Suppression of NF-kappaB activation by infection with Toxoplasma gondii

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Toxoplasma-host endoplasmic reticulum interaction: How T. gondii activates unfolded protein response and modulates immune response

Toxoplasma gondii is a neurotropic single-celled zoonotic parasite that can infect human beings and animals. Infection with T. gondii is usually asymptomatic in immune-competent individual, however, it can cause symptomatic and life-threatening conditions in immunocompromised individuals and in developing foetuses. Although the mechanisms that allow T. gondii to persist in host cells are poorly understood, studies in animal models have greatly improved our understanding of Toxoplasma-host cell interaction and how this interaction modulates parasite proliferation and development, host immune response and virulence of the parasite. T. gondii is capable of recruiting the host endoplasmic reticulum (ER), suggesting it may influence the host ER function. Herein, we provide an overview of T. gondii infection and the role of host ER during stressed conditions. Furthermore, we highlight studies that explore T. gondii's interaction with the host ER. We delve into how this interaction activates the unfolded protein response (UPR) and ER stress-mediated apoptosis. Additionally, we examine how T. gondii exploits these pathways to its advantage.

IFN-γ inhibitory molecules derived from Eimeria maxima inhibit IL-12 secretion by modulating MAPK pathways in chicken macrophages

IFN-γ plays a crucial role in resisting intracellular parasitic protozoa, such as Eimeria species. In our previous study, we identified 4 molecules derived from Eimeria maxima (E. maxima) that significantly inhibited IFN-γ production. However, the mechanism underlying this inhibitory effect remains unknown. In this study, we first investigated the effects of these 4 IFN-γ inhibitory molecules on the expression levels of chicken Toll-like receptors (chTLRs), IL-12, IL-10, TGF-β, and TNF-α in chicken macrophage HD11 and bone marrow-derived dendritic cells (BMDCs). The results demonstrated that these 4 inhibitory molecules significantly downregulated the mRNA levels of chTLR-2, chTLR-4, chTLR-21, and both mRNA and protein levels of IL-12. Subsequently, to clarify the effects of these 4 inhibitory molecules on the IL-12 secretion-related signaling pathways in chicken macrophages, qRT-PCR and Western blot were used to detect the changes of key molecules involved in the signaling pathways of IL-12 secretion (NF-κB, ERK1/2, p38, JNK, STAT3) following coincubation with these inhibitory molecules. Finally, RNAi was employed to verify the function of key molecules in the signaling pathway. The results revealed a significant upregulation in the expression of ERK1/2 phosphorylated protein induced by the 4 inhibitory molecules. Knockdown of the ERK1/2 gene significantly reduced the inhibitory effect of the 4 E. maxima inhibitory molecules on IL-12. These findings indicate that the 4 inhibitory molecules can inhibit the secretion of IL-12 by upregulating the expression of ERK1/2 phosphorylated protein, which is a key molecule in the ERK-MAPK pathway. Our study may contribute to elucidating the mechanisms underlying immune evasion during E. maxima infections, thereby providing new insights for the control of chicken coccidiosis.

Toxoplasma gondii infection regulates apoptosis of host cells via miR-185/ARAF axis

BACKGROUND

Toxoplasmosis is a zoonosis with a worldwide presence that is caused by the intracellular parasite Toxoplasma gondii. Active regulation of apoptosis is an important immune mechanism by which host cells resist the growth of T. gondii or avoid excessive pathological damage induced by this parasite. Previous studies found that upregulated expression of microRNA-185 (miR-185) during T. gondii infection has a potential role in regulating the expression of the ARAF gene, which is reported to be associated with cell proliferation and apoptosis.

METHODS

The expression levels of miR-185 and the ARAF gene were evaluated by qPCR and Western blot, respectively, in mice tissues, porcine kidney epithelial cells (PK-15) and porcine alveolar macrophages (3D4/21) following infection with the T. gondii ToxoDB#9 and RH strains. The dual luciferase reporter assay was then used to verify the relationship between miR-185 and ARAF targets in PK-15 cells. PK-15 and 3D4/21 cell lines with stable knockout of the ARAF gene were established by CRISPR, and then the apoptosis rates of the cells following T. gondii infection were detected using cell flow cytometry assays. Simultaneously, the activities of cleaved caspase-3, as a key apoptosis executive protein, were detected by Western blot to evaluate the apoptosis levels of cells.

RESULTS

Infection with both the T. gondii ToxoDB#9 and RH strains induced an increased expression of miR-185 and a decreased expression of ARAF in mice tissues, PK-15 and 3D4/21 cells. MiR-185 mimic transfections showed a significantly negative correlation in expression levels between miR-185 and the ARAF gene. The dual luciferase reporter assay confirmed that ARAF was a target of miR-185. Functional investigation revealed that T. gondii infection induced the apoptosis of PK-15 and 3D4/21 cells, which could be inhibited by ARAF knockout or overexpression of miR-185. The expression levels of cleaved caspase-3 protein were significantly lower in cells with ARAF knockout than in normal cells, which were consistent with the results of the cell flow cytometry assays.

CONCLUSIONS

Toxoplasma gondii infection could lead to the upregulation of miR-185 and the downregulation of ARAF, which was not related to the strain of T. gondii and the host cells. Toxoplasma gondii infection could regulate the apoptosis of host cells via the miR-185/ARAF axis, which represents an additional strategy used by T. gondii to counteract host-cell apoptosis in order to maintain survival and reproduce in the host cells.

Trained immunity: a cutting edge approach for designing novel vaccines against parasitic diseases?

The preventive situation of parasitosis, a global public health burden especially for developing countries, is not looking that good. Similar to other infections, vaccines would be the best choice for preventing and controlling parasitic infection. However, ideal antigenic molecules for vaccine development have not been identified so far, resulting from the complicated life history and enormous genomes of the parasites. Furthermore, the suppression or down-regulation of anti-infectious immunity mediated by the parasites or their derived molecules can compromise the effect of parasitic vaccines. Comparing the early immune profiles of several parasites in the permissive and non-permissive hosts, a robust innate immune response is proposed to be a critical event to eliminate the parasites. Therefore, enhancing innate immunity may be essential for designing novel and effective parasitic vaccines. The newly emerging trained immunity (also termed innate immune memory) has been increasingly recognized to provide a novel perspective for vaccine development targeting innate immunity. This article reviews the current status of parasitic vaccines and anti-infectious immunity, as well as the conception, characteristics, and mechanisms of trained immunity and its research progress in Parasitology, highlighting the possible consideration of trained immunity in designing novel vaccines against parasitic diseases.

The interplay between toxoplasmosis and host miRNAs: Mechanisms and consequences

Toxoplasmosis is one of the highly prevalent zoonotic diseases worldwide caused by the parasite Toxoplasma gondii (T. gondii). The infection with T. gondii could pass unidentified in immunocompetent individuals; however, latent cysts remain dormant in their digestive tract, but they could be shed and excreted with feces infesting the environment. However, active toxoplasmosis can create serious consequences, particularly in newborns and infected persons with compromised immunity. These complications include ocular toxoplasmosis, in which most cases cannot be treated. Additionally, it caused many stillbirths and miscarriages. Circulating miRNAs are important regulatory molecules ensuring that the normal physiological role of various organs is harmonious. Upon infection with T. gondii, the tightly regulated miRNA profile is disrupted to favor the parasite's survival and further participate in the disease pathogenesis. Interestingly, this dysregulated profile could be useful in acute and chronic disease discrimination and in providing insights into the pathomechanisms of the disease. Thus, this review sheds light on the various roles of miRNAs in signaling pathways regulation involved in the pathogenesis of T. gondii and provides insights into the application of miRNAs clinically for its diagnosis and prognosis.

miR-34c-3p Regulates Protein Kinase A Activity Independent of cAMP by Dicing prkar2b Transcripts in Theileria annulata-Infected Leukocytes

