The Development of Toxoplasma gondii Recombinant Trivalent Chimeric Proteins as an Alternative to Toxoplasma Lysate Antigen (TLA) in Enzyme-Linked Immunosorbent Assay (ELISA) for the Detection of Immunoglobulin G (IgG) in Small Ruminants

This study presents an evaluation of seventeen newly produced recombinant trivalent chimeric proteins (containing the same immunodominant fragment of SAG1 and SAG2 of Toxoplasma gondii antigens, and an additional immunodominant fragment of one of the parasite antigens, such as AMA1, GRA1, GRA2, GRA5, GRA6, GRA7, GRA9, LDH2, MAG1, MIC1, MIC3, P35, and ROP1) as a potential alternative to the whole-cell tachyzoite lysate (TLA) used in the detection of infection in small ruminants. These recombinant proteins, obtained by genetic engineering and molecular biology methods, were tested for their reactivity with specific anti-Toxoplasma IgG antibodies contained in serum samples of small ruminants (192 samples of sheep serum and 95 samples of goat serum) using an enzyme-linked immunosorbent assay (ELISA). The reactivity of six recombinant trivalent chimeric proteins (SAG1-SAG2-GRA5, SAG1-SAG2-GRA9, SAG1-SAG2-MIC1, SAG1-SAG2-MIC3, SAG1-SAG2-P35, and SAG1-SAG2-ROP1) with IgG antibodies generated during T. gondii invasion was comparable to the sensitivity of TLA-based IgG ELISA (100%). The obtained results show a strong correlation with the results obtained for TLA. This suggests that these protein preparations may be a potential alternative to TLA used in commercial tests and could be used to develop a cheaper test for the detection of parasite infection in small ruminants.

IL-12 Mediates T-bet-Expressing Myeloid Cell-Dependent Host Resistance against Toxoplasma gondii

To defend against intracellular pathogens such as Toxoplasma gondii, the host generates a robust type 1 immune response. Specifically, host defense against T. gondii is defined by an IL-12-dependent IFN-γ response that is critical for host resistance. Previously, we demonstrated that host resistance is mediated by T-bet-dependent ILC-derived IFN-γ by maintaining IRF8+ conventional type 1 dendritic cells during parasitic infection. Therefore, we hypothesized that innate lymphoid cells are indispensable for host survival. Surprisingly, we observed that T-bet-deficient mice succumb to infection quicker than do mice lacking lymphocytes, suggesting an unknown T-bet-dependent-mediated host defense pathway. Analysis of parasite-mediated inflammatory myeloid cells revealed a novel subpopulation of T-bet+ myeloid cells (TMCs). Our results reveal that TMCs have the largest intracellular parasite burden compared with other professional phagocytes, suggesting they are associated with active killing of T. gondii. Mechanistically, we established that IL-12 is necessary for the induction of inflammatory TMCs during infection and these cells are linked to a role in host survival.

Diagnostic Value of Circulating Antigens in the Serum of Piglets with Experimental Acute Toxoplasmosis

Toxoplasmosis, caused by Toxoplasma gondii, an apicomplexan parasite, infects all warm-blooded animals, including a third of the human population. Laboratory diagnosis of acute toxoplasmosis is based on the detection of anti-T. gondii IgM and IgG and T. gondii nucleic acid; however, these assays have certain limitations. Circulating Ags (CAgs) are reliable diagnostic indicators of acute infection. In this study, we established a model of acute T. gondii infection in Large White pigs. CAg levels peaked between 3 and 5 d after inoculation, and 28 CAgs were identified using an immunoprecipitation-shotgun approach, among which dolichol-phosphate-mannose synthase family protein (TgDPM), C3HC zinc finger-like protein (TgZFLP3), and ribosomal protein RPL7 (TgRPL7) were selected to further investigate their value in the diagnosis of acute toxoplasmosis. Immunofluorescence assays revealed that TgDPM and TgRPL7 were localized in the membrane surface, while TgZFLP3 was localized in the apical end. Western blotting revealed the presence of the three proteins in the serum during acute infection. Indirect ELISA results indicate that TgZFLP3 is likely to be a novel candidate for the diagnosis of acute toxoplasmosis. However, these three proteins may not be useful as candidate vaccines against toxoplasmosis owing to their low protective ability. In addition, deletion of the zflp3 gene partially attenuated virulence in Kunming mice. Collectively, we identified 28 CAgs in the serum of piglets with experimental acute toxoplasmosis and confirmed that TgZFLP3 is a potential biomarker for acute T. gondii infection. The results of this study provide data to improve the detection efficiency of acute toxoplasmosis.

CXCR3 regulates stem and proliferative CD8+ T cells during chronic infection by promoting interactions with DCs in splenic bridging channels

Production of effector CD8+ T cells during persistent infection requires a stable pool of stem-like cells that can give rise to effector cells via a proliferative intermediate population. In infection models marked by T cell exhaustion, this process can be transiently induced by checkpoint blockade but occurs spontaneously in mice chronically infected with the protozoan intracellular parasite Toxoplasma gondii. We observe distinct locations for parasite-specific T cell subsets, implying a link between differentiation and anatomical niches in the spleen. Loss of the chemokine receptor CXCR3 on T cells does not prevent white pulp-to-red pulp migration but reduces interactions with CXCR3 ligand-producing dendritic cells (DCs) and impairs memory-to-intermediate transition, leading to a buildup of memory T cells in the red pulp. Thus, CXCR3 increases T cell exposure to differentiation-inducing signals during red pulp migration, providing a dynamic mechanism for modulating effector differentiation in response to environmental signals.

Bangs et al. report that distinct subsets of CD8+ T cells found during chronic infection occupy distinct regions of the spleen. CXCR3 regulates differentiation of T cells but not their migration. Instead, CXCR3 promotes the interaction of T cells with ligand-producing DCs in bridging channels, resulting in effector differentiation.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Recombinant Toxoplasma gondii MIF, CDPK3, and 14-3-3 Protein Cocktail Vaccine

Toxoplasma gondii can infect almost all endotherm organisms including humans and cause life-threatening toxoplasmosis in immunocompromised individuals, which leads to serious public health problems. Developing an excellent vaccine against this disease is impending. In present study, we formulated a cocktail protein vaccine including the TgMIF, TgCDPK3, and Tg14-3-3 proteins, which play critical roles in T. gondii infection. The recombinant protein vaccines were constructed and assessed by vaccination in BALB/c mice. We organized the mice in various protein combination groups of vaccines, and all mice were immunized with corresponding proteins at 0, 2, and 4 weeks. The specific protective effects of the vaccines on mice against T. gondii were analyzed by the mensuration of cytokines, serum antibodies, splenocyte proliferation assay, survival time, and parasite cyst burden of mice after the challenge. The study indicated that mice immunized with all three multicomponent proteins vaccine triggered a strong immune response with highest levels of IFN-γ production and IgG antibody compared with the other two protein combinations and controls. Moreover, there was an increase in IL-4 production and antigen-specific lymphocyte proliferation. The parasite cysts were significantly reduced (resulting in an 82.7% reduction), and survival time was longer in immunized mice with three multicomponent proteins compared with the other groups of mice. The enhanced humoral and cell-mediated immunity indicated that the protein cocktail vaccine containing three antigens provided effective protection for mice. These results indicated that recombinant TgMIF, TgCDPK3, and Tg14-3-3 multicomponent proteins were potential candidates for vaccine against toxoplasmosis.

Protein expression of the tear film of domestic cats before and after inoculation with Toxoplasma gondii

BACKGROUND

Tear film (TF) helps maintain and protect ocular function against damage to the ocular surface. Proteins are one of its main constituents, whose expression pattern can be used as a biomarker of ocular changes and systemic diseases. The aim of this study was to evaluate the expression of proteins in the TF of domestic cats before and after infection with Toxoplasma gondii, in the phases of acute infection and chronicity. Twelve healthy cats received orally homogenized brain matter obtained from mice inoculated with T. gondii oocysts, strain ME49. Cat feces were collected daily from the third day after infection to assess the release of oocysts. TF samples were obtained from cats, by Schirmer's Tear Test 1, on day 0 (before infection), day 5 after infection (acute phase of infection, with maximum peak release of oocysts in feces) and on day 21 after infection (start of chronic phase, 7 days after total absence of oocyst release in feces). Tear samples were also submitted to proteomic analysis in a Q-Tof-Premier mass spectrometer.

RESULTS

A total of 37 proteins with scores equal to or greater than 100 were identified on D0, followed by 36 on D5 and 42 on D21. Of these, 27 were common to D0 and D5, 33 to D0 and D21, 27 to D5 and D21, and 26 were common to the three groups, totaling 54 proteins. The most abundant proteins were lipocalin allergen Fel d, serum albumin, aldehyde dehydrogenase, lactoperoxidase and lactotransferrin. There was no significant difference in the abundance of proteins found on D0 and D5, but there was a statistical difference between D0 and D21 for ACT1_AEDAE, CERU_HUMAN and GELS_HUMAN. Regarding D5 and D21, there were significant differences for KV1_CANLF, LAC_PIG, TRFL_PIG, ACT1_AEDAE, CERU_HUMAN, GELS_HUMAN and OVOS2_HUMAN.

CONCLUSIONS

The main proteins identified in the TF of domestic cats are similar to those found in humans and other animal species. Most are part of the ocular surface defense system against injuries. The most expressed proteins in animals in the chronic phase of T. gondii infection are associated with the immune response to the parasite.

