Correction: Transcriptional profiling of Toll-like receptor 2-deficient primary murine brain cells during Toxoplasma gondii infection.

[This corrects the article DOI: 10.1371/journal.pone.0187703.].

Far-East Asian Toxoplasma isolates share ancestry with North and South/Central American recombinant lineages.

Toxoplasma gondii is a global protozoan pathogen. Clonal lineages predominate in Europe, North America, Africa, and China, whereas highly recombinant parasites are endemic in South/Central America. Far East Asian T. gondii isolates are not included in current global population genetic structure analyses at WGS resolution. Here we report a genome-wide population study that compared eight Japanese and two Chinese isolates against representative worldwide T. gondii genomes using POPSICLE, a novel population structure analyzing software. Also included were 7 genomes resurrected from non-viable isolates by target enrichment sequencing. Visualization of the genome structure by POPSICLE shows a mixture of Chinese haplogroup (HG) 13 haploblocks introgressed within the genomes of Japanese HG2 and North American HG12. Furthermore, two ancestral lineages were identified in the Japanese strains; one lineage shares a common ancestor with HG11 found in both Japanese strains and North American HG12. The other ancestral lineage, found in T. gondii isolates from a small island in Japan, is admixed with genetically diversified South/Central American strains. Taken together, this study suggests multiple ancestral links between Far East Asian and American T. gondii strains and provides insight into the transmission history of this cosmopolitan organism.

The role of IFN-γ-mediated host immune responses in monitoring and the elimination of Toxoplasma gondii infection.

Toxoplasma gondii is a pathogenic protozoan parasite of the Apicomplexa family that affects approximately 30% of the world's population. Symptoms are usually mild in immunocompetent hosts, but it can pose significant health risks to immunosuppressed patients and pregnant women. Current treatment options are limited, and new therapies and vaccines are needed. The innate immune system is the first to recognize T. gondii infection and activates pro-inflammatory cytokines and chemokines to promote acquired immunity. The IL-12/IFN-γ axis is particularly important, and when this pathway is inhibited, infection becomes uncontrolled and lethal. In mice, receptors such as Toll-like receptor 11 (TLR11), TLR12, and chemokine receptors are involved in T. gondii recognition and the modulation of immune responses. In humans, where TLR11 and TLR12 are absent, other mechanisms have been reported as the innate immune sensing system in T. gondii infection. Immune cells activated in response to infection produce interleukin (IL)-12, which stimulates the proliferation of natural killer cells and T cells and promotes the production of interferon (IFN)-γ. Several IFN-γ-induced anti-T. gondii defense mechanisms inhibit parasite growth. These include nitric oxide (NO) production, indoleamine 2,3-dioxygenase, and the destruction of parasitophorous vacuoles by IFN-γ-inducible immunity related GTPase groups (IRGs and GBPs). Recent studies focusing on the diversity of IRGs in rodents and effector molecules in T. gondii suggest that host immune mechanisms and pathogen immune evasion mechanisms have co-evolved. Furthermore, it has been suggested that cysts are not simply dormant during chronic infection. This review summarizes recent findings on anti-T. gondii innate, adaptive, and cell-autonomous immune responses.

Transcriptomic Analysis of the Effects of Chemokine Receptor CXCR3 Deficiency on Immune Responses in the Mouse Brain during Toxoplasma gondii Infection.

The obligate intracellular parasite Toxoplasma gondii infects warm-blooded animals, including humans. We previously revealed through a whole-brain transcriptome analysis that infection with T. gondii in mice causes immune response-associated genes to be upregulated, for instance, chemokines and chemokine receptors such as CXC chemokine receptor 3 (CXCR3) and its ligand CXC chemokine ligand 10 (CXCL10). Here, we describe the effect of CXCR3 on responses against T. gondii infection in the mouse brain. In vivo assays using CXCR3-deficient mice showed that the absence of CXCR3 delayed the normal recovery of body weight and increased the brain parasite burden, suggesting that CXCR3 plays a role in the control of pathology in the brain, the site where chronic infection occurs. Therefore, to further analyze the function of CXCR3 in the brain, we profiled the gene expression patterns of primary astrocytes and microglia by RNA sequencing and subsequent analyses. CXCR3 deficiency impaired the normal upregulation of immune-related genes during T. gondii infection, in astrocytes and microglia alike. Collectively, our results suggest that the immune-related genes upregulated by CXCR3 perform a particular role in controlling pathology when the host is chronically infected with T. gondii in the brain.

