The role of parasite persistence in pathogenesis of Chagas heart disease

The time has come for a vaccine against Chagas disease

Despite many studies, there is still no vaccines for Chagas Disease (CD), which affects approximately 7 million people mainly in Latin America. To make matters worse, the only two drugs available have proved efficacy only when administered during the acute phase of the disease. Here, we discuss recent advances towards the development of a CD vaccine including (i) better understanding of the role of elements involved in immune responses and host defense against Trypanosoma cruzi; (ii) molecular characterization of parasite genetic diversity and the biochemical nature of T. cruzi antigens involved in protective immune responses; and (iii) the use of novel vaccine platforms that show high efficacy in experimental models. Other aspects such as the role of parasite-induced inflammation in the pathogenesis of CD is also under intense scrutiny. An essential issue discussed in this Viewpoint refers to the main use of a vaccine for CD, i.e., whether this vaccine should be used for prophylactic purposes, combined therapy to improve drug efficacy and parasitological cure, or to re-orient the immune and inflammatory response. Finally, we emphasize the necessity to attract the interest of both private and public pharmaceutical companies to translate all the pre-clinical studies into a much-needed CD vaccine.

An Update on Vaccines Against Trypanosoma cruzi and Chagas Disease

Chagas disease (CD) is a global health concern, with no existing therapies to prophylactically treat adults traveling to endemic countries or those who may already be infected with Trypanosoma cruzi. The economic burden of Chagas cardiomyopathy and heart failure, due to healthcare costs and lost productivity from premature deaths, provides a strong rationale for investment in the development of immune therapies against CD. Vaccine efficacy is proposed to depend heavily on the induction of a robust Th1 response for the clearance of intracellular pathogens like T. cruzi. In this review, updated information on the efforts for vaccine development against CD is provided.

mosGraphGPT: a foundation model for multi-omic signaling graphs using generative AI

Generative pretrained models represent a significant advancement in natural language processing and computer vision, which can generate coherent and contextually relevant content based on the pre-training on large general datasets and fine-tune for specific tasks. Building foundation models using large scale omic data is promising to decode and understand the complex signaling language patterns within cells. Different from existing foundation models of omic data, we build a foundation model, mosGraphGPT, for multi-omic signaling (mos) graphs, in which the multi-omic data was integrated and interpreted using a multi-level signaling graph. The model was pretrained using multi-omic data of cancers in The Cancer Genome Atlas (TCGA), and fine-turned for multi-omic data of Alzheimer's Disease (AD). The experimental evaluation results showed that the model can not only improve the disease classification accuracy, but also is interpretable by uncovering disease targets and signaling interactions. And the model code are uploaded via GitHub with link: https://github.com/mosGraph/mosGraphGPT.

Benznidazole-Loaded Polymeric Nanoparticles for Oral Chemotherapeutic Treatment of Chagas Disease

Chagas disease (CD) is a worldwide public health problem. Benznidazole (BZ) is the drug used to treat it. However, in its commercial formulation, it has significant side effects and is less effective in the chronic phase of the infection. The development of particulate systems containing BZ is therefore being promoted. The objective of this investigation was to develop polymeric nanoparticles loaded with BZ and examine their trypanocidal impact in vitro. Two formulas (BNP1 and BNP2) were produced through double emulsification and freeze drying. Subsequent to physicochemical and morphological assessment, both formulations exhibited adequate yield, average particle diameter, and zeta potential for oral administration. Cell viability was assessed in H9C2 and RAW 264.7 cells in vitro, revealing no cytotoxicity in cardiomyocytes or detrimental effects in macrophages at specific concentrations. BNP1 and BNP2 enhanced the effect of BZ within 48 h using a treatment of 3.90 μg/mL. The formulations notably improved NO reduction, particularly BNP2. The findings imply that the compositions are suitable for preclinical research, underscoring their potential as substitutes for treating CD. This study aids the quest for new BZ formulations, which are essential in light of the disregard for the treatment of CD and the unfavorable effects associated with its commercial product.

Fenofibrate Induces a Resolving Profile in Heart Macrophage Subsets and Attenuates Acute Chagas Myocarditis

Chagas disease, caused by Trypanosoma cruzi, stands as the primary cause of dilated cardiomyopathy in the Americas. Macrophages play a crucial role in the heart's response to infection. Given their functional and phenotypic adaptability, manipulating specific macrophage subsets could be vital in aiding essential cardiovascular functions including tissue repair and defense against infection. PPARα are ligand-dependent transcription factors involved in lipid metabolism and inflammation regulation. However, the role of fenofibrate, a PPARα ligand, in the activation profile of cardiac macrophages as well as its effect on the early inflammatory and fibrotic response in the heart remains unexplored. The present study demonstrates that fenofibrate significantly reduces not only the serum activity of tissue damage biomarker enzymes (LDH and GOT) but also the circulating proportions of pro-inflammatory monocytes (CD11b+ LY6Chigh). Furthermore, both CD11b+ Ly6Clow F4/80high macrophages (MΦ) and recently differentiated CD11b+ Ly6Chigh F4/80high monocyte-derived macrophages (MdMΦ) shift toward a resolving phenotype (CD206high) in the hearts of fenofibrate-treated mice. This shift correlates with a reduction in fibrosis, inflammation, and restoration of ventricular function in the early stages of Chagas disease. These findings encourage the repositioning of fenofibrate as a potential ancillary immunotherapy adjunct to antiparasitic drugs, addressing inflammation to mitigate Chagas disease symptoms.

Memory-like NK Cells Are a Critical Component of Vaccine-Induced Immunity to Trypanosoma cruzi Infection

Chagas disease by Trypanosoma cruzi infection is a major public health issue. The available therapeutic agents have limited efficacy and significant side effects. A reliable vaccine would reduce the threat of T. cruzi infections and prevent Chagas disease. Understanding the immune response to this infection would improve vaccine design. We previously demonstrated that adoptively transferred NK cells from mice immunized with highly attenuated T. cruzi, GFP-DDDHA strain, provided potent protection in naive recipients against secondary lethal challenge with various wild-type (WT) strains. To understand the importance of NK cells in protecting mice against T. cruzi infection, we performed an in-depth characterization of NK cell phenotype, responses, and memory-like traits during acute infections due to GFP-DDDHA and WT strains and in immunized mice during a recall response to a WT lethal challenge. NK cells robustly expanded and became more mature and cytolytic during the GFP-DDDHA strain immunization. NK cells in immunized mice responded more robustly after WT lethal challenge than during an acute primary WT infection. In addition, protection by immunization with the GFP-DDDHA strain is significantly weakened in NK cell-deficient mice and did not prevent parasitemia from WT lethal challenge, indicating that NK cells with memory-like traits were a critical component for early control of WT lethal challenge. Prior T. cruzi vaccine development studies have not included studies of this rapid NK response. These findings provide insights into overcoming existing challenges in developing a safe and effective vaccine to prevent this infection.

Influence of CK2 protein kinase activity on the interaction between Trypanosoma cruzi and its vertebrate and invertebrate hosts

Chagas disease, endemic from Latin America, is caused by Trypanosoma cruzi and is transmitted by triatomine feces. This parasite undergoes complex morphological changes through its life cycle, promoted by significant changes in signal transduction pathways. The activity of protein kinase CK2 has been described in trypanosomatids. Using a specific peptide and radioactive ATP, we identified CK2 activity on the cellular surface and the cytoplasmic content in Trypanosoma cruzi, apart from the secreted form. Dephosphorylated casein promoted an increase of 48% in the secreted CK2 activity. Total extract of peritoneal macrophages from BALB/c and inactivated human serum promoted an increase of 67% and 36%, respectively, in this activity. The protein secreted by parasites was purified by HPLC and had shown compatibility with the catalytic subunit of mammalian CK2. Incubation of the parasites with CK2 inhibitors, added to the culture medium, prevented their growth. The opposite was observed when CK2 activators were used. Results of interaction between Trypanosoma cruzi and the gut of the vector have revealed that, in the presence of CK2 inhibitors, there is a reduction in the association rate. A similar inhibition profile was seen in the Trypanosoma cruzi-macrophages interaction, confirming the importance of this enzyme in the life cycle of this protozoan.