Genetic mapping reveals Nfkbid as a central regulator of humoral immunity to Toxoplasma gondii

Protective immunity to parasitic infections has been difficult to elicit by vaccines. Among parasites that evade vaccine-induced immunity is Toxoplasma gondii, which causes lethal secondary infections in chronically infected mice. Here we report that unlike susceptible C57BL/6J mice, A/J mice were highly resistant to secondary infection. To identify correlates of immunity, we utilized forward genetics to identify Nfkbid, a nuclear regulator of NF-κB that is required for B cell activation and B-1 cell development. Nfkbid-null mice (“bumble”) did not generate parasite-specific IgM and lacked robust parasite-specific IgG, which correlated with defects in B-2 cell maturation and class-switch recombination. Though high-affinity antibodies were B-2 derived, transfer of B-1 cells partially rescued the immunity defects observed in bumble mice and were required for 100% vaccine efficacy in bone marrow chimeric mice. Immunity in resistant mice correlated with robust isotype class-switching in both B cell lineages, which can be fine-tuned by Nfkbid gene expression. We propose a model whereby humoral immunity to T. gondii is regulated by Nfkbid and requires B-1 and B-2 cells for full protection.

Eukaryotic parasitic diseases account for approximately one fifth of all childhood deaths, yet no highly protective vaccine exists for any human parasite. More research must be done to discover how to elicit protective vaccine-induced immunity to parasitic pathogens. We used an unbiased genetic screen to find key genes responsible for immunity to the eukaryotic parasite Toxoplasma gondii. Our screen found Nfkbid, a transcription factor regulator, which controls B cell activation and innate-like B-1 cell development. Mice without Nfkbid were not protected against T. gondii and were deficient at making antibodies against the parasite. Our survival studies of vaccinated mice with and without B-1 compartments found that B-1 cells improved survival, suggesting that B-1 cells act in conjunction with B-2 cells to provide vaccine-induced immunity. Nfkbid and other loci identified in our unbiased screen represent potential targets for vaccines to elicit protective immune responses against parasitic pathogens.

Characterization of extracellular vesicles isolated from types I, II and III strains of Toxoplasma gondii

This study investigated the participation extracellular vesicles (EVs) in Toxoplasma gondii-host interaction. EVs of three T. gondii strains (RH, ME-49 and VEG) were purified by chromatography and ELISA. Results of "nanoparticle tracking analysis" and scanning electron microscopy showed that RH strain released more EVs than other strains. Images of transmission electron microscopy showed that in beginning of incubation (culture medium), EVs were inside of tachyzoites preparing to be released. After 24 hours, they were largely produced inside tachyzoites and were released through plasma membrane. The parasite burden of mice infected with RH strain plus EVs was increased and with early death of 1-2 days compared of those that received only parasites. EV proteins of ME-49 and VEG strains were poorly reactive to sera of infected patients in imunoblot. However, those from RH strain were reactive against sera of patients with cerebral toxoplasmosis. EVs stimulated murine splenocytes caused similar production of IFN-γ and IL-10 levels. RH strain derived EVs stimulated more TNF-α than those stimulated by other strains. T. gondii and infected hosts can express the same miRNAs (miR-155-5p, miR-125b-5p, miR-423-3p). In conclusion, T. gondii derived EVs promote host-parasite interactions, modulate host immune responses, carry virulent factors and cause an imbalance in cellular immune response.

Toxoplasma gondii infections are associated with costly boldness toward felids in a wild host

Toxoplasma gondii is hypothesized to manipulate the behavior of warm-blooded hosts to promote trophic transmission into the parasite's definitive feline hosts. A key prediction of this hypothesis is that T. gondii infections of non-feline hosts are associated with costly behavior toward T. gondii's definitive hosts; however, this effect has not been documented in any of the parasite's diverse wild hosts during naturally occurring interactions with felines. Here, three decades of field observations reveal that T. gondii-infected hyena cubs approach lions more closely than uninfected peers and have higher rates of lion mortality. We discuss these results in light of 1) the possibility that hyena boldness represents an extended phenotype of the parasite, and 2) alternative scenarios in which T. gondii has not undergone selection to manipulate behavior in host hyenas. Both cases remain plausible and have important ramifications for T. gondii's impacts on host behavior and fitness in the wild.

Early immune responses and parasite tissue distribution in mice experimentally infected with oocysts of either archetypal or non-archetypal genotypes of Toxoplasma gondii

In most of the world Toxoplasma gondii is comprised of archetypal types (types I, II and III); however, South America displays several non-archetypal strains. This study used an experimental mouse model to characterize the immune response and parasite kinetics following infection with different parasite genotypes. An oral inoculation of 50 oocysts per mouse from T. gondii M4 type II (archetypal, avirulent), BrI or BrIII (non-archetypal, virulent and intermediate virulent, respectively) for groups (G)2, G3 and G4, respectively was used. The levels of mRNA expression of cytokines, immune compounds, cell surface markers and receptor adapters [interferon gamma (IFNγ), interleukin (IL)-12, CD8, CD4, CD25, CXCR3 and MyD88] were quantified by SYBR green reverse transcription-quantitative polymerase chain reaction. Lesions were characterized by histology and detection by immunohistochemistry established distribution of parasites. Infection in G2 mice was mild and characterized by an early MyD88-dependent pathway. In G3, there were high levels of expression of pro-inflammatory cytokines IFNγ and IL-12 in the mice showing severe clinical symptoms at 8–11 days post infection (dpi), combined with the upregulation of CD25, abundant tachyzoites and tissue lesions in livers, lungs and intestines. Significant longer expression of IFNγ and IL-12 genes, with other Th1-balanced immune responses, such as increased levels of CXCR3 and MyD88 in G4, resulted in survival of mice and chronic toxoplasmosis, with the occurrence of tissue cysts in brain and lungs, at 14 and 21 dpi. Different immune responses and kinetics of gene expression appear to be elicited by the different strains and non-archetypal parasites demonstrated higher virulence.

Toxoplasma Infection Induces Sustained Up-Regulation of Complement Factor B and C5a Receptor in the Mouse Brain via Microglial Activation: Implication for the Alternative Complement Pathway Activation and Anaphylatoxin Signaling in Cerebral Toxoplasmosis

Toxoplasma gondii is a neurotropic protozoan parasite, which is linked to neurological manifestations in immunocompromised individuals as well as severe neurodevelopmental sequelae in congenital toxoplasmosis. While the complement system is the first line of host defense that plays a significant role in the prevention of parasite dissemination, Toxoplasma artfully evades complement-mediated clearance via recruiting complement regulatory proteins to their surface. On the other hand, the details of Toxoplasma and the complement system interaction in the brain parenchyma remain elusive. In this study, infection-induced changes in the mRNA levels of complement components were analyzed by quantitative PCR using a murine Toxoplasma infection model in vivo and primary glial cells in vitro. In addition to the core components C3 and C1q, anaphylatoxin C3a and C5a receptors (C3aR and C5aR1), as well as alternative complement pathway components properdin (CFP) and factor B (CFB), were significantly upregulated 2 weeks after inoculation. Two months post-infection, CFB, C3, C3aR, and C5aR1 expression remained higher than in controls, while CFP upregulation was transient. Furthermore, Toxoplasma infection induced significant increase in CFP, CFB, C3, and C5aR1 in mixed glial culture, which was abrogated when microglial activation was inhibited by pre-treatment with minocycline. This study sheds new light on the roles for the complement system in the brain parenchyma during Toxoplasma infection, which may lead to the development of novel therapeutic approaches to Toxoplasma infection-induced neurological disorders.

Prevalence of Toxoplasma gondii Antibodies in Stray Dogs from Various Locations in West and East Malaysia

Toxoplasmosis is caused by an obligate intracellular protozoan parasite; Toxoplasma gondii, which is one of the most important zoonotic parasite worldwide. In dogs, the sexual reproductive cycle of T. gondii is lacking, and the animals are not widely consumed as food, but they are vital in the mechanical transmission of the parasite. However, there is no present data on the exposure of stray dogs to T. gondii in Malaysia. The objective of this serological survey was to determine the prevalence of T. gondii antibodies (IgG) and associated factors in stray dogs in East and West Malaysia. Antibodies to T. gondii were determined in serum samples from 222 stray dogs from 6 different states in East and West Malaysia (Peninsular Malaysia) using an Indirect ELISA. The seroprevalence for T. gondii was 23.4% (Confidence interval: CI 17.8-29.2%). Stray dogs from Selangor and Kuala Lumpur had the highest seroprevalence (32.4%; CI 13.2-45.5%) and lowest in those from Penang and Kedah (12.5%; CI 1.3-23.5%). Gender and breed were not associated with T. gondii seropositivity. However, adult dogs were more likely to be seropositive for T. gondii (OR=2.89; CI 1.1-7.7) compared with younger dogs. These results revealed that T. gondii is prevalent in stray dogs in the studied areas in Malaysia, and indicative of the level of environmental contamination of this parasite especially in urban areas.

Naïve CD8 T cell IFNγ responses to a vacuolar antigen are regulated by an inflammasome-independent NLRP3 pathway and Toxoplasma gondii ROP5

Host resistance to Toxoplasma gondii relies on CD8 T cell IFNγ responses, which if modulated by the host or parasite could influence chronic infection and parasite transmission between hosts. Since host-parasite interactions that govern this response are not fully elucidated, we investigated requirements for eliciting naïve CD8 T cell IFNγ responses to a vacuolar resident antigen of T. gondii, TGD057. Naïve TGD057 antigen-specific CD8 T cells (T57) were isolated from transnuclear mice and responded to parasite-infected bone marrow-derived macrophages (BMDMs) in an antigen-dependent manner, first by producing IL-2 and then IFNγ. T57 IFNγ responses to TGD057 were independent of the parasite’s protein export machinery ASP5 and MYR1. Instead, host immunity pathways downstream of the regulatory Immunity-Related GTPases (IRG), including partial dependence on Guanylate-Binding Proteins, are required. Multiple T. gondii ROP5 isoforms and allele types, including ‘avirulent’ ROP5A from clade A and D parasite strains, were able to suppress CD8 T cell IFNγ responses to parasite-infected BMDMs. Phenotypic variance between clades B, C, D, F, and A strains suggest T57 IFNγ differentiation occurs independently of parasite virulence or any known IRG-ROP5 interaction. Consistent with this, removal of ROP5 is not enough to elicit maximal CD8 T cell IFNγ production to parasite-infected cells. Instead, macrophage expression of the pathogen sensors, NLRP3 and to a large extent NLRP1, were absolute requirements. Other members of the conventional inflammasome cascade are only partially required, as revealed by decreased but not abrogated T57 IFNγ responses to parasite-infected ASC, caspase-1/11, and gasdermin D deficient cells. Moreover, IFNγ production was only partially reduced in the absence of IL-12, IL-18 or IL-1R signaling. In summary, T. gondii effectors and host machinery that modulate parasitophorous vacuolar membranes, as well as NLR-dependent but inflammasome-independent pathways, determine the full commitment of CD8 T cells IFNγ responses to a vacuolar antigen.