MicroRNAs (miRNAs) are small noncoding RNAs that can play critical roles in regulating various cellular processes, including during many parasitic infections. Here, we report a regulatory role for miR-34c-3p in cAMP-independent regulation of host cell protein kinase A (PKA) activity in Theileria annulata-infected bovine leukocytes. We identified prkar2b (cAMP-dependent protein kinase A type II-beta regulatory subunit) as a novel miR-34c-3p target gene and demonstrate how infection-induced upregulation of miR-34c-3p repressed PRKAR2B expression to increase PKA activity. As a result, the disseminating tumorlike phenotype of T. annulata-transformed macrophages is enhanced. Finally, we extend our observations to Plasmodium falciparum-parasitized red blood cells, where infection-induced augmentation in miR-34c-3p levels led to a drop in the amount of prkar2b mRNA and increased PKA activity. Collectively, our findings represent a novel cAMP-independent way of regulating host cell PKA activity in infections by Theileria and Plasmodium parasites. IMPORTANCE Small microRNA levels are altered in many diseases, including those caused by parasites. Here, we describe how infection by two important animal and human parasites, Theileria annulata and Plasmodium falciparum, induce changes in infected host cell miR-34c-3p levels to regulate host cell PKA kinase activity by targeting mammalian prkar2b. Infection-induced changes in miR-34c-3p levels provide a novel epigenetic mechanism for regulating host cell PKA activity independent of fluxes in cAMP to both aggravate tumor dissemination and improve parasite fitness.

The Role of Nuclear Factor Kappa B (NF-κB) in the Immune Response against Parasites

The immune system consists of various cells, organs, and processes that interact in a sophisticated manner to defend against pathogens. Upon initial exposure to an invader, nonspecific mechanisms are raised through the activation of macrophages, monocytes, basophils, mast cells, eosinophils, innate lymphoid cells, or natural killer cells. During the course of an infection, more specific responses develop (adaptive immune responses) whose hallmarks include the expansion of B and T cells that specifically recognize foreign antigens. Cell to cell communication takes place through physical interactions as well as through the release of mediators (cytokines, chemokines) that modify cell activity and control and regulate the immune response. One regulator of cell states is the transcription factor Nuclear Factor kappa B (NF-κB) which mediates responses to various stimuli and is involved in a variety of processes (cell cycle, development, apoptosis, carcinogenesis, innate and adaptive immune responses). It consists of two protein classes with NF-κB1 (p105/50) and NF-κB2 (p100/52) belonging to class I, and RelA (p65), RelB and c-Rel belonging to class II. The active transcription factor consists of a dimer, usually comprised of both class I and class II proteins conjugated to Inhibitor of κB (IκB). Through various stimuli, IκB is phosphorylated and detached, allowing dimer migration to the nucleus and binding of DNA. NF-κB is crucial in regulating the immune response and maintaining a balance between suppression, effective response, and immunopathologies. Parasites are a diverse group of organisms comprised of three major groups: protozoa, helminths, and ectoparasites. Each group induces distinct effector immune mechanisms and is susceptible to different types of immune responses (Th₁, Th₂, Th₁₇). This review describes the role of NF-κB and its activity during parasite infections and its contribution to inducing protective responses or immunopathologies.

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.

The NF-κB Pathway: Modulation by Entamoeba histolytica and Other Protozoan Parasites

Protozoan parasites have led to worldwide devastation because of their ability to cause infectious diseases. They have evolved as successful pathogens in part because of their remarkable and sophisticated ways to evade innate host defenses. This holds true for both intracellular and extracellular parasites that deploy multiple strategies to circumvent innate host defenses for their survival. The different strategies protozoan parasites use include hijacking the host cellular signaling pathways and transcription factors. In particular, the nuclear factor-κB (NF-κB) pathway seems to be an attractive target for different pathogens owing to their central role in regulating prompt innate immune responses in host defense. NF-κB is a ubiquitous transcription factor that plays an indispensable role not only in regulating immediate immune responses against invading pathogens but is also a critical regulator of cell proliferation and survival. The major immunomodulatory components include parasite surface and secreted proteins/enzymes and stimulation of host cells intracellular pathways and inflammatory caspases that directly or indirectly interfere with the NF-κB pathway to thwart immune responses that are directed for containment and/or elimination of the pathogen. To showcase how protozoan parasites exploits the NF-κB signaling pathway, this review highlights recent advances from Entamoeba histolytica and other protozoan parasites in contact with host cells that induce outside-in and inside-out signaling to modulate NF-κB in disease pathogenesis and survival in the host.

Association between ocular toxoplasmosis and APEX1 and MYD88 polymorphism

Ocular toxoplasmosis (OT) is the most common form of posterior uveitis, and in some countries, it is the most frequent cause of visual impairment. Studies demonstrate that the polymorphism in genes involved with the immune response can be related both to the occurrence and to the recurrence of OT. Thus, the present study aimed to analyze the association between OT and the polymorphism of the APEX1 (rs1130409) and MyD88 (rs7744) genes. The studied sample consisted of 48 volunteers with OT and 96 asymptomatic volunteers, but positive for anti - T. gondii IgG (control group). Blood collection was performed for serological analysis (ELISA) and DNA extraction. Genotyping of the polymorphism was performed using real-time PCR. To analyze the association between gene polymorphism and OT, logistic regression was performed. The results showed no association between the MYD88 gene polymorphism and the development of OT. However, a significant association was found between OT and APEX1 gene polymorphism, indicating that individuals expressing polymorphic (GG) or heterozygous (GT) alleles are more likely to develop the disease (P-value = 0.02 and 0.03 respectively). These results suggest that APEX1 (rs1130409) polymorphism is a risk factor for the occurrence of ocular toxoplasmosis in the studied population.

The Role of microRNAs in the Infection by T. gondii in Humans

MicroRNAs are molecules belonging to an evolutionarily conserved family of small non-coding RNAs, which act on post-transcriptional gene regulation, causing messenger RNA (mRNA) degradation or inhibiting mRNA translation into proteins. These molecules represent potential biomarkers for diagnosis, non-invasive prognosis, and monitoring the development of the disease. Moreover, they may provide additional information on the pathophysiology of parasitic infections and guide strategies for treatment. The Apicomplexan parasite Toxoplasma gondii modifies the levels of microRNAs and mRNAs in infected host cells by modulating the innate and adaptive immune responses, facilitating its survival within the host. Some studies have shown that microRNAs are promising molecular markers for developing diagnostic tools for human toxoplasmosis. MicroRNAs can be detected in human specimens collected using non-invasive procedures. changes in the circulating host microRNAs have been associated with T. gondii infection in mice and ocular toxoplasmosis in humans. Besides, microRNAs can be amplified from samples using sensitive and molecular-specific approaches such as real-time PCR. This review presents recent findings of the role that microRNAs play during T. gondii infection and discuss their potential use of these small nuclei acid molecules to different approaches such as laboratory diagnosis, modulation of cell and tissue infected as other potential applications in human toxoplasmosis.

Ex vivo infection of canine and ovine placental explants with Trypanosoma cruzi and Toxoplasma gondii: differential activation of NF kappa B signaling pathways

Chagas disease and toxoplasmosis, caused by Trypanosoma cruzi and Toxoplasma gondii, respectively, are important zoonotic diseases affecting humans, companion animals, and livestock, responsible for major health and economic burden. Both parasites can be transmitted vertically in different mammalian species through the placenta. Of note, the transmission rate of T. cruzi is low in dogs, whereas that of T. gondii is high in sheep. The probability of congenital infection depends on complex parasite-host interactions; parasite factors, maternal and fetal immune responses and placental responses all have a role in infection establishment. Since the innate immune response is regulated, at least partially, by NF-κB signaling pathways, our main objective was to determine the effect of ex vivo infection of canine (CPE) and ovine (OPE) placental explants with both parasites, on the activation of canonical and non-canonical NF-κB pathways and its relation to infection. Here, we show that T. cruzi activates both the NF-κB canonical and non-canonical pathways in CPE and OPE, unlike T. gondii, that activates only the canonical pathway in CPE and has no effect on the non-canonical pathway in both explants. Moreover, the inhibition of either or both NF-κB pathways increases the DNA load of T. cruzi in both explants, modulates, on the other hand, T. gondii infection in a differential fashion. Overall, we conclude that the differential modulation of the NF-κB pathways by both pathogens in placental explants might explain, at least partially, the differences in transmission rates of T. cruzi and T. gondii in different mammalian species.