Clinical trials for Chagas disease: etiological and pathophysiological treatment

Chagas disease (CD) is caused by the flagellate protozoan Trypanosoma cruzi. It is endemic in Latin America. Nowadays around 6 million people are affected worldwide, and 75 million are still at risk. CD has two evolutive phases, acute and chronic. The acute phase is mostly asymptomatic, or presenting unspecific symptoms which makes it hard to diagnose. At the chronic phase, patients can stay in the indeterminate form or develop cardiac and/or digestive manifestations. The two trypanocide drugs available for the treatment of CD are benznidazole (BZ) and nifurtimox (NFX), introduced in the clinic more than five decades ago. WHO recommends treatment for patients at the acute phase, at risk of congenital infection, for immunosuppressed patients and children with chronic infection. A high cure rate is seen at the CD acute phase but better treatment schemes still need to be investigated for the chronic phase. There are some limitations within the use of the trypanocide drugs, with side effects occurring in about 40% of the patients, that can lead patients to interrupt treatment. In addition, patients with advanced heart problems should not be treated with BZ. This is a neglected disease, discovered 114 years ago that still has no drug effective for their chronic phase. Multiple social economic and cultural barriers influence CD research. The high cost of the development of new drugs, in addition to the low economical return, results in the lack of investment. More economic support is required from governments and pharmaceutical companies on the development of more research for CD treatment. Two approaches stand out: repositioning and combination of drugs, witch drastically decrease the cost of this process, when compared to the development of a new drug. Here we discuss the progress of the clinical trials for the etiological and pathophysiological treatment for CD. In summary, more studies are needed to propose a new drug for CD. Therefore, BZ is still the best option for CD. The trials in course should clarify more about new treatment regimens, but it is already possible to indicate that dosage and time of treatment need to be adjusted.

Blimp-1 signaling pathways in T lymphocytes is essential to control the Trypanosoma cruzi infection-induced inflammation

In many infectious diseases, the pathogen-induced inflammatory response could result in protective immunity that should be regulated to prevent tissue damage and death. In fact, in Trypanosoma cruzi infection, the innate immune and the inflammatory response should be perfectly controlled to avoid significant lesions and death. Here, we investigate the role of Blimp-1 expression in T cells in resistance to T. cruzi infection. Therefore, using mice with Blimp-1 deficiency in T cells (CKO) we determined its role in the controlling parasites growth and lesions during the acute phase of infection. Infection of mice with Blimp-1 ablation in T cells resulted failure the cytotoxic CD8+ T cells and in marked Th1-mediated inflammation, high IFN-γ and TNF production, and activation of inflammatory monocyte. Interestingly, despite high nitric-oxide synthase activation (NOS-2), parasitemia and mortality in CKO mice were increased compared with infected WT mice. Furthermore, infected-CKO mice exhibited hepatic lesions characteristic of steatosis, with significant AST and ALT activity. Mechanistically, Blimp-1 signaling in T cells induces cytotoxic CD8+ T cell activation and restricts parasite replication. In contrast, Blimp-1 represses the Th1 response, leading to a decreased monocyte activation, less NOS-2 activation, and, consequently preventing hepatic damage and dysfunction. These data demonstrate that T. cruzi-induced disease is multifactorial and that the increased IFN-γ, NO production, and dysfunction of CD8+ T cells contribute to host death. These findings have important implications for the design of potential vaccines against Chagas disease.

Differential expression profile of genes involved in the immune response associated to progression of chronic Chagas disease

BACKGROUND

Patients with chronic Chagas disease present marked clinical and immunological heterogeneity. During the disease, multiple immune mechanisms are activated to fight the parasite. The purpose of this study was to investigate the expression patterns of genes involved in relevant immunological processes throughout the disease in patients with chronic Chagas disease.

METHODOLOGY/PRINCIPAL FINDINGS

High-throughput RT-qPCR with QuantStudio 12K Flex real-time PCR system was used to evaluate the expression of 106 immune-related genes in PBMC from a cohort of cardiac Chagas disease patients (CCC I), asymptomatic patients (IND) and healthy donors (HD) after being stimulated with T. cruzi soluble antigens. Principal component analysis (PCA), cluster analysis and volcano plots were used to identify differentially expressed genes. In addition, gene set enrichment analysis (GSEA) was employed to identify the enriched immunological pathways in which these genes are involved. PCA revealed the existence of a statistically divergent expression profile of the 36 genes correlated with PC1 between CCC I patients and HD (p < 0.0001). Differential gene expression analysis revealed upregulation of 41 genes (expression fold-change > 1.5) and downregulation of 14 genes (expression fold-change < 0.66) (p = 8.4x10-13 to p = 0.007) in CCC I patients versus HD. Furthermore, significant differences in the expression level of specific genes have been identified between CCC I and IND patients (8 up and 1 downregulated). GSEA showed that several upregulated genes in CCC I patients participate in immunological pathways such as antigen-dependent B cell activation, stress induction of HSP regulation, NO2-dependent IL12 pathway in NK cells, cytokines-inflammatory response and IL-10 anti-inflammatory signaling.

CONCLUSIONS

Cardiac Chagas disease patients show an antigen-specific differential gene expression profile in which several relevant immunological pathways seem to be activated. Assessment of gene expression profiles reveal unique insights into the immune response that occurs along chronic Chagas disease.

ASP-2/Trans-sialidase chimeric protein induces robust protective immunity in experimental models of Chagas' disease

Immunization with the Amastigote Surface Protein-2 (ASP-2) and Trans-sialidase (TS) antigens either in the form of recombinant protein, encoded in plasmids or human adenovirus 5 (hAd5) confers robust protection against various lineages of Trypanosoma cruzi. Herein we generated a chimeric protein containing the most immunogenic regions for T and B cells from TS and ASP-2 (TRASP) and evaluated its immunogenicity in comparison with our standard protocol of heterologous prime-boost using plasmids and hAd5. Mice immunized with TRASP protein associated to Poly-ICLC (Hiltonol) were highly resistant to challenge with T. cruzi, showing a large decrease in tissue parasitism, parasitemia and no lethality. This protection lasted for at least 3 months after the last boost of immunization, being equivalent to the protection induced by DNA/hAd5 protocol. TRASP induced high levels of T. cruzi-specific antibodies and IFNγ-producing T cells and protection was primarily mediated by CD8⁺ T cells and IFN-γ. We also evaluated the toxicity, immunogenicity, and efficacy of TRASP and DNA/hAd5 formulations in dogs. Mild collateral effects were detected at the site of vaccine inoculation. While the chimeric protein associated with Poly-ICLC induced high levels of antibodies and CD4⁺ T cell responses, the DNA/hAd5 induced no antibodies, but a strong CD8⁺ T cell response. Immunization with either vaccine protected dogs against challenge with T. cruzi. Despite the similar efficacy, we conclude that moving ahead with TRASP together with Hiltonol is advantageous over the DNA/hAd5 vaccine due to pre-existing immunity to the adenovirus vector, as well as the cost-benefit for development and large-scale production.

A functional assay using human whole blood and flow cytometry analysis to evaluate cytotoxicity and immunomodulatory effect of anti-Trypanosoma cruzi drugs

The discovery and development of new drugs for the treatment of Chagas disease is urgent due to the high toxicity and low cure efficacy, mainly during the chronic phase of this disease. Other chemotherapeutic approaches for Chagas disease treatment are being researched and require screening assays suitable for evaluating the effectivity of new biologically active compounds. This study aims to evaluate a functional assay using the internalization of epimastigotes forms of Trypanosoma cruzi by human peripheral blood leukocytes from healthy volunteers and analyses by flow cytometry of cytotoxicity, anti-T. cruzi activity, and immunomodulatory effect of benznidazole, ravuconazole, and posaconazole. The culture supernatant was used to measure cytokines (IL-1-β, IL-6, INF-γ, TNF and IL-10) and chemokines (MCP-1/CCL2, CCL5/RANTES and CXCL8/IL-8). The data showed a reduction in the internalization of T. cruzi epimastigote forms treated with ravuconazole, demonstrating its potential anti-T. cruzi activity. In addition, an increased amount of IL-10 and TNF cytokines was observed in the supernatant of cultures upon the addition of the drug, mainly IL-10 in the presence of benznidazole, ravuconazole and posaconazole, and TNF in the presence of ravuconazole and posaconazole. Moreover, the results revealed a decrease in the MCP-1/CCL2 index in cultures in the presence of benznidazole, ravuconazole, and posaconazole. A decrease in the CCL5/RANTES and CXCL8/IL-8 index in cultures with BZ, when compared to the culture without drugs, was also observed. In conclusion, the innovative functional test proposed in this study may be a valuable tool as a confirmatory test for selecting promising compounds identified in prospecting programs for new drugs for Chagas disease treatment.

