Impaired resistance to the development of toxoplasmic encephalitis in interleukin-6-deficient mice

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

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

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.

Association of polymorphism of IL-17A, IL-17F, and IL-6 with Toxoplasma gondii infection susceptibility in HIV/AIDS patients in Shiraz, southern Iran

INTRODUCTION

Toxoplasma gondii infection is considered as one of the most important opportunistic infections and cause of death in HIV patients.

METHODS

In this cross-sectional study, 334 HIV positive patients were included. The molecular test was performed by the restriction fragment length polymorphism-polymerase chain reaction method. Allelic frequency, haplotype analyses, and linkage disequilibrium were calculated. The odds ratio was calculated. The linear regression model was used to analysis of interleukin (IL)-17A, IL-17F, and IL-6 single-nucleotide polymorphism genotypes in HIV patients with and without toxoplasmosis.

RESULTS

In total, 95 tested'patients (28.4%) were positive for toxoplasmosis. The risk of toxoplasma infection in the current study did not correlate with IL-17 and IL-6 polymorphism and the risk of contracting toxoplasma was also not significantly correlated in this study. There was no association between the frequency of alleles and the risk of toxoplasma infection in IL-17 haplotype analysis.

CONCLUSION

The findings of this study revealed that there were significant differences in the serum levels of IL-6 and IL-17A, but not IL-17F, between the case and control groups in various genetic models. However, these polymorphisms did not show a significant relationship with toxoplasma infection in HIV-positive patients. This study represents the first investigation in Iran to explore the role of IL-6 and IL-17 polymorphisms in toxoplasma infection among HIV-positive patients.

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

CD4+ T Cell Responses to Toxoplasma gondii Are a Double-Edged Sword

CD4+ T cells have been found to play critical roles in the control of both acute and chronic Toxoplasma infection. Previous studies identified a protective role for the Toxoplasma CD4+ T cell-eliciting peptide AS15 (AVEIHRPVPGTAPPS) in C57BL/6J mice. Herein, we found that immunizing mice with AS15 combined with GLA-SE, a TLR-4 agonist in emulsion adjuvant, can be either helpful in protecting male and female mice at early stages against Type I and Type II Toxoplasma parasites or harmful (lethal with intestinal, hepatic, and spleen pathology associated with a storm of IL6). Introducing the universal CD4+ T cell epitope PADRE abrogates the harmful phenotype of AS15. Our findings demonstrate quantitative and qualitative features of an effective Toxoplasma-specific CD4+ T cell response that should be considered in testing next-generation vaccines against toxoplasmosis. Our results also are cautionary that individual vaccine constituents can cause severe harm depending on the company they keep.

Astrocytes in the pathophysiology of neuroinfection

Key homeostasis providing cells in the central nervous system (CNS) are astrocytes, which belong to the class of cells known as atroglia, a highly heterogeneous type of neuroglia and a prominent element of the brain defence. Diseases evolve due to altered homeostatic state, associated with pathology-induced astroglia remodelling represented by reactive astrocytes, astroglial atrophy and astrodegeneration. These features are hallmarks of most infectious insults, mediated by bacteria, protozoa and viruses; they are also prominent in the systemic infection. The COVID-19 pandemic revived the focus into neurotropic viruses such as SARS-CoV2 (Coronaviridae) but also the Flaviviridae viruses including tick-borne encephalitis (TBEV) and Zika virus (ZIKV) causing the epidemic in South America prior to COVID-19. Astrocytes provide a key response to neurotropic infections in the CNS. Astrocytes form a parenchymal part of the blood-brain barrier, the site of virus entry into the CNS. Astrocytes exhibit aerobic glycolysis, a form of metabolism characteristic of highly morphologically plastic cells, like cancer cells, hence a suitable milieu for multiplication of infectious agent, including viral particles. However, why the protection afforded by astrocytes fails in some circumstances is an open question to be studied in the future.

Toxoplasma gondii Infection Decreases Intestinal 5-Lipoxygenase Expression, while Exogenous LTB4 Controls Parasite Growth

5-Lipoxygenase (5-LO) is an enzyme required for the production of leukotrienes and lipoxins and interferes with parasitic infections. In vitro, Toxoplasma gondii inhibits leukotriene B₄ (LTB₄) production, and mice deficient in 5-LO are highly susceptible to infection. The aim of this study was to investigate the effects of the pharmacological inhibition of the 5-LO pathway and exogenous LTB₄ supplementation during experimental toxoplasmosis. For this purpose, susceptible C57BL/6 mice were orally infected with T. gondii and treated with LTB₄ or MK886 (a selective leukotriene inhibitor through inhibition of 5-LO-activating protein [FLAP]). The parasitism, histology, and immunological parameters were analyzed. The infection decreased 5-LO expression in the small intestine, and treatment with MK886 reinforced this reduction during infection; in addition, MK886-treated infected mice presented higher intestinal parasitism, which was associated with lower local interleukin-6 (IL-6), interferon gamma (IFN-γ), and tumor necrosis factor (TNF) production. In contrast, treatment with LTB₄ controlled parasite replication in the small intestine, liver, and lung and decreased pulmonary pathology. Interestingly, treatment with LTB₄ also preserved the number of Paneth cells and increased α-defensins expression and IgA levels in the small intestine of infected mice. Altogether, these data demonstrated that T. gondii infection is associated with a decrease in 5-LO expression, and on the other hand, treatment with the 5-LO pathway product LTB₄ resulted in better control of parasite growth in the organs, adding to the knowledge about the pathogenesis of T. gondii infection.

γδ T Cells in Brain Homeostasis and Diseases

γδ T cells are a distinct subset of T cells expressing γδ T cell receptor (TCR) rather than αβTCR. Since their discovery, the critical roles of γδ T cells in multiple physiological systems and diseases have been investigated. γδ T cells are preferentially located at mucosal surfaces, such as the gut, although a small subset of γδ T cells can circulate the blood. Additionally, a subset of γδ T cells reside in the meninges in the central nervous system. Recent findings suggest γδ T cells in the meninges have critical roles in brain function and homeostasis. In addition, several lines of evidence have shown γδ T cells can infiltrate the brain parenchyma and regulate inflammatory responses in multiple diseases, including neurodegenerative diseases. Although the importance of γδ T cells in the brain is well established, their roles are still incompletely understood due to the complexity of their biology. Because γδ T cells rapidly respond to changes in brain status and regulate disease progression, understanding the role of γδ T cells in the brain will provide critical information that is essential for interpreting neuroimmune modulation. In this review, we summarize the complex role of γδ T cells in the brain and discuss future directions for research.

