Toxoplasma gondii tachyzoites inhibit proinflammatory cytokine induction in infected macrophages by preventing nuclear translocation of the transcription factor NF-kappa B

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.

C-type lectin 4 of Toxocara canis activates NF-ĸB and MAPK pathways by modulating NOD1/2 and RIP2 in murine macrophages in vitro

Toxocara canis is a parasitic zoonose that is distributed worldwide and is one of the two pathogens causing toxocariasis. After infection, it causes serious public health and safety problems, which pose significant veterinary and medical challenges. To better understand the regulatory effects of T. canis infection on the host immune cells, murine macrophages (RAW264.7) were incubated with recombinant T. canis C-type lectin 4 (rTc-CTL-4) protein in vitro. The quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were used to analyze the nucleotide-binding oligomerization domain-containing protein 1/2 (NOD1/2), receptor-interacting protein 2 (RIP2), nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB), and mitogen-activated protein kinase (MAPK) on mRNA level and protein expression level in macrophages. Our results indicated that 10 μg/mL rTc-CTL-4 protein could modulate the expression of NOD1, NOD2, and RIP2 at both the transcriptional and translational levels. The protein translation levels of NF-κB, P-p65, p38, and P-p38 in macrophages were also modulated by rTc-CTL-4 protein. Macrophages were co-incubated with rTc-CTL-4 protein after siRNA silencing of NOD1, NOD2, and RIP2. The expression levels of NF-κB, P-p65, p38, and P-p38 were significantly changed compared with the negative control groups (Neg. Ctrl.). Taken together, rTc-CTL-4 protein seemed to act on NOD1/2-RIP2-NF-κB and MAPK signaling pathways in macrophages and might activate MAPK and NF-κB signaling pathways by regulating NOD1, NOD2, and RIP2. The insights from the above studies could contribute to our understanding of immune recognition and regulatory mechanisms of T. canis infection in the host animals.

Exploring the potential of Toxoplasma gondii in drug development and as a delivery system

Immune-mediated inflammatory diseases are various groups of conditions that result in immune system disorders and increased cancer risk. Despite the identification of causative cytokines and pathways, current clinical treatment for immune-mediated inflammatory diseases is limited. In addition, immune-mediated inflammatory disease treatment can increase the risk of cancer. Several previous studies have demonstrated that Toxoplasma gondii manipulates the immune response by inhibiting or stimulating cytokines, suggesting the potential for controlling and maintaining a balanced immune system. Additionally, T. gondii also has the unique characteristic of being a so-called "Trojan horse" bacterium that can be used as a drug delivery system to treat regions that have been resistant to previous drug delivery therapies. In this study, we reviewed the potential of T. gondii in drug development and as a delivery system through current research on inflammation-regulating mechanisms in immune-mediated inflammatory diseases.

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.

Microbiota promotes recruitment and pro-inflammatory response of caecal macrophages during E. tenella infection

BACKGROUND

Eimeria genus belongs to the apicomplexan parasite phylum and is responsible for coccidiosis, an intestinal disease with a major economic impact on poultry production. Eimeria tenella is one of the most virulent species in chickens. In a previous study, we showed a negative impact of caecal microbiota on the physiopathology of this infection. However, the mechanism by which microbiota leads to the physiopathology remained undetermined. Macrophages play a key role in inflammatory processes and their interaction with the microbiota during E. tenella infection have never been investigated. We therefore examined the impact of microbiota on macrophages during E. tenella infection. Macrophages were monitored in caecal tissues by immunofluorescence staining with KUL01 antibody in non-infected and infected germ-free and conventional chickens. Caecal cells were isolated, stained, analyzed and sorted to examine their gene expression using high-throughput qPCR.

RESULTS

We demonstrated that microbiota was essential for caecal macrophage recruitment in E. tenella infection. Furthermore, microbiota promoted a pro-inflammatory transcriptomic profile of macrophages characterized by increased gene expression of NOS2, ACOD1, PTGS2, TNFα, IL1β, IL6, IL8L1, IL8L2 and CCL20 in infected chickens. Administration of caecal microbiota from conventional chickens to germ-free infected chickens partially restored macrophage recruitment and response.

CONCLUSIONS

Taken together, these results suggest that the microbiota enhances the physiopathology of this infection through macrophage recruitment and activation. Consequently, strategies involving modulation of the gut microbiota may lead to attenuation of the macrophage-mediated inflammatory response, thereby limiting the negative clinical outcome of the disease.

The Toxoplasma gondii effector GRA83 modulates the host's innate immune response to regulate parasite infection

Toxoplasma gondii's propensity to infect its host and cause disease is highly dependent on its ability to modulate host cell functions. One of the strategies the parasite uses to accomplish this is via the export of effector proteins from the secretory dense granules. Dense granule (GRA) proteins are known to play roles in nutrient acquisition, host cell cycle manipulation, and immune regulation. Here, we characterize a novel dense granule protein named GRA83, which localizes to the parasitophorous vacuole (PV) in tachyzoites and bradyzoites. Disruption of GRA83 results in increased virulence, weight loss, and parasitemia during the acute infection, as well as a marked increase in the cyst burden during the chronic infection. This increased parasitemia was associated with an accumulation of inflammatory infiltrates in tissues in both acute and chronic infections. Murine macrophages infected with ∆gra83 tachyzoites produced less interleukin-12 (IL-12) in vitro, which was confirmed with reduced IL-12 and interferon-gamma in vivo. This dysregulation of cytokines correlates with reduced nuclear translocation of the p65 subunit of the nuclear factor-κB (NF-κB) complex. While GRA15 similarly regulates NF-κB, infection with ∆gra83/∆gra15 parasites did not further reduce p65 translocation to the host cell nucleus, suggesting these GRAs function in converging pathways. We also used proximity labeling experiments to reveal candidate GRA83 interacting T. gondii-derived partners. Taken together, this work reveals a novel effector that stimulates the innate immune response, enabling the host to limit the parasite burden. Importance Toxoplasma gondii poses a significant public health concern as it is recognized as one of the leading foodborne pathogens in the United States. Infection with the parasite can cause congenital defects in neonates, life-threatening complications in immunosuppressed patients, and ocular disease. Specialized secretory organelles, including the dense granules, play an important role in the parasite's ability to efficiently invade and regulate components of the host's infection response machinery to limit parasite clearance and establish an acute infection. Toxoplasma's ability to avoid early clearance, while also successfully infecting the host long enough to establish a persistent chronic infection, is crucial in allowing for its transmission to a new host. While multiple GRAs directly modulate host signaling pathways, they do so in various ways highlighting the parasite's diverse arsenal of effectors that govern infection. Understanding how parasite-derived effectors harness host functions to evade defenses yet ensure a robust infection is important for understanding the complexity of the pathogen's tightly regulated infection. In this study, we characterize a novel secreted protein named GRA83 that stimulates the host cell's response to limit infection.

