Induction of cardiac autoimmunity in Chagas heart disease: A case for molecular mimicry

Chronic Chagas' heart disease: a disease on its way to becoming a worldwide health problem: epidemiology, etiopathology, treatment, pathogenesis and laboratory medicine

Chagas' disease, caused by Trypanosoma cruzi infection, is ranked as the most serious parasitic disease in Latin America. Nearly 30% of infected patients develop life-threatening complications, and with a latency of 10-30 years, mostly Chagas' heart disease which is currently the major cause of morbidity and mortality in Latin America, enormously burdening economic resources and dramatically affecting patients' social and labor situations. Because of increasing migration, international tourism and parasite transfer by blood contact, intrauterine transfer and organ transplantation, Chagas' heart disease could potentially become a worldwide problem. To raise awareness of this problem, we reflect on the epidemiology and etiopathology of Chagas' disease, particularly Chagas' heart disease. To counteract Chagas' heart disease, in addition to the general interruption of the infection cycle and chemotherapeutic elimination of the infection agent, early and effective causal or symptomatic therapies would be indispensable. Prerequisites for this are improved knowledge of the pathogenesis and optimized patient management. From economic and logistics viewpoints, this last prerequisite should be performed using laboratory medicine tools. Consequently, we first summarize the mechanisms that have been suggested as driving Chagas' heart disease, mainly those associated with the presence of autoantibodies against G-protein-coupled receptors; secondly, we indicate new treatment strategies involving autoantibody apheresis and in vivo autoantibody neutralization; thirdly, we present laboratory medicine tools such as autoantibody estimation and heart marker measurement, proposed for diagnosis, risk assessment and patient guidance and lastly, we critically reflect upon the increase in inflammation and oxidative stress markers in Chagas' heart disease.

CD8+ T-cells expressing interferon gamma or perforin play antagonistic roles in heart injury in experimental Trypanosoma cruzi-elicited cardiomyopathy

In Chagas disease, CD8(+) T-cells are critical for the control of Trypanosoma cruzi during acute infection. Conversely, CD8(+) T-cell accumulation in the myocardium during chronic infection may cause tissue injury leading to chronic chagasic cardiomyopathy (CCC). Here we explored the role of CD8(+) T-cells in T. cruzi-elicited heart injury in C57BL/6 mice infected with the Colombian strain. Cardiomyocyte lesion evaluated by creatine kinase-MB isoenzyme activity levels in the serum and electrical abnormalities revealed by electrocardiogram were not associated with the intensity of heart parasitism and myocarditis in the chronic infection. Further, there was no association between heart injury and systemic anti-T. cruzi CD8(+) T-cell capacity to produce interferon-gamma (IFNγ) and to perform specific cytotoxicity. Heart injury, however, paralleled accumulation of anti-T. cruzi cells in the cardiac tissue. In T. cruzi infection, most of the CD8(+) T-cells segregated into IFNγ(+) perforin (Pfn)(neg) or IFNγ(neg)Pfn(+) cell populations. Colonization of the cardiac tissue by anti-T. cruzi CD8(+)Pfn(+) cells paralleled the worsening of CCC. The adoptive cell transfer to T. cruzi-infected cd8(-/-) recipients showed that the CD8(+) cells from infected ifnγ(-/-)pfn(+/+) donors migrate towards the cardiac tissue to a greater extent and caused a more severe cardiomyocyte lesion than CD8(+) cells from ifnγ(+/+)pfn(-/-) donors. Moreover, the reconstitution of naïve cd8(-/-) mice with CD8(+) cells from naïve ifnγ(+/+)pfn(-/-) donors ameliorated T. cruzi-elicited heart injury paralleled IFNγ(+) cells accumulation, whereas reconstitution with CD8(+) cells from naïve ifnγ(-/-)pfn(+/+) donors led to an aggravation of the cardiomyocyte lesion, which was associated with the accumulation of Pfn(+) cells in the cardiac tissue. Our data support a possible antagonist effect of CD8(+)Pfn(+) and CD8(+)IFNγ(+) cells during CCC. CD8(+)IFNγ(+) cells may exert a beneficial role, whereas CD8(+)Pfn(+) may play a detrimental role in T. cruzi-elicited heart injury.