Cleaved CD95L perturbs in vitro macrophages responses to Toxoplasma gondii

Toxoplasma gondii infects approximately 1-2 billion people, and manipulation of the macrophage response is critical to host and parasite survival. A cleaved (cl)-CD95L form can promote cellular migration and we have previously shown that cl-CD95L aggravates inflammation and pathology in systemic lupus erythematosus (SLE). Findings have shown that CD95L is upregulated during human infection, therefore we examined the effect of cl-CD95L on the macrophage response to T. gondii. . We find that cl-CD95L promotes parasite replication in macrophages, associated with increased arginase-1 levels, mediated by signal transducer and activator of transcription (STAT)6. Inhibition of both arginase-1 and STAT6 reversed the effects of cl-CD95L. Phospho-kinase array showed that cl-CD95L alters Janus Kinases (JAK)/STAT, mammalian target of rapamycin (mTOR), and Src kinase signals. By triggering changes in JAK/STAT cl-CD95L may limit anti-parasite effectors.

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.

Behavioral alterations in long-term Toxoplasma gondii infection of C57BL/6 mice are associated with neuroinflammation and disruption of the blood brain barrier

The Apicomplexa protozoan Toxoplasma gondii is a mandatory intracellular parasite and the causative agent of toxoplasmosis. This illness is of medical importance due to its high prevalence worldwide and may cause neurological alterations in immunocompromised persons. In chronically infected immunocompetent individuals, this parasite forms tissue cysts mainly in the brain. In addition, T. gondii infection has been related to mental illnesses such as schizophrenia, bipolar disorder, depression, obsessive-compulsive disorder, as well as mood, personality, and other behavioral changes. In the present study, we evaluated the kinetics of behavioral alterations in a model of chronic infection, assessing anxiety, depression and exploratory behavior, and their relationship with neuroinflammation and parasite cysts in brain tissue areas, blood-brain-barrier (BBB) integrity, and cytokine status in the brain and serum. Adult female C57BL/6 mice were infected by gavage with 5 cysts of the ME-49 type II T. gondii strain, and analyzed as independent groups at 30, 60 and 90 days postinfection (dpi). Anxiety, depressive-like behavior, and hyperactivity were detected in the early (30 dpi) and long-term (60 and 90 dpi) chronic T. gondii infection, in a direct association with the presence of parasite cysts and neuroinflammation, independently of the brain tissue areas, and linked to BBB disruption. These behavioral alterations paralleled the upregulation of expression of tumor necrosis factor (TNF) and CC-chemokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES) in the brain tissue. In addition, increased levels of interferon-gamma (IFNγ), TNF and CCL2/MCP-1 were detected in the peripheral blood, at 30 and 60 dpi. Our data suggest that the persistence of parasite cysts induces sustained neuroinflammation, and BBB disruption, thus allowing leakage of cytokines of circulating plasma into the brain tissue. Therefore, all these factors may contribute to behavioral changes (anxiety, depressive-like behavior, and hyperactivity) in chronic T. gondii infection.

Biogenic silver nanoparticles (AgNp-Bio) reduce Toxoplasma gondii infection and proliferation in HeLa cells, and induce autophagy and death of tachyzoites by apoptosis-like mechanism

Toxoplasma gondii is a protozoan parasite that can cause severe and debilitating diseases, especially in immunocompromised individuals. The available treatment is based on drugs that have low efficacy, high toxicity, several adverse effects, and need long periods of treatment. Thus, the search for therapeutic alternatives is urgently needed. Biogenic silver nanoparticles (AgNp-Bio) have been associated with several biological effects, as antiproliferative, pro-apoptotic, antioxidant, antiviral, antifungal, and antiprotozoal activity. Thus, the objective was evaluating AgNp-Bio effect on HeLa cells infected with T. gondii (RH strain). First, nontoxic AgNp-Bio concentrations for HeLa cells (1.5 - 6 µM) were determined, which were tested on cells infected with T. gondii. A significant reduction in infection, proliferation, and intracellular parasitic load was observed, also an increase in ROS and IL-6. Additionally, the evaluation of the action mechanisms of the parasite showed that AgNp-Bio acts directly on tachyzoites, inducing depolarization of the mitochondrial membrane, ROS increase, and lipid bodies accumulation, as well as triggering an autophagic process, causing damage to the parasite membrane, and phosphatidylserine exposure. Based on this, it was inferred that AgNp-Bio affects T. gondii by inducing immunomodulation and microbicidal molecules produced by infected cells, and acts on parasites, by inducing autophagy and apoptosis.

Microglia and astrocyte responses to neuropathogenic protozoan parasites

Cerebral toxoplasmosis and cerebral malaria are two important neurological diseases caused by protozoan parasites. In this review, we discuss recent findings regarding the innate immune responses of microglia and astrocytes to Toxoplasma and Plasmodium infection. In both infections, these tissue-resident glial cells perform a sentinel function mediated by alarmin crosstalk that licenses adaptive type 1 immunity in the central nervous system. Divergent protective or pathogenic effects of type 1 activation of these astrocytes and microglia are revealed depending on the inherent lytic potential of the protozoan parasite.

Heme Oxygenase-1 Induction in Human BeWo Trophoblast Cells Decreases Toxoplasma gondii Proliferation in Association With the Upregulation of p38 MAPK Phosphorylation and IL-6 Production

Heme oxygenase-1 (HO-1) enzyme exerts beneficial effects at the maternal-fetal interface, especially in trophoblasts, being involved in survival and maturation of these cell phenotypes. Trophoblast cells play essential roles throughout pregnancy, being the gateway for pathogens vertically transmitted, such as Toxoplasma gondii. It was previously shown that HO-1 activity was involved in the control of T. gondii infection in vivo; however, its contribution in trophoblast cells during T. gondii infection, remain undefined. Thus, this study aimed to investigate the influence of HO-1 in T. gondii-infected BeWo and HTR-8/SVneo human trophoblast cells. For this purpose, trophoblast cells were infected and the HO-1 expression was evaluated. T. gondii-infected BeWo cells were treated with hemin or CoPPIX, as inducers of HO-1, or with bilirubin, an end-product of HO-1, and the parasitism was quantified. The involvement of p38 MAPK, a regulator of HO-1, and the cytokine production, were also evaluated. It was found that T. gondii decreased the HO-1 expression in BeWo but not in HTR-8/SVneo cells. When treated with the HO-1 inducers or bilirubin, BeWo cells reduced the parasite proliferation. T. gondii also decreased the p38 MAPK phosphorylation in BeWo cells; on the other hand, HO-1 induction sustained its activation. Finally, the IL-6 production was upregulated by HO-1 induction in T. gondii-infected cells, which was associated with the control of infection.