Intranasal trans-sialidase-based vaccine against Trypanosoma cruzi triggers a mixed cytokine profile in the nasopharynx-associated lymphoid tissue and confers local and systemic immunogenicity

Trypanosoma cruzi, the agent of Chagas disease, can infect through conjunctive or oral mucosas. Therefore, the induction of mucosal immunity by vaccination is relevant not only to trigger local protection but also to stimulate both humoral and cell-mediated responses in systemic sites to control parasite dissemination. In a previous study, we demonstrated that a nasal vaccine based on a Trans-sialidase (TS) fragment plus the mucosal STING agonist c-di-AMP, was highly immunogenic and elicited prophylactic capacity. However, the immune profile induced by TS-based nasal vaccines at the nasopharyngeal-associated lymphoid tissue (NALT), the target site of nasal immunization, remains unknown. Hence, we analyzed the NALT cytokine expression generated by a TS-based vaccine plus c-di-AMP (TSdA+c-di-AMP) and their association with mucosal and systemic immunogenicity. The vaccine was administered intranasally, in 3 doses separated by 15 days each other. Control groups received TSdA, c-di-AMP, or the vehicle in a similar schedule. We demonstrated that female BALB/c mice immunized intranasally with TSdA+c-di-AMP boosted NALT expression of IFN-γ and IL-6, as well as IFN-β and TGF-β. TSdA+c-di-AMP increased TSdA-specific IgA secretion in the nasal passages and also in the distal intestinal mucosa. Moreover, T and B-lymphocytes from NALT-draining cervical lymph nodes and spleen showed an intense proliferation after ex-vivo stimulation with TSdA. Intranasal administration of TSdA+c-di-AMP provokes an enhancement of TSdA-specific IgG_2a and IgG₁ plasma antibodies, accompanied by an increase IgG_2a/IgG₁ ratio, indicative of a Th1-biased profile. In addition, immune plasma derived from TSdA+c-di-AMP vaccinated mice exhibit in-vivo and ex-vivo protective capacity. Lastly, TSdA+c-di-AMP nasal vaccine also promotes intense footpad swelling after local TSdA challenge. Our data support that TSdA+c-di-AMP nasal vaccine triggers a NALT mixed pattern of cytokines that were clearly associated with an evident mucosal and systemic immunogenicity. These data are useful for further understanding the immune responses elicited by the NALT following intranasal immunization and the rational design of TS-based vaccination strategies for prophylaxis against T. cruzi.

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.

Preclinical advances and the immunophysiology of a new therapeutic chagas disease vaccine

INTRODUCTION

Chronic infection with the protozoal parasite Trypanosoma cruzi leads to a progressive cardiac disease, known as chronic Chagasic cardiomyopathy (CCC). A new therapeutic Chagas disease vaccine is in development to augment existing antiparasitic chemotherapy drugs.

AREAS COVERED

We report on our current understanding of the underlying immunologic and physiologic mechanisms that lead to CCC, including parasite immune escape mechanisms that allow persistence and the subsequent inflammatory and fibrotic processes that lead to clinical disease. We report on vaccine design and the observed immunotherapeutic effects including induction of a balanced T_H1/T_H2/T_H17 immune response that leads to reduced parasite burdens and tissue pathology. Further, we report vaccine-linked chemotherapy, a dose sparing strategy to further reduce parasite burdens and tissue pathology.

EXPERT OPINION

Our vaccine-linked chemotherapeutic approach is a multimodal treatment strategy, addressing both the parasite persistence and the underlying deleterious host inflammatory and fibrotic responses that lead to cardiac dysfunction. In targeting treatment towards patients with chronic indeterminate or early determinate Chagas disease, this vaccine-linked chemotherapeutic approach will be highly economical and will reduce the global disease burden and deaths due to CCC.

Fenofibrate Increases the Population of Non-Classical Monocytes in Asymptomatic Chagas Disease Patients and Modulates Inflammatory Cytokines in PBMC

Chronic Chagas disease cardiomyopathy (CCC) is the most important clinical manifestation of infection with Trypanosma cruzi (T. cruzi) due to its frequency and effects on morbidity and mortality. Peripheral blood mononuclear cells (PBMC) infiltrate the tissue and differentiate into inflammatory macrophages. Advances in pathophysiology show that myeloid cell subpopulations contribute to cardiac homeostasis, emerging as possible therapeutic targets. We previously demonstrated that fenofibrate, PPARα agonist, controls inflammation, prevents fibrosis and improves cardiac function in a murine infection model. In this work we investigated the spontaneous release of inflammatory cytokines and chemokines, changes in the frequencies of monocyte subsets, and fenofibrate effects on PBMC of seropositive patients with different clinical stages of Chagas disease. The results show that PBMC from Chagas disease patients display higher levels of IL-12, TGF-β, IL-6, MCP1, and CCR2 than cells from uninfected individuals (HI), irrespectively of the clinical stage, asymptomatic (Asy) or with Chagas heart disease (CHD). Fenofibrate reduces the levels of pro-inflammatory mediators and CCR2 in both Asy and CHD patients. We found that CHD patients display a significantly higher percentage of classical monocytes in comparison with Asy patients and HI. Besides, Asy patients have a significantly higher percentage of non-classical monocytes than CHD patients or HI. However, no difference in the intermediate monocyte subpopulation was found between groups. Moreover, monocytes from Asy or CHD patients exhibit different responses upon stimulation in vitro with T. cruzi lysates and fenofibrate treatment. Stimulation with T. cruzi significantly increases the percentage of classical monocytes in the Asy group whereas the percentage of intermediate monocytes decreases. Besides, there are no changes in their frequencies in CHD or HI. Notably, stimulation with T. cruzi did not modify the frequency of the non-classical monocytes subpopulation in any of the groups studied. Moreover, fenofibrate treatment of T. cruzi-stimulated cells, increased the frequency of the non-classical subpopulation in Asy patients. Interestingly, fenofibrate restores CCR2 levels but does not modify HLA-DR expression in any groups. In conclusion, our results emphasize a potential role for fenofibrate as a modulator of monocyte subpopulations towards an anti-inflammatory and healing profile in different stages of chronic Chagas disease.

Cruzipain Sulfotopes-Specific Antibodies Generate Cardiac Tissue Abnormalities and Favor Trypanosoma cruzi Infection in the BALB/c Mice Model of Experimental Chagas Disease

Trypanosoma cruzi cruzipain (Cz) bears a C-terminal domain (C-T) that contains sulfated epitopes “sulfotopes” (GlcNAc6S) on its unique N-glycosylation site. The effects of in vivo exposure to GlcNAc6S on heart tissue ultrastructure, immune responses, and along the outcome of infection by T. cruzi, were evaluated in a murine experimental model, BALB/c, using three independent strategies. First, mice were pre-exposed to C-T by immunization. C-T-immunized mice (C-T_IM) showed IgG2a/IgG1 <1, induced the production of cytokines from Th2, Th17, and Th1 profiles with respect to those of dC-T_IM, which only induced IL-10 respect to the control mice. Surprisingly, after sublethal challenge, both C-T_IM and dC-T_IM showed significantly higher parasitemia and mortality than the control group. Second, mice exposed to BSA-GlcNAc6S as immunogen (BSA-GlcNAc6S_IM) showed: severe ultrastructural cardiac alterations while BSA-GlcNAc_IM conserved the regular tissue architecture with slight myofibril changes; a strong highly specific humoral-immune-response reproducing the IgG-isotype-profile obtained with C-T_IM; and a significant memory-T-cell-response demonstrating sulfotope-immunodominance with respect to BSA-GlcNAc_IM. After sublethal challenge, BSA-GlcNAc6S_IM showed exacerbated parasitemias, despite elevated IFN-γ levels were registered. In both cases, the abrogation of ultrastructural alterations when using desulfated immunogens supported the direct involvement of sulfotopes and/or indirect effect through their specific antibodies, in the induction of tissue damage. Finally, a third strategy using a passive transference of sulfotope-specific antibodies (IgG-GlcNAc6S) showed the detrimental activity of IgG-GlcNAc6S on mice cardiac tissue, and mice treated with IgG-GlcNAc6S after a sublethal dose of T. cruzi, surprisingly reached higher parasitemias than control groups. These findings confirmed the indirect role of the sulfotopes, via their IgG-GlcNAc6S, both in the immunopathogenicity as well as favoring T. cruzi infection.

Interleukin-32γ in the Control of Acute Experimental Chagas Disease

Chagas disease (CD) is an important parasitic disease caused by Trypanosoma cruzi. Interleukin-32 (IL-32) plays an important role in inflammation and in the development of Th1/Th17 acquired immune responses. We evaluated the influence of IL-32γ on the immune response profile, pathogenesis of myocarditis in acute experimental CD, and control of the disease. For this, C57BL/6 wild-type (WT) and IL-32γTg mice were infected subcutaneously with 1,000 forms of Colombian strain of T. cruzi. In the histopathological analyzes, T. cruzi nests, myocarditis, and collagen were quantified in cardiac tissue. Cytokine productions (IL-32, IFN-γ, TNF-α, IL-10, and IL-17) were measured in cardiac homogenate by ELISA. The IL-32γTg mice showed a better control of parasitemia and T. cruzi nests in the heart than WT mice. Infected-WT and -IL-32γTg mice showed similar levels of IFN-γ, TNF-α, and IL-17, but IL-10 was significantly higher expressed in IL-32γTg than in WT mice. The cytokine profile found in IL-32γTg animals contributed to body weight maintenance, parasitemia control, and survival. Our results indicate that the presence of human IL-32γ in mice infected with the Colombian strain of T. cruzi is important for infection control during the acute phase of Chagas disease.