Toxoplasma gondii manipulates host cell signaling pathways via its secreted effector molecules.

The obligate intracellular parasite Toxoplasma gondii secretes a vast variety of effector molecules from organelles known as rhoptries (ROPs) and dense granules (GRAs). ROP proteins are released into the cytosol of the host cell where they are directed to the cell nucleus or to the parasitophorous vacuole (PV) membrane. ROPs secrete proteins that enable host cell penetration and vacuole formation by the parasites, as well as hijacking host-immune responses. After invading host cells, T. gondii multiplies within a PV that is maintained by the parasite proteins secreted from GRAs. Most GRA proteins remain within the PV, but some are known to access the host cytosol across the PV membrane, and a few are able to traffic into the host-cell nucleus. These effectors bind to host cell proteins and affect host cell signaling pathways to favor the parasite. Studies on host-pathogen interactions have identified many infection-altered host signal transductions. Notably, the relationship between individual parasite effector molecules and the specific targeting of host-signaling pathways is being elucidated through the advent of forward and reverse genetic strategies. Understanding the complex nature of the host-pathogen interactions underlying how the host-signaling pathway is manipulated by parasite effectors may lead to new molecular biological knowledge and novel therapeutic methods for toxoplasmosis. In this review, we discuss how T. gondii modulates cell signaling pathways in the host to favor its survival.

Toxoplasma gondii Dense Granule Proteins 7, 14, and 15 Are Involved in Modification and Control of the Immune Response Mediated via NF-κB Pathway.

Toxoplasma gondii infects almost all warm-blooded animals, including humans, leading to both cellular and humoral immune responses in the host. The virulence of T. gondii is strain specific and is defined by secreted effector proteins that disturb host immunity. Here, we focus on nuclear factor-kappa B (NFκB) signaling, which regulates the induction of T-helper type 1 immunity. A luciferase assay for screening effector proteins, including ROPs and GRAs that have biological activity against an NFκB-dependent reporter plasmid, found that overexpression of GRA7, 14, and 15 of a type II strain resulted in a strong activity. Thus, our study was aimed at understanding the involvement of NFκB in the pathogenesis of toxoplasmosis through a comparative analysis of these three molecules. We found that GRA7 and GRA14 were partially involved in the activation of NFκB, whereas GRA15 was essential for NFκB activation. The deletion of GRA7, GRA14, and GRA15 in the type II Prugniaud (Pru) strain resulted in a defect in the nuclear translocation of RelA. Cells infected with the PruΔgra15 parasite showed reduced phosphorylation of inhibitor-κBα. GRA7, GRA14, and GRA15 deficiency decreased the levels of interleukin-6 in RAW246.7 cells, and RNA-seq analysis revealed that GRA7, GRA14, and GRA15 deficiency predominantly resulted in downregulation of gene expression mediated by NFκB. The virulence of all mutant strains increased, but PruΔgra14 only showed a slight increase in virulence. However, the intra-footpad injection of the highly-virulent type I RHΔgra14 parasites in mice resulted in increased virulence. This study shows that GRA7, 14, and 15-induced host immunity via NFκB limits parasite expansion.

Transcriptome analysis of the effect of C-C chemokine receptor 5 deficiency on cell response to Toxoplasma gondii in brain cells.