Synergistic effect of GRA7 and profilin proteins in vaccination against chronic Toxoplasma gondii infection

Toxoplasmosis is a zoonotic disease with worldwide prevalence in humans and warm-blooded animal populations. In livestock Toxoplasma gondii is the causal agent of significant economic losses since it can cause abortions in goats and sheep. It is estimated that one third of the world population is infected. Although there are effective therapies for acute infection, these are sometimes poorly tolerated, teratogenic, and have a long administration time. Considering the deficiencies that exist related to the prevention and treatment of toxoplasmosis, the development of a safe and effective vaccine would be extremely valuable in fighting against this infection. In the present work, we characterize for the first time the adjuvant and immunogenic potential of a recombinant profilin protein (rTgPF), in a vaccine formulation alone or in combination with the well-known GRA7 antigen candidate in a murine toxoplasmosis model. Since TgPF acts as a ligand for TLR11 and 12 inducing innate immune responses that promote type 1 adaptive responses, we first study the capacity of the mix rGRA7 + rTgPF to initiate an immune response by evaluating dendritic cell activation. Both rTgPF and rGRA7 induces activation of mouse BMDCs more efficiently than the single proteins, evidenced by increased expression of CD80 and CD86 co-stimulatory proteins and secretion of IL-6, IL-10 and IL-12 cytokines after in vitro stimulation. The sum of the effects of rGRA7 and rTgPF on BMDCs maturation led us to assay them in a vaccination protocol. BALB/c mice vaccinated with this mix elicited a Th1-biased immunity via the induction of lymphocyte proliferation, activation of CD4⁺T cells and increased IFN-γ production that resulted in enhanced protection against chronic Toxoplama gondii infection. Profilin per se induce only cellular immunity but augments the effect of rGRA7 immune responses when used together, thus allowing us to postulate rTgPF as a potential adjuvant in a protein vaccine.

Beneficial effects of Strongyloides venezuelensis antigen extract in acute experimental toxoplasmosis

BACKGROUND

Toxoplasma gondii is a protozoan with worldwide distribution and triggers a strong Th1 immune response in infected susceptible hosts. On the contrary, most helminth infections are characterized by Th2 immune response and the use of helminth-derived antigens to regulate immune response in inflammatory disorders has been broadly investigated.

OBJECTIVES

The aim of this study was to investigate whether treatment with Strongyloides venezuelensis antigen extract (SvAg) would alter immune response against T gondii.

METHODS

C57BL/6 mice were orally infected with T gondii and treated with SvAg, and parasitological, histological and immunological parameters were investigated.

RESULTS

It was observed that SvAg treatment improved survival rates of T gondii-infected mice. At day 7 post-infection, the parasite load was lower in the lung and small intestine of infected SvAg-treated mice than untreated infected mice. Remarkably, SvAg-treated mice infected with T gondii presented reduced inflammatory lesions in the small intestine than infected untreated mice and decreased intestinal and systemic levels of IFN-γ, TNF-α and IL-6. In contrast, SvAg treatment increased T gondii-specific IgA serum levels in infected mice.

CONCLUSIONS

S venezuelensis antigen extract has anti-parasitic and anti-inflammatory properties during T gondii infection suggesting as a possible alternative to parasite and inflammation control.

The Availability of Iron Is Involved in the Murine Experimental Toxoplasma gondii Infection Outcome

Iron is an important constituent of our environment, being necessary for both mammalian and pathogenic protozoa survival. Iron-containing proteins exert a wide range of biological processes such as biodegradation and biosynthesis, as well as immune function, fetal development, and physical and mental well-being. This work aimed to investigate the effect of iron deprivation in Toxoplasma gondii infection outcome. C57BL/6 mice were orally infected with T. gondii and treated with an iron chelator, deferoxamine, or supplemented with iron (ferrous sulfate), and the parasitism as well as immunological and histological parameters were analyzed. It was observed that the infection increased iron accumulation in the organs, as well as systemically, and deferoxamine treatment diminished the iron content in serum samples and intestine. The deferoxamine treatment decreased the parasitism and inflammatory alterations in the small intestine and lung. Additionally, they partially preserved the Paneth cells and decreased the intestinal dysbiosis. The ferrous sulfate supplementation, despite not significantly increasing the parasite load in the organs, increased the inflammatory alterations in the liver. Together, our results suggest that iron chelation, which is commonly used to treat iron overload, could be a promising medicine to control T. gondii proliferation, mainly in the small intestine, and consequently inflammation caused by infection.

Impact of Interleukin-27p28 on T and B Cell Responses during Toxoplasmosis

Interleukin-27 (IL-27) is a heterodimeric cytokine composed of the subunits IL-27p28 and EBi3, and while the IL-27 heterodimer influences T cell activities, there is evidence that IL-27p28 can have EBi3-independent activities; however, their relevance to infection is unclear. Therefore, the studies presented here compared how IL-27p28 transgenics and IL-27p28-/- mice responded to the intracellular parasite Toxoplasma gondii While the loss of IL-27p28 and its overexpression both result in increased susceptibility to T. gondii, the basis for this phenotype reveals distinct roles for IL-27p28. As a component of IL-27, IL-27p28 is critical to limit infection-induced T cell-mediated pathology, whereas the ectopic expression of IL-27p28 reduced the effector T cell population and had a major inhibitory effect on parasite-specific antibody titers and a failure to control parasite replication in the central nervous system. Indeed, transfer of immune serum to infected IL-27p28 transgenics resulted in reduced parasite burden and pathology. Thus, IL-27p28, independent of its role as a component of IL-27, can act as a negative regulator of humoral and cellular responses during toxoplasmosis.

Astroglia in Sepsis Associated Encephalopathy

Cellular pathophysiology of sepsis associated encephalopathy (SAE) remains poorly characterised. Brain pathology in SAE, which is manifested by impaired perception, consciousness and cognition, results from multifactorial events, including high levels of systemic cytokines, microbial components and endotoxins, which all damage the brain barriers, instigate neuroinflammation and cause homeostatic failure. Astrocytes, being the principal homeostatic cells of the central nervous system contribute to the brain defence against infection. Forming multifunctional anatomical barriers, astroglial cells maintain brain-systemic interfaces and restrict the damage to the nervous tissue. Astrocytes detect, produce and integrate inflammatory signals between immune cells and cells of brain parenchyma, thus regulating brain immune response. In SAE astrocytes are present in both reactive and astrogliopathic states; balance between these states define evolution of pathology and neurological outcomes. In humans pathophysiology of SAE is complicated by frequent presence of comorbidities, as well as age-related remodelling of the brain tissue with senescence of astroglia; these confounding factors further impact upon SAE progression and neurological deficits.