The Toxoplasma gondii effector GRA83 modulates the host's innate immune response to regulate parasite infection

Toxoplasma gondii 's propensity to infect its host and cause disease is highly dependent on its ability to modulate host cell functions. One of the strategies the parasite uses to accomplish this is via the export of effector proteins from the secretory dense granules. Dense granule (GRA) proteins are known to play roles in nutrient acquisition, host cell cycle manipulation, and immune regulation. Here, we characterize a novel dense granule protein named GRA83, which localizes to the parasitophorous vacuole in tachyzoites and bradyzoites. Disruption of GRA83 results in increased virulence, weight loss, and parasitemia during the acute infection, as well as a marked increase in the cyst burden during the chronic infection. This increased parasitemia was associated with an accumulation of inflammatory infiltrates in tissues in both the acute and chronic infection. Murine macrophages infected with Δ gra83 tachyzoites produced less interleukin-12 (IL-12) in vitro , which was confirmed with reduced IL-12 and interferon gamma (IFN-γ) in vivo . This dysregulation of cytokines correlates with reduced nuclear translocation of the p65 subunit of the NF-κB complex. While GRA15 similarly regulates NF-κB, infection with Δ gra83/ Δ gra15 parasites did not further reduce p65 translocation to the host cell nucleus, suggesting these GRAs function in converging pathways. We also used proximity labelling experiments to reveal candidate GRA83 interacting T. gondii derived partners. Taken together, this work reveals a novel effector that stimulates the innate immune response, enabling the host to limit parasite burden.

Importance

Toxoplasma gondii poses a significant public health concern as it is recognized as one of the leading foodborne pathogens in the United States. Infection with the parasite can cause congenital defects in neonates, life-threatening complications in immunosuppressed patients, and ocular disease. Specialized secretory organelles, including the dense granules, play an important role in the parasite's ability to efficiently invade and regulate components of the host's infection response machinery to limit parasite clearance and establish an acute infection. Toxoplasma' s ability to avoid early clearance, while also successfully infecting the host long enough to establish a persistent chronic infection, is crucial in allowing for its transmission to a new host. While multiple GRAs directly modulate host signaling pathways, they do so in various ways highlighting the parasite's diverse arsenal of effectors that govern infection. Understanding how parasite-derived effectors harness host functions to evade defenses yet ensure a robust infection are important for understanding the complexity of the pathogen's tightly regulated infection. In this study, we characterize a novel secreted protein named GRA83 that stimulates the host cell's response to limit infection.

The imbalance in the relationship between inflammatory and regulatory cytokines during gestational toxoplasmosis can be harmful to fetuses: A systematic review

Objective

To evaluate the available information on inflammatory and regulatory plasma mediators in pregnant women (PW) diagnosed with toxoplasmosis. Source: The PubMed, Embase, Scopus, and Lilacs databases were evaluated until October 2022. Study eligibility criteria: This review was carried out following the PRISMA and registered on the PROSPERO platform (CRD42020203951). Studies that reported inflammatory mediators in PW with toxoplasmosis were considered.

Evaluation methods

After excluding duplicate articles, two authors independently carried out the process of title and abstract exclusion, and a third resolved disagreements when necessary. The full text was evaluated to detect related articles. The extraction table was built from the following data: Author, year of publication, journal name and impact factors, country, study design, number of gestations and maternal age (years), gestational period, diagnosis of toxoplasmosis, levels of inflammatory markers, laboratory tests, and clinical significance. Methodological quality was assessed using Joanna Briggs Institute tools.

Results

Of the 1,024 studies reported, only eight were included. Of the 868 PW included in this review, 20.2% were IgM+/IgG- and 50.8% were IgM-/IgG+ to T. gondii, and 29.0% uninfected. Infected PW presented higher plasma levels ofIL-5, IL-6, IL-8, IL-17, CCL5, and IL-10. Regarding the methodological quality, four studies obtained high quality. Data from this review pointed out the maintenance of the inflammatory pattern during pregnancy with a closely related to the parasite.

Conclusion

Immune status in PW defined the course of the T. gondii infection, where the equilibrium between inflammatory and regulatory cytokines mitigated the harmful placenta and fetus effects.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD420203951.

Strain-specific pre-existing immunity: A key to understanding the role of chronic Toxoplasma infection in cognition and Alzheimer's diseases?

Toxoplasma exposure can elicit cellular and humoral immune responses. In the case of chronic Toxoplasma infection, these immune responses are long-lasting. Some studies suggest that pre-existing immunity from Toxoplasma infection can shape immune responses and resistance to other pathogens and brain insults later in life. Much evidence has been generated suggesting Toxoplasma infection may contribute to cognitive impairment in the elderly. However, there have also been studies that disagree with the conclusion. Toxoplasma has many strain types, with virulence being the most notable difference. There is also considerable variation in the outcomes following Toxoplasma exposure ranging from resolved to persistent infection. Therefore, the brain microenvironment, particularly cellular constituents, differs based on the infecting strain (virulent versus hypovirulent) and infection stage (resolved versus persistent). Such difference might play a critical role in determining the outcome of the host on subsequent challengings to the brain. The ability of Toxoplasma strains to set up distinct stages for neurodegenerative pathology through varying degrees of virulence provides unique experimental tools for characterizing these pathways.

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.

Toxoplasmosis: Targeting neurotransmitter systems in psychiatric disorders

The most common form of the disease caused by Toxoplasma gondii (T. gondii) is latent toxoplasmosis due to the formation of tissue cysts in various organs, such as the brain. Latent toxoplasmosis is probably a risk factor in the development of some neuropsychiatric disorders. Behavioral changes after infection are caused by the host immune response, manipulation by the parasite, central nervous system (CNS) inflammation, as well as changes in hormonal and neuromodulator relationships. The present review focused on the exact mechanisms of T. gondii effect on the alteration of behavior and neurotransmitter levels, their catabolites and metabolites, as well as the interaction between immune responses and this parasite in the etiopathogenesis of psychiatric disorders. The dysfunction of neurotransmitters in the neural transmission is associated with several neuropsychiatric disorders. However, further intensive studies are required to determine the effect of this parasite on altering the level of neurotransmitters and the role of neurotransmitters in the etiology of host behavioral changes.

Immune response against toxoplasmosis-some recent updates RH: Toxoplasma gondii immune response

AIMS

Cytokines, soluble mediators of immunity, are key factors of the innate and adaptive immune system. They are secreted from and interact with various types of immune cells to manipulate host body's immune cell physiology for a counter-attack on the foreign body. A study was designed to explore the mechanism of Toxoplasma gondii (T. gondii) resistance from host immune response.

