The Toxoplasma oxygen-sensing protein, TgPhyA, is required for resistance to interferon gamma-mediated nutritional immunity in mice.

As Toxoplasma gondii disseminates through its host, the parasite must sense and adapt to its environment and scavenge nutrients. Oxygen (O2) is one such environmental factor and cytoplasmic prolyl 4-hydroxylases (PHDs) are evolutionarily conserved O2 cellular sensing proteins that regulate responses to changes in O2 availability. Toxoplasma expresses 2 PHDs. One of them, TgPHYa hydroxylates SKP1, a subunit of the SCF-E3 ubiquitin ligase complex. In vitro, TgPHYa is important for growth at low O2 levels. However, studies have yet to examine the role that TgPHYa or any other pathogen-encoded PHD plays in virulence and disease. Using a type II ME49 Toxoplasma TgPHYa knockout, we report that TgPHYa is important for Toxoplasma virulence and brain cyst formation in mice. We further find that while TgPHYa mutant parasites can establish an infection in the gut, they are unable to efficiently disseminate to peripheral tissues because the mutant parasites are unable to survive within recruited immune cells. Since this phenotype was abrogated in IFNγ knockout mice, we studied how TgPHYa mediates survival in IFNγ-treated cells. We find that TgPHYa is not required for release of parasite-encoded effectors into host cells that neutralize anti-parasitic processes induced by IFNγ. In contrast, we find that TgPHYa is required for the parasite to scavenge tryptophan, which is an amino acid whose levels are decreased after IFNγ up-regulates the tryptophan-catabolizing enzyme, indoleamine dioxygenase (IDO). We further find, relative to wild-type mice, that IDO knockout mice display increased morbidity when infected with TgPHYa knockout parasites. Together, these data identify the first parasite mechanism for evading IFNγ-induced nutritional immunity and highlight a novel role that oxygen-sensing proteins play in pathogen growth and virulence.

Protective function and differentiation cues of brain-resident CD8+ T cells during surveillance of latent Toxoplasma gondii infection.

Chronic Toxoplasma gondii infection induces brain-resident CD8+ T cells (bTr), but the protective functions and differentiation cues of these cells remain undefined. Here, we used a mouse model of latent infection by T. gondii leading to effective CD8+ T cell-mediated parasite control. Thanks to antibody depletion approaches, we found that peripheral circulating CD8+ T cells are dispensable for brain parasite control during chronic stage, indicating that CD8+ bTr are able to prevent brain parasite reactivation. We observed that the retention markers CD69, CD49a, and CD103 are sequentially acquired by brain parasite-specific CD8+ T cells throughout infection and that a majority of CD69/CD49a/CD103 triple-positive (TP) CD8+ T cells also express Hobit, a transcription factor associated with tissue residency. This TP subset develops in a CD4+ T cell-dependent manner and is associated with effective parasite control during chronic stage. Conditional invalidation of Transporter associated with Antigen Processing (TAP)-mediated major histocompatibility complex (MHC) class I presentation showed that presentation of parasite antigens by glutamatergic neurons and microglia regulates the differentiation of CD8+ bTr into TP cells. Single-cell transcriptomic analyses revealed that resistance to encephalitis is associated with the expansion of stem-like subsets of CD8+ bTr. In summary, parasite-specific brain-resident CD8+ T cells are a functionally heterogeneous compartment which autonomously ensure parasite control during T. gondii latent infection and which differentiation is shaped by neuronal and microglial MHC I presentation. A more detailed understanding of local T cell-mediated immune surveillance of this common parasite is needed for harnessing brain-resident CD8+ T cells in order to enhance control of chronic brain infections.

Monocytes maintain central nervous system homeostasis following helminth-induced inflammation.

Neuroimmune interactions are crucial for regulating immunity and inflammation. Recent studies have revealed that the central nervous system (CNS) senses peripheral inflammation and responds by releasing molecules that limit immune cell activation, thereby promoting tolerance and tissue integrity. However, the extent to which this is a bidirectional process, and whether peripheral immune cells also promote tolerance mechanisms in the CNS remains poorly defined. Here we report that helminth-induced type 2 inflammation promotes monocyte responses in the brain that are required to inhibit excessive microglial activation and host death. Mechanistically, infection-induced monocytes express YM1 that is sufficient to inhibit tumor necrosis factor production from activated microglia. Importantly, neuroprotective monocytes persist in the brain, and infected mice are protected from subsequent lipopolysaccharide-induced neuroinflammation months after infection-induced inflammation has resolved. These studies demonstrate that infiltrating monocytes promote CNS homeostasis in response to inflammation in the periphery and demonstrate that a peripheral infection can alter the immunologic landscape of the host brain.