Parasites are excellent “students” of our immune system as they can deflect, antagonize and confuse the immune response making it difficult to vaccinate against these pathogens. In this report, we analyzed how a widespread parasite of mammals, Toxoplasma gondii, manipulates an immune cell needed for immunity to many intracellular pathogens, the CD8 T cell. Host pathways that govern CD8 T cell production of the immune protective cytokine, IFNγ, were also explored. We hypothesized the secreted T. gondii virulence factor, ROP5, work to inhibit the MHC 1 antigen presentation pathway therefore making it difficult for CD8 T cells to see T. gondii antigens sequestered inside a parasitophorous vacuole. However, manipulation through T. gondii ROP5 does not fully explain how CD8 T cells commit to making IFNγ in response to infection. Importantly, CD8 T cell IFNγ responses to T. gondii require the pathogen sensor NLRP3 to be expressed in the infected cell. Other proteins associated with NLRP3 activation, including members of the conventional inflammasome activation cascade pathway, are only partially involved. Our results identify a novel pathway by which NLRP3 regulates T cell function and underscore the need for NLRP3-activating adjuvants in vaccines aimed at inducing CD8 T cell IFNγ responses to parasites.

The zebrafish as a novel model for the in vivo study of Toxoplasma gondii replication and interaction with macrophages

Toxoplasma gondii is an obligate intracellular parasite capable of invading any nucleated cell. Three main clonal lineages (type I, II, III) exist and murine models have driven the understanding of general and strain-specific immune mechanisms underlying Toxoplasma infection. However, murine models are limited for studying parasite-leukocyte interactions in vivo, and discrepancies exist between cellular immune responses observed in mouse versus human cells. Here, we developed a zebrafish infection model to study the innate immune response to Toxoplasma in vivo By infecting the zebrafish hindbrain ventricle, and using high-resolution microscopy techniques coupled with computer vision-driven automated image analysis, we reveal that Toxoplasma invades brain cells and replicates inside a parasitophorous vacuole to which type I and III parasites recruit host cell mitochondria. We also show that type II and III strains maintain a higher infectious burden than type I strains. To understand how parasites are cleared in vivo, we further analyzed Toxoplasma-macrophage interactions using time-lapse microscopy and three-dimensional correlative light and electron microscopy (3D CLEM). Time-lapse microscopy revealed that macrophages are recruited to the infection site and play a key role in Toxoplasma control. High-resolution 3D CLEM revealed parasitophorous vacuole breakage in brain cells and macrophages in vivo, suggesting that cell-intrinsic mechanisms may be used to destroy the intracellular niche of tachyzoites. Together, our results demonstrate in vivo control of Toxoplasma by macrophages, and highlight the possibility that zebrafish may be further exploited as a novel model system for discoveries within the field of parasite immunity.This article has an associated First Person interview with the first author of the paper.

Molecular identification of Toxoplasma gondii in domesticated and broiler chickens (Gallus domesticus) that possibly augment the pool of human toxoplasmosis

Toxoplasma gondii (T. gondii) is a protozoan parasite that infects all warm-blooded animals including domesticated birds and humans. Birds normally get infected by ground feeding and human beings contract the disease by consumption of undercooked chicken meat. This study aimed to analyze seroprevalence and DNA of T. gondii in chickens (domesticated and broiler) and to assess possible transfer to humans by review of available literature from Pakistan. Blood from and tissues from domesticated and broilers chickens were analyzed for Toxo-IgM/IgG and Toxoplasma DNA through ELISA and PCR respectively. Furthermore, research articles published during 1990-2019 on the prevalence of T. gondii in humans from Pakistan, were analyzed to assess the possible infection burden in the area in connection to transmission from chickens. The overall prevalence of IgM and IgG for T. gondii was 17.83% and 8.8% respectively in the study areas. Significant seroprevalence was found in domesticated chickens than broilers. In domesticated chickens, the prevalence was high in age ≥ 2 years. Toxoplasma DNA was detected in tissues with an overall prevalence of 10.84%. Higher prevalence was observed in liver (10.50%) than heart (9.5%) and muscles (7.11%). Only 4.78% broiler and 2.38% domesticated chickens were positive for both IgM and DNA, 1.2% domesticated and 1.30% broilers were positive for IgG and DNA, while 2.98% domesticated and 2.17% broilers were positive for IgM, IgG, and DNA. Available literature showed that 25.8% of human beings were infected with T. gondii in Pakistan. The prevalence was 20.64% in male and 26.82%in the female. The rate of infections increases with age and high (37.36%) was found in humans of age range 40 to 60 years. A high prevalence of T. gondii is found in both domesticated and broiler chickens in the study area. Moreover, the literature survey indicates that a high seroprevalence of T. gondii is present in human beings of Pakistan. It is concluded that the high prevalence of T. gondii in humans may be associated with the parasite transmission through infected chicken's meat in Pakistan.

Dolphin-derived NETosis results in rapid Toxoplasma gondii tachyzoite ensnarement and different phenotypes of NETs

Toxoplasma gondii is a cosmopolitan zoonotic parasite and nowadays considered as an emerging neozoan pathogen in the marine environment. Cetacean innate immune reactions against T. gondii stages have not yet been investigated. Thus, T. gondii tachyzoites were utilized to trigger neutrophil extracellular traps (NETs) in bottlenose dolphin (Tursiops truncatus) polymorphonuclear neutrophils (PMN). Scanning electron microscopy unveiled T. gondii tachyzoites as potent and rapid inducers of cetacean-derived NETosis. Co-localization of extracellular chromatin with global histones, granulocytic myeloperoxidase and neutrophil elastase confirmed classical characteristics of NETosis. Interestingly, different phenotypes of NETs were induced by tachyzoites resulting in spread, diffuse and aggregated NET formation and moreover, 'anchored' and 'cell free' NETosis was also detected. Current data indicate that cetacean-derived NETosis might represent an early, ancient and well-conserved host innate defense mechanism that not only acts against T. gondii but might also occur in response to other closely related emerging apicomplexan parasites affecting marine cetaceans.

The ROP16III-dependent early immune response determines the subacute CNS immune response and type III Toxoplasma gondii survival

Toxoplasma gondii is an intracellular parasite that persistently infects the CNS and that has genetically distinct strains which provoke different acute immune responses. How differences in the acute immune response affect the CNS immune response is unknown. To address this question, we used two persistent Toxoplasma strains (type II and type III) and examined the CNS immune response at 21 days post infection (dpi). Contrary to acute infection studies, type III-infected mice had higher numbers of total CNS T cells and macrophages/microglia but fewer alternatively activated macrophages (M2s) and regulatory T cells (Tregs) than type II-infected mice. By profiling splenocytes at 5, 10, and 21 dpi, we determined that at 5 dpi type III-infected mice had more M2s while type II-infected mice had more pro-inflammatory macrophages and that these responses flipped over time. To test how these early differences influence the CNS immune response, we engineered the type III strain to lack ROP16 (IIIΔrop16), the polymorphic effector protein that drives the early type III-associated M2 response. IIIΔrop16-infected mice showed a type II-like neuroinflammatory response with fewer infiltrating T cells and macrophages/microglia and more M2s and an unexpectedly low CNS parasite burden. At 5 dpi, IIIΔrop16-infected mice showed a mixed inflammatory response with more pro-inflammatory macrophages, M2s, T effector cells, and Tregs, and decreased rates of infection of peritoneal exudative cells (PECs). These data suggested that type III parasites need the early ROP16-associated M2 response to avoid clearance, possibly by the Immunity-Related GTPases (IRGs), which are IFN-γ- dependent proteins essential for murine defenses against Toxoplasma. To test this possibility, we infected IRG-deficient mice and found that IIIΔrop16 parasites now maintained parental levels of PECs infection. Collectively, these studies suggest that, for the type III strain, rop16_III plays a key role in parasite persistence and influences the subacute CNS immune response.

Toxoplasma is a ubiquitous intracellular parasite that establishes an asymptomatic brain infection in immunocompetent individuals. However, in the immunocompromised and the developing fetus, Toxoplasma can cause problems ranging from fever to chorioretinitis to severe toxoplasmic encephalitis. Emerging evidence suggests that the genotype of the infecting Toxoplasma strain may influence these outcomes, possibly through the secretion of Toxoplasma strain-specific polymorphic effector proteins that trigger different host cell signaling pathways. While such strain-specific modulation of host cell signaling has been shown to affect acute immune responses, it is unclear how these differences influence the subacute or chronic responses in the CNS, the major organ affected in symptomatic disease. This study shows that genetically distinct strains of Toxoplasma provoke strain-specific CNS immune responses and that, for one strain (type III), acute and subacute immune responses and parasite survival are heavily influenced by a polymorphic parasite gene (rop16_III).

Prevalence of Anti-Toxoplasma Gondii Antibodies in Ratites from Brazil

The prevalence of anti-Toxoplasma gondii antibodies was investigated among 104 ratites: 68 rheas (Rhea americana), 16 emus (Dromaius novaehollandiae), and 20 ostriches (Struthio camelus) in 4 Brazilian states. The prevalence in rheas was 26.5% (18 of 68), and titers were 1:100 (n = 8), 1:200 (n = 1), 1:400 (n = 4), 1:800 (n = 4), and 1:1,600 (n = 1). In emus, the prevalence was 50% (8 of 16), and titers were 1:50 (n = 1) and 1:100 (n = 7). The ostriches were slaughtered for human consumption, and 80% (16 of 20) were seropositive with titers of 1:200 (n = 1), 1:400 (n = 9), and 1:800 (n = 6). Sera were tested with a modified agglutination test, and the results confirmed the distribution of the parasite in ratite species from Brazil. The data obtained in this study show that T. gondii is prevalent among ratites from Brazil, and therefore ratite meat should also be considered a potential source of human infection. This is the first report of T. gondii seroprevalence in emus.