IL-10 and IFN-γ gene expression in chronic Chagas disease patients after in vitro stimulation with recombinant antigens of Trypanosoma cruzi

Along with several other aspects of Chagas disease, the mechanisms responsible for the different clinical outcomes observed in chronic infected individuals have not yet been clarified. It is believed that the host immune response to the parasite plays an important role in the development of the pathology. Therefore, the aim of this study was to evaluate the relationship between IL-10 and IFN-γ gene expression profile, after in vitro stimulation of peripheral blood mononuclear cells (PBMC) with Trypanosoma cruzi recombinant antigens CRA (cytoplasmatic repetitive antigen) and FRA (flagellar repetitive antigen), and the clinical forms of chronic Chagas disease. Twenty patients with the cardiac form of the disease (CARD), of whom 10 had the mild cardiac form (CARD 1) and 10 the severe cardiac form (CARD 2), and 20 patients with the indeterminate form (IND), were selected at the Chagas Disease Unit of the Oswaldo Cruz University Hospital, University of Pernambuco, Recife, Pernambuco, Brazil. The PBMCs of these individuals were cultured in the presence of CRA or FRA for 3 days and IL-10 and IFN-γ gene expression was evaluated by detection of its messenger RNA using Real Time Quantitative PCR. Although no significant difference was observed between the groups of individuals studied, we found that most patients with IND displayed high levels of IFN-γ gene expression, while the majority of patients with CARD 1 presented high levels of IL-10. The results of this study thus highlight the important role that inflammatory cytokines play in patients with the IND group controlling for parasite replication, and that anti-inflammatory cytokines play in determining susceptibility to progression to symptomatic clinical forms of the disease.

Matrix metalloproteinases as therapeutic targets in protozoan parasitic infections

Matrix metalloproteinases (MMPs) are associated with processes of tissue remodeling and are expressed in all infections with protozoan parasites. We here report the status of MMP research in malaria, trypanosomiasis, leishmaniasis and toxoplasmosis. In all these infections, the balances between MMPs and endogenous MMP inhibitors are disturbed, mostly in favor of active proteolysis. When the infection is associated with leukocyte influx into specific organs, immunopathology and collateral tissue damage may occur. These pathologies include cerebral malaria, sleeping sickness (human African trypanosomiasis), Chagas disease (human American trypanosomiasis), leishmaniasis and toxoplasmic encephalitis in immunocompromised hosts. Destruction of the integrity of the blood-brain barrier (BBB) is a common denominator that may be executed by leukocytic MMPs under the control of host cytokines and chemokines as well as influenced by parasite products. Mechanisms by which parasite-derived products alter host expression of MMP and endogenous MMP inhibitors, have only been described for hemozoin (Hz) in malaria. Hence, understanding these interactions in other parasitic infections remains an important challenge. Furthermore, the involved parasites are also known to produce their own metalloproteinases, and this forms an extra stimulus to investigate MMP inhibitory drugs as therapeutics. MMP inhibitors (MMPIs) may dampen collateral tissue damage, as is anecdotically reported for tetracyclines as MMP regulators in parasite infections.

Pathogenesis of chagas' disease: parasite persistence and autoimmunity

Acute Trypanosoma cruzi infections can be asymptomatic, but chronically infected individuals can die of Chagas' disease. The transfer of the parasite mitochondrial kinetoplast DNA (kDNA) minicircle to the genome of chagasic patients can explain the pathogenesis of the disease; in cases of Chagas' disease with evident cardiomyopathy, the kDNA minicircles integrate mainly into retrotransposons at several chromosomes, but the minicircles are also detected in coding regions of genes that regulate cell growth, differentiation, and immune responses. An accurate evaluation of the role played by the genotype alterations in the autoimmune rejection of self-tissues in Chagas' disease is achieved with the cross-kingdom chicken model system, which is refractory to T. cruzi infections. The inoculation of T. cruzi into embryonated eggs prior to incubation generates parasite-free chicks, which retain the kDNA minicircle sequence mainly in the macrochromosome coding genes. Crossbreeding transfers the kDNA mutations to the chicken progeny. The kDNA-mutated chickens develop severe cardiomyopathy in adult life and die of heart failure. The phenotyping of the lesions revealed that cytotoxic CD45, CD8(+) γδ, and CD8α(+) T lymphocytes carry out the rejection of the chicken heart. These results suggest that the inflammatory cardiomyopathy of Chagas' disease is a genetically driven autoimmune disease.