METHODS AND RESULTS

The published data on aspect of host (murine and human) immune response against T. gondii was taken from Google scholar and PubMed. Most relevant literature was included in this study. The basic mechanism of immune response starts from the interactions of antigens with host immune cells to trigger the production of cytokines (pro-inflammatory and anti-inflammatory) which then act by forming a cytokinome (network of cytokine). Their secretory equilibrium is essential for endowing resistance to the host against infectious diseases, particularly toxoplasmosis. A narrow balance lying between Th1, Th2, and Th17 cytokines (as demonstrated until now) is essential for the development of resistance against T. gondii as well as for the survival of host. Excessive production of pro-inflammatory cytokines leads to tissue damage resulting in the production of anti-inflammatory cytokines which enhances the proliferation of Toxoplasma. Stress and other infectious diseases (human immunodeficiency virus (HIV)) that weaken the host immunity particularly the cellular component, make the host susceptible to toxoplasmosis especially in pregnant women.

CONCLUSION

The current review findings state that in vitro harvesting of IL12 from DCs, Np and MΦ upon exposure with T. gondii might be a source for therapeutic use in toxoplasmosis. Current review also suggests that therapeutic interventions leading to up-regulation/supplementation of SOCS-3, IL12, and IFNγ to the infected host could be a solution to sterile immunity against T. gondii infection. This would be of interest particularly in patients passing through immunosuppression owing to any reason like the ones receiving anti-cancer therapy, the ones undergoing immunosuppressive therapy for graft/transplantation, the ones suffering from immunodeficiency virus (HIV) or having AIDS. Another imortant suggestion is to launch the efforts for a vaccine based on GRA6Nt or other similar antigens of T. gondii as a probable tool to destroy tissue cysts.

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.

Toxoplasma gondii Infection Inhibits Histone Crotonylation to Regulate Immune Response of Porcine Alveolar Macrophages

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that can infect almost all warm-blooded animals, causing serious public health problems. Lysine crotonylation (Kcr) is a newly discovered posttranslational modification (PTM), which is first identified on histones and has been proved relevant to procreation regulation, transcription activation, and cell signaling pathway. However, the biological functions of histone crotonylation have not yet been reported in macrophages infected with T. gondii. As a result, a total of 1,286 Kcr sites distributed in 414 proteins were identified and quantified, demonstrating the existence of crotonylation in porcine alveolar macrophages. According to our results, identified histones were overall downregulated. HDAC2, a histone decrotonylase, was found to be significantly increased, which might be the executor of histone Kcr after parasite infection. In addition, T. gondii infection inhibited the crotonylation of H2B on K12, contributing on the suppression of epigenetic regulation and NF-κB activation. Nevertheless, the reduction of histone crotonylation induced by parasite infection could promote macrophage proliferation via activating PI3K/Akt signaling pathway. The present findings point to a comprehensive understanding of the biological functions of histone crotonylation in porcine alveolar macrophages, thereby providing a certain research basis for the mechanism research on the immune response of host cells against T. gondii infection.

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.

Molecular chaperone function of stress inducible Hsp70 is critical for intracellular multiplication of Toxoplasma gondii

Intracellular pathogens like Toxoplasma gondii often target proteins and pathways critical for host cell survival and stress response. Molecular chaperones encoded by the evolutionary conserved Heat shock proteins (Hsps) maintain proteostasis and are vital to cell survival following exposure to any form of stress. A key protein of this family is Hsp70, an ATP-driven molecular chaperone, which is stress inducible and often indiscernible in normal cells. Role of this protein with respect to intracellular survival and multiplication of protozoan parasite like T. gondii remains to be examined. We find that T. gondii infection upregulates expression of host Hsp70. Hsp70 selective inhibitor 2-phenylethynesulfonamide (PES) attenuates intracellular T. gondii multiplication. Biotinylated PES confirms selective interaction of this small molecule inhibitor with Hsp70. We show that PES acts by disrupting Hsp70 chaperone function which leads to dysregulation of host autophagy. Silencing of host Hsp70 underscores its importance for intracellular multiplication of T. gondii, however, attenuation achieved using PES is not completely attributable to host Hsp70 indicating the presence of other intracellular targets of PES in infected host cells. We find that PES is also able to target T. gondii Hsp70 homologue which was shown using PES binding assay. Detailed molecular docking analysis substantiates PES targeting of TgHsp70 in addition to host Hsp70. While establishing the importance of protein quality control in infection, this study brings to the fore a unique opportunity of dual targeting of host and parasite Hsp70 demonstrating how structural conservation of these proteins may be exploited for therapeutic design.

Overview of Poultry Eimeria Life Cycle and Host-Parasite Interactions

Apicomplexan parasites of the genus Eimeria are organisms which invade the intestinal tract, causing coccidiosis, an enteric disease of major economic importance worldwide. The disease causes high morbidity ranging from an acute, bloody enteritis with high mortality, to subclinical disease. However, the presence of intestinal lesions depends on the Eimeria species. The most important poultry Eimeria species are: E. tenella, E. necatrix, E. acervulina, E. maxima, E. brunetti, E. mitis, and E. praecox. Key points to better understanding the behavior of this species are the host-parasite interactions and its life cycle. The present paper reviews the literature available regarding the life cycle and the initial host-parasite interaction. More studies are needed to better understand these interactions in poultry Eimerias, taking into account that almost all the information available was generated from other apicomplexan parasites that generate human disease.

Delayed IL-12 production by macrophages during Toxoplasma gondii infection is regulated by miR-187

Toxoplasma gondii is an important zoonotic protozoan worldwide which infects most of warm-blooded mammals and birds, including human, and cause toxoplasmosis. As an intracellular parasite, T. gondii must evade host immune surveillance, such as IL-12 and IFN-γ, in order to survive and multiply in macrophages and other host cells. By delaying IL-12 secretion of host macrophages within 24 h after infection, T. gondii ensures not only self-survival but also the establishment of chronic infection of host cells. MicroRNA plays an important role in regulating gene transcription and translation. The mechanisms of IL-12 production during T. gondii infection are still unknown. Thus, understanding how the parasites manipulate IL-12 production by host macrophage is critical for the effective prevention and therapy of T. gondii infection. In the present study, regulation of delayed macrophage IL-12 production during T. gondii infection was explored. We found that the production of IL-12 after T. gondii infection was inhibited during the first 24 h and then resumed. The expression pattern of miR-187 production was consistent with the production pattern of IL-12 during T. gondii infection. The downregulation of miR-187 promoted Akt and P65 phosphorylation and delayed IL-12 production at late stage (after 24 h) of T. gondii infection. Dual-luciferase reporter assay indicated that MiR-187 targeted the NFKBIZ gene. Our results suggested that the delayed IL-12 production in mouse macrophages during T. gondii infection was regulated by miR-187.