Mat Seroprevalence Infers Low Rates of Toxoplasma gondii in Domestic Pigs from Yucatan, Mexico

Toxoplasma gondii is a zoonotic parasite of worldwide distribution. The consumption of infected pork meat has been suggested to be an important source for human infection in the tropical area of Yucatan, Mexico. We performed a cross-sectional study of 12 farms across the state to investigate the seroprevalence of Toxoplasma gondii infection in domestic pigs. In total, 632 samples were obtained from 2 different environmental zones (tropical deciduous low forest and tropical sub-deciduous medium forest) and 2 abattoirs. The modified agglutination test (MAT) was used to assess the seroprevalence of T. gondii in pigs and to evaluate 2 globally used serological tests, the Dye test (DT) and ID Screen® ELISA multi-species, and a commercial ELISA kit (Human Toxo IgG, Human-diagnostics), which is widely used locally in this geographical area. The overall prevalence obtained with the MAT (cut-off ≥1:25) among the 632 pigs was 1.4% (95% CI, 0.6-2.7%). The seroprevalence obtained for the different age groups was 0.6%, 0.7%, 1.8%, and 6.8% among 2-3, 3-4, 4-5, and ≥5-mo-old pigs. This increase in the seroprevalence was statistically significant for the 2 older groups (odds ratio [OR] 3.9-7.1, P < 0.05) in comparison with younger groups. DT at >4 IU dilution had a perfect agreement and 100% of sensitivity and specificity when compared with the MAT. Although ID Screen® had only a fair agreement (κ = 0.389) with the MAT, the McNemar test showed that the results of these tests were comparable (P = 0.29). The Human Toxo ELISA showed no agreement with MAT, ID Screen®, and DT (κ = 0.000-0.023, McNemar P < 0.05). This ELISA was lacking in specificity, accuracy, and precision; hence, we do not recommend its use for T. gondii diagnosis in pig serum.

QuilA-Adjuvanted T. gondii Lysate Antigens Trigger Robust Antibody and IFNγ+ T Cell Responses in Pigs Leading to Reduction in Parasite DNA in Tissues Upon Challenge Infection

Toxoplasma gondii is an intracellular parasite of all mammals and birds, responsible for toxoplasmosis. In healthy individuals T. gondii infections mostly remain asymptomatic, however this parasite causes severe morbidity and mortality in immunocompromised patients and congenital toxoplasmosis in pregnant women. The consumption of raw or undercooked pork is considered as an important risk factor to develop toxoplasmosis in humans. Since effective therapeutic interventions to treat toxoplasmosis are scarce, vaccination of meat producing animals may prevent T. gondii transmission to humans. Here, we evaluated the elicited immune responses and the efficacy of a potential vaccine candidate, generated by size fractionation of T. gondii lysate proteins, to reduce the parasite burden in tissues from experimentally T. gondii infected pigs as compared to vaccination with total lysate antigens (TLA). Our results show that both the vaccine candidate and the TLA immunization elicited strong serum IgG responses and elevated percentages of CD4+CD8+IFNγ+ T cells in T. gondii infected pigs. However, the TLA vaccine induced the strongest immune response and reduced the parasite DNA load below the detection limit in brain and skeletal muscle tissue in most animals. These findings might inform the development of novel vaccines to prevent T. gondii infections in livestock species and humans.

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.

TLR11-independent inflammasome activation is critical for CD4+ T cell-derived IFN-γ production and host resistance to Toxoplasma gondii

Innate recognition of invading intracellular pathogens is essential for regulating robust and rapid CD4+ T cell effector function, which is critical for host-mediated immunity. The intracellular apicomplexan parasite, Toxoplasma gondii, is capable of infecting almost any nucleated cell of warm-blooded animals, including humans, and establishing tissue cysts that persist throughout the lifetime of the host. Recognition of T. gondii by TLRs is essential for robust IL-12 and IFN-γ production, two major cytokines involved in host resistance to the parasite. In the murine model of infection, robust IL-12 and IFN-γ production have been largely attributed to T. gondii profilin recognition by the TLR11 and TLR12 heterodimer complex, resulting in Myd88-dependent IL-12 production. However, TLR11 or TLR12 deficiency failed to recapitulate the acute susceptibility to T. gondii infection seen in Myd88^-/- mice. T. gondii triggers inflammasome activation in a caspase-1-dependent manner resulting in cytokine release; however, it remains undetermined if parasite-mediated inflammasome activation impacts IFN-γ production and host resistance to the parasite. Using mice which lack different inflammasome components, we observed that the inflammasome played a limited role in host resistance when TLR11 remained functional. Strikingly, in the absence of TLR11, caspase-1 and -11 played a significant role for robust CD4+ T_H1-derived IFN-γ responses and host survival. Moreover, we demonstrated that in the absence of TLR11, production of the caspase-1-dependent cytokine IL-18 was sufficient and necessary for CD4+ T cell-derived IFN-γ responses. Mechanistically, we established that T. gondii-mediated activation of the inflammasome and IL-18 were critical to maintain robust CD4+ T_H1 IFN-γ responses during parasite infection in the absence of TLR11.

It is currently estimated that one third of the world’s population is seropositive for the parasite Toxoplasma gondii and this parasite can lead to serious illness and death in immunocompromised patients, and is one of the leading causes of foodborne-related deaths in the United States. Host immunity against the parasite has largely been attributed to recognition of the parasite-derived protein, profilin, by the innate Toll-like receptors (TLRs), TLR11 and TLR12. T. gondii also triggers inflammasome activation in a caspase-1-dependent manner resulting in cytokine release. However, how these innate recognition systems regulate T_H1 immunity and host resistance remains largely unknown. Therefore, using genetically modified mice, we investigated TLR11-dependent and -independent host immunity against the parasite. Our research establishes that in the absence of TLR11, inflammasome activation and subsequent production of the inflammasome-dependent molecule, IL-18 are critical for host immunity to the parasite. These data provide novel mechanistic insight into how TLR and inflammasomes cooperate in regulation of T_H1 immunity and host protection.

Infection-Induced Intestinal Dysbiosis Is Mediated by Macrophage Activation and Nitrate Production

Oral infection of C57BL/6J mice with Toxoplasma gondii results in a marked bacterial dysbiosis and the development of severe pathology in the distal small intestine that is dependent on CD4+ T cells and interferon gamma (IFN-γ). This dysbiosis and bacterial translocation contribute to the development of ileal pathology, but the factors that support the bloom of bacterial pathobionts are unclear. The use of microbial community profiling and shotgun metagenomics revealed that Toxoplasma infection induces a dysbiosis dominated by Enterobacteriaceae and an increased potential for nitrate respiration. In vivo experiments using bacterial metabolic mutants revealed that during this infection, host-derived nitrate supports the expansion of Enterobacteriaceae in the ileum via nitrate respiration. Additional experiments with infected mice indicate that the IFN-γ/STAT1/iNOS axis, while essential for parasite control, also supplies a pool of nitrate that serves as a source for anaerobic respiration and supports overgrowth of Enterobacteriaceae Together, these data reveal a trade-off in intestinal immunity after oral infection of C57BL/6J mice with T. gondii, in which inducible nitric oxide synthase (iNOS) is required for parasite control, while this host enzyme is responsible for specific modification of the composition of the microbiome that contributes to pathology.IMPORTANCEToxoplasma gondii is a protozoan parasite and a leading cause of foodborne illness. Infection is initiated when the parasite invades the intestinal epithelium, and in many host species, this leads to intense inflammation and a dramatic disruption of the normal microbial ecosystem that resides in the healthy gut (the so-called microbiome). One characteristic change in the microbiome during infection with Toxoplasma-as well as numerous other pathogens-is the overgrowth of Escherichia coli or similar bacteria and a breakdown of commensal containment leading to seeding of peripheral organs with gut bacteria and subsequent sepsis. Our findings provide one clear explanation for how this process is regulated, thereby improving our understanding of the relationship between parasite infection, inflammation, and disease. Furthermore, our results could serve as the basis for the development of novel therapeutics to reduce the potential for harmful bacteria to bloom in the gut during infection.

Evaluation of protective immunity induced by recombinant calcium-dependent protein kinase 1 (TgCDPK1) protein against acute toxoplasmosis in mice

Toxoplasma gondii is an intracellular zoonotic parasite that causes toxoplasmosis, which can cause economic losses and serious public health problems worldwide. A member of the T. gondii calcium-dependent protein kinases family, TgCDPK1 was recently identified as an essential regulator of exocytosis in T. gondii, and participated in direct parasite motility, host-cell invasion and egress. In the present study, the protective immunity of recombinant TgCDPK1 protein (rTgCDPK1) was evaluated against acute toxoplasmosis in mice. rTgCDPK1 were expressed and purified, BABL/c mice were intraperitoneally immunized with rTgCDPK1 and challenged with the highly virulent RH strain of T. gondii. The specific immune responses were analyzed by measuring the cytokine and serum antibody, and lymphocyte proliferation assays, flow cytometry of lymphocytes and the survival curve were employed to evaluate the protective efficacy. From the results we found that special humoral and cellular responses could be elicited in vaccine mice, and higher level of IgG antibody, and the significant increased levels of Th1-type cytokines IFN-γ, IL-12 (p70), IL10 and CD3⁺CD4⁺CD8^- and CD3⁺CD8⁺CD4^- T cells could also be detected comparing to control mice (P < 0.05). All vaccinated mice prolonged survival time (14.90 ± 2.89 days) challenge with 1000 tachyzoites of RH, while the control mice died within 8 days. These results indicated that TgCDPK1 protein was a potential vaccine candidate against acute toxoplasmosis.