Astrocytes: Integrative Regulators of Neuroinflammation in Stroke and Other Neurological Diseases

Astrocytes regulate neuroinflammatory responses after stroke and in other neurological diseases. Although not all astrocytic responses reduce inflammation, their predominant function is to protect the brain by driving the system back to homeostasis after injury. They receive multidimensional signals within the central nervous system and between the brain and the systemic circulation. Processing this information allows astrocytes to regulate synapse formation and maintenance, cerebral blood flow, and blood-brain barrier integrity. Similarly, in response to stroke and other central nervous system disorders, astrocytes detect and integrate signals of neuronal damage and inflammation to regulate the neuroinflammatory response. Two direct regulatory mechanisms in the astrocyte arsenal are the ability to form both physical and molecular barriers that seal the injury site and localize the neuroinflammatory response. Astrocytes also indirectly regulate the inflammatory response by affecting neuronal health during the acute injury and axonal regrowth. This ability to regulate the location and degree of neuroinflammation after injury, combined with the long time course of neuroinflammation, makes astrocytic signaling pathways promising targets for therapies.

Clinical characteristics and computed tomography findings of pulmonary toxoplasmosis after hematopoietic stem cell transplantation

The prognosis of pulmonary toxoplasmosis, including disseminated toxoplasmosis involving the lungs, following hematopoietic stem cell transplantation (HSCT) is extremely poor due to the difficulties associated with early diagnosis and the rapidly progressive deterioration of multiorgan function. In our institution, we identified nine cases of toxoplasmosis, representing incidences of 2.2 and 19.6 % among all HSCT recipients and seropositive HSCT recipients, respectively. Of the patients with toxoplasmosis, six had pulmonary toxoplasmosis. Chest computed tomography (CT) findings revealed centrilobular, patchy ground-glass opacities (n = 3), diffuse ground-glass opacities (n = 2), ground-glass opacities with septal thickening (n = 1), and marked pleural effusion (n = 1). All cases died, except for one with suspected pulmonary toxoplasmosis who was diagnosed by a polymerase chain reaction assay 2 days after the onset of symptoms. In pulmonary toxoplasmosis, CT findings are non-specific and may mimic pulmonary congestion, atypical pneumonia, viral pneumonitis, and bronchopneumonia. Early diagnosis and treatment is crucial for overcoming this serious infectious complication. Pulmonary toxoplasmosis should be considered during differential diagnosis in a recipient with otherwise unexplained signs of infection and CT findings with ground-glass opacities, regardless of the distribution.

Host and Toxoplasma gondii genetic and non-genetic factors influencing the development of ocular toxoplasmosis: A systematic review

Toxoplasmosis is a cosmopolitan infection caused by the apicomplexan parasite Toxoplasma gondii. This infectious disease is widely distributed across the world where cats play an important role in its spread. The symptomatology caused by this parasite is diverse but the ocular affectation emerges as the most important clinical phenotype. Therefore, we conducted a systematic review of the current knowledge of ocular toxoplasmosis from the genetic diversity of the pathogen towards the treatment available for this infection. This review represents an update to the scientific community regarding the genetic diversity of the parasite, the genetic factors of the host, the molecular pathogenesis and its association with disease, the available diagnostic tools and the available treatment of patients undergoing ocular toxoplamosis. This review will be an update for the scientific community in order to encourage researchers to deploy cutting-edge investigation across this field.

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.

Interleukin-6-driven inflammatory response induces retinal pathology in a model of ocular toxoplasmosis reactivation

Ocular inflammation is one of the consequences of infection with the protozoan parasite Toxoplasma gondii. Even if lesions are self-healing in immunocompetent persons, they pose a lifetime risk of reactivation and are a serious threat to vision. As there are virtually no immunological data on reactivating ocular toxoplasmosis, we established a model of direct intravitreal injection of parasites in previously infected mice with a homologous type II strain. Two different mouse strains with variable ability to control retinal infection were studied in order to describe protective and deleterious reaction patterns. In Swiss-Webster mice, which are already relatively resistant to primary infection, no peak of parasite load was observed upon reinfection. In contrast, the susceptible inbred strain C57BL/6 showed high parasite loads after 7 days, as well as marked deterioration of retinal architecture. Both parameters were back to normal on day 21. C57BL/6 mice also reacted with a strong local production of inflammatory and Th1-type cytokines, like interleukin-6 (IL-6), IL-17A, and gamma interferon (IFN-γ), while Swiss-Webster mice showed only moderate expression of the Th2 cytokine IL-31. Interestingly, rapid intraocular production of anti-Toxoplasma antibodies was observed in Swiss-Webster but not in C57BL/6 mice. We then localized the cellular source of different immune mediators within the retina by immunofluorescence. Finally, neutralization experiments of IFN-γ or IL-6 demonstrated the respective protective and deleterious roles of these cytokines for parasite control and retinal integrity during reinfection. In conclusion, we developed and immunologically characterized a promising mouse model of reactivating ocular toxoplasmosis.

CXCL9 is important for recruiting immune T cells into the brain and inducing an accumulation of the T cells to the areas of tachyzoite proliferation to prevent reactivation of chronic cerebral infection with Toxoplasma gondii

T cells are required to maintain the latency of chronic infection with Toxoplasma gondii in the brain. Here, we examined the role of non-glutamic acid-leucine-arginine CXC chemokine CXCL9 for T-cell recruitment to prevent reactivation of infection with T. gondii. Severe combined immunodeficient (SCID) mice were infected and treated with sulfadiazine to establish a chronic infection. Immune T cells from infected wild-type mice were transferred into the SCID mice in combination with treatment with anti-CXCL9 or control sera. Three days later, sulfadiazine was discontinued to initiate reactivation of infection. Numbers of CD4(+) and CD8(+) T cells isolated from the brains were markedly less in mice treated with anti-CXCL9 serum than in mice treated with control serum at 3 days after sulfadiazine discontinuation. Amounts of tachyzoite (acute stage form of T. gondii)-specific SAG1 mRNA and numbers of foci associated with tachyzoites were significantly greater in the former than the latter at 5 days after sulfadiazine discontinuation. An accumulation of CD3(+) T cells into the areas of tachyzoite growth was significantly less frequent in the SCID mice treated with anti-CXCL9 serum than in mice treated with control serum. These results indicate that CXCL9 is crucial for recruiting immune T cells into the brain and inducing an accumulation of the T cells into the areas where tachyzoites proliferate to prevent reactivation of chronic T. gondii infection.