Is a negative correlation between sTNFR1 and TNF in patients with chronic Chagas disease the key to clinical progression?

Soluble TNF receptors (sTNFR1 and sTNFR2) are natural endogenous inhibitors of TNF and are elevated in inflammatory, autoimmune, and chronic degenerative diseases. In Chagas disease, pleiotropic cytokine TNF is considered key in immunopathology. Thus, we aimed to evaluate the levels of TNF, sTNFR1, and sTNFR2 in the serum of patients with chronic Chagas disease. TNF and its soluble receptors were quantified using Cytometric Bead Array in the serum of 132 patients, of which 51 had the indeterminate form (IND), 39 the mild cardiac form (CARD 1), 42 the severe cardiac form (CARD 2), and 20 non-infected individuals (NI). The results indicate that the soluble receptors may regulate TNF in Chagas disease, as their leves were higher in T. cruzi-infected individuals when compared to non-infected individuals. We found a moderate negative correlation between sTNFR1 and TNF in individuals with the IND form, suggesting a relationship with non-progression to more severe forms, such as heart disease. sTNFR1 and sTNFR2 were increased in all clinical forms, but with a moderate positive correlation in more severe patients (r = 0.50 and p = 0.0005). TNF levels showed no statistical differences in the groups of patients. These findings suggest the importance of the endogenous balance of the levels of soluble TNF receptors in the protection and balance in patients with chronic Chagas disease, besides revealing the immunological complexity in chronic T. cruzi-infected individuals.

Live attenuated vaccines, a favorable strategy to provide long-term immunity against protozoan diseases

The control of diseases caused by protozoan parasites is one of the United Nations' Sustainable Development Goals. In recent years much research effort has gone into developing a new generation of live attenuated vaccines (LAVs) against malaria, Chagas disease and leishmaniasis. However, there is a bottleneck related to their biosafety, production, and distribution that slows downs further development. The success of irradiated or genetically attenuated sporozoites against malaria, added to the first LAV against leishmaniasis to be evaluated in clinical trials, is indicative that the drawbacks of LAVs are gradually being overcome. However, whether persistence of LAVs is a prerequisite for sustained long-term immunity remains to be clarified, and the procedures necessary for clinical evaluation of vaccine candidates need to be standardized.

A Novel High-Content Screening-Based Method for Anti-Trypanosoma cruzi Drug Discovery Using Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Chagas disease is caused by Trypanosoma cruzi infection and remains a relevant cause of chronic heart failure in Latin America. The pharmacological arsenal for Chagas disease is limited, and the available anti-T. cruzi drugs are not effective when administered during the chronic phase. Cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) have the potential to accelerate the process of drug discovery for Chagas disease, through predictive preclinical assays in target human cells. Here, we aimed to establish a novel high-content screening- (HCS-) based method using hiPSC-CMs to simultaneously evaluate anti-T. cruzi activity and cardiotoxicity of chemical compounds. To provide proof-of-concept data, the reference drug benznidazole and three compounds with known anti-T. cruzi activity (a betulinic acid derivative named BA5 and two thiazolidinone compounds named GT5A and GT5B) were evaluated in the assay. hiPSC-CMs were infected with T. cruzi and incubated for 48 h with serial dilutions of the compounds for determination of EC50 and CC50 values. Automated multiparametric analyses were performed using an automated high-content imaging system. Sublethal toxicity measurements were evaluated through morphological measurements related to the integrity of the cytoskeleton by phalloidin staining, nuclear score by Hoechst 33342 staining, mitochondria score following MitoTracker staining, and quantification of NT-pro-BNP, a peptide released upon mechanical myocardial stress. The compounds showed EC₅₀ values for anti-T. cruzi activity similar to those previously described for other cell types, and GT5B showed a pronounced trypanocidal activity in hiPSC-CMs. Sublethal changes in cytoskeletal and nucleus scores correlated with NT-pro-BNP levels in the culture supernatant. Mitochondrial score changes were associated with increased cytotoxicity. The assay was feasible and allowed rapid assessment of anti-T. cruzi action of the compounds, in addition to cardiotoxicity parameters. The utilization of hiPSC-CMs in the drug development workflow for Chagas disease may help in the identification of novel compounds.

α-Gal immunization positively impacts Trypanosoma cruzi colonization of heart tissue in a mouse model

Chagas disease, caused by the parasite Trypanosoma cruzi, is considered endemic in more than 20 countries but lacks both an approved vaccine and limited treatment for its chronic stage. Chronic infection is most harmful to human health because of long-term parasitic infection of the heart. Here we show that immunization with a virus-like particle vaccine displaying a high density of the immunogenic α-Gal trisaccharide (Qβ-αGal) induced several beneficial effects concerning acute and chronic T. cruzi infection in α1,3-galactosyltransferase knockout mice. Approximately 60% of these animals were protected from initial infection with high parasite loads. Vaccinated animals also produced high anti-αGal IgG antibody titers, improved IFN-γ and IL-12 cytokine production, and controlled parasitemia in the acute phase at 8 days post-infection (dpi) for the Y strain and 22 dpi for the Colombian strain. In the chronic stage of infection (36 and 190 dpi, respectively), all of the vaccinated group survived, showing significantly decreased heart inflammation and clearance of amastigote nests from the heart tissue.

Virulence of Trypanosoma cruzi Strains Is Related to the Differential Expression of Innate Immune Receptors in the Heart

Resistance or susceptibility to T. cruzi infection is dependent on the host immunological profile. Innate immune receptors, such as Toll-like receptors (TLRs/TLR2, TLR4, TLR7, and TLR9) and Nod-like receptors (NLRs/NOD1 and NLRP3 inflammasome) are involved with the resistance against acute experimental T. cruzi infection. Here, we evaluated the impact of T. cruzi virulence on the expression of innate immune receptors and its products in mice. For that, we used six T. cruzi strains/isolates that showed low (AM64/TcIV and 3253/Tc-V), medium (PL1.10.14/TcIII and CL/TcVI), or high (Colombian/Tc-I and Y/TcII) virulence and pathogenicity to the vertebrate host and belonging to the six discrete typing units (DTUs)—TcI to TcVI. Parasitemia, mortality, and myocarditis were evaluated and correlated to the expression of TLRs, NLRs, adapter molecules, cytokines, and iNOS in myocardium by real time PCR. Cytokines (IL-1β, IL-12, TNF-α, and IFN-γ) were quantified in sera 15 days after infection. Our data indicate that high virulent strains of T. cruzi, which generate high parasitemia, severe myocarditis, and 100% mortality in infected mice, inhibit the expression of TLR2, TLR4, TLR9, TRIF, and Myd88 transcripts, leading to a low IL-12 production, when compared to medium and low virulent T. cruzi strains. On the other hand, the high virulent T. cruzi strains induce the upregulation of NLRP3, caspase-1, IL-1β, TNF-α, and iNOS mRNA in heart muscle, compared to low and medium virulent strains, which may contribute to myocarditis and death. Moreover, high virulent strains induce higher levels of IL-1β and TNF-α in sera compared to less virulent parasites. Altogether the data indicate that differential TLR and NLR expression in heart muscle is correlated with virulence and pathogenicity of T cruzi strains. A better knowledge of the immunological mechanisms involved in resistance to T. cruzi infection is important to understand the natural history of Chagas disease, can lead to identification of immunological markers and/or to serve as a basis for alternative therapies.

Host Genetics Background Influence in the Intragastric Trypanosoma cruzi Infection

Background

Considering the complexity of the factors involved in the immunopathology of Chagas disease, which influence the Chagas' disease pathogenesis, anti-T. cruzi immune response, and chemotherapy outcome, further studies are needed to improve our understanding about these relationships. On this way, in this article we analyzed the host genetic influence on hematological, histopathological and immunological aspects after T. cruzi infection.

Methods

BALB/c and A mice were intragastrically infected with T. cruzi SC2005 strain, isolated from a patient of an outbreak of Chagas disease. Parameters such as parasite load, survival rates, cytokines production, macrophages, T and B cell frequencies, and histopathology analysis were carried out.