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.

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.

Immunocompetent host develops mild intestinal inflammation in acute infection with Toxoplasma gondii

Toxoplasma gondii (T. gondii) is the causative agent of toxoplasmosis, common zoonosis among vertebrates and high incidence worldwide. During the infection, the parasite needs to transpose the intestinal barrier to spread throughout the body, which may be a trigger for an inflammatory reaction. This work evaluated the inflammatory alterations of early T. gondii infection in peripheral blood cells, in the mesenteric microcirculation, and small intestinal tissue by measurement of MPO (myeloperoxidase) activity and NO (nitric oxide) level in rats. Animals were randomly assigned into control group (CG) that received saline orally and groups infected with 5,000 oocysts for 6 (G6), 12 (G12), 24 (G24), 48 (G48) and 72 hours (G72). Blood samples were collected for total and differential leukocyte count. Intravital microscopy was performed in the mesentery to evaluate rolling and adhesion of leukocytes. After euthanasia, 0.5cm of the duodenum, jejunum and ileum were collected for the determination of MPO activity, NO level and PCR to identify the parasite DNA and also the mesentery were collected to perform immunohistochemistry on frozen sections to quantify adhesion molecules ICAM-1, PECAM-1 and P-Selectin. The parasite DNA was identified in all infected groups and there was an increase in leukocytes in the peripheral blood and in expression of ICAM-1 and PECAM-1 in G6 and G12, however, the expression of P-selectin was reduced in G12. Leukocytes are in rolling process during the first 12 hours and they are adhered at 24 hours post-infection. The activity of MPO increased in the duodenum at 12 hours, and NO increased in the jejunum in G72 and ileum in G24, G48 and G72. Our study demonstrated that T. gondii initiates the infection precociously (at 6 hours) leading to a systemic activation of innate immune response resulting in mild inflammation in a less susceptible experimental model.

Characteristic pro-inflammatory cytokines and host defence cathelicidin peptide produced by human monocyte-derived macrophages infected withNeospora caninum

Neospora caninumis a coccidian intracellular protozoan capable of infecting a wide range of mammals, although severe disease is mostly reported in dogs and cattle. Innate defences triggered by monocytes/macrophages are key in the pathogenesis of neosporosis, as these cells are first-line defenders against intracellular infections. The aim of this study was to characterize infection and innate responses in macrophages infected withN. caninumusing a well-known cell model to study macrophage functions (human monocyte THP-1 cells). Intracellular invasion of live tachyzoites occurred as fast as 4 h (confirmed with immunofluorescence microscopy usingN. caninum-specific antibodies). Macrophages infected byN. caninumhad increased expression of pro-inflammatory cytokines (TNFα, IL-1β, IL-8, IFNγ). Interestingly,N. caninuminduced expression of host-defence peptides (cathelicidins), a mechanism of defence never reported forN. caninuminfection in macrophages. The expression of cytokines and cathelicidins in macrophages invaded byN. caninumwas mediated by mitogen-activated protein kinase (MEK 1/2). Secretion of such innate factors fromN. caninum-infected macrophages reduced parasite internalization and promoted the secretion of pro-inflammatory cytokines in naïve macrophages. We concluded that rapid invasion of macrophages byN. caninumtriggered protective innate defence mechanisms against intracellular pathogens.

Activation of ERK Signaling via TLR11 Induces IL-12p40 Production in Peritoneal Macrophages Challenged by Neospora caninum

Neospora caninum, an obligate intracellular protozoan parasite, can infect a large variety of vertebrate hosts including the most economically important cattle. Infection with N. caninum is a main cause of abortion in both dairy and beef cattle, which causes great economic losses worldwide. However, the mechanism of host cell infection by N. caninum has not been fully elucidated, especially in terms of inflammatory responses. In this study, the effect of TLR-ERK signaling pathway on the synthesis of pro-inflammatory interleukin-12p40 in mouse peritoneal macrophages (PMϕ) challenged by N. caninum was investigated. Our results suggested that N. caninum infection quickly activated MEK-ERK signaling via TLR11 in PMϕ. In addition, N. caninum infection also caused upregulated production of IL-12p40 by PMϕ, which was significantly reduced with the blockade of TLR11/MEK/ERK pathway, suggesting that this upregulation of IL-12 p40 was TLR11 and MEK-ERK-activation dependent.

Effects of Recombinant Toxoplasma gondii Citrate Synthase I on the Cellular Functions of Murine Macrophages In vitro

Toxoplasmosis, which is one of the most widespread zoonoses worldwide, has a high incidence and infection can result in severe disease in humans and livestock. Citrate synthase (CS) is a component of nearly all living cells that plays a vital role in the citric acid cycle, which is the central metabolic pathway of aerobic organisms. In the present study, the citrate synthase I gene of Toxoplasma gondii (T. gondii) (TgCSI) was cloned and characterized. The TgCSI gene had an open reading frame of 1665 bp nucleotides encoding a 555 amino acid protein with a molecular weight of 60 kDa. Using western blotting assay, the recombinant protein was successfully recognized by the sera of rats experimentally infected with T. gondii, while the native protein in the T. gondii tachyzoites was detected in sera from rats immunized with the recombinant protein of TgCSI. Binding of the protein to murine macrophages was confirmed by immuno fluorescence assay. Following incubation of macrophages with rTgCSI, the rTgCSI protein was found to have a dual function, with low concentrations (5-10 μg/mL) enhancing phagocytosis and high levels (80 μg/mL) inhibiting phagocytosis. Investigation of murine macrophage apoptosis illustrated that 5 μg/mL rTgCSI protein can significantly induce early apoptosis and late stage apoptosis (*p < 0.05), while 10 μg/mL rTgCSI protein significantly induced early apoptosis, but had no effect on late stage of apoptosis (**p < 0.01), and 80 μg/mL rTgCSI protein inhibited late stage apoptosis of macrophages (*p < 0.05). Cytokine detection revealed that the secretion of interleukin-10, interleukin-1β, transforming growth factor-β1 and tumor necrosis factor-α of macrophages increased after the cells were incubated with all concentration of rTgCSI, with the exception that 5 μg/mL rTgCSI had no effect on the secretion of interleukin-10 and interleukin-1β. However, secretion of NO and cell proliferation of the macrophages were substantially reduced. Taken together, these results suggested that TgCSI can affect the immune functions of murine macrophages by binding to the cells in vitro.