Regulatory T cells phenotype in different clinical forms of Chagas' disease

CD25(High) CD4+ regulatory T cells (Treg cells) have been described as key players in immune regulation, preventing infection-induced immune pathology and limiting collateral tissue damage caused by vigorous anti-parasite immune response. In this review, we summarize data obtained by the investigation of Treg cells in different clinical forms of Chagas' disease. Ex vivo immunophenotyping of whole blood, as well as after stimulation with Trypanosoma cruzi antigens, demonstrated that individuals in the indeterminate (IND) clinical form of the disease have a higher frequency of Treg cells, suggesting that an expansion of those cells could be beneficial, possibly by limiting strong cytotoxic activity and tissue damage. Additional analysis demonstrated an activated status of Treg cells based on low expression of CD62L and high expression of CD40L, CD69, and CD54 by cells from all chagasic patients after T. cruzi antigenic stimulation. Moreover, there was an increase in the frequency of the population of Foxp3+ CD25(High)CD4+ cells that was also IL-10+ in the IND group, whereas in the cardiac (CARD) group, there was an increase in the percentage of Foxp3+ CD25(High) CD4+ cells that expressed CTLA-4. These data suggest that IL-10 produced by Treg cells is effective in controlling disease development in IND patients. However, in CARD patients, the same regulatory mechanism, mediated by IL-10 and CTLA-4 expression is unlikely to be sufficient to control the progression of the disease. These data suggest that Treg cells may play an important role in controlling the immune response in Chagas' disease and the balance between regulatory and effector T cells may be important for the progression and development of the disease. Additional detailed analysis of the mechanisms on how these cells are activated and exert their function will certainly give insights for the rational design of procedure to achieve the appropriate balance between protection and pathology during parasite infections.

Immunoneuroendocrine alterations in patients with progressive forms of chronic Chagas disease

We studied the features of parallel immunoneuroendocrine responses in patients with different degrees of chronic Chagas myocarditis (indeterminate, mild/moderate or severe). A systemic inflammatory scenario was evident in patients with severe myocarditis compared to healthy subjects. This was paralleled by a disrupted activation of the hypothalamus-pituitary-adrenal axis, characterized by decreased concentrations of dehydroepiandrosterone-sulfate (DHEA-s) and an unbalanced cortisol/DHEA-s ratio, reinforcing the view that severe Chagas disease is devoid of an adequate anti-inflammatory milieu, likely involved in pathology. Our study constitutes the first demonstration of neuroendocrine disturbances, in parallel to a systemic inflammatory profile, during progressive human Chagas disease.

Trypanosoma cruzi in the chicken model: Chagas-like heart disease in the absence of parasitism

BACKGROUND

The administration of anti-trypanosome nitroderivatives curtails Trypanosoma cruzi infection in Chagas disease patients, but does not prevent destructive lesions in the heart. This observation suggests that an effective treatment for the disease requires understanding its pathogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

To understand the origin of clinical manifestations of the heart disease we used a chicken model system in which infection can be initiated in the egg, but parasite persistence is precluded. T. cruzi inoculation into the air chamber of embryonated chicken eggs generated chicks that retained only the parasite mitochondrial kinetoplast DNA minicircle in their genome after eight days of gestation. Crossbreeding showed that minicircles were transferred vertically via the germ line to chicken progeny. Minicircle integration in coding regions was shown by targeted-primer thermal asymmetric interlaced PCR, and detected by direct genomic analysis. The kDNA-mutated chickens died with arrhythmias, shortness of breath, cyanosis and heart failure. These chickens with cardiomyopathy had rupture of the dystrophin and other genes that regulate cell growth and differentiation. Tissue pathology revealed inflammatory dilated cardiomegaly whereby immune system mononuclear cells lyse parasite-free target heart fibers. The heart cell destruction implicated a thymus-dependent, autoimmune; self-tissue rejection carried out by CD45(+), CD8γδ(+), and CD8α lymphocytes.

CONCLUSIONS/SIGNIFICANCE

These results suggest that genetic alterations resulting from kDNA integration in the host genome lead to autoimmune-mediated destruction of heart tissue in the absence of T. cruzi parasites.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Myocardial gene and protein expression profiles after autoimmune injury in Chagas' disease cardiomyopathy