BACKGROUND: Infection with Toxoplasma gondii is thought to damage the brain and be a risk factor for neurological and psychotic disorders. The immune response-participating chemokine system has recently been considered vital for brain cell signaling and neural functioning. Here, we investigated the effect of the deficiency of C-C chemokine receptor 5 (CCR5), which is previously reported to be associated with T. gondii infection, on gene expression in the brain during T. gondii infection and the relationship between CCR5 and the inflammatory response against T. gondii infection in the brain. RESULTS: We performed a genome-wide comprehensive analysis of brain cells from wild-type and CCR5-deficient mice. Mouse primary brain cells infected with T. gondii were subjected to RNA sequencing. The expression levels of some genes, especially in astrocytes and microglia, were altered by CCR5-deficiency during T. gondii infection, and the gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed an enhanced immune response in the brain cells. The expression levels of genes which were highly differentially expressed in vitro were also investigated in the mouse brains during the T. gondii infections. Among the genes tested, only Saa3 (serum amyloid A3) showed partly CCR5-dependent upregulation during the acute infection phase. However, analysis of the subacute phase showed that in addition to Saa3, Hmox1 may also contribute to the protection and/or pathology partly via the CCR5 pathway. CONCLUSIONS: Our results indicate that CCR5 is involved in T. gondii infection in the brain where it contributes to inflammatory responses and parasite elimination. We suggest that the inflammatory response by glial cells through CCR5 might be associated with neurological injury during T. gondii infection to some extent.

Involvement of Toll-like receptor 2 in the cerebral immune response and behavioral changes caused by latent Toxoplasma infection in mice.

Subacute and chronic infections with the intracellular protozoan parasite Toxoplasma gondii are associated with an increased risk of psychiatric diseases like schizophrenia. However, little is known about the mechanisms involved in T. gondii-induced neuronal disorders. Recently, we reported that Toll-like receptor 2 (TLR2) was required to initiate the innate immune response in cultured mouse brain cells. However, how TLR2 contributes to latent infection with T. gondii remains unclear. Therefore, we examined the role of TLR2 in brain pathology and behavior using wild-type (TLR2+/+) and TLR2-deficient (TLR2-/-) mice. The behavioral analyses showed that TLR2 deficiency increased the anxiety state of the uninfected and infected animals alike, and TLR2 deficiency showed no relationship with the infection. In the contextual and cued fear-conditioning tests, T. gondii infection decreased the mouse freezing reaction while TLR2 deficiency increased it, but there was no interaction between the two factors. Our histopathological analysis showed that the TLR2+/+ and TLR2-/- mice had similar brain lesions at 30 days post infection (dpi) with T. gondii. Higher numbers of parasites were detected in the brains of the TLR2-/- mice than in those from the TLR2+/+ mice at 30 dpi, but not at 7 and 14 dpi. No significant differences were observed in the proinflammatory gene expression levels in the TLR2+/+ and TLR2-/- mice. Therefore, it appears that TLR2 signaling in the brain might contribute to the control of parasite growth, but not to brain pathology or the impaired fear memory response induced by infection with T. gondii.

Neospora caninum Dense Granule Protein 7 Regulates the Pathogenesis of Neosporosis by Modulating Host Immune Response.