Toxoplasma gondii excretory/secretory antigens (TgESAs) suppress pro-inflammatory cytokine secretion by inhibiting TLR-induced NF-κB activation in LPS-stimulated murine macrophages

Excretory/secretory antigens (ESAs) produced by Toxoplasma gondii enable this parasite to invade and survive within the host cells through immunomodulation. In this study, the modulating effects of T. gondii excretory/secretory antigens (TgESAs) on the Ana-1 murine macrophage cell line were evaluated. Ana-1 cells were incubated with several concentrations of TgESAs, and the resulting effects on cellular viability, phagocytotic ability, and apoptosis induction were determined. Pro-inflammatory and anti-inflammatory cytokine secretion, nitric oxide production, toll-like receptor expression, and nuclear translocation of NF-κB were all measured after incubation with TgESAs. After TgESAs treatment, the proliferation and phagocytosis ability of Ana-1 cells decreased, and apoptosis was induced in a dose dependent manner. Analysis of Ana-1 cell culture supernatants showed that TgESAs not only upregulated secretion of anti-inflammatory cytokines (interleukin-10 and transforming growth factor-β1), they also inhibited secretion of pro-inflammatory cytokines (tumor necrosis factor-α and interleukin-1β). Additionally, TgESAs inhibited nitric oxide production, toll-like receptor (TLR) 2 and 4 activation, and the nuclear translocation of NF-κB in lipopolysaccharide-stimulated Ana-1 macrophages. These results suggest TgESAs inhibit the functional activity of Ana-1 murine macrophages by inhibiting TLR-induced NF-κB activation, which suppresses pro-inflammatory cytokine secretion.

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.

Dendritic cells provide a therapeutic target for synthetic small molecule analogues of the parasitic worm product, ES-62

ES-62, a glycoprotein secreted by the parasitic filarial nematode Acanthocheilonema viteae, subverts host immune responses towards anti-inflammatory phenotypes by virtue of covalently attached phosphorylcholine (PC). The PC dictates that ES-62 exhibits protection in murine models of inflammatory disease and hence a library of drug-like PC-based small molecule analogues (SMAs) was synthesised. Four sulfone-containing SMAs termed 11a, 11e, 11i and 12b were found to reduce mouse bone marrow-derived dendritic cell (DC) pathogen-associated molecular pattern (PAMP)-induced pro-inflammatory cytokine production, inhibit NF-κB p65 activation, and suppress LPS-induced up-regulation of CD40 and CD86. Active SMAs also resulted in a DC phenotype that exhibited reduced capacity to prime antigen (Ag)-specific IFN-γ production during co-culture with naïve transgenic TCR DO.11.10 T cells in vitro and reduced their ability, following adoptive transfer, to prime the expansion of Ag-specific T lymphocytes, specifically TH17 cells, in vivo. Consistent with this, mice receiving DCs treated with SMAs exhibited significantly reduced severity of collagen-induced arthritis and this was accompanied by a significant reduction in IL-17+ cells in the draining lymph nodes. Collectively, these studies indicate that drug-like compounds that target DCs can be designed from parasitic worm products and demonstrate the potential for ES-62 SMA-based DC therapy in inflammatory disease.

Immunization with Toxoplasma gondii peroxiredoxin 1 induces protective immunity against toxoplasmosis in mice

To develop a vaccine against Toxoplasma gondii, a vaccine antigen with immune-stimulating activity is required. In the present study, we investigated the immunogenicity and prophylactic potential of T. gondii peroxiredoxin 1 (TgPrx1). The TgPrx1 was detected in the ascitic fluid of mice 6 days postinfection, while specific antibody levels were low in the sera of chronically infected mice. Treatment of murine peritoneal macrophages with recombinant TgPrx1 triggered IL-12p40 and IL-6 production, but not IL-10 production. In response to TgPrx1, activation of NF-kB and IL-6 production were confirmed in mouse macrophage cell line (RAW 264.7). These results suggest the immune-stimulating potentials of TgPrx1. Immunization of mice with recombinant TgPrx1 stimulated specific antibody production (IgG1 and IgG2c). Moreover, spleen cell proliferation and interferon-gamma production significantly increased in the TgPrx1- sensitized cells from mice immunized with the same antigen. Immunization with TgPrx1 also increased mouse survival and decreased cerebral parasite burden against lethal T. gondii infection. Thus, our results suggest that TgPrx1 efficiently induces humoral and cellular immune responses and is useful as a new vaccine antigen against toxoplasmosis.

Acute stress diminishes M-current contributing to elevated activity of hypothalamic-pituitary-adrenal axis

Acute stress stimulates corticotrophin-releasing hormone (CRH)-expressing neurons in the hypothalamic paraventricular nucleus (PVN), which is an essential component of hypothalamic-pituitary-adrenal (HPA) axis. However, the cellular and molecular mechanisms remain unclear. The M-channel is a voltage-dependent K⁺ channel involved in stabilizing the neuronal membrane potential and regulating neuronal excitability. In this study, we tested our hypothesis that acute stress suppresses expression of Kv7 channels to stimulate PVN-CRH neurons and the HPA axis. Rat PVN-CRH neurons were identified by expressing enhanced green fluorescent protein driven by Crh promoter. Acute restraint stress attenuated the excitatory effect of Kv7 blocker XE-991 on the firing activity of PVN-CRH neurons and blunted the increase in plasma corticosterone (CORT) levels induced by microinjection of XE-991 into the PVN. Furthermore, acute stress significantly decreased the M-currents in PVN-CRH neurons and reduced PVN expression of Kv7.3 subunit in the membrane. In addition, acute stress significantly increased phosphorylated AMP-activated protein kinase (AMPK) levels in the PVN tissue. Intracerebroventricular injection of the AMPK inhibitor dorsomorphin restored acute stress-induced elevation of CORT levels and reduction of membrane Kv7.3 protein level in the PVN. Dorsomorphin treatment increased the M-currents and reduced the firing activity of PVN-CRH neurons in acutely stressed rats. Collectively, these data suggest that acute stress diminishes Kv7 channels to stimulate PVN-CRH neurons and the HPA axis potentially via increased AMPK activity.