In vitro infection of human nervous cells by two strains of Toxoplasma gondii: a kinetic analysis of immune mediators and parasite multiplication

The severity of toxoplasmic infection depends mainly on the immune status of the host, but also on the Toxoplasma gondii strains, which differ by their virulence profile. The relationship between the human host and T. gondii has not yet been elucidated because few studies have been conducted on human models. The immune mechanisms involved in the persistence of T. gondii in the brains of immunocompetent subjects and during the reactivation of latent infections are still unclear. In this study, we analyzed the kinetics of immune mediators in human nervous cells in vitro, infected with two strains of T. gondii. Human neuroblast cell line (SH SY5Y), microglial (CMH5) and endothelial cells (Hbmec) were infected separately by RH (type I) or PRU (type II) strains for 8 h, 14 h, 24 h and 48 h (ratio 1 cell: 2 tachyzoites). Pro-inflammatory protein expression was different between the two strains and among different human nervous cells. The cytokines IL-6, IL-8 and the chemokines MCP-1 and GROα, and SERPIN E1 were significantly increased in CMH5 and SH SY5Y at 24 h pi. At this point of infection, the parasite burden declined in microglial cells and neurons, but remained high in endothelial cells. This differential effect on the early parasite multiplication may be correlated with a higher production of immune mediators by neurons and microglial cells compared to endothelial cells. Regarding strain differences, PRU strain, but not RH strain, stimulates all cells to produce pro-inflammatory growth factors, G-CSF and GM-CSF. These proteins could increase the inflammatory effect of this type II strain. These results suggest that the different protein expression profiles depend on the parasitic strain and on the human nervous cell type, and that this could be at the origin of diverse brain lesions caused by T. gondii.

VCAM-1/α4β1 integrin interaction is crucial for prompt recruitment of immune T cells into the brain during the early stage of reactivation of chronic infection with Toxoplasma gondii to prevent toxoplasmic encephalitis

Reactivation of chronic infection with Toxoplasma gondii can cause life-threatening toxoplasmic encephalitis in immunocompromised individuals. We examined the role of VCAM-1/α4β1 integrin interaction in T cell recruitment to prevent reactivation of the infection in the brain. SCID mice were infected and treated with sulfadiazine to establish a chronic infection. VCAM-1 and ICAM-1 were the endothelial adhesion molecules detected on cerebral vessels of the infected SCID and wild-type animals. Immune T cells from infected wild-type mice were treated with anti-α4 integrin or control antibodies and transferred into infected SCID or nude mice, and the animals received the same antibody every other day. Three days later, sulfadiazine was discontinued to initiate reactivation of infection. Expression of mRNAs for CD3δ, CD4, CD8β, gamma interferon (IFN-γ), and inducible nitric oxide synthase (NOS2) (an effector molecule to inhibit T. gondii growth) and the numbers of CD4(+) and CD8(+) T cells in the brain were significantly less in mice treated with anti-α4 integrin antibody than in those treated with control antibody at 3 days after sulfadiazine discontinuation. At 6 days after sulfadiazine discontinuation, cerebral tachyzoite-specific SAG1 mRNA levels and numbers of inflammatory foci associated with tachyzoites were markedly greater in anti-α4 integrin antibody-treated than in control antibody-treated animals, even though IFN-γ and NOS2 mRNA levels were higher in the former than in the latter. These results indicate that VCAM-1/α4β1 integrin interaction is crucial for prompt recruitment of immune T cells and induction of IFN-γ-mediated protective immune responses during the early stage of reactivation of chronic T. gondii infection to control tachyzoite growth.

A toxoplasma patatin-like protein changes localization and alters the cytokine response during toxoplasmic encephalitis

Toxoplasma gondii is an obligate intracellular parasite that forms a lifelong infection within the central nervous system of its host. The T. gondii genome encodes six members of the patatin-like phospholipase family; related proteins are associated with host-microbe interactions in bacteria. T. gondii patatin-like protein 1 (TgPL1) was previously determined to be necessary for parasites to suppress nitric oxide and prevent degradation in activated macrophages. Here, we show that in the rapidly replicating tachyzoite stage, TgPL1 is localized within vesicles inside the parasite that are distinct from the dense granules; however, in the encysted bradyzoite stage, TgPL1 localizes to the parasitophorous vacuole (PV) and cyst wall. While we had not previously seen a defect of the TgPL1 deletion mutant (ΔTgPL1) during acute and early chronic infection, the localization change of TgPL1 in bradyzoites caused us to reevaluate the ΔTgPL1 mutant during late chronic infection and in a toxoplasmic encephalitis (TE) mouse model. Mice infected with ΔTgPL1 are more resistant to TE and have fewer inflammatory lesions than mice infected with the wild type and ΔTgPL1 genetically complemented with TgPL1. This increased resistance to TE could result from several contributing factors. First, we found that ΔTgPL1 bradyzoites did not convert back to tachyzoites readily in tissue culture. Second, a subset of cytokine levels were higher in ΔTgPL1-infected mice, including gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), and monocyte chemotactic protein 1 (MCP-1). These studies suggest that TgPL1 plays a role in the maintenance of chronic T. gondii infection.

The protein kinase double-stranded RNA-dependent (PKR) enhances protection against disease cause by a non-viral pathogen

PKR is well characterized for its function in antiviral immunity. Using Toxoplasma gondii, we examined if PKR promotes resistance to disease caused by a non-viral pathogen. PKR(-/-) mice infected with T. gondii exhibited higher parasite load and worsened histopathology in the eye and brain compared to wild-type controls. Susceptibility to toxoplasmosis was not due to defective expression of IFN-γ, TNF-α, NOS2 or IL-6 in the retina and brain, differences in IL-10 expression in these organs or to impaired induction of T. gondii-reactive T cells. While macrophages/microglia with defective PKR signaling exhibited unimpaired anti-T. gondii activity in response to IFN-γ/TNF-α, these cells were unable to kill the parasite in response to CD40 stimulation. The TRAF6 binding site of CD40, but not the TRAF2,3 binding sites, was required for PKR phosphorylation in response to CD40 ligation in macrophages. TRAF6 co-immunoprecipitated with PKR upon CD40 ligation. TRAF6-PKR interaction appeared to be indirect, since TRAF6 co-immunoprecipitated with TRAF2 and TRAF2 co-immunoprecipitated with PKR, and deficiency of TRAF2 inhibited TRAF6-PKR co-immunoprecipitation as well as PKR phosphorylation induced by CD40 ligation. PKR was required for stimulation of autophagy, accumulation the autophagy molecule LC3 around the parasite, vacuole-lysosomal fusion and killing of T. gondii in CD40-activated macrophages and microglia. Thus, our findings identified PKR as a mediator of anti-microbial activity and promoter of protection against disease caused by a non-viral pathogen, revealed that PKR is activated by CD40 via TRAF6 and TRAF2, and positioned PKR as a link between CD40-TRAF signaling and stimulation of the autophagy pathway.

