trauma.

ANIMALS

41 horses (no neurologic signs [n = 12], CSM [8], WNV encephalitis [9], EPM [6], and spinal cord trauma [6]).

PROCEDURES

Total RNA was extracted from nucleated cells and converted into cDNA. Gene expression was measured by use of real-time PCR assay and final quantitation via the comparative threshold cycle method.

RESULTS

Cytokine genes expressed by nucleated cells of horses without neurologic signs comprised a balance between proinflammatory tumor necrosis factor-alpha (TNF-alpha), anti-inflammatory cytokines (interleukin [IL]-10 and transforming growth factor [TGF]-beta), and Th1 mediators (interferon [IFN]-gamma). Cells of horses with CSM mainly expressed genes for TNF-alpha, TGF-beta, and IL-10. Cells of horses with WNV encephalitis mainly expressed genes for IL-6 and TGF-beta. Cells of horses with EPM mainly had expression of genes for IL-6, IL-8, IL-10, TNF-alpha, IFN-gamma, and TGF-beta. Cells from horses with spinal cord trauma had expression mainly for IL-6; IFN-gamma; TGF-beta; and less frequently, IL-2, IL-10, and TNF-alpha. Interleukin-8 gene expression was only detected in CSF of horses with infectious diseases.

CONCLUSIONS AND CLINICAL RELEVANCE

Despite the small number of CSF samples for each group, results suggest distinct gene signatures expressed by nucleated cells in the CSF of horses without neurologic signs versus horses with inflammatory or traumatic neurologic disorders.

Dynamics of transcription of immunomodulatory genes in endothelial cells infected with different coccidian parasites

Sporozoites of Eimeria bovis and tachyzoites of Neospora caninum and Toxoplasma gondii are able to invade and to replicate in endothelial cells. Here we report on responses of bovine umbilical vein endothelial cells (BUVEC) in vitro to these coccidial infections by determining mRNA levels of the CXC chemokines GRO-alpha, IL-8 and IP-10, the CC chemokines MCP-1 and RANTES and of GM-CSF, COX-2 and iNOS relative to the level of housekeeping gene (GAPDH) transcription. T. gondii and N. caninum tachyzoites caused profound transcriptional upregulation of all genes in question. In general, upregulation started 2-4 h p.i. and maximum transcript levels were observed 4 h p.i. GRO-alpha and IL-8 gene transcription had decreased to almost control levels by 12 h p.i.; in the case of the other chemokines enhanced transcript levels persisted longer or showed a biphasic time-course. A similar time-course to CC chemokines was observed for GM-CSF mRNA, whilst COX-2 gene transcript peaks were detected at 2-4 h p.i. and 48-72 h p.i. iNOS mRNA levels increased from 4 to 48 h p.i. In contrast, E. bovis sporozoites failed to induce the transcription of CXC chemokine genes and of COX-2, and only caused moderate transcription upregulation of the other genes considered. In conclusion, infections of BUVEC with these coccidian parasites result in host cell activation associated with enhanced transcription of genes encoding for proinflammatory and immunomodulatory molecules, which are important for innate immune reactions and the transition to adaptive immunity. Differences between E. bovis versus T. gondii and N. caninum may illustrate a particular evasion strategy of E. bovis sporozoites, which is related to their need to persist in the host cell for a long period of time and to the avoidance of inflammatory process-induction.

Murine glia express the immunosuppressive cytokine, interleukin-10, following exposure toBorrelia burgdorferi orNeisseria meningitidis

There is growing appreciation that resident glial cells can initiate and/or regulate inflammation following trauma or infection in the central nervous system (CNS). We have previously demonstrated the ability of microglia and astrocytes, resident glial cells of the CNS, to respond to bacterial pathogens by rapid production of inflammatory mediators. However, inflammation within the brain parenchyma is notably absent during some chronic bacterial infections in humans and nonhuman primates. In the present study, we demonstrate the ability of the immunosuppressive cytokine, interleukin-10 (IL-10), to inhibit inflammatory immune responses of primary microglia and astrocytes to B. burgdorferi and N. meningitidis, two disparate gram negative bacterial species that can cross the blood-brain barrier in humans. Importantly, we demonstrate that these organisms induce the delayed production of significant quantities of IL-10 by both microglia and astrocytes. Furthermore, we demonstrate that such production occurs independent of the actions of bacterial lipopolysaccharide and is secondary to the autocrine or paracrine actions of other glia-derived soluble mediators. The late onset of IL-10 production by resident glia following activation, the previously documented expression of specific receptors for this cytokine on microglia and astrocytes, and the ability of IL-10 to inhibit bacterially induced immune responses by these cells, suggest a mechanism by which resident glial cells can limit potentially damaging inflammation within the CNS in response to invading pathogens, and could explain the suppression of inflammation seen within the brain parenchyma during chronic bacterial infections.

Toxoplasma gondii prevents neuron degeneration by interferon-gamma-activated microglia in a mechanism involving inhibition of inducible nitric oxide synthase and transforming growth factor-beta1 production by infected microglia

Interferon (IFN)-gamma, the main cytokine responsible for immunological defense against Toxoplasma gondii, is essential in all infected tissues, including the central nervous system. However, IFN-gamma-activated microglia may cause tissue injury through production of toxic metabolites such as nitric oxide (NO), a potent inducer of central nervous system pathologies related to inflammatory neuronal disturbances. Despite potential NO toxicity, neurodegeneration is not commonly found during chronic T. gondii infection. In this study, we describe decreased NO production by IFN-gamma-activated microglial cells infected by T. gondii. This effect involved strong inhibition of iNOS expression in IFN-gamma-activated, infected microglia but not in uninfected neighboring cells. The inhibition of NO production and iNOS expression were parallel with recovery of neurite outgrowth when neurons were co-cultured with T. gondii-infected, IFN-gamma-activated microglia. In the presence of transforming growth factor (TGF)-beta1-neutralizing antibodies, the beneficial effect of the parasite on neurons was abrogated, and NO production reverted to levels similar to IFN-gamma-activated uninfected co-cultures. In addition, we observed Smad-2 nuclear translocation, a hallmark of TGF-beta1 downstream signaling, in infected microglial cultures, emphasizing an autocrine effect restricted to infected cells. Together, these data may explain a neuropreservation pattern observed during immunocompetent host infection that is dependent on T. gondii-triggered TGF-beta1 secretion by infected microglia.