Results

BALB/c mice presented higher parasitemia and mortality rates than A mice. Both mouse lineages exhibited hematological alterations suggestive of microcytic hypochromic anemia and histopathological alterations in stomach, heart and liver. The increase of CD8+ T cells, in heart, liver and blood, and the increase of CD19+ B cells, in liver, associated with a high level of proinflammatory cytokines (IL-6, TNF-α, IFN-γ), confer a resistance profile to the host. Although BALB/c animals exhibited the same findings observed in A mice, the response to infection occurred later, after a considerable parasitemia increase. By developing an early response to the infection, A mice were found to be less susceptible to T. cruzi SC2005 infection.

Conclusions

Host genetics background shaping the response to infection. The early development of a cytotoxic cellular response profile with the production of proinflammatory cytokines is important to lead a less severe manifestation of Chagas disease.

Animal models of Chagas disease and their translational value to drug development

INTRODUCTION

American trypanosomiasis, better known as Chagas disease, is a global public health issue. Current treatments targeting the causative parasite, Trypanosoma cruzi, are limited to two old nitroheterocyclic compounds; new, safer drugs are needed. New tools to identify compounds suitable for parasitological cure in humans have emerged through efforts in drug discovery.

AREAS COVERED

Animal disease models are an integral part of the drug discovery process. There are numerous experimental models of Chagas disease described and in use; rather than going through each of these and their specific features, the authors focus on developments in recent years, in particular the imaging technologies that have dramatically changed the Chagas R&D landscape, and provide a critical view on their value and limitations for moving compounds forward into further development.

EXPERT OPINION

The application of new technological advances to the field of drug development for Chagas disease has led to the implementation of new and robust/standardized in vivo models that contributed to a better understanding of host/parasite interactions. These new models should also build confidence in their translational value for moving compounds forward into clinical development.

Understanding the oral transmission of Trypanosoma cruzi as a veterinary and medical foodborne zoonosis

Chagas disease is a neglected tropical disease transmitted by the protozoan Trypanosoma cruzi that lately has been highlighted because several outbreaks attributed to oral transmission of the parasite have occurred. These outbreaks are characterized by high mortality rates and massive infections that cannot be related to other types of transmission such as the vectorial route. Oral transmission of Chagas disease has been reported in Brazil, Colombia, Venezuela, Bolivia, Ecuador, Argentina and French Guiana, most of them are massive oral outbreaks caused by the ingestion of beverages and food contaminated with triatomine feces or parasites' reservoirs secretions and considered since 2012 as a foodborne disease. In this review, we present the current status and all available data regarding oral transmission of Chagas disease, highlighting its relevance as a veterinary and medical foodborne zoonosis.

HIF-1α and CD73 expression in cardiac leukocytes correlates with the severity of myocarditis in end-stage Chagas disease patients

Chronic Chagas cardiomyopathy is the main infectious myocarditis worldwide. Almost 30% of Trypanosoma cruzi infected individuals develop slow and progressive myocarditis that leads to ventricular dilation and heart failure. Heart transplantation is an established, valuable therapeutic option for end-stage Chagas disease patients. Although the pathophysiology of Chagas disease has been addressed for decades by numerous groups, the cardiac immunologic mechanisms involved in the progression of clinical manifestation are still unknown. Growing evidence demonstrates that hypoxia-inducible factor (HIF)-1α plays indispensable roles in driving immune response by triggering the expression of CD73 purinergic ecto-enzyme. Purinergic system controls the duration and magnitude of purine signals directed to modulate immune cells through the conversion of extracellular ATP (microbicide/proinflammatory) to the immunoregulatory metabolite adenosine. In the present work, we described that infiltrating leukocytes within cardiac explants from patients with end-stage Chagas cardiomyopathy up-regulated HIF-1α and CD73 expression. Moreover, the number of HIF-1α+ and CD73+ leukocytes positively correlated with the myocarditis severity and the local parasite load. Furthermore, we demonstrated a direct relationship between tissue parasite persistence and the influx of immune cells to the infected hearts, which ultimately determine the severity of the myocarditis. These findings provide evidence that CD73-dependent regulatory pathways are locally triggered in the myocardium of patients with end-stage Chagas disease.

Catalytic mechanism and properties of pyridoxal 5'-phosphate independent racemases: how enzymes alter mismatched acidity and basicity

Covering: up to March 2019 Amino acid racemases and epimerases are key enzymes that invert the configuration of common amino acids and supply many corresponding d-isomers in living organisms. Some d-amino acids are inherently bioactive, whereas others are building blocks for important biomolecules, for example lipid II, the bacterial cell wall precursor. Peptides containing them have enhanced proteolytic stability and can act as important recognition elements in mammalian systems. Selective inhibition of certain amino acid racemases (e.g. glutamate racemase) is believed to offer a promising target for new antibacterial drugs effective against pathogens resistant to current antibiotics. Many amino acid racemases employ imine formation with pyridoxal phosphate (PLP) as a cofactor to accelerate the abstraction of the alpha proton. However, the group reviewed herein achieves racemization of free amino acids without the use of cofactors or metals, and uses a thiol/thiolate pair for deprotonation and reprotonation. All bacteria and higher plants contain such enzymes, for example diaminopimelate epimerase, which is required for lysine biosynthesis in these organisms. This process cannot be accomplished without an enzyme catalyst as the acidities of a thiol and the substrate α-hydrogen are inherently mismatched by at least 10 orders of magnitude. This review describes the structural and mechanistic studies on PLP-independent racemases and the evolving view of key enzymatic machinery that accomplishes these remarkable transformations.

Drug-cured experimental Trypanosoma cruzi infections confer long-lasting and cross-strain protection

BACKGROUND

The long term and complex nature of Chagas disease in humans has restricted studies on vaccine feasibility. Animal models also have limitations due to technical difficulties in monitoring the extremely low parasite burden that is characteristic of chronic stage infections. Advances in imaging technology offer alternative approaches that circumvent these problems. Here, we describe the use of highly sensitive whole body in vivo imaging to assess the efficacy of recombinant viral vector vaccines and benznidazole-cured infections to protect mice from challenge with Trypanosoma cruzi.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were infected with T. cruzi strains modified to express a red-shifted luciferase reporter. Using bioluminescence imaging, we assessed the degree of immunity to re-infection conferred after benznidazole-cure. Those infected for 14 days or more, prior to the onset of benznidazole treatment, were highly protected from challenge with both homologous and heterologous strains. There was a >99% reduction in parasite burden, with parasites frequently undetectable after homologous challenge. This level of protection was considerably greater than that achieved with recombinant vaccines. It was also independent of the route of infection or size of the challenge inoculum, and was long-lasting, with no significant diminution in immunity after almost a year. When the primary infection was benznidazole-treated after 4 days (before completion of the first cycle of intracellular infection), the degree of protection was much reduced, an outcome associated with a minimal T. cruzi-specific IFN-γ+ T cell response.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that a protective Chagas disease vaccine must have the ability to eliminate parasites before they reach organs/tissues, such as the GI tract, where once established, they become largely refractory to the induced immune response.

The role of fat on cardiomyopathy outcome in mouse models of chronic Trypanosoma cruzi infection

The underlying pathogenic mechanisms of cardiomyopathy in Chagas disease are still unsolved. In order to better clarify the role of fat on the evolution of cardiomyopathy, the present study employed three murine models of chronic Trypanosoma cruzi infection: (1) aP2-RIDα/β transgenic mice (RID mice; an adipose tissue model which express a gain-of-function potent anti-inflammatory activity), (2) allograft inflammatory factor-1 knockout mice (Aif1^-/-), and (3) a Swiss outbred mice. RID mice and non-transgenic mice (wild type, WT) were infected with blood trypomastigotes of Brazil strain. During the acute stage of infection, RID mice had lower parasitemia, lower heart inflammation, and a decrease in the relative distribution of parasite load from cardiac muscle tissue toward epididymal fat. Nevertheless, comparable profiles of myocardial inflammatory infiltrates and relative distribution of parasite load were observed among RID and WT at the chronic stage of infection. Aif1^-/- and Aif1^+/+ mice were infected with bloodstream trypomastigotes of Tulahuen strain and fed with high-fat diet (HFD) or regular diet (RD). Interestingly, Aif1^+/+ HFD infected mice showed the highest mortality. Swiss mice infected with blood trypomastigotes of Berenice-78 strain on a HFD had higher levels of TNFα and more inflammation in their heart tissue than infected mice fed a RD. These various murine models implicate adipocytes in the pathogenesis of chronic Chagas disease and suggest that HFD can lead to a significant increase in the severity of parasite-induced chronic cardiac damage. Furthermore, these data implicate adipocyte TLR4-, TNFα-, and IL-1β-mediated signaling in pro-inflammatory pathways and Aif-1 gene expression in the development of chronic Chagas disease.