Brain endothelial STING1 activation by Plasmodium-sequestered heme promotes cerebral malaria via type I IFN response.

Cerebral malaria (CM) is a life-threatening form of Plasmodium falciparum infection caused by brain inflammation. Brain endothelium dysfunction is a hallmark of CM pathology, which is also associated with the activation of the type I interferon (IFN) inflammatory pathway. The molecular triggers and sensors eliciting brain type I IFN cellular responses during CM remain largely unknown. We herein identified the stimulator of interferon response cGAMP interactor 1 (STING1) as the key innate immune sensor that induces Ifnß1 transcription in the brain of mice infected with Plasmodium berghei ANKA (Pba). This STING1/IFNß-mediated response increases brain CXCL10 governing the extent of brain leukocyte infiltration and blood-brain barrier (BBB) breakdown, and determining CM lethality. The critical role of brain endothelial cells (BECs) in fueling type I IFN-driven brain inflammation was demonstrated in brain endothelial-specific IFNß-reporter and STING1-deficient Pba-infected mice, which were significantly protected from CM lethality. Moreover, extracellular particles (EPs) released from Pba-infected erythrocytes activated the STING1-dependent type I IFN response in BECs, a response requiring intracellular acidification. Fractionation of the EPs enabled us to identify a defined fraction carrying hemoglobin degradation remnants that activates STING1/IFNß in the brain endothelium, a process correlated with heme content. Notably, stimulation of STING1-deficient BECs with heme, docking experiments, and in vitro binding assays unveiled that heme is a putative STING1 ligand. This work shows that heme resultant from the parasite heterotrophic activity operates as an alarmin, triggering brain endothelial inflammatory responses via the STING1/IFNß/CXCL10 axis crucial to CM pathogenesis and lethality.

Toxoplasma gondii Infection of Alzheimer's Disease Mice Reduces Brain Amyloid Density Globally and Regionally.

BACKGROUND: Toxoplasma gondii infection of Alzheimer's disease model mice decreases amyloid ß plaques. We aimed to determine if there is a brain regional difference in amyloid ß reduction in the brains of T. gondii-infected compared to control mice. METHOD: Three-month-old 5xFAD (AD model) mice were injected with T. gondii or with phosphate-buffered saline as a control. Intact brains were harvested at 6 weeks postinfection, optically cleared using iDISCO+, and brain-wide amyloid burden was visualized using volumetric light-sheet imaging. Amyloid signal was quantified across each brain and computationally mapped to the Allen Institute Brain Reference Atlas to determine amyloid density in each region. RESULTS: A brain-wide analysis of amyloid in control and T. gondii-infected 5xFAD mice revealed that T. gondii infection decreased amyloid burden in the brain globally as well as in the cortex and hippocampus, and many daughter regions. Daughter regions that showed reduced amyloid burden included the prelimbic cortex, visual cortex, and retrosplenial cortex. The olfactory tubercle, a region known to have increased monocytes following T. gondii infection, also showed reduced amyloid after infection. CONCLUSIONS: T. gondii infection of AD mice reduces amyloid burden in a brain region-specific manner that overlaps with known regions of T. gondii infection and peripheral immune cell infiltration.

Toxoplasma infection induces an aged neutrophil population in the CNS that is associated with neuronal protection.

