Immunisation with a major Trypanosoma cruzi antigen promotes pro-inflammatory cytokines, nitric oxide production and increases TLR2 expression

Immunopathological Mechanisms Underlying Cardiac Damage in Chagas Disease

In Chagas disease, the mechanisms involved in cardiac damage are an active field of study. The factors underlying the evolution of lesions following infection by Trypanosoma cruzi and, in some cases, the persistence of its antigens and the host response, with the ensuing development of clinically observable cardiac damage, are analyzed in this review.

Differential Expression of Immune Response Genes in Asymptomatic Chronic Chagas Disease Patients Versus Healthy Subjects

Infection by the Trypanosoma cruzi parasite causes Chagas disease and triggers multiple immune mechanisms in the host to combat the pathogen. Chagas disease has a variable clinical presentation and progression, producing in the chronic phase a fragile balance between the host immune response and parasite replication that keeps patients in a clinically silent asymptomatic stage for years. Since the parasite is intracellular and replicates within cells, the cell-mediated response of the host adaptive immunity plays a critical role. This function is mainly orchestrated by T lymphocytes, which recognize parasite antigens and promote specific functions to control the infection. However, little is known about the immunological markers associated with this asymptomatic stage of the disease. In this large-scale analysis, the differential expression of 106 immune system-related genes has been analyzed using high-throughput qPCR in T. cruzi antigen-stimulated PBMC from chronic Chagas disease patients with indeterminate form (IND) and healthy donors (HD) from endemic and non-endemic areas of Chagas disease. This analysis revealed that there were no differences in the expression level of most genes under study between healthy donors from endemic and non-endemic areas determined by PCA and differential gene expression analysis. Instead, PCA revealed the existence of different expression profiles between IND patients and HD (p < 0.0001), dependent on the 32 genes included in PC1. Differential gene expression analysis also revealed 23 upregulated genes (expression fold change > 2) and 11 downregulated genes (expression fold change < 0.5) in IND patients versus HD. Enrichment analysis showed that several upregulated genes in IND patients participate in relevant immunological pathways such as antigen-dependent B cell activation, stress induction of HSP regulation, NO2-dependent IL12 pathway in NK cells, and cytokine-inflammatory response. The antigen-specific differential gene expression profile detected in these patients and the relevant immunological pathways that seem to be activated could represent potential biomarkers of the asymptomatic form of Chagas disease, helpful to diagnosis and infection control.

Wnt Signaling Plays a Key Role in the Regulation of the Immune Response and Cardiac Damage during Trypanosoma cruzi Infection

Chagas cardiomyopathy is the consequence of a compromised electrical and mechanical cardiac function, with parasite persistence, unbalanced inflammation, and pathological tissue remodelling, being intricately related to myocardial aggression and impaired function. Recent studies have shown that Wnt signaling pathways play a critical role in the pathogenesis of cardiac and vascular diseases. In addition, we have reported that Trypanosoma cruzi infection activates Wnt signaling to promote intracellular replication of the parasites in macrophages, with the treatment of mice with IWP-L6 (an inhibitor of the O-acyl-transferase, PORCN, responsible for the post-translational modifications necessary for Wnt protein secretion) being able to diminish parasitemia and tissue parasitism. Here, we show that inhibition of Wnt signaling during the acute phase of T. cruzi infection controls the parasite replication, inhibits the development of parasite-prone and fibrosis-prone Th2-type immune response, and prevents the development of cardiac abnormalities characteristics of chronic Chagas disease. Our results suggest that the Wnt signaling pathway might be a potential target to prevent the development of T. cruzi-induced cardiomyopathy.

Heterologous Chimeric Construct Comprising a Modified Bacterial Superantigen and a Cruzipain Domain Confers Protection Against Trypanosoma cruzi Infection