One third of the 16 million of individuals infected by the protozoan Trypanosoma cruzi in Latin America eventually develop chronic Chagas' disease cardiomyopathy (CCC), an inflammatory dilated cardiomyopathy with shorter survival than non-inflammatory cardiomyopathies. The presence of a T cell-rich mononuclear inflammatory infiltrate and the relative scarcity of parasites in the heart suggested that chronic inflammation secondary to the autoimmune recognition of cardiac proteins could be a major pathogenetic mechanism. Sera from CCC patients crossreactively recognize cardiac myosin and T. cruzi protein B13. T cell clones elicited from peripheral blood with T. cruzi B13 protein or its peptides could crossreactively recognize epitopes from cardiac myosin heavy chain. Likewise, CD4+ T cell clones infiltrating CCC myocardium crossreactively recognize cardiac myosin and T. cruzi protein B13, and intralesional T cell lines produce the inflammatory cytokines IFN-γ and TNF-α. Conversely, IFN-γ-induced genes and chemokines were found to be upregulated in CCC heart samples, and IFN-γ is able to induce cardiomyocyte expression of atrial natriuretic factor, a key member of the hypertrophy/heart failure signature. Proteomic analysis of CCC heart tissue showed reduced expression of the energy metabolism enzymes. It can be hypothesized that cytokine-induced modulation of cardiomyocyte gene/protein expression may be a novel disease mechanism in CCC, in addition to direct inflammatory damage.

The endless race between Trypanosoma cruzi and host immunity: lessons for and beyond Chagas disease

Infection with the protozoan parasite Trypanosoma cruzi, the agent of Chagas disease, is characterised by a variable clinical course - from symptomless cases to severe chronic disease with cardiac and/or gastrointestinal involvement. The variability in disease outcome has been attributed to host responses as well as parasite heterogeneity. In this article, we review studies indicating the importance of immune responses as key determinants of host resistance to T. cruzi infection and the pathogenesis of Chagas disease. Particular attention is given to recent studies defining the role of cognate innate immune receptors and immunodominant CD8+ T cells that recognise parasite components - both crucial for host-parasite interaction and disease outcome. In light of these studies we speculate about parasite strategies that induce a strong and long-lasting T-cell-mediated immunity but at the same time allow persistence of the parasite in the vertebrate host. We also discuss what we have learned from these studies for increasing our understanding of Chagas pathogenesis and for the design of new strategies to prevent the development of Chagas disease. Finally, we highlight recent studies employing a genetically engineered attenuated T. cruzi strain as a vaccine shuttle that elicits potent T cell responses specific to a tumour antigen and protective immunity against a syngeneic melanoma cell line.

Chagas disease: changes in knowledge and management

More than 100 years after the discovery of human American trypanosomiasis by Carlos Chagas, our knowledge and management of the disease are profoundly changing. Substantial progress made by disease control programmes in most endemic areas contrasts with persisting difficulties in the Gran Chaco region in South America and the recent emergence of the disease in non-endemic areas because of population movements. In terms of pathogenesis, major discoveries have been made about the life cycle and genomics of Trypanosoma cruzi, and the role of the parasite itself in the chronic phase of the disease. From a clinical perspective, a growing number of arguments have challenged the notion of an indeterminate phase, and suggest new approaches to manage patients. New methods such as standardised PCR will be necessary to ensure follow-up of this chronic infection. Although drugs for treatment of Chagas disease are limited, poorly tolerated, and not very effective, treatment indications are expanding. The results of the Benznidazole Evaluation For Interrupting Trypanosomiasis (BENEFIT) trial in 2012 will also help to inform treatment. Mobilisation of financial resources to fund research on diagnosis and randomised controlled trials of treatment are international health priorities.

Is there a link between the human TRIM21 and Trypanosoma cruzi Clone 36 genes in Chagas' disease?

The homology between TRIM21 and Trypanosoma cruzi Antigen Clone 36 nucleotide sequence was discovered in 1998 (Winkler et al., Parasite 5, 94-95) prior to the functions of Ro52, the TRIM21 protein product, being understood. Ro52 has since been shown to be an Ubiquitin ligase targeting transcription factors, Interferon Regulatory Factor 1 (IRF1) and Interferon Regulatory Factor 3 (IRF3), in immune cells. This communication explores the possibility that there is a connection between the Clone 36 homologous sequence and perturbation of the host immune system in Chagas' disease. RNA interference by the Clone 36 transcripts is hypothesized as a mechanism for host immune suppression during acute Chagas' disease and/or for autoimmunity in chronic Chagas' disease through down-regulation of Ro52. In the chronic forms of the disease such as Chagas Cardiomyopathy, Clone 36 RNA containing its repetitive motif may down-regulate levels of Ro52 in monocytes, fibroblasts, or T cells, allowing IRF 1 and IRF3 to continuously stimulate transcription of interferons alpha and beta, a pro-inflammatory state favoring autoimmunity. In acute Chagas' disease, messenger RNA from Clone 36 could interfere with host macrophage Ro52 RNA, down-regulating the level of Ro52 so that it would stimulate less cytokine production, including IL-12/p40. This theory is thought to help the parasite avoid attack by the innate immune system early in the acute phase of the disease. Experiments with transgenic mice and genetically modified T. cruzi are discussed which may provide insight to addressing these questions.