Neospora caninum is a protozoan parasite closely related to Toxoplasma gondii Neosporosis caused by N. caninum is considered one of the main causes of abortion in cattle and nervous-system dysfunction in dogs, and identification of the virulence factors of this parasite is important for the development of control measures. Here, we used a luciferase reporter assay to screen the dense granule proteins genes of N. caninum, and we found that NcGRA6, NcGRA7, and NcGRA14 are involved in the activation of the NF-κB, calcium/calcineurin, and cAMP/PKA signals. To analyze the functions of these proteins and Neospora cyclophilin, we successfully knocked out their genes in the Nc1 strain using plasmids containing the CRISPR/Cas9 components. Among the deficient lines, the NcGRA7-deficient parasites showed reduced virulence in mice. An RNA sequencing analysis of infected macrophage cultures showed that NcGRA7 mainly regulates the host cytokine and chemokine production. The levels of gamma interferon in the ascites fluid, CXCL10 expression in the peritoneal cells, and CCL2 expression in the spleen were lower 5 days after infection with the NcGRA7-deficient parasite than after infection with the parental strain. The parasite burden and the degree of necrosis in the brains of mice infected with the NcGRA7-deficient parasite were also lower than in those of the parental strain. Collectively, our data suggest that both the NcGRA7-dependent activation of the inflammatory response and the parasite burden are important in Neospora virulence.IMPORTANCENeospora caninum invades and replicates in a broad range of host species and cells within those hosts. The effector proteins exported by Neospora induce its pathogenesis by modulating the host immunity. We show that most of the transcriptomic effects in N. caninum-infected cells depend upon the activity of NcGRA7. A deficiency in NcGRA7 reduced the virulence of the parasite in mice. This study demonstrates the importance of NcGRA7 in the pathogenesis of neosporosis.

Development and evaluation of the first immunochromatographic test that can detect specific antibodies against Cryptosporidium parvum.

Cryptosporidium parvum is a major cause of diarrhea among human and calves, resulting in severe health hazards and drastic economic losses, respectively. Although C. parvum infection leads to high morbidity and mortality in immunocompromised patients and bovine calves, this infection remains a neglected disease. Currently available diagnostic tests for C. parvum are primarily based on detection of oocysts, DNA, or secreted antigens in fecal specimens. Demonstration of specific antibodies with a rapid immunochromatographic test (ICT) will be advantageous not only in providing a simple, rapid, accurate, and affordable tool but also in surveillance because of the ability to recognize recent and past infections. Herein, we developed two ICTs using the diagnostic antigen CpP23 and immunodominant antigen CpGP15 to detect C. parvum-specific antibodies in cattle sera. Because of unavailability of a reference test for antibody detection, evaluation and validation of our developed ICTs were conducted using reference cattle samples and unknown field cattle sera. Serum samples were simultaneously tested by a previously validated enzyme-linked immunosorbent assay (ELISA) using the same antigens (CpGP15 and CpP23). ICTs showed substantial ability to discriminate between positive and negative control cattle sera for both CpGP15 and CpP23. Even against field sera, high sensitivity, specificity, and agreement rates were recorded for ICTs compared with the previously validated ELISA with the same antigens (CpGP15 = 78.78%, 100%, and 85.11%; CpP23 = 80%, 100%, and 80.56%, respectively). Moreover, a high correlation was observed between the test band intensity of ICTs and optical density of ELISA, particularly in the case of CpP23-specific IgM. To our knowledge, this study represents the first development of ICTs that can detect C. parvum-specific antibodies. Our tests will contribute greatly to C. parvum infection control in cattle by providing a method for on-site diagnosis of early and latent infections.

Transcriptional profiling of Toll-like receptor 2-deficient primary murine brain cells during Toxoplasma gondii infection.

BACKGROUND: Toxoplasma gondii is capable of persisting in the brain, although it is efficiently eliminated by cellular immune responses in most other sites. While Toll-like receptor 2 (TLR2) reportedly plays important roles in protective immunity against the parasite, the relationship between neurological disorders induced by T. gondii infection and TLR2 function in the brain remains controversial with many unknowns. In this study, primary cultured astrocytes, microglia, neurons, and peritoneal macrophages obtained from wild-type and TLR2-deficient mice were exposed to T. gondii tachyzoites. To characterize TLR2-dependent functional pathways activated in response to T. gondii infection, gene expression of different cell types was profiled by RNA sequencing. RESULTS: During T. gondii infection, a total of 611, 777, 385, and 1105 genes were upregulated in astrocytes, microglia, neurons, and macrophages, respectively, while 163, 1207, 158, and 1274 genes were downregulated, respectively, in a TLR2-dependent manner. Overrepresented Gene Ontology (GO) terms for TLR2-dependently upregulated genes were associated with immune and stress responses in astrocytes, immune responses and developmental processes in microglia, metabolic processes and immune responses in neurons, and metabolic processes and gene expression in macrophages. Overrepresented GO terms for downregulated genes included ion transport and behavior in astrocytes, cell cycle and cell division in microglia, metabolic processes in neurons, and response to stimulus, signaling and cell motility in macrophages. CONCLUSIONS: To our knowledge, this is the first transcriptomic study of TLR2 function across different cell types during T. gondii infection. Results of RNA-sequencing demonstrated roles for TLR2 varied by cell type during T. gondii infection. Our findings facilitate understanding of the detailed relationship between TLR2 and T. gondii infection, and elucidate mechanisms underlying neurological changes during infection.