Chagas disease is an endemic chronic parasitosis in Latin America affecting more than 7 million people. Around 100 million people are currently at risk of acquiring the infection; however, no effective vaccine has been developed yet. Trypanosoma cruzi is the etiological agent of this parasitosis and as an intracellular protozoan it can reside within different tissues, mainly muscle cells, evading host immunity and allowing progression towards the chronic stage of the disease. Considering this intracellular parasitism triggers strong cellular immunity that, besides being necessary to limit infection, is not sufficient to eradicate the parasite from tissues, a differential immune response is required and new strategies for vaccines against Chagas disease need to be explored. In this work, we designed, cloned and expressed a chimeric molecule, named NCz-SEGN24A, comprising a parasite antigen, the N-terminal domain of the major cysteine protease of T. cruzi, cruzipain (Nt-Cz), and a non-toxic form of the staphylococcal superantigen (SAg) G, SEG, with the residue Asn24 mutated to Ala (N24A). The mutant SAg SEGN24A, retains its ability to trigger classical activation of macrophages without inducing T cell apoptosis. To evaluate, as a proof of concept, the immunogenicity and efficacy of the chimeric immunogen vs. its individual antigens, C3H mice were immunized intramuscularly with NCz-SEGN24A co-adjuvanted with CpG-ODN, or the recombinant proteins Nt-Cz plus SEGN24A with the same adjuvant. Vaccinated mice significantly produced Nt-Cz-specific IgG titers after immunization and developed higher IgG2a than IgG1 titers. Specific cell-mediated immunity was assessed by in-vivo DTH and significant responses were obtained. To assess protection, mice were challenged with trypomastigotes of T. cruzi. Both schemes reduced the parasite load throughout the acute phase, but only mice immunized with NCz-SEGN24A showed significant differences against control; moreover, these mice maintained 100% survival. These results encourage testing mutated superantigens fused to specific antigens as immune modulators against pathogens.

Polysaccharide from black currant (Ribes nigrum L.) stimulates dendritic cells through TLR4 signaling

Black currant (Ribes nigrum) has various beneficial properties for human health. In particular, polysaccharide from black currant was found to be an immunostimulating food ingredient and was reported to have antitumor activity in a mouse model. We named it cassis polysaccharide (CAPS). In a previous study, CAPS administration caused tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) production in vitro and in vivo, but the immunological mechanism of CAPS was not demonstrated. In this study, we revealed the CAPS immunostimulating mechanism in vitro. First, we found that CAPS activated dendritic cells (DCs). Second, we investigated whether it depends on Toll-like receptor 4 (TLR4) and myeloid differentiation primary response (Myd). We concluded that CAPS stimulates DCs through Myd88 depending TLR4 signaling and activates Th1-type cytokine release.

Interactions between Trypanosoma cruzi Secreted Proteins and Host Cell Signaling Pathways

Chagas disease is one of the prevalent neglected tropical diseases, affecting at least 6-7 million individuals in Latin America. It is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted to vertebrate hosts by blood-sucking insects. After infection, the parasite invades and multiplies in the myocardium, leading to acute myocarditis that kills around 5% of untreated individuals. T. cruzi secretes proteins that manipulate multiple host cell signaling pathways to promote host cell invasion. The primary secreted lysosomal peptidase in T. cruzi is cruzipain, which has been shown to modulate the host immune response. Cruzipain hinders macrophage activation during the early stages of infection by interrupting the NF-kB P65 mediated signaling pathway. This allows the parasite to survive and replicate, and may contribute to the spread of infection in acute Chagas disease. Another secreted protein P21, which is expressed in all of the developmental stages of T. cruzi, has been shown to modulate host phagocytosis signaling pathways. The parasite also secretes soluble factors that exert effects on host extracellular matrix, such as proteolytic degradation of collagens. Finally, secreted phospholipase A from T. cruzi contributes to lipid modifications on host cells and concomitantly activates the PKC signaling pathway. Here, we present a brief review of the interaction between secreted proteins from T. cruzi and the host cells, emphasizing the manipulation of host signaling pathways during invasion.

Autoimmune pathogenesis of Chagas heart disease: looking back, looking ahead

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of individuals infected with the protozoan parasite Trypanosoma cruzi. Since the discovery of T. cruzi by Carlos Chagas >100 years ago, much has been learned about Chagas disease pathogenesis; however, the outcome of T. cruzi infection is highly variable and difficult to predict. Many mechanisms have been proposed to promote tissue inflammation, but the determinants and the relative importance of each have yet to be fully elucidated. The notion that some factor other than the parasite significantly contributes to the development of myocarditis was hypothesized by the first physician-scientists who noted the conspicuous absence of parasites in the hearts of those who succumbed to Chagas disease. One of these factors-autoimmunity-has been extensively studied for more than half a century. Although questions regarding the functional role of autoimmunity in the pathogenesis of Chagas disease remain unanswered, the development of autoimmune responses during infection clearly occurs in some individuals, and the implications that this autoimmunity may be pathogenic are significant. In this review, we summarize what is known about the pathogenesis of Chagas heart disease and conclude with a view of the future of Chagas disease diagnosis, pathogenesis, therapy, and prevention, emphasizing recent advances in these areas that aid in the management of Chagas disease.