Specific chemotherapy of Chagas disease: relevance, current limitations and new approaches

A critical review of the development of specific chemotherapeutic approaches for the management of American Trypanosomiasis or Chagas disease is presented, including controversies on the pathogenesis of the disease, the initial efforts that led to the development of currently available drugs (nifurtimox and benznidazole), limitations of these therapies and novel approaches for the development of anti-Trypanosoma cruzi drugs, based on our growing understanding of the biology of this parasite. Among the later, the most promising approaches are ergosterol biosynthesis inhibitors such as posaconazole and ravuconazole, poised to enter clinical trials for chronic Chagas disease in the short term; inhibitors of cruzipain, the main cysteine protease of T. cruzi, essential for its survival and proliferation in vitro and in vivo; bisphosphonates, metabolic stable pyrophosphate analogs that have trypanocidal activity through the inhibition of the parasite's farnesyl-pyrophosphate synthase or hexokinase; inhibitors of trypanothione synthesis and redox metabolism and inhibitors of hypoxanthine-guanine phosphoribosyl-transferase, an essential enzyme for purine salvage in T. cruzi and related organisms. Finally, the economic and political challenges faced by development of drugs for the treatment of neglected tropical diseases, which afflict almost exclusively poor populations in developing countries, are analyzed and recent potential solutions for this conundrum are discussed.

Cardiac involvement with parasitic infections

Parasitic infections previously seen only in developing tropical settings can be currently diagnosed worldwide due to travel and population migration. Some parasites may directly or indirectly affect various anatomical structures of the heart, with infections manifested as myocarditis, pericarditis, pancarditis, or pulmonary hypertension. Thus, it has become quite relevant for clinicians in developed settings to consider parasitic infections in the differential diagnosis of myocardial and pericardial disease anywhere around the globe. Chagas' disease is by far the most important parasitic infection of the heart and one that it is currently considered a global parasitic infection due to the growing migration of populations from areas where these infections are highly endemic to settings where they are not endemic. Current advances in the treatment of African trypanosomiasis offer hope to prevent not only the neurological complications but also the frequently identified cardiac manifestations of this life-threatening parasitic infection. The lack of effective vaccines, optimal chemoprophylaxis, or evidence-based pharmacological therapies to control many of the parasitic diseases of the heart, in particular Chagas' disease, makes this disease one of the most important public health challenges of our time.

Chagas disease

Chagas disease is a chronic, systemic, parasitic infection caused by the protozoan Trypanosoma cruzi, and was discovered in 1909. The disease affects about 8 million people in Latin America, of whom 30-40% either have or will develop cardiomyopathy, digestive megasyndromes, or both. In the past three decades, the control and management of Chagas disease has undergone several improvements. Large-scale vector control programmes and screening of blood donors have reduced disease incidence and prevalence. Although more effective trypanocidal drugs are needed, treatment with benznidazole (or nifurtimox) is reasonably safe and effective, and is now recommended for a widened range of patients. Improved models for risk stratification are available, and certain guided treatments could halt or reverse disease progression. By contrast, some challenges remain: Chagas disease is becoming an emerging health problem in non-endemic areas because of growing population movements; early detection and treatment of asymptomatic individuals are underused; and the potential benefits of novel therapies (eg, implantable cardioverter defibrillators) need assessment in prospective randomised trials.

Cellular and genetic mechanisms involved in the generation of protective and pathogenic immune responses in human Chagas disease

Perhaps one of the most intriguing aspects of human Chagas disease is the complex network of events that underlie the generation of protective versus pathogenic immune responses during the chronic phase of the disease. While most individuals do not develop patent disease, a large percentage may develop severe forms that eventually lead to death. Although many efforts have been devoted to deciphering these mechanisms, there is still much to be learned before we can fully understand the pathogenesis of Chagas disease. It is clear that the host's immune response is decisive in this process. While characteristics of the parasite influence the immune response, it is becoming evident that the host genetic background plays a fundamental role in the establishment of pathogenic versus protective responses. The involvement of three complex organisms, host, parasite and vector, is certainly one of the key aspects that calls for multidisciplinary approaches towards the understanding of Chagas disease. We believe that now, one hundred years after the discovery of Chagas disease, it is imperative to continue with highly interactive research in order to elucidate the immune response associated with disease evolution, which will be essential in designing prophylactic or therapeutic interventions.