Toxoplasma gondii infection triggers chronic cachexia and sustained commensal dysbiosis in mice

Toxoplasma gondii is a protozoan parasite with a predation-mediated transmission cycle between rodents and felines. Intermediate hosts acquire Toxoplasma by eating parasite cysts which invade the small intestine, disseminate systemically and finally establish host life-long chronic infection in brain and muscles. Here we show that Toxoplasma infection can trigger a severe form of sustained cachexia: a disease of progressive lean weight loss that is a causal predictor of mortality in cancer, chronic disease and many infections. Toxoplasma cachexia is characterized by acute anorexia, systemic inflammation and loss of 20% body mass. Although mice recover from symptoms of peak sickness, they fail to regain muscle mass or visceral adipose depots. We asked whether the damage to the intestinal microenvironment observed at acute time points was sustained in chronic infection and could thereby play a role in sustaining cachexia. We found that parasites replicate in the same region of the distal jejunum/proximal ileum throughout acute infection, inducing the development of secondary lymphoid structures and severe, regional inflammation. Small intestine pathology was resolved by 5 weeks post-infection. However, changes in the commensal populations, notably an outgrowth of Clostridia spp., were sustained in chronic infection. Importantly, uninfected animals co-housed with infected mice display similar changes in commensal microflora but never display symptoms of cachexia, indicating that altered commensals are not sufficient to explain the cachexia phenotype alone. These studies indicate that Toxoplasma infection is a novel and robust model to study the immune-metabolic interactions that contribute to chronic cachexia development, pathology and potential reversal.

First report on the sero-epidemiology of Toxoplasma gondii infection in German roe deer (Capreolus capreolus)

While the roe deer (Capreolus capeolus) is the most important game species in Germany and its venison is popular, there is limited knowledge about the prevalence of Toxoplasma gondii in this animal population in the country, and in wild ungulates in Germany generally. Between 2013 and 2015, we collected 295 blood samples from roe deer belonging to a central German population. Sera were analysed using a modified agglutination test (MAT, cut-off 1:20), and antibodies were detected in 86 of the 295 samples (29%). Seroprevalence values differed significantly between the different age classes, with antibodies more frequently observed in adults. In contrast, seroprevalence did not differ significantly between the sexes or collection years. Venison is frequently consumed raw or undercooked and may be a potential source of human infection with T. gondii.

Toxoplasma Chinese 1 Strain of WH3Δrop16I/III /gra15II Genetic Background Contributes to Abnormal Pregnant Outcomes in Murine Model

Toxoplasma gondii infection evokes a strong Th1-type response with interleukin (IL)-12 and interferon (IFN)-γ secretion. Recent studies suggest that the infection of pregnant mice with T. gondii may lead to adverse pregnancy results caused by subversion of physiological immune tolerance at maternofetal interface rather than direct invasion of the parasite. Genotype-associated dense granule protein GRA15II tends to induce classically activated macrophage (M1) differentiation and subsequently activating NK, Th1, and Th17 cells whereas rhoptry protein ROP16I/III drives macrophages to alternatively activated macrophage (M2) polarization and elicits Th2 immune response. Unlike the archetypal strains of types I, II, and III, type Chinese 1 strains possess both GRA15II and ROP16I/III, suggesting a distinct pathogenesis of Toxoplasma-involved adverse pregnancies. We constructed T. gondii type Chinese 1 strain of WH3Δrop16 based on CRISPR/Cas9 technology to explore the ROP16I/III-deficient/GRA15II-dominant parasites in induction of trophoblast apoptosis in vitro and abnormal pregnant outcomes of mice in vivo. Our study showed that Toxoplasma WH3Δrop16 remarkably induced apoptosis of trophoblasts. C57BL/6 pregnant mice injected with the tachyzoites of WH3Δrop16 presented increased absorptivity of fetuses in comparison with the mice infected with WH3 wild type (WH3 WT) parasites although no remarkable difference of virulence to mice was seen between the two strains. Additionally, the mice inoculated with WH3Δrop16 tachyzoites exhibited a notable expression of both IL-17A and IFN-γ, while the percentage of CD4+CD25+FoxP3 [T regulatory cells (Tregs)] were diminished in splenocytes and placenta tissues compared to those infected with WH3 WT parasites. Accordingly, expressions of IL-4, IL-10, and transforming growth factor beta 1, the pivotal cytokines of Th2 and Tregs response, were significantly dampened whereas IFN-γ and IL-12 expressions were upregulated in WH3Δrop16-infected mice, which gave rise to more prominent outcomes of abnormal pregnancies. Our results indicated that the WH3Δrop16 parasites with gra15II background of T. gondii type Chinese 1 strains may cause miscarriage and stillbirth due to subversion of the maternal immune tolerance and system immunity of the animals and the GRA15II effector contributes to the process of adverse pregnant consequences.

Loss of Paneth Cell Autophagy Causes Acute Susceptibility to Toxoplasma gondii-Mediated Inflammation

The protozoan parasite Toxoplasma gondii triggers severe small intestinal immunopathology characterized by IFN-γ- and intestinal microbiota-mediated inflammation, Paneth cell loss, and bacterial dysbiosis. Paneth cells are a prominent secretory epithelial cell type that resides at the base of intestinal crypts and releases antimicrobial peptides. We demonstrate that the microbiota triggers basal Paneth cell-specific autophagy via induction of IFN-γ, a known trigger of autophagy, to maintain intestinal homeostasis. Deletion of the autophagy protein Atg5 specifically in Paneth cells results in exaggerated intestinal inflammation characterized by complete destruction of the intestinal crypts resembling that seen in pan-epithelial Atg5-deficient mice. Additionally, lack of functional autophagy in Paneth cells within intestinal organoids and T. gondii-infected mice causes increased sensitivity to the proinflammatory cytokine TNF along with increased intestinal permeability, leading to exaggerated microbiota- and IFN-γ-dependent intestinal immunopathology. Thus, Atg5 expression in Paneth cells is essential for tissue protection against cytokine-mediated immunopathology during acute gastrointestinal infection.

Experimental Toxoplasma gondii and Eimeria tenella co-infection in chickens

The widespread apicomplexan parasites Toxoplasma gondii (T. gondii) and Eimeria tenella (E. tenella) are important pathogens with high prevalence in poultry. The aim of our study was the investigation of mutual influences in co-infected chickens, focusing on immune response and course of infection. Two separate trials were performed using in total 96 1-day-old chickens, divided into four study groups: group NC (negative control, uninfected), group PC-T (oral or intramuscular infection with T. gondii oocysts (trial 1) or tachyzoites (trial 2), respectively), group PC-E (oral infection with E. tenella (trial 1) or E. tenella and Eimeria acervulina (trial 2)), and group TE (co-infection). T. gondii and Eimeria infections were validated by different parameters, and cytokine expression in the gut and spleen was investigated. T. gondii-specific antibodies were detected earliest 4 days post infection (p.i.) by immunoblot and direct DNA detection was possible in 22.1% of all tissue samples from infected chickens. Eimeria spp. merogony seemed to be enhanced by co-infection with T. gondii, interestingly without marked differences in oocyst excretion between co-infected and Eimeria spp. mono-infected chickens. An increase of messenger RNA (mRNA) expression of Th1- (IFN-γ, IL-12, TNF-α) and Th2-related cytokines (IL-10) mainly in groups PC-E and TE was observed, however, without statistically significant differences between co-infection and single infection with Eimeria. In conclusion, most of the measurable immune response could be attributed to Eimeria infection. To the best of our knowledge, this is the first report on co-infection experiments of T. gondii with Eimeria spp. in chickens.

Immunization with Toxoplasma gondii aspartic protease 3 increases survival time of infected mice

Aspartic proteases in the Toxoplasma gondii, called TgASP1, 2, 3, and 5, play essential roles in the life cycle. In a previous study, we have demonstrated that TgASP1 is an antigen that prolongs survival time of infected mice. As an in-depth study, we have investigated the protective immunity of TgSAP3. A bioinformatic analysis was used to predict the linear B-cell epitopes and potential Th-cell epitopes on TgASP3, the results suggested that it has a large number of excellent epitopes. Mice were inoculated with a recombinant eukaryotic expression vector to evaluate the immune protection against an infection with the virulent RH strain of T. gondii. The enhanced immune response and increased survival time (up to 18days) were observed for vaccinated mice, showing that the TgASP3 antigen can provides partial protection.

Protection induced by virus-like particles containing Toxoplasma gondii microneme protein 8 against highly virulent RH strain of Toxoplasma gondii infection

Toxoplasma gondii (T. gondii) microneme protein 8 (MIC8) represents a novel, functional distinct invasion factor. In this study, we generated virus-like particles (VLPs) targeting Toxoplasma gondii MIC8 for the first time, and investigated the protection against highly virulent RH strain of T. gondii in a mouse model. We found that VLP vaccination induced Toxoplasma gondii-specific IgG and IgG1 antibody responses in the sera. Upon challenge infection with RH strain of T. gondii tachyzoites, vaccinated mice showed a significant increase of both IgG antibodies in sera and IgA antibodies in feces compared to those before challenge, and a rapid expansion of both germinal center B cell (B220+, GL7+) and T cell (CD4+, CD8+) populations. Importantly, intranasally immunized mice showed higher neutralizing antibodies and displayed no proinflammatory cytokine IFN-γ in the spleen. Mice were completely protected from a lethal challenge infection with the highly virulent T. gondii (RH) showing no body weight loss (100% survival). Our study shows the effective protection against T. gondii infection provided by VLPs containing microneme protein 8 of T. gondii, thus indicating a potential T. gondii vaccine candidate.