Epidemiology and pathogenesis of maternal-fetal transmission of Trypanosoma cruzi and a case for vaccine development against congenital Chagas disease

Trypanos o ma cruzi (T. cruzi or Tc) is the causative agent of Chagas disease (CD). It is common for patients to suffer from non-specific symptoms or be clinically asymptomatic with acute and chronic conditions acquired through various routes of transmission. The expecting women and their fetuses are vulnerable to congenital transmission of Tc. Pregnant women face formidable health challenges because the frontline antiparasitic drugs, benznidazole and nifurtimox, are contraindicated during pregnancy. However, it is worthwhile to highlight that newborns can be cured if they are diagnosed and given treatment in a timely manner. In this review, we discuss the pathogenesis of maternal-fetal transmission of Tc and provide a justification for the investment in the development of vaccines against congenital CD.

Immunity and vaccine development efforts against Trypanosoma cruzi

Trypanosoma cruzi (T. cruzi) is the causative agent for Chagas disease (CD). There is a critical lack of methods for prevention of infection or treatment of acute infection and chronic disease. Studies in experimental models have suggested that the protective immunity against T. cruzi infection requires the elicitation of Th1 cytokines, lytic antibodies and the concerted activities of macrophages, T helper cells, and cytotoxic T lymphocytes (CTLs). In this review, we summarize the research efforts in vaccine development to date and the challenges faced in achieving an efficient prophylactic or therapeutic vaccine against human CD.

Increased heart fibrosis and acute infection in a murine Chagas disease model associated with organophosphorus pesticide metabolite exposure

Some reports suggest that exposure to organophosphorus (OP) pesticides increases the incidence of infections. Ethylated dialkylphosphates (EtDAPs) are metabolites of OP pesticides widely distributed with immunomodulatory potential. Chagas disease is produced by Trypanosoma cruzi parasites, and resolution of this infection requires the activation of inflammatory macrophages (MΦ), which results in cardiac fibrosis. Some reports indicate that EtDAPs increase the amount of the anti-inflammatory alternatively activated MΦ (M2; CD206⁺F4/80⁺). Therefore, we analyzed the course of T. cruzi infection, MΦ profiles from peritoneal exudate cells (PECs), inflammatory cell infiltration and fibrosis in the heart of BALB/c mice exposed to diethyldithiophosphate (DEDTP), diethylthiophosphate (DETP) or diethylphosphate (DEP, 0.01 g/kg), common DAPs produced by OP pesticides, 24 h before infection with T. cruzi. We found that DEDTP increased the parasite burden in blood by 99% at the peak of the infection and enhanced the myocardial damage due to an increase in infiltrated inflammatory cells (induced by DEDTP or DETP) and fibrosis (induced by EtDAPs). In the PECs, exposure to EtDAPs increased the proportion of the MΦ subpopulations of M2a, M2b and M2d, which are associated with tissue repair. These results indicate that exposure to EtDAPs can exacerbate the acute phase of a parasitic infection and increase the long-term damage to the heart.

Monocyte glycolysis determines CD8+ T cell functionality in human Chagas disease

Chagas disease is a lifelong pathology resulting from Trypanosoma cruzi infection. It represents one of the most frequent causes of heart failure and sudden death in Latin America. Herein, we provide evidence that aerobic glycolytic pathway activation in monocytes drives nitric oxide (NO) production, triggering tyrosine nitration (TN) on CD8+ T cells and dysfunction in patients with chronic Chagas disease. Monocytes from patients exhibited a higher frequency of hypoxia-inducible factor 1α and increased expression of its target genes/proteins. Nonclassical monocytes are expanded in patients' peripheral blood and represent an important source of NO. Monocytes entail CD8+ T cell surface nitration because both the frequency of nonclassical monocytes and that of NO-producing monocytes positively correlated with the percentage of TN+ lymphocytes. Inhibition of glycolysis in in vitro-infected peripheral blood mononuclear cells decreased the inflammatory properties of monocytes/macrophages, diminishing the frequency of IL-1β- and NO-producing cells. In agreement, glycolysis inhibition reduced the percentage of TN+CD8+ T cells, improving their functionality. Altogether, these results clearly show that glycolysis governs oxidative stress on monocytes and modulates monocyte-T cell interplay in human chronic Chagas disease. Understanding the pathological immune mechanisms that sustain an inflammatory environment in human pathology is key to designing improved therapies.

Trypanosoma cruzi: A review of biological and methodological factors in Mexican strains

Trypanosoma cruzi, responsible for Chagas disease, is a serious public health problem in Latin America with eight million people infected in the world. Clinical manifestations observed in humans due to T. cruzi infection are largely associated with the wide biological and genetic heterogeneity of the parasite. This review presents an overview of the parasitological aspects of various strains of T. cruzi isolated mainly in Mexico, as well as an analysis of the methodological processes used to determine their virulence that could be influencing their biological characterization. We emphasize the importance of using uniform protocols to study T. cruzi virulence, taking into account factors related to: strain (i.e. developmental stage, lineage, biological origin, genetic variability), animal model used (i.e. role of hormones, host immune response, age) and methodology (i.e. inoculum size, inoculation route, and laboratory conditions used during strain maintenance). These uniform protocols will then allow proposing elements for understanding clinical evolution and management of the disease, for providing adequate treatment, and for developing tools for future vaccines against Chagas disease.

Does Prolactin treatment trigger imunoendocrine alterations during experimental T. cruzi infection?

Prolactin (PRL) is a pleiotropic polypeptide hormone produced by the anterior pituitary gland and negatively controlled by dopamine. Some researchers have associated the immune regulatory functions of PRL with some infectious diseases like Toxoplasma gondii and T. cruzi. This work aimed to analyze the possible immuno-modulatory effects of this hormone through the subcutaneous administration of PRL during the experimental Chagas disease. On the 14th day post-infection (dpi), PRL triggered increased percentages of NK cells in treated infected animals as compared to the infected and untreated ones. For early and late apoptosis, our results showed that in chronically infected groups, PRL counteracted splenocyte apoptosis as revealed by the reduced percentages of both, early and late apoptosis. Reduced percentages of spleen CD4⁺ and CD8⁺ T cells were detected in infected PRL treated rats (60 days post-infection). Concerning to B cells, a significant increased percentage of these cells was found for all PRL treated infected animals (14th dpi), but no statistically significant alteration was observed on the 60th days post-infection. Furthermore, PRL treatment triggered a significant increase in the percentage of CD4⁺ T lymphocytes IFN-γ producers, while on the 60th dpi, a reduced percentage of IFN-γ in these cells was observed in prolactin-treated rats compared to infected and untreated ones. Enhanced serum IL-12 levels were detected in infected and PRL treated subjects (60th dpi). Only on 7th day post-infection, the flow cytometric analysis of CFSE-stained CD3⁺ T cells showed an enhanced proliferation of polyclonal stimulated T cells in PRL-treated and infected animals. In this study, we demonstrated that PRL can influence many aspects of the immune response during the experimental Chagas' disease, and this substance could be used as a supporting trial along with the conventional drug treatment.

The influence of parasitism by Trypanosoma cruzi in the hematological parameters of the white ear opossum (Didelphis albiventris) from Campo Grande, Mato Grosso do Sul, Brazil

Considered ecologically generalist, Didelphis albiventris is reported as reservoir for different species of parasites, especially Trypanosoma cruzi. However, the knowledge about the influence of T. cruzi on hematological parameters of free-living opossum remains scarce. The present study aimed to evaluate the influence of T. cruzi on hematological parameters of white-ear opossums (D. albiventris) from Campo Grande, Mato Grosso do Sul, Brazil. The blood samples and biometric data were collected from 40 opossums captured by Tomahawk and Sherman traps in six urban forest fragments located in the city. The health of these animals was inferred, mainly, by means of blood parameters (PCV, RBC, WBC, MCV and WBC differential). Molecular detection of T. cruzi infection was performed by nested polymerase chain reaction (nPCR), using 18S and 24Sα rDNA region as target. Paired-t-test and simple linear regression were used for statistical analysis. No significant difference was observed between the averages of hematological variables in relation to gender and body condition. The molecular diagnosis showed that 32.5% (13/40) of the opossums were infected by T. cruzi, which presented lymphocytosis (3.4 ± 1.5) and eosinophilia (0.09 ± 0.13). Path analysis showed that T. cruzi infection resulted in increased numbers of lymphocytes and indirectly decreased the body condition of opossums. Moreover T. cruzi infection resulted in a direct effect on decrease of MCV. Overall, our results suggest that T. cruzi infection may represent a risk to health of opossums since the lymphocytosis may cause a secondary damage on body condition of infected animals.