Interleukin-6 gene polymorphism (-174 G/C) is associated with toxoplasmic retinochoroiditis

PURPOSE

Experimental data have demonstrated a relevant role for IL-6 in the modulation of acute ocular toxoplasmosis. Therefore, we aim to investigate the possible association between the IL-6 gene polymorphism at position -174 and toxoplasmic retinochoroiditis (TR) in humans.

METHODS

Ninety-seven patients with diagnosed TR were recruited from the Uveitis Section, Federal University of Minas Gerais. For comparison, 83 healthy blood donors with positive serology for toxoplasmosis and without retinal signs of previous TR were included in the study. Genomic DNA was obtained from oral swabs of individuals and amplified using polymerase chain reaction (PCR) with specific primers flanking the locus -174 of IL-6 (-174G/C). PCR products were submitted to restriction endonuclease digestion and analysed by polyacrylamide gel electrophoresis to distinguish allele G and C of the IL-6 gene, allowing the detection of the polymorphism and determination of genotypes.

RESULTS

There was a significant difference in the genotype (χ(2) = 12.9, p = 0.001) and allele (χ(2) = 6.62, p = 0.01) distribution between TR patients and control subjects. In a subgroup analysis, there was no significant difference in genotypes and allele frequencies regarding TR recurrence.

CONCLUSIONS

This study suggests that the genotypes related with a lower production of IL-6 may be associated with the occurrence of TR.

Neonatal levels of acute phase proteins and later risk of non-affective psychosis

Mounting evidence suggests that immune disturbances in early life may be implicated in the etiology of non-affective psychoses. Our aim was to assess the levels of neonatal acute phase proteins (APPs), central to innate immune function as well as central nervous system development, in neonatal dried blood spots and their association with later risk of non-affective psychoses. This case-control study included 196 individuals with a verified register-based diagnosis of non-affective psychosis and 502 controls matched on age, sex and hospital of birth. Concentrations of nine different APPs were measured in eluates from dried blood spots using a bead-based multiplex assay. Odds ratios (OR) for non-affective psychoses were calculated for log(2)-transformed (continuous) as well as tertiles of APP concentrations. In continuous analysis, higher concentrations of two APPs, tissue plasminogen activator (tPA; OR: 0.90, 95% confidence interval (CI): 0.85-0.96) and serum amyloid P (SAP; OR: 0.88, 95% CI: 0.78-0.99) were protective in terms of risk of non-affective psychosis. These relationships were not affected by the addition of covariates relevant to maternal health, pregnancy and delivery to the model. Tertile analysis confirmed a protective relationship for higher levels of tPA and SAP, as well as for procalcitonin (highest tertile OR: 0.54, 95% CI:0.32-0.91). Our results suggest that persons who develop non-affective psychoses have lower levels of certain APPs at the time of birth. These differences may render individuals more susceptible to infectious diseases or cause deficiencies in pathways critical for neurodevelopment.

Trophoblast cells are able to regulate monocyte activity to control Toxoplasma gondii infection

INTRODUCTION

Toxoplasma gondii is an intracellular parasite that causes severe disease when the infection occurs during pregnancy. Trophoblast cells constitute an important maternal-fetal barrier, with monocytes concentrating around them. Thus, interactions between trophoblasts and monocytes are important for maintaining a successful pregnancy, especially in cases of infection. This study aimed to evaluate the role of trophoblast cells (BeWo line) on monocyte (THP-1 line) activity in the presence or absence of T. gondii infection.

METHODS

THP-1 cells were stimulated with supernatants of BeWo cells, previously infected or not with T. gondii, and then infected with parasites. The supernatant of both cells were collected and analyzed for cytokine production and T. gondii proliferation in THP-1 cells was determined.

RESULTS

The results showed that after infection, the pattern of cytokines secreted by THP-1 and BeWo cells was characterized as a pro-inflammatory profile. Furthermore, supernatant of BeWo cells infected or not, was able to change the cytokine profile secreted by infected THP-1 cells, and this supernatant became THP-1 cells more able to control T. gondii proliferation than those that had not been stimulated.

DISCUSSION

This effect was associated with secretion of interleukin (IL)-6 by the THP-1 cells and soluble factors secreted by BeWo cells, such as IL-6 and MIF.

CONCLUSION

Together, these results suggest that trophoblast cells are able to modulate monocyte activity, resulting in the control of T. gondii infection and subsequent maintenance of pregnancy.

Association between IgG subclasses against Toxoplasma gondii and clinical signs in newborns with congenital toxoplasmosis

BACKGROUND

The aim of this study was to evaluate the association between clinical signs of congenital toxoplasmosis and IgG subclasses found in newborns participating in the Minas Gerais State Neonatal Screening Program.

METHODS

Neonates with confirmed congenital toxoplasmosis underwent standardized ophthalmologic evaluation, neuroimaging studies and hearing assessment, as well as enzyme-linked immunosorbent assay testing for total IgG and its subclasses (IgG1, IgG2, IgG3 and IgG4) against soluble (STAg) and recombinant (rSAG1 and rMIC3) antigens of Toxoplasma gondii.

RESULTS

Newborns with congenital toxoplasmosis but without ocular lesions were more likely to present anti-rMIC3 total IgG when compared with those newborns with active or cicatricial retinochoroidal lesions. Detection of anti-rMIC3 IgG2 and IgG4 was associated with presence of retinochoroidal lesions and intracranial calcifications, with higher mean reactivity index values than unaffected newborns with congenital toxoplasmosis. Anti-STAg IgG3 was associated with newborns without neurologic damage.

CONCLUSIONS

Specific subclasses of IgG antibodies reacting with recombinant antigens of T. gondii may serve as biomarkers of neurologic and ocular changes in newborns with congenital toxoplasmosis.