Biogenic Silver Nanoparticles Can Control Toxoplasma gondii Infection in Both Human Trophoblast Cells and Villous Explants

The combination of sulfadiazine and pyrimethamine plus folinic acid is the conventional treatment for congenital toxoplasmosis. However, this classical treatment presents teratogenic effects and bone marrow suppression. In this sense, new therapeutic strategies are necessary to reduce these effects and improve the control of infection. In this context, biogenic silver nanoparticles (AgNp-Bio) appear as a promising alternative since they have antimicrobial, antiviral, and antiparasitic activity. The purpose of this study to investigate the action of AgNp-Bio in BeWo cells, HTR-8/SVneo cells and villous explants and its effects against Toxoplasma gondii infection. Both cells and villous explants were treated with different concentrations of AgNp-Bio or combination of sulfadiazine + pyrimethamine (SDZ + PYZ) in order to verify the viability. After, cells and villi were infected and treated with AgNp-Bio or SDZ + PYZ in different concentrations to ascertain the parasite proliferation and cytokine production profile. AgNp-Bio treatment did not reduce the cell viability and villous explants. Significant reduction was observed in parasite replication in both cells and villous explants treated with silver nanoparticles and classical treatment. The AgNp-Bio treatment increased of IL-4 and IL-10 by BeWo cells, while HTR8/SVneo cells produced macrophage migration inhibitory factor (MIF) and IL-4. In the presence of T. gondii, the treatment induced high levels of MIF production by BeWo cells and IL-6 by HTR8SV/neo. In villous explants, the AgNp-Bio treatment downregulated production of IL-4, IL-6, and IL-8 after infection. In conclusion, AgNp-Bio can decrease T. gondii infection in trophoblast cells and villous explants. Therefore, this treatment demonstrated the ability to reduce the T. gondii proliferation with induction of inflammatory mediators in the cells and independent of mediators in chorionic villus which we consider the use of AgNp-Bio promising in the treatment of toxoplasmosis in BeWo and HTR8/SVneo cell models and in chorionic villi.

Curcumin as an indirect methylation inhibitor modulates the effects of Toxoplasma gondii on genes involved in male fertility

Toxoplasma gondii is a common protozoan parasite, which infects warm-blooded mammals, including mice and humans, throughout the world. The negative effects of T. gondii infection on the human reproductive system have been documented, especially in females. However, only few studies have examined the effects of T. gondii infection on the male reproductive system. Previous research shows that T. gondii can induce DNA methylation in some gene promoters, which are key regulators of spermatogenesis. Therefore, this study aimed to evaluate the effects of curcumin on the activity of DNA methyltransferases (DNMTs), as well as selected genes, involved in spermatogenesis in spermatogenic cells. In the spermatogenic cells exposed to T. gondii, there was a significant increase in DNMT1 and DNMT3A gene expression and a significant reduction in HSPA1A, MTHR, and DAZL gene expression, compared to the controls. The present results showed that curcumin could regulate changes in T. gondii-mediated gene expression. The effect of T. gondii on DNMT activity was also investigated in this study. A 40 % increase in DNMT activity was observed due to T. gondii infection. However, DNMT activity was restored by treatment with 20 μM curcumin for eight hours. The results revealed that T. gondii increases the NF-κB activity, compared to the control group. The increase in NF-κB activity, induced by T. gondii, was inhibited by curcumin. In conclusion, T. gondii, by increasing DNMT expression and activity, leads to an increase in NF-κB activity in cells. On the other hand, curcumin reduced DNA methylation, induced by T. gondii, owing to its NF-κB-inhibiting properties. Therefore, curcumin, as a hypomethylating agent, can be potentially used to alleviate the negative effects of T. gondii on the male reproductive system.

Biogenic silver nanoparticles reduce adherence, infection, and proliferation of toxoplasma gondii RH strain in HeLa cells without inflammatory mediators induction

The highlights of biogenic silver nanoparticles (AgNp-Bio) include low toxicity - depending on size and concentration - and efficient antiparasitic activity. Therefore, the objective of this study was to assess the action of the AgNp-Bio on HeLa cells in an infection with strain of RH Toxoplasma gondii. Firstly, we performed a cellular viability test and characterized the AgNp-Bio to proceed with the infection of HeLa cells with T. gondii to be treated using AgNp-Bio or conventional drugs. Subsequently, we determined the level of standard cytokines Th1/Th2 as well as the content of nitric oxide (NO) and reactive oxygen species (ROS). Results indicated a mean size of 69 nm in diameter for the AgNp-Bio and obtained a dose-dependent toxicity. In addition, the concentrations of 3 and 6 μM promoted a significant decrease in adherence, infection, and intracellular proliferation. We also found lower IL-8 and production of inflammatory mediators. Thus, the nanoparticles reduced the adherence, infection, and proliferation of ROS and NO, in addition to immunomodulating the IL-8. Therefore, our data proved relevant to introduce a promising therapeutic alternative to toxoplasmosis.

Ex vivo infection of human placental explants with Trypanosoma cruzi and Toxoplasma gondii: Differential activation of NF kappa B signaling pathways

Trypanosoma cruzi (T. cruzi) and Toxoplasma gondii (T. gondii) are the causative agents of Chagas disease and Toxoplasmosis. T. cruzi and T. gondii present, respectively, low and high congenital transmission rates and induce a distinctive cytokine/chemokine profile in ex vivo infected human placental explants (HPE). Since the innate immune response is regulated, at least partially, by NF-κB signaling pathways, our main objective was to determine the effect of ex vivo infection with both parasites on the activation of canonical and non-canonical NF-κB pathways and its relation to parasite infection. T. cruzi activates both, the canonical and non-canonical pathways of NF-κB, unlike T. gondii, which has no effect on the canonical pathway and inhibits the non-canonical pathway. The inhibition of both pathways of NF-κB increases the DNA load of T. cruzi and T. gondii in HPE. Therefore, the differential modulation of NF-κB signal transduction pathways by both parasites might explain, at least partially, the low and high congenital transmission rates of T. cruzi and T. gondii.

Detection of Humoral and Cellular Immune Responses in Buffaloes Naturally Infected with Sarcocystosis with Risk Factor Assessment

Sarcocystosis is a silent, parasitic disease which affects various animal species and causes significant economic losses. It is caused by a number of different intracellular Sarcocystis spp. This study was aimed to detect the host humoral and cellular immune response due to natural infection. Adding to the determination of the infection rate in Monufia Governorate, Egypt. A total number of 127 Egyptian buffaloes (Bubalus bubalis); 30 males and 97 females between 2-11 years of age were examined during 2018. An infection rate of 74% (94/127) was detected by macroscopic examination. The old age females were found to be at a high risk of 90.7% (88/97) in comparison with the young males 20% (6/30). Immunologically, the cellular and humoral immune response was determined using ELISA. A marked down-regulation of the proinflammatory Th-1 cytokine (IFN-γ) and up-regulation of the anti-inflammatory Th-2 cytokine (IL-5) adding to a high level of IgG and IgE were detected in the infected animals compared to the non infected ones. The local cellular immune response in the infected tissues was characterized by an accumulation of mixed inflammatory cells, granuloma formation, eosinophilic infiltration, muscular edema, and necrotic degeneration. In conclusion, the Sarcocystis infection rate in the naturally infected buffaloes in Monufia Governorate was high. This is the first study to provide a fundamental insight into the immune profile in buffaloes infected with Sarcocystis spp. So, it will provide valuable insights to develop novel effective vaccines in future studies. Moreover, sensitive and specific tools should be established for the accurate diagnosis of this disease in the different Egyptian governorates through well-structured serological surveys.