Toxoplasma gondii Infection in Mice Impairs Long-Term Fear Memory Consolidation through Dysfunction of the Cortex and Amygdala.

Chronic infection with Toxoplasma gondii becomes established in tissues of the central nervous system, where parasites may directly or indirectly modulate neuronal function. Epidemiological studies have revealed that chronic infection in humans is a risk factor for developing mental diseases. However, the mechanisms underlying parasite-induced neuronal dysfunction in the brain remain unclear. Here, we examined memory associated with conditioned fear in mice and found that T. gondii infection impairs consolidation of conditioned fear memory. To examine the brain pathology induced by T. gondii infection, we analyzed the parasite load and histopathological changes. T. gondii infects all brain areas, yet the cortex exhibits more severe tissue damage than other regions. We measured neurotransmitter levels in the cortex and amygdala because these regions are involved in fear memory expression. The levels of dopamine metabolites but not those of dopamine were increased in the cortex of infected mice compared with those in the cortex of uninfected mice. In contrast, serotonin levels were decreased in the amygdala and norepinephrine levels were decreased in the cortex and amygdala of infected mice. The levels of cortical dopamine metabolites were associated with the time spent freezing in the fear-conditioning test. These results suggest that T. gondii infection affects fear memory through dysfunction of the cortex and amygdala. Our findings provide insight into the mechanisms underlying the neurological changes seen during T. gondii infection.

Changes in neurotransmitter levels and expression of immediate early genes in brain of mice infected with Neospora caninum.

Neospora caninum is an obligate intracellular parasite that causes neurological disorders in dogs and cattle. The majority of host animals are asymptomatic at the chronic stage of infection. However, it remains unclear whether cerebral function is normal in asymptomatic animals. In this study, mice were infected with N. caninum (strain Nc-1) and their brains were examined to understand changes in cerebral function at the chronic stage of infection. Mice infected with N. caninum showed impaired locomotor activity, but no differences in clinical symptoms were observed. In the brains of infected mice, parasites were distributed throughout the brain and histological lesions were observed everywhere except for the cerebellum. Expression levels of proinflammatory cytokines, interferon-gamma and tumour necrosis factor-alpha, were highly upregulated in several brain regions of infected mice. Additionally, the level of neurotransmitters glutamate, glycine, gamma-aminobutyric acid, dopamine and 5-hydroxytryptamine, were altered in infected mice compared with those of uninfected mice. Interestingly, the expression levels of immediately early genes, c-Fos and Arc, in the brain of infected mice were lower than those of in uninfected mice. Our findings may provide insight into neurological disorders associated with N. caninum infection.

Induction of depression-related behaviors by reactivation of chronic Toxoplasma gondii infection in mice.

Although Toxoplasma gondii (T. gondii) infection is relevant to many psychiatric disorders, the fundamental mechanisms of its neurobiological correlation with depression are poorly understood. Here, we show that reactivation of chronic infection by an immunosuppressive regimen caused induction of depressive-like behaviors without obvious sickness symptoms. However, the depression-related behaviors in T. gondii-infected mice, specifically, reduced sucrose preference and increased immobility in the forced-swim test were observed at the reactivation stage, but not in the chronic infection. Interestingly, reactivation of T. gondii was associated with production of interferon-gamma and activation of brain indoleamine 2, 3-dioxygenase, which converts tryptophan to kynurenine and makes it unavailable for serotonin synthesis. Furthermore, serotonin turnover to its major metabolite, 5-hydroxyindoleacetic acid, was also enhanced at the reactivation stage. Thus, enhanced tryptophan catabolic shunt and serotonin turnover may be implicated in development of depressive-like behaviors in mice with reactivated T. gondii.