BACKGROUND: Infection with the protozoan parasite Toxoplasma gondii leads to the formation of lifelong cysts in neurons that can have devastating consequences in the immunocompromised. In the immunocompetent individual, anti-parasitic effector mechanisms and a balanced immune response characterized by pro- and anti-inflammatory cytokine production establishes an asymptomatic infection that rarely leads to neurological symptoms. Several mechanisms are known to play a role in this successful immune response in the brain including T cell production of IFNγ and IL-10 and the involvement of CNS resident cells. This limitation of clinical neuropathology during chronic infection suggests a balance between immune response and neuroprotective mechanisms that collectively prevent clinical manifestations of disease. However, how these two vital mechanisms of protection interact during chronic Toxoplasma infection remains poorly understood. MAIN TEXT: This study demonstrates a previously undescribed connection between innate neutrophils found chronically in the brain, termed "chronic brain neutrophils" (CBNeuts), and neuroprotective mechanisms during Toxoplasma infection. Lack of CBNeuts during chronic infection, accomplished via systemic neutrophil depletion, led to enhanced infection and deleterious effects on neuronal regeneration and repair mechanisms in the brain. Phenotypic and transcriptomic analysis of CBNeuts identified them as distinct from peripheral neutrophils and revealed two main subsets of CBNeuts that display heterogeneity towards both classical effector and neuroprotective functions in an age-dependent manner. Further phenotypic profiling defined expression of the neuroprotective molecules NRG-1 andErbB4 by these cells, and the importance of this signaling pathway during chronic infection was demonstrated via NRG-1 treatment studies. CONCLUSIONS: In conclusion, this work identifies CBNeuts as a heterogenous population geared towards both classical immune responses and neuroprotection during chronic Toxoplasma infection and provides the foundation for future mechanistic studies of these cells.

Contrasting alterations in brain chemistry in a crustacean intermediate host of two acanthocephalan parasites.

The dynamic properties of neural systems throughout life can be hijacked by so-called manipulative parasites. This study investigated changes in the brain chemistry of the amphipod Gammarus fossarum in response to infection with two trophically-transmitted helminth parasites known to induce distinct behavioral alterations: the bird acanthocephalan Polymorphus minutus and the fish acanthocephalan Pomphorhynchus tereticollis. We quantified brain antioxidant capacity as a common marker of homeostasis and neuroprotection, and brain total protein, on 72 pools of six brains. We analyzed the concentration of serotonin (5HT), dopamine (DA) and tyramine in 52 pools of six brains, by using ultrafast high performance liquid chromatography with electrochemical detection (UHPLC-ECD). Brain total protein concentration scaled hypo-allometrically to dry body weight, and was increased in infected gammarids compared to uninfected ones. The brain of gammarids infected with P. minutus had significantly lower total antioxidant capacity relative to total proteins. Infection with P. tereticollis impacted DA level compared to uninfected ones, and in opposite direction between spring and summer. Brain 5HT level was higher in summer compared to spring independently of infection status, and was decreased by infection after correcting for brain total protein concentration estimated from dry whole-body weight. The potential implication of 5HT/DA balance in parasite manipulation, as a major modulator of the reward-punishment axis, is discussed. Taken together, these findings highlight the need to consider both brain homeostatic and/or structural changes (antioxidant and total protein content) together with neurotransmission balance and flexibility, in studies investigating the impact of parasites on brain and behavior.

Oxfendazole Nitazoxanide combination in experimental neurocysticercosis - Anti-inflammatory and cysticidal effects.

Neurocysticercosis (NCC) is a parasitic infection caused by the larval stage of the pork tapeworm, Taenia solium. The complications of NCC include seizures, headaches, cognitive impairment, and focal neurological deficits. In addition to antiparasitic drugs and surgery, the management of NCC includes the use of corticosteroids to reduce inflammation and control symptoms. The traditional treatment with albendazole and praziquantel has not been altered over 30 years and present several side effects. There are other anti-helminthic drugs such as oxfendazole and nitazoxanide that may show efficacy in NCC treatment. The aim of this study was to determine the histopathologic aspects of experimental NCC after in vivo treatment with the combination of oxfendazole and nitazoxanide. Balb/c mice were infected with T. crassiceps cysticerci and divided into groups of 10 animals each that received a single dose through gavage as follows: group treated with NaCl 0.9% (control group); group treated by monotherapy of the anti-helminthic drugs, 30 mg/kg in single dose of oxfendazole (OXF) or nitazoxanide (NTZ); and groups treated with the combination of the drugs (OXF/NTZ group). Macroscopic and microscopic analysis were performed. There was greater presence of final stage cysticerci after treatment. The microscopic analysis of the general pathological processes showed that the monotherapy with all treatment groups induced higher perivasculitis than what was observed in the control group. In contrast, the combination treatment showed a lower observation of PMN and MN inflammatory infiltration in comparison to the other treatments and to the control one. These results show that indeed the association of benzimidazole derivatives which present both anti-helminthic and anti-inflammatory properties with other cysticidal drugs are beneficial for the NCC treatment in which the aim is to destroy parasite without inducing inflammatory damage in the brain tissue.