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.

Toxoplasma gondii Modulates the Host Cell Responses: An Overview of Apoptosis Pathways

Infection with Toxoplasma gondii has a major implication in public health. Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect all nucleated cells belonging to a wide range of host species. One of the particularities of this parasite is its invasion and persistence in host cells of immunocompetent people. This infection is usually asymptomatic. In immunocompromised patients, the infection is severe and symptomatic. The mechanisms by which T. gondii persists are poorly studied in humans. In mouse models, many aspects of the interaction between the parasite and the host cells are being studied. Apoptosis is one of these mechanisms that could be modulated by Toxoplasma to persist in host cells. Indeed, Toxoplasma has often been implicated in the regulation of apoptosis and viability mechanisms in both human and murine infection models. Several of these studies centered on the regulation of apoptosis pathways have revealed interference of this parasite with host cell immunity, cell signalling, and invasion mechanisms. This review provides an overview of recent studies concerning the effect of Toxoplasma on different apoptotic pathways in infected host cells.

Parasites as negative regulators of cancer

Several environmental factors (chemical, physical, and biological) can cause the initiation, promotion, and progression of cancer. Regarding the biological factors, several studies have found that infections caused by some bacteria, viruses and protozoan, and helminth parasites are related to carcinogenesis. However, in recent years a different approach has been implemented on the antitumor impact of parasitic diseases caused by some protozoan and helminths, mainly because such infections may affect several hallmarks of cancer, but the involved mechanisms still remain unknown. The beneficial effects reported for some parasitic diseases on tumorigenesis range from the induction of apoptosis, activation of the immune response, avoiding metastasis and angiogenesis, inhibition of proliferative signals, to the regulation of inflammatory responses that promote cancer. In this work, we reviewed the available information regarding how parasitic infections may modulate cancer progression. Despite the fact that specific mechanisms of action on tumors are not yet totally clear, we consider that detailed studies of the antitumor action of these organisms and their products could lead to the discovery and use of new molecules from these biological agents that may work as adjuvant therapy in the treatment of various types of cancer.

Transcriptomic analysis reveals Toxoplasma gondii strain-specific differences in host cell response to dense granule protein GRA15

Growth and replication of the protozoan parasite Toxoplasma gondii within host cell entail the production of several effector proteins, which the parasite exploits for counteracting the host's immune response. Despite considerable research to define the host signaling pathways manipulated by T. gondii and their effectors, there has been limited progress into understanding how individual members of the dense granule proteins (GRAs) modulate gene expression within host cells. The aim of this study was to evaluate whether T. gondii GRA15 protein plays any role in regulating host gene expression. Baby hamster kidney cells (BHK-21) were transfected with plasmids encoding GRA15 genes of either type I GT1 strain (GRA15_I) or type II PRU strain (GRA15_II). Gene expression patterns of transfected and nontransfected BHK-21 cells were investigated using RNA-sequencing analysis. GRA15_I and GRA15_II induced both known and novel transcriptional changes in the transfected BHK-21 cells compared with nontransfected cells. Pathway analysis revealed that GRA15_II was mainly involved in the regulation of tumor necrosis factor (TNF), NF-κB, HTLV-I infection, and NOD-like receptor signaling pathways. GRA15_I preferentially influenced the synthesis of unsaturated fatty acids in host cells. Our findings support the hypothesis that certain functions of GRA15 protein are strain dependent and that GRA15 modulates the expression of signaling pathways and genes with important roles in T. gondii pathophysiology. A greater understanding of host signaling pathways influenced by T. gondii effectors would allow the development of more efficient anti-T. gondii therapeutic schemes, capitalizing on disrupting parasite virulence factors to advance the treatment of toxoplasmosis.

The Toxoplasma gondii ME-49 strain upregulates levels of A20 that inhibit NF-κB activation and promotes apoptosis in human leukaemia T-cell lines

Background

Acute T-lymphocyte leukaemia is a form of haematological malignancy with abnormal activation of NF-κB pathway, which results in high expression of A20 and ABIN1, which constitute a negative feedback mechanism for the regulation of NF-κB activation. Clinical studies have found that acute T-lymphocyte leukaemia patients are susceptible to Toxoplasma gondii infection; however, the effect of T. gondii on the proliferation and apoptosis of human leukaemia T-cells remains unclear. Here, we used the T. gondii ME-49 strain to infect human leukaemia T-cell lines Jurkat and Molt-4, to explore the effect of T. gondii on proliferation and apoptosis, which is mediated by NF-κB in human leukaemia T-cells.

Methods

The Tunel assay was used to detect cell apoptosis. Cell Counting Kit-8 was used to detect cell proliferation viability. The apoptosis level and the expression level of NF-κB related proteins in human leukaemia T-cells were detected by flow cytometry and Western blotting.

Results

Western blotting analyses revealed that the T. gondii ME-49 strain increased the expression of A20 and decreased both ABIN1 expression and NF-κB p65 phosphorylation. By constructing a lentiviral-mediated shRNA to knockdown the A20 gene in Jurkat T-cells and Molt-4 T-cells, the apoptosis levels of the two cell lines decreased after T. gondii ME-49 infection, and levels of NF-κB p65 phosphorylation and ABIN1 were higher than in the non-konckdown group. After knockingdown ABIN1 gene expression by constructing the lentiviral-mediated shRNA and transfecting the recombinant expression plasmid containing the ABIN1 gene into two cell lines, apoptosis levels and cleaved caspase-8 expression increased or decreased in response to T. gondii ME-49 infection, respectively.

Conclusions

Our data suggest that ABIN1 protects human leukaemia T-cells by allowing them to resist the apoptosis induced by T. gondii ME-49 and that the T. gondii ME-49 strain induces the apoptosis of human leukaemia T-cells via A20-mediated downregulation of ABIN1 expression.

Microarray analysis of long non-coding RNA expression profiles uncovers a Toxoplasma-induced negative regulation of host immune signaling

BACKGROUND

Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect mammalian cells and thereby regulate host gene expression. The long non-coding RNAs (lncRNAs) have been demonstrated to be an important class of RNA molecules that regulate many biological processes, including host-pathogen interactions. However, the role of host lncRNAs in the response to T. gondii infection remains largely unknown.

METHODS

We applied a microarray approach to determine the differential expression profiles of both lncRNAs and mRNAs in the human foreskin fibroblast (HFF) cells after T. gondii infection. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to reveal the potential functions of T. gondii-induced genes. Based on the co-expression networks of lncRNAs and immune-related genes, the role of NONSHAT022487 on the regulation of UNC93B1 related immune signaling was investigated by the knockdown and over-expression of lncRNA in human macrophage derived from the PMA-induced promonocytic cell line THP-1.

RESULTS

Our data showed that 996 lncRNAs and 109 mRNAs in HFF cells were significantly and differentially expressed following T. gondii infection (fold change ≥ 5, P < 0.05). The results from the GO and KEGG pathway analyses indicated that the mRNAs with differential expression were mainly involved in the host immune response. Remarkably, we identified a novel lncRNA, NONSHAT022487, which suppresses the expression of the immune-related molecule UNC93B1. After T. gondii infection, NONSHAT022487 impaired the secretion of the cytokines IL-12, TNF-α, IL-1β and IFN-γ by downregulating UNC93B1 expression in human macrophage cells.