Gene-deleted live-attenuated Trypanosoma cruzi parasites as vaccines to protect against Chagas disease

Chagas disease is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi. This illness is now becoming global, mainly due to congenital transmission, and so far, there are no prophylactic or therapeutic vaccines available to either prevent or treat Chagas disease. Therefore, different approaches aimed at identifying new protective immunogens are urgently needed. Live vaccines are likely to be more efficient in inducing protection, but safety issues linked with their use have been raised. The development of improved protozoan genetic manipulation tools and genomic and biological information has helped to increase the safety of live vaccines. These advances have generated a renewed interest in the use of genetically attenuated parasites as vaccines against Chagas disease. This review discusses the protective capacity of genetically attenuated parasite vaccines and the challenges and perspectives for the development of an effective whole-parasite Chagas disease vaccine.

Experimental Chagas disease. Innate immune response in Balb/c mice previously vaccinated with Trypanosoma rangeli. I. The macrophage shows immunological memory: Reality or fiction?

Chagas' disease, caused by Trypanosoma cruzi, is a major vector borne health problem in Latin America and an emerging or re-emerging infectious disease in several countries. Immune response to T. cruzi infection is highly complex and involves many components, both regulators and effectors. Although different parasites have been shown to activate different mechanisms of innate immunity, T. cruzi is often able to survive and replicate in its host because they are well adapted to resisting host defences. An experimental model for vaccinating mice with Trypanosoma rangeli, a parasite closely related to T. cruzi, but nonpathogenic to humans, has been designed in our laboratory, showing protection against challenge with T. cruzi infection. The aim of this work was to analyze some mechanisms of the early innate immune response in T. rangeli vaccinated mice challenged with T. cruzi. For this purpose, some interactions were studied between T. cruzi and peritoneal macrophages of mice vaccinated with T. rangeli, infected or not with T. cruzi and the levels of some molecules or soluble mediators which could modify these interactions. The results in vaccinated animals showed a strong innate immune response, where the adherent cells of the vaccinated mice revealed important phagocytic activity, and some soluble mediator (Respiratory Burst: significantly increase, p ≤ 0.03; NO: the levels of vaccinated animals were lower than those of the control group; Arginasa: significantly increase, p ≤ 0.04). The results showed an important role in the early elimination of the parasites and their close relation with the absence of histological lesions that these animals present with regard to the only infected mice. This behaviour reveals that the macrophages act with some type of memory, recognizing the antigens to which they have previously been exposed, in mice were vaccinated with T. rangeli, which shares epitopes with T. cruzi.

Production of cytokine and chemokines by human mononuclear cells and whole blood cells after infection with Trypanosoma cruzi

INTRODUCTION: The innate immune response is the first mechanism of protection against Trypanosoma cruzi, and the interaction of inflammatory cells with parasite molecules may activate this response and modulate the adaptive immune system. This study aimed to analyze the levels of cytokines and chemokines synthesized by the whole blood cells (WBC) and peripheral blood mononuclear cells (PBMC) of individuals seronegative for Chagas disease after interaction with live T. cruzi trypomastigotes. METHODS: IL-12, IL-10, TNF-α, TGF-β, CCL-5, CCL-2, CCL-3, and CXCL-9 were measured by ELISA. Nitrite was determined by the Griess method. RESULTS: IL-10 was produced at high levels by WBC compared with PBMC, even after incubation with live trypomastigotes. Production of TNF-α by both PBMC and WBC was significantly higher after stimulation with trypomastigotes. Only PBMC produced significantly higher levels of IL-12 after parasite stimulation. Stimulation of cultures with trypomastigotes induced an increase of CXCL-9 levels produced by WBC. Nitrite levels produced by PBMC increased after the addition of parasites to the culture. CONCLUSIONS: Surface molecules of T. cruzi may induce the production of cytokines and chemokines by cells of the innate immune system through the activation of specific receptors not evaluated in this experiment. The ability to induce IL-12 and TNF-α contributes to shift the adaptive response towards a Th1 profile.