Spiramycin-loaded maltodextrin nanoparticles as a promising treatment of toxoplasmosis on murine model.

Despite being the initial choice for treating toxoplasmosis, sulfadiazine and pyrimethamine have limited effectiveness in eliminating the infection and were linked to a variety of adverse effects. Therefore, the search for new effective therapeutic strategies against toxoplasmosis is still required. The current work is the first research to assess the efficacy of spiramycin-loaded maltodextrin nanoparticles (SPM-loaded MNPs) as a novel alternative drug therapy against toxoplasmosis in a murine model. Fifty laboratory-bred Swiss albino mice were divided into five groups: normal control group (GI, n = 10), positive control group (GII, n = 10), orally treated with spiramycin (SPM) alone (GIII, n = 10), intranasal treated with SPM-loaded MNPs (GIV, n = 10), and orally treated with SPM-loaded MNPs (GV, n = 10). Cysts of Toxoplasma gondii ME-49 strain were used to infect the mice. Tested drugs were administered 2 months after the infection. Drug efficacy was assessed by counting brain cysts, histopathological examination, and measures of serum CD19 by flow cytometer. The orally treated group with SPM-loaded MNPs (GV) showed a marked reduction of brain cyst count (88.7%), histopathological improvement changes, and an increasing mean level of CD19 (80.2%) with significant differences. SPM-loaded MNPs showed potent therapeutic effects against chronic toxoplasmosis. Further research should be conducted to assess it in the treatment of human toxoplasmosis, especially during pregnancy.

Assessment of nebivolol efficacy in experimental models of toxoplasmosis: insights into parasite burden reduction and neuronal protection.

This study investigates the efficacy of nebivolol (NBV) in experimental models of toxoplasmosis, focusing on parasite burden reduction and neuronal protection. In the acute model of experimental toxoplasmosis, Swiss mice infected with RH strain tachyzoites received oral NBV chlorhydrate doses of 2 mg/kg/day and 4 mg/kg/day for 8 days. Treatment with NBV significantly reduced parasite burden compared to vehicle and standard drug (PYR) groups. In the chronic model of experimental toxoplasmosis, C57/BL6 mice infected with the ME49 strain received NBV chlorhydrate 41 days post-infection and were evaluated after 10 days of treatment. NBV chlorhydrate effectively reduced cyst number and area, as well as bradyzoite burden compared to controls. Histological analysis demonstrated that NBV chlorhydrate preserved neuronal count, with the 4 mg/kg/day dose yielding counts similar to non-infected mice. Statistical analysis confirmed significant differences compared to control groups. Furthermore, immunohistochemical analysis revealed a significant reduction in iNOS labeling in the brains of mice treated with NBV chlorhydrate, indicating a decrease in nitric oxide production compared to control groups. These findings suggest NBV's potential as a promising candidate for toxoplasmosis treatment, highlighting its ability to reduce parasite burden and protect neuronal integrity. Further research is warranted to elucidate NBV's mechanisms of action and its clinical application in managing toxoplasmosis.

Myxobolus acanthogobii Hoshina, 1952 and Myxobolus selari n. sp. (Myxosporea: Myxobolidae) infecting brain of commercial fishes in Terengganu, Malaysia.

Myxosporean infection in marine water fishes has drawn less attention than in freshwater fishes, which resulted in a higher taxonomic variety in freshwater in Malaysia. This study aimed to address the gap by conducting a myxosporean survey on two commercially significant marine fish species, Nemipterus furcosus (Valenciennes) (Eupercaria incertae sedis: Nemipteridae) and Selar crumenophthalmus (Bloch) (Carangiformes: Carangidae), collected from the northeastern part of peninsular Malaysia. During the examination of the organs, two distinct Myxobolus Bütschli, 1882 species were discovered in the brain tissue of these fishes, despite the absence of any observable pathological signs. The two Myxobolus species were characterized through morphometry, morphology, and analysis of partial small subunit ribosomal RNA (18S rDNA) gene. As a result, Myxobolus acanthogobii Hoshina, 1952, which infects 2.3% of N. furcosus, is synonymous with a myxobolid species commonly found in Japanese waters, based on its morphological traits, tissue tropism, and molecular diagnostics. Furthermore, a novel species, Myxobolus selari n. sp., was described, infecting the brain of one (11%) individual S. crumenophthalmus. This unique species displayed distinctive features, placing it within a well-supported subclade primarily comprising brain-infecting myxobolids. Maximum likelihood analysis further revealed the close relationships among these brain-infecting myxobolids, underscoring the significance of tissue tropism and host taxonomy for myxobolids. This study represents the initial documentation of Myxobolus species within the southern South China Sea, shedding light on the potential diversity of marine myxosporean in this region. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:7C400E35-7CB8-4DEE-92B7-F75FF3926441.