Role of the chemokine receptor CCR5-dependent host defense system in Neospora caninum infections.

BACKGROUND: Neospora caninum, a Toxoplasma gondii-like obligate intracellular parasite, causes abortion in cattle and neurological signs in canines. To understand neosporosis better, studies on host cell migration and host immune responses during the early phase of infection are important. Although the C-C chemokine receptor 5 (CCR5) plays a crucial role in immune cell migration, the role played by it in protective immunity against N. caninum is poorly understood. METHODS: CCR5(-/-) mice were used to investigate their sensitivity levels to N. caninum infection and their ability to activate immune cells against this parasite. RESULTS: Increased mortality and neurological impairment were observed in the N. caninum-infected CCR5(-/-) mice. In comparison with wild-type mice, CCR5(-/-) mice experienced poor migration of dendritic cells and natural killer T cells to the site of infection. Dendritic cells in an in vitro culture from CCR5(-/-) mice could not be activated upon infection with N. caninum. Furthermore, higher levels of IFN-γ and CCL5 expression, which are associated with brain tissue damage, were observed in the brain tissue of CCR5(-/-) mice during the acute phase of the infection, while there was no significant difference in the parasite load between the wild-type and CCR5(-/-) animals. Additionally, a primary microglia culture from CCR5(-/-) mice showed lower levels of IL-6 and IL-12 production against N. caninum parasites. CONCLUSIONS: Our findings show that migration and activation of immune cells via CCR5 is required for controlling N. caninum parasites during the early phase of the infection.

Transcriptome and histopathological changes in mouse brain infected with Neospora caninum.

Neospora caninum is a protozoan parasite that causes neurological disorders in dogs and cattle. It can cause nonsuppurative meningoencephalitis and a variety of neuronal symptoms are observed, particularly in dogs. However, the pathogenic mechanism, including the relationship between the parasite distribution and the clinical signs, is unclear. In this study, to understand the pathogenic mechanism of neosporosis, parasite distribution and lesions were assessed in the brain of mice infected with N. caninum (strain Nc-1). Host gene expression was also analyzed with RNA sequencing (RNA-Seq). The histopathological lesions in the frontal lobe and the medulla oblongata were significantly more severe in symptomatic mice than in asymptomatic mice, although no association between the severity of the lesions and parasite numbers was found. In infected mice, the expression of 772 mouse brain genes was upregulated. A GOstat analysis predicted that the upregulated genes were involved in the host immune response. Genes whose expression correlated positively and negatively with parasite numbers were involved in the host immune response, and neuronal morphogenesis and lipid metabolic processes, respectively. These results suggest that changes in the gene expression profile associated with neuronal functions as well as immune responses can contribute to the pathogenesis in N. caninum-infected animals.

Starvation of low-density lipoprotein-derived cholesterol induces bradyzoite conversion in Toxoplasma gondii.