Effects of the organophosphate insecticides phosmet and chlorpyrifos on trophoblast JEG-3 cell death, proliferation and inflammatory molecule production

Epidemiological data have associated environmental organophosphate insecticide (OP) exposure during pregnancy with fetal growth deficits. To better understand OP injury that may adversely affect pregnancy, we used the JEG-3 choriocarcinoma cell line, which provide a recognized in vitro model to study placental function. The effects of the OP phosmet (Pm) and chlorpyrifos (Cp) on JEG-3 cells viability, proliferation, cell cycle and inflammatory molecule production were evaluated. Both insecticides affected cellular viability in a concentration- and time-dependent manner, inducing apoptosis and decreasing [(3)H]-thymidine incorporation. However, only Pm reduced DNA synthesis independently of cellular death and decreased the cell percentage at the S-phase. Unlike apoptosis, TNFα production varied with the concentration tested, suggesting that other TNFα independent mechanisms might trigger cell death. No induction of the inflammatory molecule nitric oxide was detected. The mRNA levels of pro-inflammatory IL-6, IL-17 and the anti-inflammatory IL-13 cytokines were differentially modulated. These findings show that Pm and Cp generate a specific toxicity signature, altering cell viability and inducing an inflammatory cytokine profile, suggesting that trophoblasts may represent a possible target for OP adverse effects.

The role of Toll-like receptors and adaptive immunity in the development of protective or pathological immune response triggered by the Trypanosoma cruzi protozoan

Trypanosoma cruzi, the causal agent of Chagas disease, is an intracellular protozoan parasite that predominantly invades macrophages and cardiomyocytes, leading to persistent infection. Several members of the Toll-like receptor family are crucial for innate immunity to infection and are involved in maintaining tissue homeostasis. This review focuses on recent experimental findings of the innate and adaptive immune response in controlling the parasite and/or in generating heart and liver tissue injury. We also describe the importance of the host’s genetic background in the outcome of the disease and emphasize the importance of studying the response to specific parasite antigens. Understanding the dual participation of the immune response may contribute to the design of new therapies for Chagas disease.

Nonimmune Cells Contribute to Crosstalk between Immune Cells and Inflammatory Mediators in the Innate Response to Trypanosoma cruzi Infection

Chagas myocarditis, which is caused by infection with the intracellular parasite Trypanosoma cruzi, remains the major infectious heart disease worldwide. Innate recognition through toll-like receptors (TLRs) on immune cells has not only been revealed to be critical for defense against T. cruzi but has also been involved in triggering the pathology. Subsequent studies revealed that this parasite activates nucleotide-binding oligomerization domain- (NOD-)like receptors and several particular transcription factors in TLR-independent manner. In addition to professional immune cells, T. cruzi infects and resides in different parenchyma cells. The innate receptors in nonimmune target tissues could also have an impact on host response. Thus, the outcome of the myocarditis or the inflamed liver relies on an intricate network of inflammatory mediators and signals given by immune and nonimmune cells. In this paper, we discuss the evidence of innate immunity to the parasite developed by the host, with emphasis on the crosstalk between immune and nonimmune cell responses.

Intraphagosomal peroxynitrite as a macrophage-derived cytotoxin against internalized Trypanosoma cruzi: consequences for oxidative killing and role of microbial peroxiredoxins in infectivity

Macrophage-derived radicals generated by the NADPH oxidase complex and inducible nitric-oxide synthase (iNOS) participate in cytotoxic mechanisms against microorganisms. Nitric oxide ((•)NO) plays a central role in the control of acute infection by Trypanosoma cruzi, the causative agent of Chagas disease, and we have proposed that much of its action relies on macrophage-derived peroxynitrite (ONOO(-) + ONOOH) formation, a strong oxidant arising from the reaction of (•)NO with superoxide radical (O(2)(-)). Herein, we have shown that internalization of T. cruzi trypomastigotes by macrophages triggers the assembly of the NADPH oxidase complex to yield O(2)(-) during a 60-90-min period. This does not interfere with IFN-γ-dependent iNOS induction and a sustained (•)NO production (∼24 h). The major mechanism for infection control via reactive species formation occurred when (•)NO and O(2)() were produced simultaneously, generating intraphagosomal peroxynitrite levels compatible with microbial killing. Moreover, biochemical and ultrastructural analysis confirmed cellular oxidative damage and morphological disruption in internalized parasites. Overexpression of cytosolic tryparedoxin peroxidase in T. cruzi neutralized macrophage-derived peroxynitrite-dependent cytotoxicity to parasites and favored the infection in an animal model. Collectively, the data provide, for the first time, direct support for the action of peroxynitrite as an intraphagosomal cytotoxin against pathogens and the premise that microbial peroxiredoxins facilitate infectivity via decomposition of macrophage-derived peroxynitrite.