Noradrenergic Signaling and Neuroinflammation Crosstalk Regulate Toxoplasma gondii-Induced Behavioral Changes.

Infections of the nervous system elicit neuroimmune responses and alter neurotransmission, affecting host neurological functions. Chronic infection with the apicomplexan parasite Toxoplasma correlates with certain neurological disorders in humans and alters behavior in rodents. Here, we propose that the crosstalk between neurotransmission and neuroinflammation may underlie some of these cognitive changes. We discuss how T. gondii infection suppresses noradrenergic signaling and how the restoration of this pathway improves behavioral aberrations, suggesting that altered neurotransmission and neuroimmune responses may act in concert to perturb behavior. This interaction might apply to other infectious agents, such as viruses, that elicit cognitive changes. We hypothesize that neurotransmitter signaling in immune cells can contribute to behavioral changes associated with brain infection, offering opportunities for potential therapeutic targeting.

Human neutrophil-like cells demonstrate antimicrobial responses to the chronic cyst form of Toxoplasma gondii.

The protozoan parasite Toxoplasma gondii infects approximately 2.5 billion people worldwide. Infection induces a rapid dissemination of parasites throughout the body followed by the formation of lifelong cysts within neurons of the host brain. Both stages require a dynamic immune response comprised of both innate and adaptive cells. Neutrophils are a primary responding cell to acute infection and have been observed in the brain during murine chronic infection. Previous studies investigating human neutrophils found that invasion by Toxoplasma tachyzoites inhibits apoptosis of neutrophils, prolonging their survival under inflammatory conditions. Here, we demonstrate the differentiation of two distinct subsets following exposure of human neutrophil-like-cells (HNLC) to Toxoplasma cysts. In vitro stimulation and imaging studies show cyst-specific induction of cytokines and cyst clearance by HNLCs. Further testing demonstrates that aged HNLCs perform less phagocytosis of cysts compared to non-aged HNLCs. In conclusion, this study identifies a novel response of HNLCs to Toxoplasma cysts and may indicate a role for neutrophils in the clearance of cysts during human infection with Toxoplasma.

The effect of chronic experimental toxoplasmosis on some brain neurotransmitters level and behavior changes.

Toxoplasma is capable of causing long-lasting brain cysts in its hosts, which can lead to physiological disturbances in brain neurotransmitters and result in changes in the host's behavior. This study aimed to investigate these changes using an experimental model. Twenty-five female Wistar rats, weighing 220-220 g and six weeks old, were selected for the study. The rats were divided into two control and experimental groups. The experimental group was injected with 5 × 105 tachyzoites of Toxoplasma gondii (virulent RH strain) intra-peritoneally. Four months after the injection, the rats were subjected to behavioral tests, including learning, memory, depression, and locomotor activity tests. The rats were then euthanized, and their brain and serum samples were analyzed for dopamine and serotonin levels. To ensure the presence of cysts in the brain tissue, a PCR test and preparation of pathological slides from the brain tissue were performed. The results showed that the amount of dopamine in the brain of the infected group was significantly higher than that of the control group, while the level of serotonin in brain of the infected group was significantly lower than that of the control group (P < 0.05). However, no significant difference was observed in the amount of these neurotransmitters in the blood of the two groups (P > 0.05). Behavioral changes were evaluated, and it was found that the learning and memory levels of the infected rats were significantly lower than those of the control group (P < 0.05), but no difference was observed in locomotor activity between the two groups (P > 0.05). This experimental infection model indicated that changes in neurotransmitter levels lead to behavior changes. CONCLUSION: The presence of parasite cysts in the brain can affect some of the host's behaviors through changes in neurotransmitter levels. Therefore, there is a possibility that there is a relationship between the presence of Toxoplasma cysts in the brain and neurological disorders. The results of this study suggest that chronic toxoplasmosis may play a role in behavior changes in psychotic diseases.