BACKGROUND: Lacking enzymes for sterol synthesis, the intracellular protozoan Toxoplasma gondii scavenges cholesterol from host cells to multiply. T. gondii has a complex life cycle consisting of two asexual stages; the proliferative stage (tachyzoite), and the latent stage characterized by tissue cysts (bradyzoite). In vitro, bradyzoite development can be induced by mimicking host immune response stressors through treatment with IFN-γ, heat shock, nitric oxide, and high pH. However, the extent to which host nutrients contribute to stage conversion in T. gondii is unknown. In this study, we examined the impact of host cholesterol levels on stage conversion in this parasite. METHODS: Growth of T. gondii tachyzoites (ME49 strain) was investigated in Chinese hamster ovary (CHO) cells using various concentrations of low-density lipoprotein (LDL), oleic acid, or glucose. Squalestatin, which is an inhibitor of squalene synthase and is, therefore, an inhibitor of sterol synthesis, was used to treat the CHO cells. Tachyzoite to bradyzoite conversion rates were analyzed by indirect fluorescent antibody tests. RESULTS: Parasite growth was significantly enhanced by addition of exogenous LDL, whereas no such enhancement occurred with oleic acids or glucose. In ME49, growth inhibition from squalestatin treatment was not obvious. Although growth of the RH strain was unaffected by squalestatin in the presence of lipoprotein, in its absence growth of this strain was suppressed. The frequency of BAG1-positive vacuoles in ME49 increased under lipoprotein-free conditions. However, addition of exogenous LDL did not increase tachyzoite to bradyzoite conversion in this strain. Furthermore, treatment with squalestatin did not enhance stage conversion. CONCLUSION: Our results suggest that LDL-derived cholesterol levels play a crucial role in bradyzoite conversion in T. gondii.

Macrophage depletion prior to Neospora caninum infection results in severe neosporosis in mice.

We observed that murine macrophages showed greater activation and increased interleukin 6 (IL-6), IL-12p40, and interferon gamma (IFN-γ) production during Neospora caninum infection. Many macrophages migrated to the site of infection. Furthermore, macrophage-depleted mice exhibited increased sensitivity to N. caninum infection. This study indicates that macrophages are required for achieving protective immunity against N. caninum.

Vaccination with profilin encapsulated in oligomannose-coated liposomes induces significant protective immunity against Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular parasite that can infect a variety of mammals and birds, causing toxoplasmosis. Several types of vaccines against T. gondii have been developed, but these have limitations in terms of their safety and inadequate efficacy. T. gondii profilin (TgPF) is a potential immunodominant antigen for a candidate vaccine. In this study, we encapsulated TgPF in oligomannose-coated liposomes (OMLs) to evaluate the immune response induced by this vaccine. C57BL/6 mice were immunized with TgPF-OML three times at 14-day intervals and challenged with T. gondii. TgPF-OML increased the survival of the mice and reduced the parasite burden in their brains after T. gondii infection. Immunization with TgPF-OML also induced TgPF-specific interferon-γ production and IgG antibodies in mice. Our results demonstrate that OML-encapsulated TgPF triggers strong humoral and cellular responses against T. gondii, and that TgPF-OML is a candidate vaccine that warrants further development.

Transcriptome analysis of mouse brain infected with Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular parasite that invades a wide range of vertebrate host cells. Chronic infections with T. gondii become established in the tissues of the central nervous system, where the parasites may directly or indirectly modulate neuronal function. However, the mechanisms underlying parasite-induced neuronal disorder in the brain remain unclear. This study evaluated host gene expression in mouse brain following infection with T. gondii. BALB/c mice were infected with the PLK strain, and after 32 days of infection, histopathological lesions in the frontal lobe were found to be more severe than in other areas of the brain. Total RNA extracted from infected and uninfected mouse brain samples was subjected to transcriptome analysis using RNA sequencing (RNA-seq). In the T. gondii-infected mice, 935 mouse brain genes were upregulated, whereas 12 genes were downregulated. GOstat analysis predicted that the upregulated genes were primarily involved in host immune responses and cell activation. Positive correlations were found between the numbers of parasites in the infected mouse brains and the expression levels of genes involved in host immune responses. In contrast, genes that had a negative correlation with parasite numbers were predicted to be involved in neurological functions, such as small-GTPase-mediated signal transduction and vesicle-mediated transport. Furthermore, differential gene expression was observed between mice exhibiting the clinical signs of toxoplasmosis and those that did not. Our findings may provide insights into the mechanisms underlying neurological changes during T. gondii infection.