Cruzain : the path from target validation to the clinic

Cruzain is the major papain-like cysteine protease of Trypanosoma cruzi, the etiological agent causing Chagas' disease in humans in South America. Cruzain is indispensable for the survival and propagation of this protozoan parasite and therefore, it has attracted considerable interest as a potential drug target. This chapter charts the path from the initial identification of this proteases activity and its validation as a bone fide drug target to the arduous task of the discovery of an inhibitor targeting this protease and finally the path towards the clinic.

Splenectomy increases mortality in murine Trypanosoma cruzi infection

The spleen is a secondary lymphoid organ that harbours a variety of cells such as T and B lymphocytes and antigen-presenting cells important to immune response development. In this study, we evaluated the impact of spleen removal in the immune response to experimental Trypanosoma cruzi infection. C57BL/6 mice were infected with Y strain of the parasite and infection was followed daily. Mice that underwent splenectomy had fewer parasites in peripheral blood at the peak of infection; however, mortality was increased. Histological analysis of heart and liver tissues revealed an increased number of parasites and inflammatory infiltrates at these sites. Spleen removal was associated with reduction in IFN-γ and TNF-α production during infection as well as with a decrease in specific antibody secretion. Haematological disorders were also detected. Splenectomized mice exhibited severe anaemia and decreased bone marrow cell numbers. Our results indicate that spleen integrity is critical in T. cruzi infection for the immune response against the parasite, as well as for the control of bone marrow haematological function.

Induction of NADPH oxidase activity and reactive oxygen species production by a single Trypanosoma cruzi antigen

Trypanosoma cruzi is an intracellular protozoan parasite that predominantly invades mononuclear phagocytes and is able to establish a persistent infection. The production of reactive oxygen species (ROS) by phagocytes is an innate defence mechanism against microorganisms. It has been postulated that ROS such as superoxide anion (O(2)), hydrogen peroxide and peroxynitrite, may play a crucial role in the control of pathogen growth. However, information on parasite molecules able to trigger ROS production is scarce. In this work, we investigated whether cruzipain, an immunogenic glycoprotein from T. cruzi, was able to trigger the oxidative burst by murine cells. By employing chemiluminiscense and flow-cytometric analysis, we demonstrated that cruzipain induced ROS production in splenocytes from non-immune and cruzipain immune C57BL/6 mice and in a Raw 264.7 macrophage cell line. We also identified an O(2)(-) molecule as one of the ROS produced after antigen stimulation. Cruzipain stimulation induced NOX2 (gp91(phox)) and p47(phox) expression, as well as the co-localisation of both NADPH oxidase enzyme subunits. In the current study, we provide evidence that cruzipain not only increased ROS production but also promoted IL-6 and IL-1β cytokine production. Taken together, we believe these results demonstrate for the first time that cruzipain, a single parasite molecule, in the absence of infection, favors oxidative burst in murine cells. This represents an important advance in the knowledge of parasite molecules that interact with the phagocyte defence mechanism.

Angiotensin-converting enzyme limits inflammation elicited by Trypanosoma cruzi cysteine proteases: a peripheral mechanism regulating adaptive immunity via the innate kinin pathway

Tissue injury by pathogens induces a stereotyped inflammatory response that alerts the innate immune system of the potential threat to host integrity. Here, we review knowledge emerging from investigations of the role of the kinin system in the mechanisms that link innate to the adaptive phase of immunity. Progress in this field started with results demonstrating that bradykinin is an endogenous danger signal that induces dendritic cell (DC) maturation via G protein-coupled bradykinin B2 receptors (B2R). The immunostimulatory role of kinins was recently confirmed in two different mouse models of Trypanosoma cruzi infection, a parasitic protozoan equipped with kinin-releasing cysteine proteases (cruzipain). Infection by the intraperitoneal route showed that DCs from B2R-/- mice (susceptible phenotype) failed to sense kinin 'danger' signals proteolytically released by parasites, explaining why these mutant mice display lower frequencies of interferon-gamma-producing effector T-cells. Studies of the dynamics of inflammation in the subcutaneous model of infection revealed that the balance between cruzipain and angiotensin-converting enzyme, respectively acting as kinin-generating and degrading enzymes, governs extent of DC maturation and TH1 development via the B2R-dependent innate pathway. Studies of the kinin role in immunity may shed light on the relationship between proteolytic networks and the cytokine circuits that guide T-cell development.