RTP4 inhibits IFN-I response and enhances experimental cerebral malaria and neuropathology.

Infection by malaria parasites triggers dynamic immune responses leading to diverse symptoms and pathologies; however, the molecular mechanisms responsible for these reactions are largely unknown. We performed Trans-species Expression Quantitative Trait Locus analysis to identify a large number of host genes that respond to malaria parasite infections. Here we functionally characterize one of the host genes called receptor transporter protein 4 (RTP4) in responses to malaria parasite and virus infections. RTP4 is induced by type I IFN (IFN-I) and binds to the TANK-binding kinase (TBK1) complex where it negatively regulates TBK1 signaling by interfering with expression and phosphorylation of both TBK1 and IFN regulatory factor 3. Rtp4-/- mice were generated and infected with malaria parasite Plasmodiun berghei ANKA. Significantly higher levels of IFN-I response in microglia, lower parasitemia, fewer neurologic symptoms, and better survival rates were observed in Rtp4-/- than in wild-type mice. Similarly, RTP4 deficiency significantly reduced West Nile virus titers in the brain, but not in the heart and the spleen, of infected mice, suggesting a specific role for RTP4 in brain infection and pathology. This study reveals functions of RTP4 in IFN-I response and a potential target for therapy in diseases with neuropathology.

Using a new three-dimensional CUBIC tissue-clearing method to examine the brain during experimental cerebral malaria.

Cerebral malaria (CM) is a life-threatening complication of the malaria disease caused by Plasmodium falciparum infection and is responsible for the death of half a million people annually. The molecular pathogenesis underlying CM in humans is not completely understood, although sequestration of infected erythrocytes in cerebral microvessels is thought to play a major role. In contrast, experimental cerebral malaria (ECM) models in mice have been thought to be distinct from human CM, and are mainly caused by inflammatory mediators. Here, to understand the spatial distribution and the potential sequestration of parasites in the whole-brain microvessels during a mouse model of ECM, we utilized the new tissue-clearing method CUBIC (Clear, Unobstructed, Brain/Body Imaging Cocktails and Computational analysis) with light-sheet fluorescent microscopy (LSFM), and reconstructed images in three dimensions (3D). We demonstrated significantly greater accumulation of Plasmodium berghei ANKA (PbANKA) parasites in the olfactory bulb (OB) of mice, compared with the other parts of the brain, including the cerebral cortex, cerebellum and brainstem. Furthermore, we show that PbANKA parasites preferentially accumulate in the brainstem when the OB is surgically removed. This study therefore not only highlights a successful application of CUBIC tissue-clearing technology to visualize the whole brain and its microvessels during ECM, but it also shows CUBIC's future potential for visualizing pathological events in the whole ECM brain at the cellular level, an achievement that would greatly advance our understanding of human cerebral malaria.

The Significance of Perfusion-Weighted Magnetic Resonance Imaging in Evaluating the Pathological Biological Activity of Cerebral Alveolar Echinococcosis.

OBJECTIVES: This study aimed to evaluate the value of perfusion-weighted magnetic resonance imaging (MR-PWI) in assessing cerebral alveolar echinococcosis (CAE) biological activity. METHODS: Totally, 15 cases of CAE patients who underwent surgery were enrolled. The MR-PWI perfusion parameters were measured and compared. RESULTS: The MR-PWI perfusion parameters cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time were different among different areas. Their values were in the descending order of lesion marginal area > contralateral normal brain area > lesion center area. However, time-to-peak value was in the ascending order of lesion marginal area < contralateral normal brain area < lesion center area. Spearman correlation analysis showed that CBF and CBV at the edge of the lesion were significantly positively correlated with microvessel density. Moreover, CBF and CBV at the edge of the lesion were also significantly positively correlated with maximum standardized uptake value. CONCLUSIONS: Perfusion-weighted magnetic resonance imaging can be used to dynamically reflect the neovascularization of CAE lesions and may have a good application prospect in evaluating the biological activity of CAE.

A brain cyst load-associated antigen is a Toxoplasma gondii biomarker for serodetection of persistent parasites and chronic infection.