Interferon-γ restricts Toxoplasma gondii development in murine skeletal muscle cells via nitric oxide production and immunity-related GTPases

The apicomplexan parasite Toxoplasma gondii is regularly transmitted to humans via the ingestion of contaminated meat products from chronically infected livestock. This route of transmission requires intracellular development and long-term survival of the parasite within muscle tissue. In this study, we determined the cell-autonomous immunity of mature primary embryonic or C2C12 skeletal muscle cells (SkMCs) to infection with T. gondii. Non-activated SkMCs and control fibroblasts sustained parasite replication; however, interferon (IFN)-γ significantly inhibited parasite growth in SkMCs but not in fibroblasts. Intracellular parasite replication was diminished by IFN-γ whereas host cell invasion was not affected. Tumor necrosis factor (TNF) did not further increase the IFN-γ-triggered host defense of SkMCs against Toxoplasma. Remarkably, IFN-γ alone or in combination with TNF decreased the high level of T. gondii bradyzoite formation being observed in non-activated SkMCs. Stimulation of SkMCs with IFN-γ strongly triggered expression of inducible nitric oxide synthase (iNOS) transcripts, and induced significantly higher levels of nitric oxide (NO) in SkMCs than in fibroblasts. Consequently, pharmacological inhibition of iNOS partially abrogated the IFN-γ-induced toxoplasmacidal activity of SkMCs. In addition, SkMCs strongly up-regulated immunity-regulated GTPases (IRGs) following stimulation with IFN-γ. IRGs accumulated on Toxoplasma-containing vacuoles in SkMCs in a parasite strain-dependent manner. Subsequent vacuole disruption and signs of degenerating parasites were regularly recognized in IFN-γ-treated SkMCs infected with type II parasites. Together, murine SkMCs exert potent toxoplasmacidal activity after stimulation with IFN-γ and have to be considered active participants in the local immune response against Toxoplasma in skeletal muscle.

Immune response and immunopathology during toxoplasmosis

Toxoplasma gondii is a protozoan parasite of medical and veterinary significance that is able to infect any warm-blooded vertebrate host. In addition to its importance to public health, several inherent features of the biology of T. gondii have made it an important model organism to study host-pathogen interactions. One factor is the genetic tractability of the parasite, which allows studies on the microbial factors that affect virulence and allows the development of tools that facilitate immune studies. Additionally, mice are natural hosts for T. gondii, and the availability of numerous reagents to study the murine immune system makes this an ideal experimental system to understand the functions of cytokines and effector mechanisms involved in immunity to intracellular microorganisms. In this article, we will review current knowledge of the innate and adaptive immune responses required for resistance to toxoplasmosis, the events that lead to the development of immunopathology, and the natural regulatory mechanisms that limit excessive inflammation during this infection.

Interleukin-6 enhances porcine parthenote development in vitro, through the IL-6/Stat3 signaling pathway

Signal transducer and activator of transcription-3 (Stat3) plays a central role in interleukin-6 (IL-6)-mediated cell proliferation by inhibiting apoptosis in a variety of cell types. The Stat3 pathway is essential for embryonic development. The aim of this study was to determine the effects of recombinant IL-6 on the viability and development of porcine diploid parthenotes cultured in vitro. Four-cell parthenotes, derived in vitro, were cultured to the blastocyst stage, with or without recombinant IL-6. The addition of 10 or 100 ng/ml of recombinant swine IL-6 into PZM3 medium increased the development rate of parthenotes to the blastocyst stage (P<0.05). When supplemented with 10 ng/ml of recombinant swine IL-6, the number of parthenotes at the blastocyst stage increased (P<0.05) and apoptosis decreased (P<0.05). Real-time RT-PCR experiments revealed that the addition of recombinant swine IL-6 decreased the mRNA expression of the pro-apoptotic gene Caspase3 (P<0.01) but increased the expression levels of the anti-apoptotic genes Bcl2l1 and Survivin. IL-6 receptors and Stat3 mRNA expression were upregulated after treatment with 10 ng/ml recombinant swine IL-6. Immunoblots and fluorescence labeling experiments showed that the levels of phosphorylated Stat3 were upregulated. These results suggest that recombinant swine IL-6 prevents apoptosis of porcine parthenotes and enhances porcine embryo viability through the IL-6/Stat3 signaling pathway in vitro.

Stromal-derived IL-6 alters the balance of myeloerythroid progenitors during Toxoplasma gondii infection

Inflammation alters hematopoiesis, often by decreasing erythropoiesis and enhancing myeloid output. The mechanisms behind these changes and how the BM stroma contributes to this process are active areas of research. In this study, we examine these questions in the setting of murine Toxoplasma gondii infection. Our data reveal that infection alters early myeloerythroid differentiation, blocking erythroid development beyond the Pre MegE stage, while expanding the GMP population. IL-6 was found to be a critical mediator of these differences, independent of hepcidin-induced iron restriction. Comparing the BM with the spleen showed that the hematopoietic response was driven by the local microenvironment, and BM chimeras demonstrated that radioresistant cells were the relevant source of IL-6 in vivo. Finally, direct ex vivo sorting revealed that VCAM(+)CD146(lo) BM stromal fibroblasts significantly increase IL-6 secretion after infection. These data suggest that BMSCs regulate the hematopoietic changes during inflammation via IL-6.

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.

Animal models for Toxoplasma gondii infection

Toxoplasma gondii is a protozoan of worldwide distribution. This unit describes murine models of acute T. gondii infection, toxoplasmic encephalitis, and Toxoplasma retinochoroiditis. T. gondii infection in SCID mice allows the study of T cell-independent mechanisms of defense. The uracil auxotroph strain cps1-1 and temperature-sensitive mutant strains of T. gondii allow studies of immunization and adoptive transfer. In vivo study of parasite host-interaction is possible with the use of parasites that express fluorescent proteins and model antigens, plus the use of transgenic mice that express the appropriate T cell receptor and fluorescently labeled leukocytes. Parasites that express bioluminescent markers make it possible to study the dynamics of infection in real time using bioluminescence imaging. Support protocols present methodology for evaluation of progression of infection and immune response to the parasite, the maintenance of T. gondii tissue cysts and tachyzoites, as well as preparation of T. gondii lysate antigens.