CONCLUSIONS

Our study identified infection-induced lncRNA expression as a novel mechanism by which the Toxoplasma parasite regulates host immune signaling, which advances our understanding of the interaction of T. gondii parasites and host cells.

Global miRNA expression profiling of domestic cat livers following acute Toxoplasma gondii infection

Although microRNAs (miRNAs) play an important role in liver homeostasis, the extent to which they can be altered by Toxoplasma gondii infection is unknown. Here, we utilized small RNA sequencing and bioinformatic analyses to characterize miRNA expression profiles in the liver of domestic cats at 7 days after oral infection with T. gondii (Type II) strain. A total of 384 miRNAs were identified and 82 were differentially expressed, of which 33 were up-regulated and 49 down-regulated. Also, 5690 predicted host gene targets for the differentially expressed miRNAs were identified using the bioinformatic algorithm miRanda. Gene ontology analysis revealed that the predicted gene targets of the dysregulated miRNAs were significantly enriched in apoptosis. Kyoto Encyclopedia of Genes and Genomes analysis showed that the predicted gene targets were involved in several pathways, including acute myeloid leukemia, central carbon metabolism in cancer, choline metabolism in cancer, estrogen signaling pathway, fatty acid degradation, lysosome, nucleotide excision repair, progesterone-mediated oocyte maturation, and VEGF signaling pathway. The expression level of 6 upregulated miRNAs (mmu-miR-21a-5p, mmu-miR-20a-5p, mmu-miR-17-5p, mmu-miR-30e-3p, mmu-miR-142a-3p, and mmu-miR-106b-3p) was confirmed by stem-loop quantitative reverse transcription PCR, which yielded results consistent with the sequencing data. These findings expand our understanding of the regulatory mechanisms of miRNAs underlying T. gondii pathogenesis and contribute new database information on cat miRNAs, opening a new perspective on the prevention and treatment of T. gondii infection.

Evasion of Human Neutrophil-Mediated Host Defense during Toxoplasma gondii Infection

Neutrophils are a major player in host immunity to infection; however, the mechanisms by which human neutrophils respond to the intracellular protozoan parasite Toxoplasma gondii are still poorly understood. In the current study, we found that, whereas primary human monocytes produced interleukin-1beta (IL-1β) in response to T. gondii infection, human neutrophils from the same blood donors did not. Moreover, T. gondii inhibited lipopolysaccharide (LPS)-induced IL-1β synthesis in human peripheral blood neutrophils. IL-1β suppression required active parasite invasion, since heat-killed or mycalolide B-treated parasites did not inhibit IL-1β release. By investigating the mechanisms involved in this process, we found that T. gondii infection of neutrophils treated with LPS resulted in reduced transcript levels of IL-1β and NLRP3 and reduced protein levels of pro-IL-1β, mature IL-1β, and the inflammasome sensor NLRP3. In T. gondii-infected neutrophils stimulated with LPS, the levels of MyD88, TRAF6, IKKα, IKKβ, and phosphorylated IKKα/β were not affected. However, LPS-induced IκBα degradation and p65 phosphorylation were reduced in T. gondii-infected neutrophils, and degradation of IκBα was reversed by treatment with the proteasome inhibitor MG-132. Finally, we observed that T. gondii inhibited the cleavage and activity of caspase-1 in human neutrophils. These results indicate that T. gondii suppression of IL-1β involves a two-pronged strategy whereby T. gondii inhibits both NF-κB signaling and activation of the NLRP3 inflammasome. These findings represent a novel mechanism of T. gondii evasion of human neutrophil-mediated host defense by targeting the production of IL-1β.

Toxoplasma gondii is an obligate intracellular parasite that infects approximately one-third of humans worldwide and can invade virtually any nucleated cell in the human body. Although it is well documented that neutrophils infiltrate the site of acute T. gondii infection, there is limited understanding of how human neutrophils respond to T. gondii. Neutrophils control infectious pathogens by a variety of mechanisms, including the release of the cytokine IL-1β, a major driver of inflammation during infection. This study reveals that T. gondii is able to inhibit IL-1β production in human neutrophils by impairing the activation of the NF-κB signaling pathway and by inhibiting the inflammasome, the protein complex responsible for IL-1β maturation. This two-pronged strategy of targeting the IL-1β pathway may facilitate the survival and spread of T. gondii during acute infection.

Modulation of host immune responses to Toxoplasma gondii by microRNAs

To survive successfully, Toxoplasma counteracts the strictly regulated host innate response to downregulate inflammation that could be deleterious for the parasite. MicroRNAs are vital regulators of both innate and adaptive immunity, controlling the maintenance and development of immune progenitors as well as the differentiation and the functions of host mature immune cells. Thus, the complexity of mechanisms underlying the connection between Toxoplasma and host immunity has led to investigations of miRNAs as additional key molecular players. The knowledge acquired from these studies will be useful for aiding the discovery of new targets for diagnosis or therapeutic approaches for toxoplasmosis and insight into the interaction between host and parasite.

Toxoplasma Effectors Targeting Host Signaling and Transcription

Early electron microscopy studies revealed the elaborate cellular features that define the unique adaptations of apicomplexan parasites. Among these were bulbous rhoptry (ROP) organelles and small, dense granules (GRAs), both of which are secreted during invasion of host cells. These early morphological studies were followed by the exploration of the cellular contents of these secretory organelles, revealing them to be comprised of highly divergent protein families with few conserved domains or predicted functions. In parallel, studies on host-pathogen interactions identified many host signaling pathways that were mysteriously altered by infection. It was only with the advent of forward and reverse genetic strategies that the connections between individual parasite effectors and the specific host pathways that they targeted finally became clear. The current repertoire of parasite effectors includes ROP kinases and pseudokinases that are secreted during invasion and that block host immune pathways. Similarly, many secretory GRA proteins alter host gene expression by activating host transcription factors, through modification of chromatin, or by inducing small noncoding RNAs. These effectors highlight novel mechanisms by which T. gondii has learned to harness host signaling to favor intracellular survival and will guide future studies designed to uncover the additional complexity of this intricate host-pathogen interaction.

Long-Term Relationships: the Complicated Interplay between the Host and the Developmental Stages of Toxoplasma gondii during Acute and Chronic Infections

Toxoplasma gondii represents one of the most common parasitic infections in the world. The asexual cycle can occur within any warm-blooded animal, but the sexual cycle is restricted to the feline intestinal epithelium. T. gondii is acquired through consumption of tissue cysts in undercooked meat as well as food and water contaminated with oocysts. Once ingested, it differentiates into a rapidly replicating asexual form and disseminates throughout the body during acute infection. After stimulation of the host immune response, T. gondii differentiates into a slow-growing, asexual cyst form that is the hallmark of chronic infection. One-third of the human population is chronically infected with T. gondii cysts, which can reactivate and are especially dangerous to individuals with reduced immune surveillance. Serious complications can also occur in healthy individuals if infected with certain T. gondii strains or if infection is acquired congenitally. No drugs are available to clear the cyst form during the chronic stages of infection. This therapeutic gap is due in part to an incomplete understanding of both host and pathogen responses during the progression of T. gondii infection. While many individual aspects of T. gondii infection are well understood, viewing the interconnections between host and parasite during acute and chronic infection may lead to better approaches for future treatment. The aim of this review is to provide an overview of what is known and unknown about the complex relationship between the host and parasite during the progression of T. gondii infection, with the ultimate goal of bridging these events.