Isolation and Phenotypic Characterization of Inflammatory Cells from Clinical Samples: Purification of Macrophages from Trypanosoma cruzi-Infected Hearts

Trypanosoma cruzi, the causal agent of chronic Chagas cardiomyopathy, exhibits an important tropism for cardiac tissue. In consequence, T. cruzi experimental infection represents a unique model to study cardiac macrophage behavior and effector functions during either acute or chronic immune response. In this chapter we describe a protocol to isolate immune cells from T. cruzi-infected murine cardiac tissue and to determine the percentage, absolute number, phenotype, and functionality of monocytes and macrophages by using flow cytometry. Moreover, we describe the parameters to discriminate between resident and infiltrating mononuclear phagocytic cells within infected hearts. The investigations in this field will provide mechanistic insights about the roles of these innate immune cells in the context of a clinically relevant target tissue.

Leptin Functions in Infectious Diseases

Leptin, a pleiotropic protein has long been recognized to play an important role in the regulation of energy homeostasis, metabolism, neuroendocrine function, and other physiological functions through its effects on the central nervous system (CNS) and peripheral tissues. Leptin is secreted by adipose tissue and encoded by the obese (ob) gene. Leptin acts as a central mediator which regulates immunity as well as nutrition. Importantly, leptin can modulate both innate and adaptive immune responses. Leptin deficiency/resistance is associated with dysregulation of cytokine production, increased susceptibility toward infectious diseases, autoimmune disorders, malnutrition and inflammatory responses. Malnutrition induces a state of immunodeficiency and an inclination to death from communicable diseases. Infectious diseases are the disease of poor who invariably suffer from malnutrition that could result from reduced serum leptin levels. Thus, leptin has been placed at the center of many interrelated functions in various pathogenic conditions, such as bacterial, viruses and parasitic infections. We review herein, the recent advances on the role of leptin in malnutrition in pathogenesis of infectious diseases with a particular emphasis on parasitic diseases such as Leishmaniasis, Trypanosomiasis, Amoebiasis, and Malaria.

Pathology and Pathogenesis of Chagas Heart Disease

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of people infected with the protozoan parasite Trypanosoma cruzi. One way T. cruzi is transmitted to people is through contact with infected kissing bugs, which are found in much of the Western Hemisphere, including in vast areas of the United States. The epidemiology of T. cruzi and Chagas heart disease and the varied mechanisms leading to myocyte destruction, mononuclear cell infiltration, fibrosis, and edema in the heart have been extensively studied by hundreds of scientists for more than 100 years. Despite this wealth of knowledge, it is still impossible to predict what will happen in an individual infected with T. cruzi because of the tremendous variability in clonal parasite virulence and human susceptibility to infection and the lack of definitive molecular predictors of outcome from either side of the host-parasite equation. Further, while several distinct mechanisms of pathogenesis have been studied in isolation, it is certain that multiple coincident mechanisms combine to determine the ultimate outcome. For these reasons, Chagas disease is best considered a collection of related but distinct illnesses. This review highlights the pathology and pathogenesis of the most common adverse sequela of T. cruzi infection-Chagas heart disease-and concludes with a discussion of key unanswered questions and a view to the future.

IL-17RA-Signaling Modulates CD8+ T Cell Survival and Exhaustion During Trypanosoma cruzi Infection

The IL-17 family contributes to host defense against many intracellular pathogens by mechanisms that are not fully understood. CD8+ T lymphocytes are key elements against intracellular microbes, and their survival and ability to mount cytotoxic responses are orchestrated by several cytokines. Here, we demonstrated that IL-17RA-signaling cytokines sustain pathogen-specific CD8+ T cell immunity. The absence of IL-17RA and IL-17A/F during Trypanosoma cruzi infection resulted in increased tissue parasitism and reduced frequency of parasite-specific CD8+ T cells. Impaired IL-17RA-signaling in vivo increased apoptosis of parasite-specific CD8+ T cells, while in vitro recombinant IL-17 down-regulated the pro-apoptotic protein BAD and promoted the survival of activated CD8+ T cells. Phenotypic, functional, and transcriptomic profiling showed that T. cruzi-specific CD8+ T cells derived from IL-17RA-deficient mice presented features of cell dysfunction. PD-L1 blockade partially restored the magnitude of CD8+ T cell responses and parasite control in these mice. Adoptive transfer experiments established that IL-17RA-signaling is intrinsically required for the proper maintenance of functional effector CD8+ T cells. Altogether, our results identify IL-17RA and IL-17A as critical factors for sustaining CD8+ T cell immunity to T. cruzi.

Outcomes of Trypanosoma cruzi and Trypanosoma evansi infections on health of Southern coati (Nasua nasua), crab-eating fox (Cerdocyon thous), and ocelot (Leopardus pardalis) in the Brazilian Pantanal

The occurrence of Trypanosoma spp. in wild carnivore populations has been intensively investigated during the last decades. However, the impact of these parasites on the health of free-living infected animals has been largely neglected. The Pantanal biome is the world’s largest seasonal wetland, harboring a great diversity of species and habitats. This includes 174 species of mammals, of which 20 belong to the order Carnivora. The present study aimed to investigate the effect of Trypanosoma evansi and Trypanosoma cruzi infections and coinfections on the health of the most abundant carnivores in the Pantanal: coati (Nasua nasua), crab-eating fox (Cerdocyon thous), and ocelot (Leopardus pardalis). We captured 39 coatis, 48 crab-eating foxes, and 19 ocelots. Diagnostic tests showed T. cruzi infection in 7 crab-eating foxes and 5 coatis. Additionally, 7 crab-eating foxes, 10 coatis, and 12 ocelots were positive for T. evansi. We observed coinfections in 9 crab-eating foxes, 8 coatis, and 2 ocelots. This is the first report of T. evansi and T. cruzi infection on the health of free-living ocelots and crab-eating foxes. We showed that single T. evansi or T. cruzi infection, as well as coinfection, caused some degree of anemia in all animals, as well as an indirect negative effect on body condition in coatis and crab-eating foxes via anemia indicators and immune investment, respectively. Furthermore, the vigorous immune investment observed in sampled coatis, crab-eating foxes and ocelots infected by T. evansi, T. cruzi and coinfected can be highly harmful to their health. Overall, our results indicate that single and combined infection with T. evansi and T. cruzi represent a severe risk to the health of wild carnivores in the Pantanal region.

Autoimmunity in Chronic Chagas Disease: A Road of Multiple Pathways to Cardiomyopathy?

Chagas disease (CD), a neglected tropical disease caused by the protozoan Trypanosoma cruzi, affects around six million individuals in Latin America. Currently, CD occurs worldwide, becoming a significant public health concern due to its silent aspect and high morbimortality rate. T. cruzi presents different escape strategies which allow its evasion from the host immune system, enabling its persistence and the establishment of chronic infection which leads to the development of chronic Chagas cardiomyopathy (CCC). The potent immune stimuli generated by T. cruzi persistence may result in tissue damage and inflammatory response. In addition, molecular mimicry between parasites molecules and host proteins may result in cross-reaction with self-molecules and consequently in autoimmune features including autoantibodies and autoreactive cells. Although controversial, there is evidence demonstrating a role for autoimmunity in the clinical progression of CCC. Nevertheless, the exact mechanism underlying the generation of an autoimmune response in human CD progression is unknown. In this review, we summarize the recent findings and hypotheses related to the autoimmune mechanisms involved in the development and progression of CCC.

Innate immune receptors over expression correlate with chronic chagasic cardiomyopathy and digestive damage in patients

Chronic chagasic cardiomyopathy (CCC) is observed in 30% to 50% of the individuals infected by Trypanosoma cruzi and heart failure is the important cause of death among patients in the chronic phase of Chagas disease. Although some studies have elucidated the role of adaptive immune responses involving T and B lymphocytes in cardiac pathogenesis, the role of innate immunity receptors such as Toll-like receptors (TLRs) and Nod-like receptors (NLRs) in CCC pathophysiology has not yet been determined. In this study, we evaluated the association among innate immune receptors (TLR1-9 and nucleotide-binding domain-like receptor protein 3/NLRP3), its adapter molecules (Myd88, TRIF, ASC and caspase-1) and cytokines (IL-1β, IL-6, IL-12, IL-18, IL-23, TNF-α, and IFN-β) with clinical manifestation, digestive and cardiac function in patients with different clinical forms of chronic Chagas disease. The TLR8 mRNA expression levels were enhanced in the peripheral blood mononuclear cells (PBMC) from digestive and cardiodigestive patients compared to indeterminate and cardiac patients. Furthermore, mRNA expression of IFN-β (cytokine produced after TLR8 activation) was higher in digestive and cardiodigestive patients when compared to indeterminate. Moreover, there was a positive correlation between TLR8 and IFN-β mRNA expression with sigmoid and rectum size. Cardiac and cardiodigestive patients presented higher TLR2, IL-12 and TNF-α mRNA expression than indeterminate and digestive patients. Moreover, cardiac patients also expressed higher levels of NLRP3, ASC and IL-1β mRNAs than indeterminate patients. In addition, we showed a negative correlation among TLR2, IL-1β, IL-12 and TNF-α levels with left ventricular ejection fraction, and positive correlation between NLRP3 with cardiothoracic index, and TLR2, IL-1β and IL-12 with left ventricular mass index. Together, our data suggest that high expression of innate immune receptors in cardiac and digestive patients may induce an enhancement of cytokine expression and participate of cardiac and digestive dysfunction.