Interferon-gamma- and perforin-mediated immune responses for resistance against Toxoplasma gondii in the brain

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes various diseases, including lymphadenitis, congenital infection of fetuses and life-threatening toxoplasmic encephalitis in immunocompromised individuals. Interferon-gamma (IFN-γ)-mediated immune responses are essential for controlling tachyzoite proliferation during both acute acquired infection and reactivation of infection in the brain. Both CD4+ and CD8+ T cells produce this cytokine in response to infection, although the latter has more potent protective activity. IFN-γ can activate microglia, astrocytes and macrophages, and these activated cells control the proliferation of tachyzoites using different molecules, depending on cell type and host species. IFN-γ also has a crucial role in the recruitment of T cells into the brain after infection by inducing expression of the adhesion molecule VCAM-1 on cerebrovascular endothelial cells, and chemokines such as CXCL9, CXCL10 and CCL5. A recent study showed that CD8+ T cells are able to remove T. gondii cysts, which represent the stage of the parasite in chronic infection, from the brain through their perforin-mediated activity. Thus, the resistance to cerebral infection with T. gondii requires a coordinated network using both IFN-γ- and perforin-mediated immune responses. Elucidating how these two protective mechanisms function and collaborate in the brain against T. gondii will be crucial in developing a new method to prevent and eradicate this parasitic infection.

Redundancy of interleukin-6 in the differentiation of T cell and monocyte subsets during cutaneous leishmaniasis

Leishmania (L.) major is a protozoan parasite that infects mammalian hosts and causes a spectrum of disease manifestations that is strongly associated with the genetic background of the host. Interleukin (IL)-6 is an acute phase proinflammatory cytokine, known in vitro to be involved in the inhibition of the generation of regulatory T cells. IL-6-deficient mice were infected with L. major, and T cell and monocyte subsets were analyzed with flow cytometry. Our data show that at the site of infection in the footpad and in the draining popliteal lymph node, numbers of regulatory T cells remain unchanged between WT and IL-6-deficient mice. However, the spleens of IL-6(-/-) mice contained fewer regulatory T cells after infection with L. major. The development of cutaneous lesions is similar between WT and IL-6-deficient mice, while parasite burden in IL-6(-/-) mice is reduced compared to WT. The development of IFN-γ or IL-10 producing T cells is similar in IL-6(-/-) mice. Despite a comparable adaptive T cell response, IL-6-deficient mice develop an earlier peak of some inflammatory cytokines than WT mice. This data indicate that the role of IL-6 in the differentiation of regulatory T cells is complex in vivo, and the effect of an absence of this cytokine can be counter-intuitive.

Migratory activation of primary cortical microglia upon infection with Toxoplasma gondii

Disseminated toxoplasmosis in the central nervous system (CNS) is often accompanied by a lethal outcome. Studies with murine models of infection have focused on the role of systemic immunity in control of toxoplasmic encephalitis, while knowledge remains limited on the contributions of resident cells with immune functions in the CNS. In this study, the role of glial cells was addressed in the setting of recrudescent Toxoplasma infection in mice. Activated astrocytes and microglia were observed in the close vicinity of foci with replicating parasites in situ in the brain parenchyma. Toxoplasma gondii tachyzoites were allowed to infect primary microglia and astrocytes in vitro. Microglia were permissive to parasite replication, and infected microglia readily transmigrated across transwell membranes and cell monolayers. Thus, infected microglia, but not astrocytes, exhibited a hypermotility phenotype reminiscent of that recently described for infected dendritic cells. In contrast to gamma interferon-activated microglia, Toxoplasma-infected microglia did not upregulate major histocompatibility complex (MHC) class II molecules and the costimulatory molecule CD86. Yet Toxoplasma-infected microglia and astrocytes exhibited increased sensitivity to T cell-mediated killing, leading to rapid parasite transfer to effector T cells in vitro. We hypothesize that glial cells and T cells, besides their role in triggering antiparasite immunity, may also act as "Trojan horses," paradoxically facilitating dissemination of Toxoplasma within the CNS. To our knowledge, this constitutes the first report of migratory activation of a resident CNS cell by an intracellular parasite.

IL-6 mediates the susceptibility of glycoprotein 130 hypermorphs to Toxoplasma gondii

IL-6 and IL-27 are closely related cytokines that play critical but distinct roles during infection with Toxoplasma gondii. Thus, IL-6 is required for the development of protective immunity to this pathogen, whereas IL-27 is required to limit infection-induced pathology. Paradoxically, these factors both signal through gp130, but little is known about how the signals downstream of gp130 are integrated to coordinate the immune response to infection. To better understand these events, gp130 Y757F mice that have a mutation in gp130 at the binding site for suppressor of cytokine signaling 3, a critical negative regulator of gp130 signaling, were infected with T. gondii. These mutant mice were acutely susceptible to this challenge, characterized by an early defect in the production of IL-12 and IFN-γ and increased parasite burdens. Consistent with the reduced IL-12 levels, IL-6, but not other gp130 cytokines, was a potent antagonist of IL-12 production by gp130 Y757F macrophages and dendritic cells in vitro. Moreover, in gp130 Y757F mice, blocking IL-6 in vivo, or administration of rIL-12, during infection restored IFN-γ production and protective immunity. Collectively, these studies highlight that a failure to abbreviate IL-6-mediated gp130 signaling results in a profound anti-inflammatory signal that blocks the generation of protective immunity to T. gondii.

Intracellular transport of Toxoplasma gondii through the blood-brain barrier

Toxoplasma gondii establishes latent infection in the central nervous system of immunocompentent hosts. Toxoplasmic encephalitis is a life threatening reactivation of latent infection in the brain of immunocompromised patients. To further understand the mechanisms of entry into the brain of T. gondii we investigated host molecules and cells involved in the passage of the parasite through the blood-brain barrier. First, using microarrays brain endothelial cells were found to upregulate, among others, chemokines and adhesion molecules following infection with tachyzoites. Using flow cytometry we observed upregulated ICAM-1 expression on the surface of brain endothelial cells following infection; ICAM-1 expression was further increased after pre-incubation with IFN-γ. Compared to RH tachyzoites, ME49 tachyzoites induced a stronger upregulation of ICAM-1 and an earlier and stronger IL-6 and MCP-1 secretion by brain endothelial cells. Using an in vitro coculture model of the BBB (primary glia cells and brain endothelial cells) we found a stronger migration of infected antigen-presenting cells compared to lymphocytes (4.63% vs. 0.6% of all cells) across the BBB. Among all antigen-presenting cells CD11b(+)/CD11c(+) cells showed the highest infection rate, whereas the majority of infected cells that migrated through the blood-brain barrier were CD11b(+)/CD11c(-) cells. Infection of PBMCs with type I or type II Toxoplasma strains resulted in similar patterns of cell migration across the in vitro BBB model. In conclusion, these results suggest that T. gondii modulates gene expression of brain endothelial cells to promote its own migration through the blood-brain barrier in a 'Trojan horse' manner. Cells expressing CD11b either with or without CD11c are likely candidate cells for the intracellular transport of T. gondii across the BBB. T. gondii type I and type II strains induced similar migration patterns of antigen-presenting cells across the in vitro BBB.