Proteomic Profiling of Mouse Liver following Acute Toxoplasma gondii Infection

Toxoplasma gondii remains a global public health problem. However, its pathophysiology is still not-completely understood particularly the impact of infection on host liver metabolism. We performed iTRAQ-based proteomic analysis to evaluate early liver protein responses in BALB/c mice following infection with T. gondii PYS strain (genotype ToxoDB#9) infection. Our data revealed modification of protein expression in key metabolic pathways, as indicated by the upregulation of immune response and downregulation of mitochondrial respiratory chain, and the metabolism of fatty acids, lipids and xenobiotics. T. gondii seems to hijack host PPAR signaling pathway to downregulate the metabolism of fatty acids, lipids and energy in the liver. The metabolism of over 400 substances was affected by the downregulation of genes involved in xenobiotic metabolism. The top 10 transcription factors used by upregulated genes were Stat2, Stat1, Irf2, Irf1, Sp2, Egr1, Stat3, Klf4, Elf1 and Gabpa, while the top 10 transcription factors of downregulated genes were Hnf4A, Ewsr1, Fli1, Hnf4g, Nr2f1, Pparg, Rxra, Hnf1A, Foxa1 and Foxo1. These findings indicate global reprogramming of the metabolism of the mouse liver after acute T. gondii infection. Functional characterization of the altered proteins may enhance understanding of the host responses to T. gondii infection and lead to the identification of new therapeutic targets.

MicroRNAs in the Host-Apicomplexan Parasites Interactions: A Review of Immunopathological Aspects

MicroRNAs (miRNAs), a class of small non-coding regulatory RNAs, have been detected in a variety of organisms ranging from ancient unicellular eukaryotes to mammals. They have been associated with numerous molecular mechanisms involving developmental, physiological and pathological changes of cells and tissues. Despite the fact that miRNA-silencing mechanisms appear to be absent in some Apicomplexan species, an increasing number of studies have reported a role for miRNAs in host-parasite interactions. Host miRNA expression can change following parasite infection and the consequences can lead, for instance, to parasite clearance. In this context, the immune system signaling appears to have a crucial role.

Analysis of miRNA expression profiling in mouse spleen affected by acute Toxoplasma gondii infection

Toxoplasma gondii is a worldwide prevalent pathogen that infects most of the warm-blood vertebrates. To investigate the regulation network of splenic miRNAs altered by acute infection with T. gondii, we herein investigated the changes of miRNA profile in mouse spleen via next generation sequencing and bioinformatics analysis. A total of 379 miRNAs was identified, 131 miRNAs of them were differentially expressed (including 97 upregulated and 34 downregulated miRNAs). 48 differentially expressed miRNAs had validated targets in the miRWalk2.0 database. Gene Ontology (GO) enrichment analysis revealed that the validated targets of differently expressed miRNAs were significantly enriched in gene transcription regulation. It suggested that T. gondii can modulate host gene expression through targeting to trans-regulation factors. The genes involved in apoptosis or anti-apoptosis were both targeted by differentially expressed miRNAs. The change of power balance between the miRNAs targeting host apoptosis genes and those regulating host anti-apoptosis genes contributes to the fate of host apoptosis process. Twelve pathways were significantly enriched in KEGG analysis with most of them being cancer related, including pathways in cancer, pancreatic cancer, colorectal cancer, axon guidance, MAPK signaling pathway, focal adhesion, chronic myeloid leukemia, renal cell carcinoma, prostate cancer, glioma, regulation of actin cytoskeleton, and Wnt signaling pathway. Our study showed a changed miRNA regulation network in mouse spleen infected by T. gondii. These findings will be helpful for better understanding of miRNA regulation network in host-T. gondii interaction, revealing the relationship among T. gondii infection, gene regulation, apoptosis and cancer process alterations in infected spleen.

Phytoecdysteroids as modulators of the Toxoplasma gondii growth rate in human and mouse cells

Background

Searching for new effective drugs against human and animal toxoplasmosis we decided to test the anti-Toxoplasma potential of phytoecdysteroids (α-ecdysone and 20-hydroxyecdysone) characterized by the pleiotropic activity on mammalian organisms including the enhancement of host’s anti-parasitic defence. This objective was accomplished by the in vitro evaluation of T. gondii growth in phytoecdysteroid-treated immunocompetent cells of selected hosts: humans and two strains of inbred mice with genetically determined different susceptibility to toxoplasmosis.

Methods

Peripheral mononuclear blood cells were isolated from Toxoplasma-positive and Toxoplasma-negative women (N = 43) and men (N = 21). Non-infected mice (C57BL/6, N = 10 and BALB/c, N = 14) and mice (BALB/c, N = 10) challenged intraperitoneally with 5 tissue cysts of the T. gondii DX strain were also used in this study as a source of splenocytes. The effects of phytoecdysteroids on the viability of human PBMC and mouse splenocytes were evaluated using the MTT assay. The influence of phytoecdysteroids on PBMCs, splenocytes and T. gondii proliferation was measured using radioactivity tests (the level of 3[H] uracil incorporation by toxoplasms or 3[H] thymidine by PBMCs and splenocytes), which was confirmed by quantitative Real-Time PCR. Statistical analysis was performed using SigmaStat 3.5 (Systat Software GmbH). The best-fit IC50 curves were plotted using GraphPad Prism 6.0 (GraphPad Software, Inc.).

Results

Our results showed that phytoecdysteroids promote the multiplication of Toxoplasma in cultures of human or murine immune cells, in contrast to another apicomplexan parasite, Babesia gibsoni. Additionally, the tested phytoecdysteroids did not stimulate the in vitro secretion of the essential protective cytokines (IFN-γ, IL-2 and IL-10), neither by human nor by murine immune cells involved in an effective intracellular killing of the parasite.

Conclusions

Judging by the effect of phytoecdysteroids on the T. gondii proliferation, demonstrated for the first time in this study, it seems that these compounds should not be taken into consideration as potential medications to treat toxoplasmosis. Phytoecdysteroids included in the food are most likely not harmful for human or animal health but certain nutrients containing ecdysteroids at high concentrations could promote T. gondii proliferation in chronically infected and immunocompromised individuals. In order to assess the real impact of ecdysteroids on the course of natural T. gondii invasion, in vivo research should be undertaken because it cannot be ruled out that the in vivo effect will be different than the in vitro one. However, taking into account the possible stimulating effect of ecdysteroids on some opportunistic parasites (such as Toxoplasma or Strongyloides) further studies are necessary and should focus on the mechanisms of their action, which directly or indirectly enhance the parasite growth. Since ecdysteroids are considered as potential drugs, it is essential to determine their effect on various parasitic pathogens, which may infect the host at the same time, especially in immunocompromised individuals.

Secreted Toxoplasma gondii molecules interfere with expression of MHC-II in interferon gamma-activated macrophages

The obligate intracellular protozoan parasite Toxoplasma gondii interferes with major histocompatibility complex class II antigen presentation to dampen host CD4(+) T cell responses. While it is known that T. gondii inhibits major histocompatibility complex class II gene transcription and expression in infected host cells, the mechanism of this host manipulation is unknown. Here, we show that soluble parasite proteins inhibit IFNγ-induced expression of major histocompatibility complex class II on the surface of the infected cell in a dose-dependent response that was abolished by protease treatment. Subcellular fractionation of T. gondii tachyzoites revealed that the major histocompatibility complex class II inhibitory activity co-partitioned with rhoptries and/or dense granules. However, parasite mutants deleted for single rhoptries or dense granules genes (ROP1, 4/7, 14, 16 and 18 or GRA 2-9 and 12 knock-out strains) retained the ability to inhibit expression of major histocompatibility complex class II. In addition, excreted/secreted antigens released by extracellular tachyzoites displayed immunomodulatory activity characterized by an inhibition of major histocompatibility complex class II expression, and reduced expression and release of TNFα by macrophages. Tandem MS analysis of parasite excreted/secreted antigens generated a list of T. gondii secreted proteins that may participate in major histocompatibility complex class II inhibition and the modulation of host immune functions.