Virus-Like Nanoparticle Vaccine Confers Protection against Toxoplasma gondii

The inner membrane complex (IMC) of Toxoplasma gondii as a peripheral membrane system has unique and critical roles in parasite replication, motility and invasion. Disruption of IMC sub-compartment protein produces a severe defect in T. gondii endodyogeny, the form of internal cell budding. In this study, we generated T. gondii virus-like particle particles (VLPs) containing proteins derived from IMC, and investigated their efficacy as a vaccine in mice. VLP vaccination induced Toxoplasma gondii-specific total IgG, IgG1 and IgG2a antibody responses in the sera and IgA antibody responses in the feces. Upon challenge infection with a lethal dose of T. gondii (ME49), all vaccinated mice survived, whereas all naïve control mice died. Vaccinated mice showed significantly reduced cyst load and cyst size in the brain. VLP vaccination also induced IgA and IgG antibody responses in feces and intestines, and antibody-secreting plasma cells, mixed Th1/Th2 cytokines and CD4+/CD8+ T cells from spleen. Taken together, these results indicate that non-replicating VLPs containing inner membrane complex of T. gondii represent a promising strategy for the development of a safe and effective vaccine to control the spread of Toxoplasma gondii infection.

TGF-β1 levels and intraocular tissue alterations in mice infected with a virulent type I RH Toxoplasma gondii strain

Toxoplasmosis is generally self-limiting in healthy adults but it may cause toxoplasmic retinochoroiditis in cases of congenital infection leading to blindness. The importance of host genetics in determining disease severity in ocular toxoplasmosis has been shown in different inbred mouse strains using low-virulence toxoplasma strain. In this study, we studied intraocular immune response and tissue alterations in the genetically resistant BALB/c and susceptible MF1 mice infected with a virulent type I RH Toxoplasma gondii strain by intravitreal route. We observed a significant up-regulation of IFN-γ and TNF-α to >2200 pg/ml and >300 pg/ml respectively in the blood of both BALB/c and MF1mice during the early stages of post intraocular infection (p < 0.01) but the levels dropped sharply to normal during the late stages of the infection on day 26. The cytokine levels detected were higher in the MF1 mice compared with the BALB/c mice and a relatively higher levels were observed in the aqueous humour (AqH) than in the blood of both group of mice. The TGF-β1 level in the blood and AqH of BALB/c mice remained low throughout the infection period compared with MF1 mice which showed gradual increase to 50 pg/ml in the blood and AqH during the early stages of infection which then further increased 2-fold-132 pg/ml on day 11 (p < 0.01) and remained high till the last day of observation on day 26 except that the TGF-β1 level in AqH dropped sharply to normal level. In summary, our results support that TGF-β1 may down-regulate the effector functions of anti-Toxoplasma cellular immunity during acute toxoplasmosis. We document that a mild Th1 pro-inflammatory response in the BALB/c mice with high IFN-γ and TNF-α and, low TGF-β1 levels during the early stages of infection may have contributed to an effective cellular immune response leading to lower morbidity, mortality and less ocular tissue damage. However in the MF1 mice, a significantly high TGF-β1 level in the blood as well as in the AqH during the acute intra-ocular toxoplasma infection may have adversely interfered with an effective cellular immune response leading to an increased mortality and extensive ocular tissue damage with parasite tachyzoites observed in the pigment epithelium layers.

Prevalence of anti-Toxoplasma gondii antibody in domestic horses in Japan

The present study is the first report that investigated the seroprevalence of Toxoplasma gondii infection in domestic horses in various prefectures of Japan and analyzed risk factors for seropositivity. We performed a latex agglutination test for riding/racing horses from 11 prefectures in Japan (783 samples) and 4 groups of Japanese native horses (254 samples). The total seroprevalence of anti-T. gondii antibody in horses examined in this study was 4.24% (44/1037). As for riding/racing horses, we did not find a statistically different T. gondii seroprevalence between sampling prefectures. In contrast, seroprevalence of T. gondii in older horses (>21 years) was significantly higher than that in younger horses (<5 years and 11-15 years). There was no significant difference in T. gondii seroprevalence between riding/racing horses and Japanese native horses. Logistical regression analysis revealed that age, but not sex and usage, is a significant risk factor of T. gondii infection for domestic horses in Japan. These findings suggest that domesticated horses in Japan can be horizontally infected with T. gondii by ingestion of food or water contaminated with oocysts.

Serosurvey of Smooth Brucella, Leptospira spp. and Toxoplasma gondii in Free-Ranging Jaguars (Panthera onca) and Domestic Animals from Brazil

This study investigated the exposure of jaguar populations and domestic animals to smooth Brucella, Leptospira spp. and Toxoplasma gondii in the Cerrado, Pantanal and Amazon biomes of Brazil. Between February 2000 and January 2010, serum samples from 31 jaguars (Panthera onca), 1,245 cattle (Bos taurus), 168 domestic dogs (Canis lupus familiaris) and 29 domestic cats (Felis catus) were collected and analysed by rose bengal test for smooth Brucella, microscopic agglutination test for Leptospira spp. and modified agglutination test for T. gondii. Cattle populations from all sites (9.88%) were exposed to smooth Brucella, but only one jaguar from Cerrado was exposed to this agent. Jaguars captured in the Cerrado (60.0%) and in the Pantanal (45.5%) were seropositive for different serovars of Leptospira spp., cattle (72.18%) and domestic dogs (13.1%) from the three sites and one domestic cat from Pantanal were also seropositive for the agent. The most prevalent serotype of Leptospira spp. identified in jaguars from the Cerrado (Grippotyphosa) and the Pantanal (Pomona) biomes were distinct from those found in the domestic animals sampled. Jaguars (100%), domestic dogs (38.28%) and domestic cats (82.76%) from the three areas were exposed to T. gondii. Our results show that brucellosis and leptospirosis could have been transmitted to jaguars by domestic animals; and jaguars probably play an important role in the maintenance of T. gondii in nature.

Cutting Edge: IFN-γ Produced by Brain-Resident Cells Is Crucial To Control Cerebral Infection with Toxoplasma gondii

In vitro studies demonstrated that microglia and astrocytes produce IFN-γ in response to various stimulations, including LPS. However, the physiological role of IFN-γ production by brain-resident cells, including glial cells, in resistance against cerebral infections remains unknown. We analyzed the role of IFN-γ production by brain-resident cells in resistance to reactivation of cerebral infection with Toxoplasma gondii using a murine model. Our study using bone marrow chimeric mice revealed that IFN-γ production by brain-resident cells is essential for upregulating IFN-γ-mediated protective innate immune responses to restrict cerebral T. gondii growth. Studies using a transgenic strain that expresses IFN-γ only in CD11b(+) cells suggested that IFN-γ production by microglia, which is the only CD11b(+) cell population among brain-resident cells, is able to suppress the parasite growth. Furthermore, IFN-γ produced by brain-resident cells is pivotal for recruiting T cells into the brain to control the infection. These results indicate that IFN-γ produced by brain-resident cells is crucial for facilitating both the protective innate and T cell-mediated immune responses to control cerebral infection with T. gondii.

Adaptive immune-mediated host resistance to Toxoplasma gondii is governed by the NF-κB regulator Bcl-3 in dendritic cells

The atypical IκB family member Bcl-3 associates with p50/NF-κB1 or p52/NF-κB2 homodimers in nuclei, thereby either positively or negatively modulating transcription in a context-dependent manner. Previously we reported that Bcl-3 was critical for host resistance to Toxoplasma gondii. Bcl-3-deficient mice succumbed within 3-5 weeks after infection, correlating with an apparently impaired Th1-type adaptive immune response. However in which cell type(s) Bcl-3 functioned to assure resistance remained unknown. We now show that Bcl-3 expression in dendritic cells is required to generate a protective Th1-type immune response and confer resistance to T. gondii. Surprisingly, mice lacking Bcl-3 in dendritic cells were as susceptible as mice globally deficient for Bcl-3. Furthermore, early innate defenses were not compromised by the absence of Bcl-3, as initial production of IL-12 by dendritic cells and IFN-γ by NK cells were preserved. However, subsequent production of IFN-γ by CD4(+) and CD8(+) T-cells was compromised when dendritic cells lacked Bcl-3, and these mice succumbed at a time when T-cell-mediated IFN-γ production was essential for host resistance. These findings demonstrate that Bcl-3 is required in dendritic cells to prime protective T-cell-mediated immunity to T. gondii.

The Group 3 Innate Lymphoid Cell Defect in Aryl Hydrocarbon Receptor Deficient Mice Is Associated with T Cell Hyperactivation during Intestinal Infection

Intestinal infection with the intracellular parasite Toxoplasma gondii results in the translocation of commensal bacteria to peripheral organs and the development of a T cell response specific to the microbiota. In naïve mice, the recently described RORγt+ group 3 innate lymphoid cell (ILC) population plays a critical role in promoting intestinal barrier function and limiting responses to gut-resident commensal bacteria. Given this role for group 3 ILCs, studies were performed to evaluate whether these cells might influence the immune response to mucosal infection with T. gondii. Phenotypic characterization of RORγt+ ILCs in T. gondii infected mice revealed that this population decreased following challenge but the population that remained expressed costimulatory molecules and IL-22. One factor that influences the maintenance of RORγt+ ILCs is the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, and Ahr-/- mice have a marked defect in the lamina propria group 3 ILC population. When Ahr-/- mice were challenged with T. gondii, they lost more weight than wild type controls. This disease course in Ahr-/- animals was associated with increased T cell responses to Toxoplasma antigen and crude commensal antigen preparations. Together, these data suggest that group 3 ILCs have a role in limiting T cell activation during intestinal infection.