The BENEFIT trial: testing the hypothesis that trypanocidal therapy is beneficial for patients with chronic Chagas heart disease

Among the pathophysiological derangements operating in the chronic phase of Chagas disease, parasite persistence is likely to constitute the main mechanism of myocardial injury in patients with chronic chagasic cardiomyopathy. The presence of Trypanosoma cruzi in the heart causes a low-grade, but relentless, inflammatory process and induces myocardial autoimmune injury. These facts suggest that trypanocidal therapy may positively impact the clinical course of patients with chronic Chagas heart disease. However, the experimental and clinical evidence currently available is insufficient to support the routine use of etiologic treatment in these patients. The BENEFIT project--Benznidazole Evaluation for Interrupting Trypanosomiasis--is an international, multicenter, double-blind, placebo-controlled trial of trypanocidal treatment with benznidazole in patients with chronic Chagas heart disease. This project is actually comprised of two studies. The pilot study investigates whether etiologic treatment significantly reduces parasite burden, as assessed by polymerase chain reaction-based techniques and also determines the safety and tolerability profile of the trypanocidal drug in this type of chagasic population. The full-scale study determines whether antitrypanosomal therapy with benznidazole reduces mortality and other major cardiovascular clinical outcomes in patients with chronic Chagas heart disease.

Chagas cardiomyopathy--where do we stand after a hundred years?

A hundred years from its description, Chagas cardiomyopathy remains a challenging disease. Although successful vector-control strategies have decreased the incidence of Chagas disease in several Latin American countries, both migration to urban areas and immigration have spread the disease worldwide; and now, blood transfusion, organ transplantation, and vertical transmission are a concern. The pathogenesis of Chagas cardiomyopathy involves complex host-parasite interactions, where low-grade but incessant systemic infection and triggered autoimmune reaction are the main mechanisms for its development, with the contribution of autonomic damage and microvascular disturbances. Chagas cardiomyopathy is the most important clinical presentation of Chagas disease and comprises a wide range of manifestations, including heart failure, arrhythmias, heart blocks, sudden death, thromboembolism, and stroke. Recently, simple clinical prognostic scores have been developed to identify high-risk patients and help with management. The treatment of Chagas cardiomyopathy focuses mostly on managing heart failure, arrhythmias, and thromboembolism. The role of specific antiparasitic therapy in the chronic form is not yet defined, and a randomized trial is now under way to address this crucial point. In this article, we review the main clinical aspects of Chagas cardiomyopathy and underscore some upcoming challenges for the appropriate control, diagnosis, and management of this complex disease.

Risk of autoimmune disease: challenges for immunotoxicity testing

Autoimmunity represents a potentially diverse and complex category among the range of adverse outcomes for detection with immunotoxicity testing. For this reason, the risk of autoimmune disease is discussed in this overview chapter with additional mention among the later specific protocol chapters. Improvements in clinical diagnostic capabilities and disease recognition have led to a more accurate picture of the extent of autoimmune diseases across different human populations. While the risk of any single autoimmune disease remains modest when compared with that of lung or heart disease, the cumulative prevalence of autoimmune diseases is both significant and increasing. Autoimmune diseases are usually viewed in the context of the damaged tissue or organ (e.g., as a thyroid, gastrointestinal, cardiovascular or neurological disease). But improved recognition that underlying immune dysfunction can connect the risks for these as well as other diseases is critical for optimizing risk assessment. Since autoimmune diseases are chronic in nature with many first appearing in children or in young adults, these diseases exert a serious impact on both health care costs and quality of life. This chapter provides a discussion of the issues that should be considered with immunotoxicity testing for risk of autoimmunity.

Increased frequency of anti-retina antibodies in asymptomatic patients with chronic t. gondii infection

PURPOSE

To search for anti-retina antibodies that serve as markers for eye disease in uveitis.

MATERIALS AND METHODS

Stored sera from patients with uveitis, ocular toxoplasmosis (n = 30) and non-infectious, immune-mediated uveitis (n = 50) and from asymptomatic individuals who were positive (n = 250) and negative (n = 250) for anti-Toxoplasma antibodies were tested. Serum anti-retina IgG was detected by an optimized ELISA using a solid-phase whole human retina extract, bovine S-antigen or interphotoreceptor retinoid-binding protein.