Role of glucocorticoids and Toxoplasma gondii infection on murine intestinal epithelial cells

Glucocorticoids (GCs) are stress hormones secreted in response to perceived psychological and or physiological stress. GCs have been shown to reduce tissue inflammation by down-regulating the production of inflammatory chemokines produced by epithelial cells. The protozoan parasite Toxoplasma gondii is known to increase cytokine, chemokine, and Toll-like receptors (TLRs) expression in parasite infected mouse intestinal epithelial cells (IECs). We sought to analyze the role of an anti-inflammatory protein, glucocorticoid-induced leucine zipper (GILZ) in MODE-K cells during infection with T. gondii. GILZ expression in MODE-K cells was assessed by PCR and immunoblotting after stimulation with GCs (corticosterone, CORT) or T. gondii infection. GILZ mRNA was constitutively expressed in MODE-K cells but not its protein product. While infection and pre-exposure to CORT decreased GILZ isoforms of 28 and 17 kD, the presence of CORT during infection increased levels of 17 kD isoform. Infected cells treated with CORT had decreased expression of chemokines (IP-10/CXCL10, MCP-1/CCL2, MIP-2/CXCL8) while their expression was increased when endogenous GILZ was removed by siRNA treatment. GILZ up-regulation during infection may serve as a mechanism to decrease epithelial cell responses and facilitate parasite replication.

WITHDRAWN: Toxoplasma gondii virulence factor ROP18 inhibits the host NF-κB pathway by promoting p65 degradation

The obligate intracellular parasite Toxoplasma gondii secretes effector molecules into the host cell to modulate host immunity. Previous studies have shown that T. gondii could interfere with host NF-κB signaling to promote their survival, but the effectors of type I strains remain unclear. The polymorphic rhoptry protein ROP18 is a key serine/threonine kinase that phosphorylates host proteins to modulate acute virulence. Our data demonstrated that the N-terminal portion of ROP18 is associated with the dimerization domain of p65. ROP18 phosphorylates p65 at Ser-468 and targets this protein to the ubiquitin-dependent degradation pathway. The kinase activity of ROP18 is required for p65 degradation and suppresses NF-κB activation. Consistently, compared with wild-type ROP18 strain, ROP18 kinase-deficient type I parasites displayed a severe inability to inhibit NF-κB, culminating in the enhanced production of IL-6, IL-12, and TNF-α in infected macrophages. In addition, studies have shown that transgenic parasites carrying kinase-deficient ROP18 induce M1-biased activation. These results demonstrate for the first time that the virulence factor ROP18 in T. gondii type I strains is responsible for inhibiting the host NF-κB pathway and for suppressing proinflammatory cytokine expression, thus providing a survival advantage to the infectious agent.

Modulation of the host Th1 immune response in pigeon protozoal encephalitis caused by Sarcocystis calchasi

Pigeon protozoal encephalitis (PPE) is an emerging central-nervous disease of domestic pigeons (Columba livia f. domestica) reported in Germany and the United States. It is caused by the apicomplexan parasite Sarcocystis calchasi which is transmitted by Accipter hawks. In contrast to other members of the Apicomplexa such as Toxoplasma and Plasmodium, the knowledge about the pathophysiology and host manipulation of Sarcocystis is scarce and almost nothing is known about PPE. Here we show by mRNA expression profiling a significant down-modulation of the interleukin (IL)-12/IL-18/interferon (IFN)-γ axis in the brains of experimentally infected pigeons during the schizogonic phase of disease. Concomitantly, no cellular immune response was observed in histopathology while immunohistochemistry and nested PCR detected S. calchasi. In contrast, in the late central-nervous phase, IFN-γ and tumor necrosis factor (TNF) α-related cytokines were significantly up-modulated, which correlated with a prominent MHC-II protein expression in areas of mononuclear cell infiltration and necrosis. The mononuclear cell fraction was mainly composed of T-lymphocytes, fewer macrophages and B-lymphocytes. Surprisingly, the severity and composition of the immune cell response appears unrelated to the infectious dose, although the severity and onset of the central nervous signs clearly was dose-dependent. We identified no or only very few tissue cysts by immunohistochemistry in pigeons with severe encephalitis of which one pigeon repeatedly remained negative by PCR despite severe lesions. Taken together, these observations may suggest an immune evasion strategy of S. calchasi during the early phase and a delayed-type hypersensitivity reaction as cause of the extensive cerebral lesions during the late neurological phase of disease.

Modulation of innate immunity by Toxoplasma gondii virulence effectors

Toxoplasma gondii is a common parasite of animals and humans and can cause serious opportunistic infections. However, the majority of infections are asymptomatic, possibly because the organism has co-evolved with its many vertebrate hosts and has developed multiple strategies to persist asymptomatically for the lifetime of the host. Over the past two decades, infection studies in the mouse, combined with forward-genetics approaches aimed at unravelling the molecular basis of infection, have revealed that T. gondii virulence is mediated, in part, by secretion of effector proteins into the host cell during invasion. Here, we review recent advances that illustrate how these virulence factors disarm innate immunity and promote survival of the parasite.

The role of NF-κB activation during protection against Leishmania infection

Members of the nuclear factor-κB (NF-κB) family of transcription factors regulate a variety of molecules involved in host defense against pathogens. A prominent role of NF-κB in innate and adoptive immunity is based on the regulation of inducible transcription of various genes whose products are essential components of the immune response such as cytokines, chemokines, and adhesion molecules. Since the discovery of the five members of the NF-κB transcription factor family, RelA, c-Rel, RelB, p50 and p52, considerable progress has been made toward better understanding how the different NF-κB homo- and heterodimers regulate such distinct subsets of target genes. All of the NF-κB molecules are activated by various infectious stimuli; however, there are still open questions related to the selective functions of individual NF-κB family members during a coordinated immune response to infection. Diverse parasites such as Toxoplasma gondii, Leishmania donovani, Leishmania major, and Trichuris muris have been reported to activate NF-κB signaling cascades, and a number of distinct parasite-derived molecules may actively interfere with the pathways that lead to NF-κB activation. In this review, we provide an overview on the role of NF-κB activation in leishmaniasis and discuss how individual NF-κB family members might perform their distinct and non-overlapping functions in the regulation of protective immunity to Leishmania infection.

A critical role for SOCS3 in innate resistance to Toxoplasma gondii

The innate and adaptive immune responses that confer resistance to the intracellular pathogen Toxoplasma gondii critically depend on IL-12 production, which drives interferon-γ (IFN-γ) expression. Certain cytokines can activate STAT3 and limit IL-12 production to prevent infection-associated immune pathology, but T. gondii also directly activates STAT3 to evade host immunity. We show that suppressor of cytokine signaling molecule 3 (SOCS3), a target of STAT3 that limits signaling by the pleiotropic cytokine IL-6, is upregulated in response to infection but is dispensable for the immune-inhibitory effects of T. gondii. Unexpectedly, mice with targeted deletion of SOCS3 in macrophages and neutrophils have reduced IL-12 responses and succumb to toxoplasmosis. Anti-IL-6 administration or IL-12 treatment blocked disease susceptibility, suggesting that in the absence of SOCS3, macrophages are hypersensitive to the anti-inflammatory properties of IL-6. Thus, SOCS3 has a critical role in suppressing IL-6 signals and promoting immune responses to control T. gondii infection.

An inside job: hacking into Janus kinase/signal transducer and activator of transcription signaling cascades by the intracellular protozoan Toxoplasma gondii

The intracellular protozoan Toxoplasma gondii is well known for its skill at invading and living within host cells. New discoveries are now also revealing the astounding ability of the parasite to inject effector proteins into the cytoplasm to seize control of the host cell. This review summarizes recent advances in our understanding of one such secretory protein called ROP16. This molecule is released from rhoptries into the host cell during invasion. The ROP16 molecule acts as a kinase, directly activating both signal transducer and activator of transcription 3 (STAT3) and STAT6 signaling pathways. In macrophages, an important and preferential target cell of parasite infection, the injection of ROP16 has multiple consequences, including downregulation of proinflammatory cytokine signaling and macrophage deviation to an alternatively activated phenotype.