SEROPREVALENCE OF TOXOPLASMA GONDII IN RODENTS FROM VARIOUS LOCATIONS IN PENINSULAR MALAYSIA

Numerous studies have reported the prevalence of toxoplasmosis among Malaysians and various domestic animals; but there is paucity of information on its prevalence among rodents which could potentially contribute to the transmission of Toxoplasma gondii in both domestic and sylvatic fauna. Five hundred twenty-six rodents were captured from six locations in Malaysia and identified to species. Serum samples were collected from these rodents and tested for T.gondii antibodies using an immunofluorescent antibody test (IFAT). T.gondii antibodies were found in 5.9% (31/526) of the tested samples. Most of the positive antibodies were from commensal rats: Rattus exulans (9/64, 14.0%), Rattus argentiventer (2/8, 25%), Rattus rattus diardii (10/166, 6.0%) and Rattus tiomanicus (6/215, 2.7%). Only two of the forest rats were positive: Maxomys rajah (1/9, 11.1%) and Rattus bowersi (1/12, 8.3%). Eighteen point one percent of ground squirrels (Tupaia glis) tested (2/11) were positive for antibodies. The highest antibodies titer (1:1024) was found in Rattus exulans followed by T.glis (1:256). Sabak Bernam, Selangor had the highest prevalence (10.8%) followed by Baling, Kedah (5.0%) and Bagan Terap, Selangor (4.0%). None of the serum samples of rodents collected from Gua Musang, Kelantan; Jasin, Malacca; or Labis, Johor were positive. Our study reports for the first time the serologic prevalence of T.gondii antibodies among rodents in Peninsular Malaysia. Further studies are needed to confirm T.gondii infection among wild rodents, such as a bioassay, to assess their potential role in transmission of the parasite.

Exploring early and late Toxoplasma gondii strain RH infection by two-dimensional immunoblots of chicken immunoglobulin G and M profiles

Toxoplasma gondii is an intracellular apicomplexan parasite infecting warm-blooded vertebrate hosts, with only early infection stage being contained with drugs. But diagnosis differencing early and late infection was not available. In the present investigation, 2-dimensional immunobloting was used to explore early and late infections in chickens. The protein expression of T. gondii was determined by image analysis of the tachyzoites proteome separated by standard-one and conventional two-dimentional gel polyacrylamide electrophoresis (2D- PAGE). Pooled gels were prepared from tachyzoites of T. gondii. A representative gel spanning a pH range of 3-10 of the tachyzoite proteome consisted of 1306 distinct polypeptide spots. Two-dimensional electrophoresis (2-DE) combined with 2-DE immunoblotting was used to resolve and compare immunoglobulins (Igs) M & G patterns against Toxoplasma gondii strain RH (mouse virulent strain). Total tachyzoite proteins of T. gondii were separated by two-dimensional gel electrophoresis and analyzed by Western blotting for their reactivity with the 7 and 56 days post-infection (dpi) SPF chicken antisera. Different antigenic determinant patterns were detected during analysis with M and G immunoglobulins. Of the total number of polypeptide spots analyzed (1306 differentially expressed protein spots), 6.97% were identified as having shared antigenic polypeptide spots on immunoblot profiles with IgG and IgM antibodies regardless the time after infection. Furthermore, some of the immunoreactive polypeptide spots seemed to be related to the stage of infection. Interestingly, we found natural antibodies to toxoplasmic antigens, in addition to the highly conserved antigenic determinants that reacted with non-specific secondary antibody; goat anti-chicken IgG antibodies conjugated with horseradish peroxidase. In conclusion, unique reactive polypeptide spots are promising candidates for designation of molecular markers to discriminate early and late chicken infection.

Polarization of macrophages induced by Toxoplasma gondii and its impact on abnormal pregnancy in rats

Toxoplasma gondii infection is the leading cause of fetal intrauterine growth retardation among the five kinds of pathogens termed as TORCH, including Toxoplasma, Rubella virus, Cytomegalo virus, herpes virus and others during pregnancy. Pathogens infect the fetus through the placenta. T. gondii infection may result in congenital toxoplasmosis, miscarriage, stillbirth, and preemie, and increase pregnancy complications. Adaptive immune response induced by T. gondii infection stimulates T cells and macrophages to produce high levels of cytokines. Physiologically, the microenvironment of pregnancy was Th2-dominant. Here we set up a pregnant Sprague-Dawley rat model, and reported the polarization of macrophages induced by genotype Chinese 1 strain (Wh6) of Toxoplasma, and its adverse impact on pregnancy. The results showed that Wh6 infection pre- or in-gestation both led to abnormal pregnancy outcomes. Peritoneal macrophages in pre-gestation infection were polarized toward classically activated macrophages (M1), while in-gestation infection drove macrophages to polarize toward M2 activation. The Th2-dominant immune response in pregnant rat somewhat inhibits the excessive bias of the macrophages toward M1, and partially, toward M2. Infection of pre- and in-gestation may alter the physiological immune microenvironment in pregnant rats, giving rise to abnormal pregnancy outcomes.

Atg5 but not Atg7 in dendritic cells enhances IL-2 and IFN-γ production by Toxoplasma gondii-reactive CD4+ T cells

The autophagy proteins (Atg) modulate not only innate but also adaptive immunity against pathogens. We examined the role of dendritic cell Atg5 and Atg7 in the production of IL-2 and IFN-γ by Toxoplasma gondii-reactive CD4(+) T cells. T. gondii-reactive mouse CD4(+) T cells exhibited unimpaired production of IL-2 and IFN-γ when stimulated with Atg7-deficient mouse dendritic cells that were infected with T. gondii or pulsed with T. gondii lysate antigens. In marked contrast, dendritic cells deficient in Atg5 induced diminished CD4(+) T cell production of IL-2 and IFN-γ. This defect was not accompanied by changes in costimulatory ligand expression on dendritic cells or impaired production of IL-12 p70, IL-1β or TNF-α. Knockdown of Irg6a in dendritic cells did not affect CD4(+) T cell cytokine production. These results indicate that Atg5 and Atg7 in dendritic cells play differential roles in the modulation of IL-2 and IFN-γ production by T. gondii-reactive CD4(+) T cells.

[Isolation and identification of Toxoplasma gondii strains from cats in Xuzhou region]

OBJECTIVE

To isolate Toxoplasma gondii (T. gondii) strains from stray cats and explore their prevalence in Xuzhou City.

METHODS

The sera of 41 stray cats were collected to detect the antibodies of T. gondii by using a commercial enzyme-linked immunosorbent (ELISA) kit. The tissues including the heart, brain and tongue from these cats were digested by acid pepsin solution and inoculated to Kunming mice. These suspicious isolates were subsequently identified by a specific PCR method.

RESULTS

A total of 11 strains were isolated from 41 stray cats, which were confirmed by the PCR results. Moreover, 17 cats (41.5%) were found to be positive with the antibodies of T. gondii.

CONCLUSION

A high prevalence of T. gondii infection was found in Xuzhou City, which indicates that the stray cats infected with T. gondii would be an important infection source that may infect humans and other animals in this area.

Lupus-prone mice fail to raise antigen-specific T cell responses to intracellular infection

Systemic lupus erythematosus (SLE) is characterized by multiple cellular abnormalities culminating in the production of autoantibodies and immune complexes, resulting in tissue inflammation and organ damage. Besides active disease, the main cause of morbidity and mortality in SLE patients is infections, including those from opportunistic pathogens. To understand the failure of the immune system to fend off infections in systemic autoimmunity, we infected the lupus-prone murine strains B6.lpr and BXSB with the intracellular parasite Toxoplasma gondii and survival was monitored. Furthermore, mice were sacrificed days post infection and parasite burden and cellular immune responses such as cytokine production and cell activation were assessed. Mice from both strains succumbed to infection acutely and we observed greater susceptibility to infection in older mice. Increased parasite burden and a defective antigen-specific IFN-gamma response were observed in the lupus-prone mice. Furthermore, T cell:dendritic cell co-cultures established the presence of an intrinsic T cell defect responsible for the decreased antigen-specific response. An antigen-specific defect in IFN- gamma production prevents lupus-prone mice from clearing infection effectively. This study reveals the first cellular insight into the origin of increased susceptibility to infections in SLE disease and may guide therapeutic approaches.

Diagnostic value of a Rec-ELISA using Toxoplasma gondii recombinant SporoSAG, BAG1, and GRA1 proteins in murine models infected orally with tissue cysts and oocysts

Toxoplasma gondii causes congenital toxoplasmosis in newborns resulting with fetal anomalies. Determining the initiation time of infection is very important for pregnant women and current serological assays have drawbacks in distinguishing the recently acute toxoplasmosis. Diagnosis of recently acute infection may be improved by using stage specific antigens in serological assays. In the present study, the diagnostic value of sporozoite specific SporoSAG, bradyzoite specific BAG1 proteins and GRA1 protein expressed by all forms of the parasite have been evaluated ELISA using sera systematically collected from mice administered orally with tissue cyst and oocysts. The anti-SporoSAG IgM antibodies in sera obtained from mice infected with oocysts peaked significantly at days 1, 10, and 15 (P<0.01). The anti-BAG1 IgM antibodies in sera obtained from mice infected with tissue cysts peaked significantly at days 15, 40, and 120 (P<0.05). The anti-GRA1 IgM antibodies in sera obtained from mice infected with oocysts peaked significantly at days 2, 10, and 40 (P<0.01). The anti-GRA1 IgM antibodies in sera obtained from mice infected with tissue cysts peaked significantly only at day 40 (P<0.05). The anti-SporoSAG, anti-BAG1, and anti-GRA1 IgG titers of mice showed significant increases at day 40 (P<0.05) and decrement started for only anti-GRA1 IgG at day 120. The presence of anti-SporoSAG IgM and IgG antibodies can be interpreted as recently acute infection between days 10-40 because IgM decreases at day 40. Similarly, presence of anti-BAG1 IgM and absence of IgG can be evaluated as a recently acute infection that occurred 40 days before because IgG peaks at day 40. A peak in anti-GRA1 antibody level at first testing and reduction in consecutive sample can be considered as an infection approximately around day 40 or prior. Overall, recombinant SporoSAG, BAG1 and GRA1 proteins can be accepted as valuable diagnostic markers of recently acute toxoplasmosis.