BACKGROUND: Biomarker discovery remains a major challenge for predictive medicine, in particular, in the context of chronic diseases. This is true for the widespread protozoan Toxoplasma gondii which establishes long-lasting parasitism in metazoans, humans included. This microbe successively unfolds distinct genetic programs that direct the transition from high to low replicative potential inside host cells. As a slow-replicating cell, the T. gondii bradyzoite developmental stage persists enclosed in a cyst compartment within tissues including the nervous system, being held by a sustained immune equilibrium which accounts for the prolonged clinically silent phase of parasitism. Serological surveys indicate that nearly one third of the human population has been exposed to T. gondii and possibly host bradyzoites. Because any disruption of the immune balance drives the reverse transition from bradyzoite to fast replicating tachyzoite and uncontrolled growth of the latter, these people are at risk for life-threatening disease. While serological tests for discriminating recent from past infection are available, there is yet no immunogenic biomarker used in the serological test to allow ascertaining the presence of persistent bradyzoites. RESULTS: Capitalizing on genetically engineered parasites induced to produce mature bradyzoites in vitro, we have identified the BCLA/MAG2 protein being restricted to the bradyzoite and the cyst envelope. Using laboratory mice as relevant T. gondii host models, we demonstrated that BCLA/MAG2 drives the generation of antibodies that recognize bradyzoite and the enveloping cyst structure. We have designed an ELISA assay based on a bacterially produced BCLA recombinant polypeptide, which was validated using a large collection of sera from mice of different genetic backgrounds and infected with bcla+ or bcla-null cystogenic and non-cystogenic T. gondii strains. To refine the design of the ELISA assay, we applied high-resolution BCLA epitope mapping and identified a specific combination of peptides and accordingly set up a selective and sensitive ELISA assay which allowed the detection of anti-BCLA/MAG2 antibodies in the sera of human patients with various forms of toxoplasmosis. CONCLUSIONS: We brought proof of principle that anti-BCLA/MAG2 antibodies serve as specific and sensitive serological markers in the perspective of a combinatorial strategy for detection of persistent T. gondii parasitism.

IL-10 and ICOS Differentially Regulate T Cell Responses in the Brain during Chronic Toxoplasma gondii Infection.

Control of chronic CNS infection with the parasite Toxoplasma gondii requires ongoing T cell responses in the brain. Immunosuppressive cytokines are also important for preventing lethal immunopathology during chronic infection. To explore the loss of suppressive cytokines exclusively during the chronic phase of infection, we blocked IL-10R in chronically infected mice. Consistent with previous reports, IL-10R blockade led to severe, fatal tissue destruction associated with widespread changes in the inflammatory response, including increased APC activation, expansion of CD4+ T cells, and neutrophil recruitment to the brain. We then sought to identify regulatory mechanisms contributing to IL-10 production, focusing on ICOS, a molecule implicated in IL-10 production. Unexpectedly, ICOS ligand (ICOSL) blockade led to a local expansion of effector T cells in the brain without affecting IL-10 production or APC activation. Instead, we found that ICOSL blockade led to changes in T cells associated with their proliferation and survival. We observed increased expression of IL-2-associated signaling molecules CD25, STAT5 phosphorylation, Ki67, and Bcl-2 in T cells in the brain, along with decreased apoptosis. Interestingly, increases in CD25 and Bcl-2 were not observed following IL-10R blockade. Also, unlike IL-10R blockade, ICOSL blockade led to an expansion of both CD8+ and CD4+ T cells in the brain, with no expansion of peripheral T cells or neutrophil recruitment to the brain and no severe tissue destruction. Overall, these results suggest that IL-10 and ICOS differentially regulate T cell responses in the brain during chronic T. gondii infection.

Infection with Trypanosoma lewisi or Trypanosoma musculi may promote the spread of Toxoplasma gondii.

Toxoplasma gondii can infect almost all warm-blooded vertebrates with pathogensis being largely influenced by the host immune status. As important epidemiological hosts, rodents are globally distributed and are also commonly found infected with haemoflagellates, such as those in the genus Trypanosoma. We here address whether and how co-infection with trypanosomes can influence T. gondii infection in laboratory models. Rats of five strains, co-infected with T. lewisi and mice of four strains, co-infected with T. musculi, were found to be more or less susceptible to T. gondii infection, respectively, with corresponding increased or decreased brain cyst burdens. Downregulation of iNOS expression and decreased NO production or reverse were observed in the peritoneal macrophages of rats or mice, infected with trypanosomes, respectively. Trypanosoma lewisi and T. musculi can modulate host immune responses, either by enhancement or suppression and influence the outcome of Toxoplasma infection.