RESULTS

Uveitis patients showed a higher mean reactivity to whole human retina extract, interphotoreceptor retinoid-binding protein and S-antigen in comparison to the asymptomatic population. These findings were independent of the uveitis origin and allowed the determination of the lower anti-retina antibody cut-off for the three antigens. Asymptomatic anti-Toxoplasma serum-positive individuals showed a higher frequency of antihuman whole retina extract antibodies in comparison to asymptomatic anti-Toxoplasma serum-negative patients. The bovine S-antigen and interphotoreceptor retinoid-binding protein ELISAs also showed a higher mean reactivity in the uveitis groups compared to the asymptomatic group, but the observed reactivities were lower and overlapped without discrimination.

CONCLUSION

We detected higher levels of anti-retina antibodies in uveitis patients and in a small fraction of asymptomatic patients with chronic toxoplasmosis. The presence of anti-retina antibodies in sera might be a marker of eye disease in asymptomatic patients, especially when whole human retina extract is used in a solid-phase ELISA.

Critical role of glycosylation in determining the length and structure of T cell epitopes

Background

Using a combined in silico approach, we investigated the glycosylation of T cell epitopes and autoantigens. The present systems biology analysis was made possible by currently available databases (representing full proteomes, known human T cell epitopes and autoantigens) as well as glycosylation prediction tools.

Results

We analyzed the probable glycosylation of human T cell epitope sequences extracted from the ImmuneEpitope Database. Our analysis suggests that in contrast to full length SwissProt entries, only a minimal portion of experimentally verified T cell epitopes is potentially N- or O-glycosylated (2.26% and 1.22%, respectively). Bayesian analysis of entries extracted from the Autoantigen Database suggests a correlation between N-glycosylation and autoantigenicity. The analysis of random generated sequences shows that glycosylation probability is also affected by peptide length. Our data suggest that the lack of peptide glycosylation, a feature that probably favors effective recognition by T cells, might have resulted in a selective advantage for short peptides to become T cell epitopes. The length of T cell epitopes is at the intersection of curves determining specificity and glycosylation probability. Thus, the range of length of naturally occurring T cell epitopes may ensure the maximum specificity with the minimal glycosylation probability.

Conclusion

The findings of this bioinformatical approach shed light on fundamental factors that might have shaped adaptive immunity during evolution. Our data suggest that amino acid sequence-based hypo/non-glycosylation of certain segments of proteins might be substantial for determining T cell immunity/autoimmunity.

Biological, ultrastructural effect and subcellular localization of aromatic diamidines in Trypanosoma cruzi

No vaccines or safe chemotherapy are available for Chagas disease. Pentamidine and related di-cations are DNA minor groove-binders with broad-spectrum anti-protozoal activity. Therefore our aim was to evaluate the in vitro efficacy of di-cationic compounds - DB1645, DB1582, DB1651, DB1646, DB1670 and DB1627 - against bloodstream trypomastigotes (BT) and intracellular forms of Trypanosoma cruzi. Cellular targets of these compounds in treated parasites were also analysed by fluorescence and transmission electron microscopy (TEM). DB1645, DB1582 and DB1651 were the most active against BT showing IC50 values ranging between 0.15 and 6.9 microm. All compounds displayed low toxicity towards mammalian cells and DB1645, DB1582 and DB1651 were also the most effective against intracellular parasites, with IC50 values ranging between 7.3 and 13.3 microm. All compounds localized in parasite nuclei and kDNA (with greater intensity in the latter structure), and DB1582 and DB1651 also concentrated in non-DNA-containing cytoplasmic organelles possibly acidocalcisomes. TEM revealed alterations in mitochondria and kinetoplasts, as well as important disorganization of microtubules. Our data provide further information regarding the activity of this class of compounds upon T. cruzi which should aid future design and synthesis of agents that could be used for Chagas disease therapy.

Trypanosoma cruzi: Immunological predictors of benznidazole efficacy during experimental infection

C3H/HeN male mice were infected with a lethal population of Trypanosoma cruzi and treated with benznidazole (Bz). Parasitemia, body weight and survival rate were registered during the therapy with significant improvement for T. cruzi-infected Bz-treated animals. Besides, flow cytometry resulted a useful method to discriminate between cured animals from those not cured by monitoring IgG(1) bound to live trypomastigotes levels. At the end of Bz therapy, the LT splenocyte compartment was studied for activation/memory cell surface markers (CD(69)(+) and CD(44)(+)). Cytofluorometric analysis showed that T. cruzi-infected untreated mice increased their activated LT numbers and this effect was completely abolished only in cured mice at the end of Bz administration. The same behavior was observed for the memory LT subpopulation correlating to an effector memory (CD(62L)(-)) displayed by T. cruzi infection. Bz treatment was able to modulate the immunological response by reducing the deleterious effect of the acute phase in all T. cruzi-infected mice.