An experimental Toxoplasma gondii dose response challenge model to study therapeutic or vaccine efficacy in cats

High numbers of Toxoplasma gondii oocysts in the environment are a risk factor to humans. The environmental contamination might be reduced by vaccinating the definitive host, cats. An experimental challenge model is necessary to quantitatively assess the efficacy of a vaccine or drug treatment. Previous studies have indicated that bradyzoites are highly infectious for cats. To infect cats, tissue cysts were isolated from the brains of mice infected with oocysts of T. gondii M4 strain, and bradyzoites were released by pepsin digestion. Free bradyzoites were counted and graded doses (1000, 100, 50, 10), and 250 intact tissue cysts were inoculated orally into three cats each. Oocysts shed by these five groups of cats were collected from faeces by flotation techniques, counted microscopically and estimated by real time PCR. Additionally, the number of T. gondii in heart, tongue and brains were estimated, and serology for anti T. gondii antibodies was performed. A Beta-Poisson dose-response model was used to estimate the infectivity of single bradyzoites and linear regression was used to determine the relation between inoculated dose and numbers of oocyst shed. We found that real time PCR was more sensitive than microscopic detection of oocysts, and oocysts were detected by PCR in faeces of cats fed 10 bradyzoites but by microscopic examination. Real time PCR may only detect fragments of T. gondii DNA without the presence of oocysts in low doses. Prevalence of tissue cysts of T. gondii in tongue, heart and brains, and anti T. gondii antibody concentrations were all found to depend on the inoculated bradyzoite dose. The combination of the experimental challenge model and the dose response analysis provides a suitable reference for quantifying the potential reduction in human health risk due to a treatment of domestic cats by vaccination or by therapeutic drug application.

Immune responses of different mouse strains after challenge with equivalent lethal doses oftoxoplasma Gondii

Most immunological studies that utilize different strains of inbred mice following T. gondii infection fail to compensate for differences in host susceptibility to the size of the parasite innoculum. To address this concern, susceptible C57BL/6 and resistant CBA/J mice were orally infected with either an equivalent 50% lethal dose (LD50) of brain cysts of the 76K strain of T. gondii (15 cysts in C57BL/6, 400 cysts in CBA/J) or the same dose of parasites in each mouse strain. C57BL/6 mice receiving 400 cysts (LD50 of CBA/J mice) died post infection, whereas CBA/J mice that received 15 cysts (LD50 of C57BL/6 mice) survived. Parasite loads in the brains and serum Toxoplasma-specific IgG1 titers of LD50-infected C57BL/6 mice were significantly higher than those in LD50- or 15 cysts-infected CBA/J mice, whereas splenocyte proliferation to Toxoplasma antigen and the percentage of CD8 alpha+ T cells were reduced in LD50-infected C57BL/6 mice. In contrast, serum IgG2a and IgM titers, the percentage of gamma delta T cells and IFN-gamma expression of spleen of LD50-infected CBA/J mice were higher than those of either 15 cysts-infected CBA/J mice or LD50-infected C57BL/6 mice. These observations demonstrate that the immune response between LD50-infected C57BL/6 and CBA/J mice was more prominent when compared to C57BL/6 or CBA/J mice receiving the same parasite inoculum. These observations would suggest that caution must be excersized in the planning and interpretation of data when the size of the parasite inoculum has not been adjusted for mouse strain.

Toxoplasma gondii profilin promotes recruitment of Ly6Chi CCR2+ inflammatory monocytes that can confer resistance to bacterial infection

Ly6C⁺ inflammatory monocytes are essential to host defense against Toxoplasma gondii, Listeria monocytogenes and other infections. During T. gondii infection impaired inflammatory monocyte emigration results in severe inflammation and failure to control parasite replication. However, the T. gondii factors that elicit these monocytes are unknown. Early studies from the Remington laboratory showed that mice with a chronic T. gondii infection survive lethal co-infections with unrelated pathogens, including L. monocytogenes, but a mechanistic analysis was not performed. Here we report that this enhanced survival against L. monocytogenes is due to early reduction of bacterial burdens and elicitation of Ly6C⁺ inflammatory monocytes. We demonstrate that a single TLR11/TLR12 ligand profilin (TgPRF) was sufficient to reduce bacterial burdens similar to T. gondii chronic infection. Stimulation with TgPRF was also sufficient to enhance animal survival when administered either pre- or post-Listeria infection. The ability of TgPRF to reduce L. monocytogenes burdens was dependent on TLR11 and required IFN-γ but was not dependent on IL-12 signaling. TgPRF induced rapid production of MCP-1 and resulted in trafficking of Ly6C^hi CCR2⁺ inflammatory monocytes and Ly6G⁺ neutrophils into the blood and spleen. Stimulation with TgPRF reduced L. monocytogenes burdens in mice depleted with the Ly6G specific MAb 1A8, but not in Ly6C/Ly6G specific RB6-8C5 depleted or CCR2^−/− mice, indicating that only inflammatory monocytes are required for TgPRF-induced reduction in bacterial burdens. These results demonstrate that stimulation of TLR11 by TgPRF is a mechanism to promote the emigration of Ly6C^hi CCR2⁺ monocytes, and that TgPRF recruited inflammatory monocytes can provide an immunological benefit against an unrelated pathogen.

Toxoplasma gondii is an apicomplexan parasite that can infect all warm blooded animals, but rodent species are considered the primary reservoirs. Mice that are infected with T. gondii become more resistant to lethal infection with other pathogens. Ly6C⁺ inflammatory monocytes are innate immune cells that are critical for defense against T. gondii and other infections. Mice with defects in the ability to recruit inflammatory monocytes fail to control T. gondii replication and succumb to overwhelming inflammation. In this study we used a co-infection model to explain why T. gondii-infected mice are more resistant to the bacterium Listeria monocytogenes. We show that stimulation of the rodent specific Toll-like receptor TLR11 by the T. gondii ligand profilin can recruit inflammatory monocytes, and that these monocytes can protect the host against L. monocytogenes. These findings make profilin an important tool for the study of monocyte biology during T. gondii infection of rodents and are especially interesting given that TLR11 is nonfunctional in humans and other vertebrates.

Dectin-1-CD37 association regulates IL-6 expression during Toxoplasma gondii infection

Toxoplasma gondii can establish chronic infection and is characterized by the formation of tissue cysts in the brain. Although T. gondii can infect any kind of nucleated cells, macrophages and related mononuclear phagocytes are its preferred targets in vivo. Microglial cells are the resident macrophages in the central nervous system. It has been reported that CD37, a tetraspanin molecule, is expressed exclusively in the immune system; Dectin-1, an important pattern-recognition receptor, is expressed on the surface of murine primary microglia. The Dectin-1-CD37 association can affect Dectin-1-mediated IL-6 secretion. However, there is no report concerning the relationship among the expressions of Dectin-1, IL-6, and CD37 during T. gondii infection. In the present study, Kunming outbred mice were infected with Prugniaud (Pru), a type II strain of T. gondii by oral gavage, and BV-2 murine microglial cells were cocultured with RH tachyzoites of T. gondii. By H&E and immunohistochemical staining, the results showed that marked inflammation and a significantly increased activation of Iba1-positive microglial cells were observed in the brain tissues of mice infected with T. gondii Pru strain at 5 weeks postinfection (p.i.) in comparison of uninfected controls. Using quantitative real-time PCR detection, Dectin-1 messenger RNA (mRNA) expressions were significantly upregulated in both brains at 3 (P < 0.01), 5 (P < 0.01), 7 (P < 0.01), and 9 (P < 0.05) weeks p.i. and spleens at 3, 5, 7, and 9 weeks p.i. (P < 0.01). IL-6 expressions showed similar dynamic tendency as that of Dectin-1 in both the brains and spleens at the same times in comparison of uninfected controls; CD37 expressions were significantly increased in the brain tissues at all the times (P < 0.01) and no significant differences in the spleens at 3 weeks p.i. but significantly downregulated in the spleens at 5, 7, and 9 weeks p.i. (P < 0.01). In vitro study showed that compared with uninfected controls, the mRNA expressions of Dectin-1 at 2, 4, 8, and 10 h (P < 0.01); IL-6 at 8 and 10 h (P < 0.01); and CD37 at 4 (P < 0.05), 8 (P < 0.01), and 10 h (P < 0.01) were significantly upregulated in BV-2 murine microglial cells stimulated with RH tachyzoites of T. gondii. Our data suggested that the expression of Dectin-1 was positively correlated with that of IL-6 in toxoplasmic encephalitis (TE) mouse model; Dectin-1 interaction with tetraspanin CD37 regulated IL-6 expression in both the brain tissues of TE mouse model and in the T. gongdii-infected BV-2 murine microglial cells.

West Greenland harbour porpoises assayed for antibodies against Toxoplasma gondii: false positives with the direct agglutination method

We assayed blood/tissue fluid samples from 20 harbour porpoises Phocoena phocoena from western Greenland coastal waters for antibodies against the protozoan parasite Toxoplasma gondii by the direct agglutination test (DAT). Nine individuals (45%) were interpreted to be seropositive at 1:40 dilution and 4 (20%) were seropositive up to 1:160. Samples from these individuals were assayed by an enzyme-linked immunosorbent assay (ELISA), and tissue samples of the DAT-positive animals were tested by a nested polymerase chain reaction (nPCR). Results from both methods were negative, suggesting the absence of infection in the tested animals. After chloroform clean-up, all were negative when re-assayed by DAT. We concluded that infection with T. gondii was absent in all 20 animals, despite the initially positive DAT results, and that the false positives resulted from non-specific adherence to tachyzoites in the DAT assay which could be removed by the chloroform clean-up method. Our results suggest that detecting antibodies against T. gondii using the DAT or the modified agglutination technique, particularly on samples from Arctic marine animals which often are rich in lipids, may lead to false positive results. For such samples, the use of ELISA or PCR on available tissue samples may be advocated as confirmatory tests in order to avoid false positives and overestimating seroprevalence.