Z-DNA Binding Protein Mediates Host Control of Toxoplasma gondii Infection

Intrinsic to Toxoplasma gondii infection is the parasite-induced modulation of the host immune response, which ensures establishment of a chronic lifelong infection. This manipulation of the host immune response allows T. gondii to not only dampen the ability of the host to eliminate the parasite but also trigger parasite differentiation to the slow-growing, encysted bradyzoite form. We previously used RNA sequencing (RNA-seq) to profile the transcriptomes of mice and T. gondii during acute and chronic stages of infection. One of the most abundant host transcripts during acute and chronic infection was Z-DNA binding protein 1 (ZBP1). In this study, we determined that ZBP1 functions to control T. gondii growth. In activated macrophages isolated from ZBP1 deletion (ZBP1(-/-)) mice, T. gondii has an increased rate of replication and a decreased rate of degradation. We also identified a novel function for ZBP1 as a regulator of nitric oxide (NO) production in activated macrophages, even in the absence of T. gondii infection. Upon stimulation, T. gondii-infected ZBP1(-/-) macrophages display increased proinflammatory cytokines compared to wild-type macrophages under the same conditions. These in vitro phenotypes were recapitulated in vivo, with ZBP1(-/-) mice having increased susceptibility to oral challenge, higher cyst burdens during chronic infection, and elevated inflammatory cytokine responses. Taken together, these results highlight a role for ZBP1 in assisting host control of T. gondii infection.

Innate recognition of Toxoplasma gondii in humans involves a mechanism distinct from that utilized by rodents

Toxoplasma gondii is an intracellular protozoan parasite that infects rodents as part of its natural transmission cycle and induces disease in humans, an end-stage host. As one of the natural hosts of T. gondii, the mouse has been used extensively for elucidating the cellular and molecular basis of immunity to this pathogen while relatively few studies have focused on the response of humans. In our recent work, we identified CD16⁺ monocytes and DC1 dendritic cells as the major myeloid cell populations that respond to T. gondii in human peripheral blood. Interestingly, these myeloid subsets represent the opposite counterparts from those triggered by the parasite in mice. Moreover, whereas the innate cytokine response to T. gondii in the mouse involves stimulation of Toll-like receptors by a soluble parasite ligand, the response of human cells instead requires phagocytosis of the live pathogen. We speculate that these marked distinctions in the pathways utilized for innate recognition of toxoplasma in mouse and man reflect the differing roles of the two hosts in the biology of this parasite.

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.

Beta-catenin signaling drives differentiation and proinflammatory function of IRF8-dependent dendritic cells

Beta-catenin signaling has recently been tied to the emergence of tolerogenic dendritic cells (DCs). In this article, we demonstrate a novel role for beta-catenin in directing DC subset development through IFN regulatory factor 8 (IRF8) activation. We found that splenic DC precursors express beta-catenin, and DCs from mice with CD11c-specific constitutive beta-catenin activation upregulated IRF8 through targeting of the Irf8 promoter, leading to in vivo expansion of IRF8-dependent CD8a+, plasmacytoid, and CD103+ CD11b2 DCs. beta-catenin–stabilized CD8a+ DCs secreted elevated IL-12 upon in vitro microbial stimulation, and pharmacological beta-catenin inhibition blocked this response in wild-type cells. Upon infections with Toxoplasma gondii and vaccinia virus, mice with stabilized DC beta-catenin displayed abnormally high Th1 and CD8+ T lymphocyte responses, respectively. Collectively, these results reveal a novel and unexpected function for beta-catenin in programming DC differentiation toward subsets that orchestrate proinflammatory immunity to infection.

Impact of Toxoplasma gondii on Dendritic Cell Subset Function in the Intestinal Mucosa

The function of mucosal dendritic cell (DC) subsets in immunity and inflammation is not well understood. In this study, we define four DC subsets present within the lamina propria and mesenteric lymph node compartments based on expression of CD103 and CD11b. Using IL-12p40 YFP (Yet40) reporter mice, we show that CD103(+)CD11b(-) mucosal DCs are primary in vivo sources of IL-12p40; we also identified CD103(-)CD11b(-) mucosal DCs as a novel population producing this cytokine. Infection was preferentially found in CD11b(+) DCs that were negative for CD103. Lamina propria DCs containing parasites were negative for IL-12p40. Instead, production of the cytokine was strictly a property of noninfected cells. We also show that vitamin A metabolism, as measured by ALDH activity, was preferentially found in CD103(+)CD11b(+) DC and was strongly downregulated in all mucosal DC subsets during infection. Finally, overall apoptosis of lamina propria DC subsets was increased during infection. Combined, these results highlight the ability of intestinal Toxoplasma infection to alter mucosal DC activity at both the whole population level and at the level of individual subsets.

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.

Identification of Toxoplasma gondii protein fractions induce immune response against melanoma in mice

Dendritic cells (DCs) play a crucial role in the initiation of adaptive immune responses against tumor cells. We recently found that protein components of Toxoplasma gondii (T. gondii) could mature DCs efficiently. Therefore, in this study, we aimed to find the most effective protein components of T. gondii which are able to mature DCs and consequently instruct immune responses in tumor-bearing mice. Soluble tachyzoite antigens (STAgs) were fractionated by ammonium sulfate precipitation and subsequently by anion-exchange HPLC. Immature DCs (iDCs) were treated by these protein fractions and were monitored for IL-12p70 and IL-10 production. Moreover, the capacity of mature DCs (mDCs) to induce lymphocyte proliferation was investigated. Ultimately, we analyzed the ability of mDCs in instructing immune responses in tumor-bearing mice. We found that ammonium sulfate fraction one (A1) matured-DCs produced higher IL-12 level and IL-12/IL-10 ratio; therefore, this fraction was selected for further fractionation by anion-exchange HPLC. The results showed that anion-exchange HPLC fraction 14 (C14) matured-DCs secrete higher levels of IL-12p70 and IL-12p70/IL-10 ratio. Survival of the mice matured by A1 fraction increased significantly compared to other groups. Moreover, SDS-PAGE electrophoresis showed that different obtained fractions have distinct proteins based on their size. These results demonstrate that two protein fractions of T. gondii are able to mature DCs more efficient.

Fasciola hepatica fatty acid binding protein inhibits TLR4 activation and suppresses the inflammatory cytokines induced by lipopolysaccharide in vitro and in vivo

TLR4, the innate immunity receptor for bacterial endotoxins, plays a pivotal role in the induction of inflammatory responses. There is a need to develop molecules that block either activation through TLR4 or the downstream signaling pathways to inhibit the storm of inflammation typically elicited by bacterial LPS, which is a major cause of the high mortality associated with bacterial sepsis. We report in this article that a single i.p. injection of 15 μg fatty acid binding protein from Fasciola hepatica (Fh12) 1 h before exposure to LPS suppressed significantly the expression of serum inflammatory cytokines in a model of septic shock using C57BL/6 mice. Because macrophages are a good source of IL-12p70 and TNF-α, and are critical in driving adaptive immunity, we investigated the effect of Fh12 on the function of mouse bone marrow-derived macrophages (bmMΦs). Although Fh12 alone did not induce cytokine expression, it significantly suppressed the expression of IL-12, TNF-α, IL-6, and IL-1β cytokines, as well as inducible NO synthase-2 in bmMΦs, and also impaired the phagocytic capacity of bmMΦs. Fh12 had a limited effect on the expression of inflammatory cytokines induced in response to other TLR ligands. One mechanism used by Fh12 to exert its anti-inflammatory effect is binding to the CD14 coreceptor. Moreover, it suppresses phosphorylation of ERK, p38, and JNK. The potent anti-inflammatory properties of Fh12 demonstrated in this study open doors to further studies directed at exploring the potential of this molecule as a new class of drug against septic shock or other inflammatory diseases.