Host cell signalling and leishmania mechanisms of evasion

Leishmania parasites are able to secure their survival and propagation within their host by altering signalling pathways involved in the ability of macrophages to kill pathogens or to engage adaptive immune system. An important step in this immune evasion process is the activation of host protein tyrosine phosphatase SHP-1 by Leishmania. SHP-1 has been shown to directly inactivate JAK2 and Erk1/2 and to play a role in the negative regulation of several transcription factors involved in macrophage activation. These signalling alterations contribute to the inactivation of critical macrophage functions (e.g., Nitric oxide, IL-12, and TNF-α). Additionally, to interfere with IFN-γ receptor signalling, Leishmania also alters several LPS-mediated responses. Recent findings from our laboratory revealed a pivotal role for SHP-1 in the inhibition of TLR-induced macrophage activation through binding to and inactivating IL-1-receptor-associated kinase 1 (IRAK-1). Furthermore, we identified the binding site as an evolutionarily conserved ITIM-like motif, which we named kinase tyrosine-based inhibitory motif (KTIM). Collectively, a better understanding of the evasion mechanisms utilized by Leishmania parasite could help to develop more efficient antileishmanial therapies in the near future.

Immunology of Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite. Following oral infection the parasite crosses the intestinal epithelial barrier to disseminate throughout the body and establish latent infection in central nervous tissues. The clinical presentation ranges from asymptomatic to severe neurological disorders in immunocompromised individuals. Since the clinical presentation is diverse and depends, among other factors, on the immune status of the host, in the present review, we introduce parasitological, epidemiological, clinical, and molecular biological aspects of infection with T. gondii to set the stage for an in-depth discussion of host immune responses. Since immune responses in humans have not been investigated in detail the present review is exclusively referring to immune responses in experimental models of infection. Systemic and local immune responses in different models of infection are discussed, and a separate chapter introduces commonly used animal models of infection.

Modulation of early β-defensin-2 production as a mechanism developed by type I Toxoplasma gondii to evade human intestinal immunity

We investigated the early innate immune responses induced in human intestinal epithelial cells (IEC) by the three defined Toxoplasma gondii genotype strains. Transcriptome analysis revealed that among differentially expressed genes, β-defensins distinguished the most IEC infected by fast- or slow-replicating T. gondii genotypes. Although β-defensin 1 and 3 genes were not expressed in host cells at early time points postinfection, the slow-replicating type II and III parasites induced high levels of β-defensin 2 gene expression. Notably, no β-defensin 2 gene expression occurred early after infection with the fast-replicating type I parasite. However, activation of this gene in IEC by poly(I:C) treatment prior to infection substantially decreased parasite viability, and pretreatment of parasites with synthetic β-defensin 2 significantly reduced their infectivity of IEC. These findings strongly support the modulation of early β-defensin 2 expression as a mechanism used by type I T. gondii parasites to mediate immune evasion.

Strain-specific activation of the NF-kappaB pathway by GRA15, a novel Toxoplasma gondii dense granule protein

NF-κB is an integral component of the immune response to Toxoplasma gondii. Although evidence exists that T. gondii can directly modulate the NF-κB pathway, the parasite-derived effectors involved are unknown. We determined that type II strains of T. gondii activate more NF-κB than type I or type III strains, and using forward genetics we found that this difference is a result of the polymorphic protein GRA15, a novel dense granule protein which T. gondii secretes into the host cell upon invasion. A GRA15-deficient type II strain has a severe defect in both NF-κB nuclear translocation and NF-κB-mediated transcription. Furthermore, human cells expressing type II GRA15 also activate NF-κB, demonstrating that GRA15 alone is sufficient for NF-κB activation. Along with the rhoptry protein ROP16, GRA15 is responsible for a large part of the strain differences in the induction of IL-12 secretion by infected mouse macrophages. In vivo bioluminescent imaging showed that a GRA15-deficient type II strain grows faster compared with wild-type, most likely through its reduced induction of IFN-γ. These results show for the first time that a dense granule protein can modulate host signaling pathways, and dense granule proteins can therefore join rhoptry proteins in T. gondii's host cell-modifying arsenal.

A history of studies that examine the interactions of Toxoplasma with its host cell: Emphasis on in vitro models

This review is a historical look at work carried out over the past 50 years examining interactions of Toxoplasma with the host cell and attempts to focus on some of the seminal experiments in the field. This early work formed the foundation for more recent studies aimed at identifying the host and parasite factors mediating key Toxoplasma-host cell interactions. We focus especially on those studies that were performed in vitro and provide discussions of the following general areas: (i) establishment of the parasitophorous vacuole, (ii) the requirement of specific host cell molecules for parasite replication, (iii) the scenarios under which the host cell can resist parasite replication and/or persistence, (iv) host species-specific and host strain-specific responses to Toxoplasma infection, and (v) Toxoplasma-induced immune modulation.

NF-kappaB1 contributes to T cell-mediated control of Toxoplasma gondii in the CNS

In this study, the role of NF-kappaB1 was examined during toxoplasmosis. While wildtype BALB/c mice generated protective responses, NF-kappaB1(-/-) mice developed Toxoplasmic encephalitis, characterized by increased parasite burden and necrosis in the brain. Susceptibility was primarily associated with a local decrease in the number of CD8(+) T cells and IFN-gamma production, while accessory cell function appeared intact in NF-kappaB1(-/-) mice. Consistent with these findings, T cell transfer studies revealed that NF-kappaB1(-/-) T cells provided SCID mice less protection than wildtype T cells. These results demonstrate an intrinsic role for NF-kappaB1 in T cell-mediated immunity to Toxoplasmagondii.

Dysregulation of macrophage signal transduction by Toxoplasma gondii: past progress and recent advances

The opportunistic protozoan parasite Toxoplasma gondii is well known as a strong inducer of cell-mediated immunity, largely as a result of proinflammatory cytokine induction during in vivo infection. Yet, during intracellular infection the parasite suppresses signal transduction pathways leading to these proinflammatory responses. The opposing responses are likely to reflect the parasite's need to stimulate immunity allowing host survival and parasite persistence, and at the same time avoiding excessive responses that could result in parasite elimination and host immunopathology. This Review summarizes past and present investigations into the effects of Toxoplasma on host cell signal transduction. These studies reveal insight into the profound suppression of proinflammatory cytokine responses that occurs when the parasite infects macrophages and other cells of innate immunity.

Early response of mucosal epithelial cells during Toxoplasma gondii infection

The innate immune response of mucosal epithelial cells during pathogen invasion plays a central role in immune regulation in the gut. Toxoplasma gondii is a protozoan intracellular parasite that is usually transmitted through oral infection. Although much of the information on immunity to T. gondii has come from i.p. infection models, more recent studies have revealed the importance of studying immunity following infection through the natural peroral route. Oral infection studies have identified many of the key players in the intestinal response; however, they have relied on responses detected days to weeks following infection. Much less is known about how the gut epithelial layer senses and reacts during initial contact with the pathogen. Given the importance of epithelial cells during pathogen invasion, this study uses an in vitro approach to isolate the key players and examine the early response of intestinal epithelial cells during infection by T. gondii. We show that human intestinal epithelial cells infected with T. gondii elicit rapid MAPK phosphorylation, NF-kappaB nuclear translocation, and secretion of IL-8. Both ERK1/2 activation and IL-8 secretion responses were shown to be MyD88 dependent and TLR2 was identified to be involved in the recognition of the parasite regardless of the parasite genotype. Furthermore, we were able to identify additional T. gondii-regulated genes in the infected cells using a pathway-focused array. Together, our findings suggest that intestinal epithelial cells were able to recognize T. gondii during infection, and the outcome is important for modulating intestinal immune responses.