BALB/c and C57BL/6 Mice Cytokine Responses to Trypanosoma cruzi Infection Are Independent of Parasite Strain Infectivity

Trypanosoma cruzi is the etiologic agent of Chagas’ disease, which affects 6–7 million people worldwide. Different strains of T. cruzi present specific genotypic and phenotypic characteristics that affect the host–pathogen interactions, and thus, the parasite has been classified into six groups (TcI to TcVI). T. cruzi infection presents two clinical phases, acute and chronic, both with distinct characteristics and important participation by the immune system. However, the specific contributions of parasite and host factors in the disease phases are not yet fully understood. The murine model for Chagas’ disease is well-established and reproduces important features of the human infection, providing an experimental basis for the study of host lineages and parasite strains. Thus, we evaluated acute and chronic infection by the G (TcI) and CL (TcVI) strains of T. cruzi, which have distinct tropisms and infectivity, in two inbred mice lineages (C57BL/6 and BALB/c) that display variable degrees of susceptibility to different T. cruzi strains. Analysis of the parasite loads in host tissues by qPCR showed that CL strain established an infection faster than the G strain; at the same time, the response in BALB/c mice, although diverse in terms of cytokine secretion, was initiated earlier than that in C57BL/6 mice. At the parasitemia peak in the acute phase, we observed, either by confocal microscopy or by qPCR, that the infection was disseminated in all groups analyzed, with some differences concerning parasite tropism; at this point, all animals responded to infection by increasing the serum concentrations of cytokines. However, BALB/c mice seemed to better regulate the immune response than C57BL/6 mice. Indeed, in the chronic phase, C57BL/6 mice still presented exacerbated cytokine and chemokine responses. In summary, our results indicate that in these experimental models, the deregulation of immune response that is typical of chronic Chagas’ disease may be due to control loss over pro- and anti-inflammatory cytokines early in the acute phase of the disease, depending primarily on the host background rather than the parasite strain.

Th-17 cytokines are associated with severity of Trypanosoma cruzi chronic infection in pediatric patients from endemic areas of Mexico

In Chagas disease the clinical, acute and chronic manifestations are the result of the interaction between the parasite and the host factors. The balance between inflammatory and anti-inflammatory immune responses is essential for the increase or resolution of the manifestations in individuals infected with T. cruzi. To identify if children with chronic Chagas disease and heart injury is related with non-regulated Th1, Th2 and Th17 responses. We included 31 children with T. cruzi confirmed chronic infection from endemic areas of Mexico. Subsequently, they were separated according to their ECHO and ECG results into three groups according to the severity of cardiac involvement. Circulating Th1, Th2 and Th17 cytokine profiles were performed by Luminex assays and the results were analyzed by bivariate and multivariable analysis. Patients were classified in asymptomatic chronic (group 1, N=12); individuals with IRBBB in ECG and incipient lesions in ECHO (Group 2, N=8) and Patients with severe chronic symptomatic disease (Group 3, N=11). The analysis of immune mediators revealed that patients with severe cardiac manifestations had significant higher levels (p <0.05) of Th17 related cytokines including IL-17 and IL-6 as well as IFN-γ and IL-2. Also patients with severe cardiomyopathy exhibit increased levels of IL-13 (p <0.05) after multivariate analysis. High levels of Th17 related cytokines including IL-17, IFN-γ, IL-6 and IL-2 and pro-fibrotic factors such as IL-13 could be associated to the severity of cardiac involvement in children with chronic T. cruzi infection. These cytokines could be useful as indicators for the early identification of cardiac damage associated to the T. cruzi infection.

New Insights into the Immunobiology of Mononuclear Phagocytic Cells and Their Relevance to the Pathogenesis of Cardiovascular Diseases

Macrophages are the primary immune cells that reside within the myocardium, suggesting that these mononuclear phagocytes are essential in the orchestration of cardiac immunity and homeostasis. Independent of the nature of the injury, the heart triggers leukocyte activation and recruitment. However, inflammation is harmful to this vital terminally differentiated organ with extremely poor regenerative capacity. As such, cardiac tissue has evolved particular strategies to increase the stress tolerance and minimize the impact of inflammation. In this sense, growing evidences show that mononuclear phagocytic cells are particularly dynamic during cardiac inflammation or infection and would actively participate in tissue repair and functional recovery. They respond to soluble mediators such as metabolites or cytokines, which play central roles in the timing of the intrinsic cardiac stress response. During myocardial infarction two distinct phases of monocyte influx have been identified. Upon infarction, the heart modulates its chemokine expression profile that sequentially and actively recruits inflammatory monocytes, first, and healing monocytes, later. In the same way, a sudden switch from inflammatory macrophages (with microbicidal effectors) toward anti-inflammatory macrophages occurs within the myocardium very shortly after infection with Trypanosoma cruzi, the causal agent of Chagas cardiomyopathy. While in sterile injury, healing response is necessary to stop tissue damage; during an intracellular infection, the anti-inflammatory milieu in infected hearts would promote microbial persistence. The balance of mononuclear phagocytic cells seems to be also dynamic in atherosclerosis influencing plaque initiation and fate. This review summarizes the participation of mononuclear phagocyte system in cardiovascular diseases, keeping in mind that the immune system evolved to promote the reestablishment of tissue homeostasis following infection/injury, and that the effects of different mediators could modulate the magnitude and quality of the immune response. The knowledge of the effects triggered by diverse mediators would serve to identify new therapeutic targets in different cardiovascular pathologies.

Comprehensive analysis of three TYK2 gene variants in the susceptibility to Chagas disease infection and cardiomyopathy

Tyrosine kinase 2 (TYK2) is a member of the Janus kinases family implicated in the signal transduction of type I interferons and several interleukins. It has been described that genetic mutations within TYK2 lead to multiple deleterious effects in the immune response. In this work, we have analyzed three functional independent variants from the frequency spectrum on the TYK2 gene (common and low-frequency variants) suggested to reduce the function of the gene in mediating cytokine signaling and the susceptibility to infections by Trypanosoma cruzi and/or the development of Chagas cardiomyopathy in the Colombian population. A total of 1,323 individuals from a Colombian endemic region for Chagas disease were enrolled in the study. They were classified as seronegative (n = 445), seropositive asymptomatic (n = 336), and chronic Chagas Cardiomyopathy subjects (n = 542). DNA samples were genotyped using TaqMan probes. Our results showed no statistically significant differences between the allelic frequencies of the three analyzed variants when seropositive and seronegative individuals were compared, therefore these variants were not associated with susceptibility to Chagas disease. Moreover, when Chagas cardiomyopathy patients were compared to asymptomatic patients, no significant associations were found. Previous reports highlighted the association of this gene in immune-related disorders under an autoimmunity context, but not predisposing patients to infectious diseases, which is consistent with our findings. Therefore, according to our results, TYK2 gene variants do not seem to play an important role in Chagas disease susceptibility and/or chronic Chagas cardiomyopathy.

Phenotypic screening approaches for Chagas disease drug discovery

INTRODUCTION

Chagas disease, caused by the parasite Trypanosoma cruzi, is a global public health issue. Current treatments targeting the parasite are limited to two old nitroheterocyclic drugs with serious side effects. The need for new and safer drugs has prompted numerous drug discovery efforts to identify compounds suitable for parasitological cure in the last decade. Areas covered: Target-based drug discovery has been limited by the small number of well-validated targets - the latest example being the failure of azoles, T. cruzi CYP51 inhibitors, in proof-of-concept clinical trials; instead phenotypic-based drug discovery has become the main pillar of Chagas R&D. Rather than focusing on the technical features of these screening assays, the authors describe the different assays developed and available in the field, and provide a critical view on their values and limitations in the screening cascade for Chagas drug development. Expert opinion: The application of technological advances to the field of Chagas disease has led to a variety of phenotypic assays that have not only changed the disease discovery landscape but have also helped us to gain a better understanding of parasite/host interactions. Recent examples of target resolution from phenotypic hits will uncover new opportunities for drug discovery for Chagas disease.