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.

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.

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

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

CXCR3-dependent CD4⁺ T cells are required to activate inflammatory monocytes for defense against intestinal infection

Chemokines and their receptors play a critical role in orchestrating immunity to microbial pathogens, including the orally acquired Th1-inducing protozoan parasite Toxoplasma gondii. Chemokine receptor CXCR3 is associated with Th1 responses, and here we use bicistronic CXCR3-eGFP knock-in reporter mice to demonstrate upregulation of this chemokine receptor on CD4⁺ and CD8⁺ T lymphocytes during Toxoplasma infection. We show a critical role for CXCR3 in resistance to the parasite in the intestinal mucosa. Absence of the receptor in Cxcr3⁻/⁻ mice resulted in selective loss of ability to control T. gondii specifically in the lamina propria compartment. CD4⁺ T cells were impaired both in their recruitment to the intestinal lamina propria and in their ability to secrete IFN-γ upon stimulation. Local recruitment of CD11b⁺Ly6C/G⁺ inflammatory monocytes, recently reported to be major anti-Toxoplasma effectors in the intestine, was not impacted by loss of CXCR3. However, inflammatory monocyte activation status, as measured by dual production of TNF-α and IL-12, was severely impaired in Cxcr3⁻/⁻ mice. Strikingly, adoptive transfer of wild-type but not Ifnγ⁻/⁻ CD4⁺ T lymphocytes into Cxcr3⁻/⁻ animals prior to infection corrected the defect in inflammatory macrophage activation, simultaneously reversing the susceptibility phenotype of the knockout animals. Our results establish a central role for CXCR3 in coordinating innate and adaptive immunity, ensuring generation of Th1 effectors and their trafficking to the frontline of infection to program microbial killing by inflammatory monocytes.

Differential apoptosis in BeWo cells after infection with highly (RH) or moderately (ME49) virulent strains of Toxoplasma gondii is related to the cytokine profile secreted, the death receptor Fas expression and phosphorylated ERK1/2 expression

INTRODUCTION

Alterations of apoptosis are commonly associated with pregnancy complications and abortion. Modulation of apoptosis is a relevant feature of Toxoplasma gondii infection and it is related to parasite strain types. The aim of the present study was to evaluate the possible factors that are involved in the differential apoptosis of BeWo cells infected with distinct T. gondii strain types.

METHODS

Human trophoblastic cells (BeWo cell line) were infected with RH or ME49 strains, the cytokine production was measured and the phosphorylation of anti-apoptotic ERK1/2 protein was analyzed. Also, cells were treated with different cytokines, infected with RH or ME49 strain, and analyzed for apoptosis index and Fas/CD95 death receptor expression.

RESULTS

ME49-infected BeWo cells exhibited a predominantly pro-inflammatory cytokine profile, whereas cells infected with RH strain had a higher production of anti-inflammatory cytokines. Also, the incidence of apoptosis was higher in ME49-infected cells, which have been treated with pro-inflammatory cytokines compared to cells infected with RH and treated with anti-inflammatory cytokines. Moreover, Fas/CD95 expression was higher in cells infected with either ME49 or RH strain and treated with pro-inflammatory cytokines compared to anti-inflammatory cytokine treatment. The phosphorylation of ERK1/2 protein increased after 24 h of infection only with the RH strain.

CONCLUSION

These results suggest that opposing mechanisms of interference in apoptosis of BeWo cells after infection with RH or ME49 strains of T. gondii can be associated with the differential cytokine profile secreted, the Fas/CD95 expression and the phosphorylated ERK1/2 expression.

Kurarinone promotes TRAIL-induced apoptosis by inhibiting NF-κB-dependent cFLIP expression in HeLa cells

This study was designed to investigate the effects of the prenylated flavonoid kurarinone on TNF-related apoptosis inducing ligand (TRAIL)-induced apoptosis and its underlying mechanism. A low dose of kurarinone had no significant effect on apoptosis, but this compound markedly promoted tumor cell death through elevation of Bid cleavage, cytochrome c release and caspase activation in HeLa cells treated with TRAIL. Caspase inhibitors inhibited kurarinone-mediated cell death, which indicates that the cytotoxic effect of this compound is mediated by caspase-dependent apoptosis. The cytotoxic effect of kurarinone was not associated with expression levels of Bcl-2 and IAP family proteins, such as Bcl-2, Bcl-x_L, Bid, Bad, Bax, XIAP, cIAP-1 and cIAP-2. In addition, this compound did not regulate the death-inducing receptors DR4 and DR5. On the other hand, kurarinone significantly inhibited TRAIL-induced IKK activation, IκB degradation and nuclear translocation of NF-κB, as well as effectively suppressed cellular FLICE-inhibitory protein long form (cFLIP_L) expression. The synergistic effects of kurarinone on TRAIL-induced apoptosis were mimicked when kurarinone was replaced by the NF-κB inhibitor withaferin A or following siRNA-mediated knockdown of cFLIP_L. Moreover, cFLIP overexpression effectively antagonized kurarinone-mediated TRAIL sensitization. These data suggest that kurarinone sensitizes TRAIL-induced tumor cell apoptosis via suppression of NF-κB-dependent cFLIP expression, indicating that this compound can be used as an anti-tumor agent in combination with TRAIL.

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.

Identification of the major proteins of an immune modulating fraction from adult Fasciola hepatica released by Nonidet P40

Fasciola hepatica NP-40 released protein extract (FhNPE) exhibits potent Th1 immunosuppressive properties in vitro and in vivo. However, the protein composition of this active fraction, responsible for Th1 immune modulatory activity, has yet to be resolved. Therefore, FhNPE, a Nonidet P-40 extract, was subjected to a proteomic analysis in order to identify individual protein components. This was performed using an in house F. hepatica EST database following 2D electrophoresis combined with de novo sequencing based mass spectrometry. The identified proteins, a mixture of excretory/secretory and membrane-associated proteins, are associated with stress response and chaperoning, energy metabolism and cytoskeletal components. The immune modulatory properties of these identified protein(s) are discussed and HSP70 from F. hepatica is highlighted as a potential host immune modulator for future study.

Chitohexaose activates macrophages by alternate pathway through TLR4 and blocks endotoxemia

Sepsis is a consequence of systemic bacterial infections leading to hyper activation of immune cells by bacterial products resulting in enhanced release of mediators of inflammation. Endotoxin (LPS) is a major component of the outer membrane of Gram negative bacteria and a critical factor in pathogenesis of sepsis. Development of antagonists that inhibit the storm of inflammatory molecules by blocking Toll like receptors (TLR) has been the main stay of research efforts. We report here that a filarial glycoprotein binds to murine macrophages and human monocytes through TLR4 and activates them through alternate pathway and in the process inhibits LPS mediated classical activation which leads to inflammation associated with endotoxemia. The active component of the nematode glycoprotein mediating alternate activation of macrophages was found to be a carbohydrate residue, Chitohexaose. Murine macrophages and human monocytes up regulated Arginase-1 and released high levels of IL-10 when incubated with chitohexaose. Macrophages of C3H/HeJ mice (non-responsive to LPS) failed to get activated by chitohexaose suggesting that a functional TLR4 is critical for alternate activation of macrophages also. Chitohexaose inhibited LPS induced production of inflammatory molecules TNF-α, IL-1β and IL-6 by macropahges in vitro and in vivo in mice. Intraperitoneal injection of chitohexaose completely protected mice against endotoxemia when challenged with a lethal dose of LPS. Furthermore, Chitohexaose was found to reverse LPS induced endotoxemia in mice even 6/24/48 hrs after its onset. Monocytes of subjects with active filarial infection displayed characteristic alternate activation markers and were refractory to LPS mediated inflammatory activation suggesting an interesting possibility of subjects with filarial infections being less prone to develop of endotoxemia. These observations that innate activation of alternate pathway of macrophages by chtx through TLR4 has offered novel opportunities to cell biologists to study two mutually exclusive activation pathways of macrophages being mediated through a single receptor.

Sepsis is one of the leading causes of death contributing to mortality as high as 54 percent in intensive care units across the world. Hyper inflammation induced by bacteria or bacterial products through Toll like receptors leads to sepsis and hence current approaches are directed towards blockade such receptors. While many such candidate antagonists have shown promise they also result in induction of inappropriate innate immune responses thus increasing risk of development of shock leading to death. In this study we describe a novel approach to treat endotoxemia associated with sepsis, fundamentally different from other reports. Chitohexaose a small molecular weight polysaccharide by virtue of its ability to bind to active sites of TLR4 inhibited LPS induced production of inflammatory mediators by murine macrophages and human monocytes. Administration of chitohexaose with LPS blocked endotoxemia leading to mortality of mice. More significantly, Chitohexaose reversed inflammation and protected mice even 24/48 hrs after onset of endotoxemia. Apart from competitively inhibiting LPS induced inflammation chitohexaose also activated alternate pathway of macrophages. Such macrophages are known to display increased phagocytic activity, are resistant to LPS induced activation and associated with resolution of inflammation and tissue repair.

Anti-apoptotic effects of SERPIN B3 and B4 via STAT6 activation in macrophages after infection with Toxoplasma gondii

Toxoplasma gondii penetrates all kinds of nucleated eukaryotic cells but modulates host cells differently for its intracellular survival. In a previous study, we found out that serine protease inhibitors B3 and B4 (SERPIN B3/B4 because of their very high homology) were significantly induced in THP-1-derived macrophages infected with T. gondii through activation of STAT6. In this study, to evaluate the effects of the induced SERPIN B3/B4 on the apoptosis of T. gondii-infected THP-1 cells, we designed and tested various small interfering (si-) RNAs of SERPIN B3 or B4 in staurosporine-induced apoptosis of THP-1 cells. Anti-apoptotic characteristics of THP-1 cells after infection with T. gondii disappeared when SERPIN B3/B4 were knock-downed with gene specific si-RNAs transfected into THP-1 cells as detected by the cleaved caspase 3, poly-ADP ribose polymerase and DNA fragmentation. This anti-apoptotic effect was confirmed in SERPIN B3/B4 overexpressed HeLa cells. We also investigated whether inhibition of STAT6 affects the function of SERPIN B3/B4, and vice versa. Inhibition of SERPIN B3/B4 did not influence STAT6 expression but SERPIN B3/B4 expression was inhibited by STAT6 si-RNA transfection, which confirmed that SERPIN B3/B4 was induced under the control of STAT6 activation. These results suggest that T. gondii induces SERPIN B3/B4 expression via STAT6 activation to inhibit the apoptosis of infected THP-1 cells for longer survival of the intracellular parasites themselves.

Discovery of a novel Toxoplasma gondii conoid-associated protein important for parasite resistance to reactive nitrogen intermediates

Toxoplasma gondii modifies its host cell to suppress its ability to become activated in response to IFN-γ and TNF-α and to develop intracellular antimicrobial effectors, including NO. Mechanisms used by T. gondii to modulate activation of its infected host cell likely underlie its ability to hijack monocytes and dendritic cells during infection to disseminate to the brain and CNS where it converts to bradyzoites contained in tissue cysts to establish persistent infection. To identify T. gondii genes important for resistance to the effects of host cell activation, we developed an in vitro murine macrophage infection and activation model to identify parasite insertional mutants that have a fitness defect in infected macrophages following activation but normal invasion and replication in naive macrophages. We identified 14 independent T. gondii insertional mutants out of >8000 screened that share a defect in their ability to survive macrophage activation due to macrophage production of reactive nitrogen intermediates (RNIs). These mutants have been designated counter-immune mutants. We successfully used one of these mutants to identify a T. gondii cytoplasmic and conoid-associated protein important for parasite resistance to macrophage RNIs. Deletion of the entire gene or just the region encoding the protein in wild-type parasites recapitulated the RNI-resistance defect in the counter-immune mutant, confirming the role of the protein in resistance to macrophage RNIs.

Toxoplasma gondii and the blood-brain barrier

Infection with the protozoan parasite Toxoplasma gondii is characterized by asymptomatic latent infection in the central nervous system and skeletal muscle tissue in the majority of immunocompentent individuals. Life-threatening reactivation of the infection in immunocompromized patients originates from rupture of Toxoplasma cysts in the brain. While major progress has been made in our understanding of the immunopathogenesis of infection the mechanism(s) of neuroinvasion of the parasite remains poorly understood. The present review presents the current understanding of blood-brain barrier (patho)physiology and the interaction of Toxoplasma gondii with cells of the blood-brain barrier.

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.