Differential distribution of Trypanosoma cruzi clones in human chronic chagasic cardiopathic and non-cardiopathic individuals

PCR and Southern blot hybridization were used to determine the distribution of Trypanosoma cruzi clones in 37 chronic chagasic cardiopathic and non-cardiopathic patients. Parasite DNA amplified from peripheral blood or dejections of Triatoma infestans fed on patient blood was hybridized with probes containing hypervariable minicircle nucleotide sequences capable of detecting three sublineages of T. cruzi. Probes Z-I and Z-IIb detect unique sequences in lineages TcI and TcIIb, respectively. Probe Z-hybrid detects sequences of lineages TcIId and TcIIe. T. cruzi clones of the Z-I sublineage were detected in 62.2% of T. infestans dejections and 5.4% of peripheral blood samples. Clones of Z-IIb and Z-hybrid sublineages had similar distribution in blood and dejection samples. Interestingly, clones of the Z-IIb sublineage were significantly lower in cardiopathic than in non-cardiopathic patients (23.5% versus 75%; P=0.0006). Clones of the Z-hybrid sublineage were found in 29.4% of cardiopathic and 75% of non-cardiopathic patients, respectively (P=0.0051). By contrast, clones of sublineage Z-I were similarly distributed in both groups of patients. The low frequency of Z-IIb and Z-hybrid sublineage clones detected in cardiopathic patients suggests that the immunological mechanisms involved in controlling and eliminating these T. cruzi parasites may be detrimental to the host, leading to the development of chagasic cardiomyopathy.

The role of infections in autoimmune disease

Autoimmunity occurs when the immune system recognizes and attacks host tissue. In addition to genetic factors, environmental triggers (in particular viruses, bacteria and other infectious pathogens) are thought to play a major role in the development of autoimmune diseases. In this review, we (i) describe the ways in which an infectious agent can initiate or exacerbate autoimmunity; (ii) discuss the evidence linking certain infectious agents to autoimmune diseases in humans; and (iii) describe the animal models used to study the link between infection and autoimmunity.

Trypanosoma cruzi calreticulin: a possible role in Chagas' disease autoimmunity

Trypanosoma cruzi (T. cruzi) is the causative agent of Chagas' disease, an endemic and chronic illness that affects 18 million people in Latin America. The mechanisms underlying its pathogenesis are controversial. There is a growing body of evidence supporting the view that T. cruzi infection elicits severe autoimmune responses in the host, which significantly contribute to the pathogenesis of Chagas' disease, and several recent studies have reported the presence of autoantibodies and effector T lymphocytes against parasite and self antigens in infected patients and experimentally infected animals. T. cruzi calreticulin (TcCRT) is a 45kDa protein, immunogenic in humans, rabbits and mice. It has a high degree of homology with human (HuCRT) and mouse calreticulin (MoCRT), which would explain why an immune response to TcCRT could contribute to autoimmune reactions in Chagas' disease. Anti-TcCRT antibodies generated in A/J mice immunized with recombinant TcCRT (rTcCRT) reacted with rHuCRT and bound to neonatal and adult isogenic cardiomyocytes cultured in vitro. Interestingly, histological alterations, such as edema formation and cell infiltrates, which include CD3(+) cells, were detected in heart sections from immunized animals. Therefore, in rTcCRT-immunized mice, an autoimmune reaction against host CRT, paralleled by histological cardiac alterations, suggests a role of the parasite molecule in the induction of immunologically mediated heart tissue damage. The data presented here propose that TcCRT participates in the induction of cardiac autoimmunity in Chagas' disease.

Infections and autoimmunity: a panorama

For more than 2,000 years, it was thought that malignant spirits caused diseases. By the end of nineteenth century, these beliefs were displaced by more modern concepts of disease, namely, the formulation of the “germ theory,” which asserted that bacteria or other microorganisms caused disease. With the emergence of chronic degenerative and of autoimmune diseases in the last century, the causative role of microorganisms has been intensely debated; however, no clear explanatory models have been achieved. In this review, we examine the current available literature regarding the relationships between infections and 16 autoimmune diseases. We critically analyzed clinical, serological, and molecular associations, and reviewed experimental models of induction of and, alternatively, protection from autoimmune diseases by infection. After reviewing several studies and reports, a clinical and experimental pattern emerges: Chronic and multiple infections with viruses, such as Epstein–Barr virus and cytomegalovirus, and bacteria, such as H. pylori, may, in susceptible individuals, play a role in the evolvement of autoimmune diseases. As the vast majority of infections pertain to our resident microbiota and endogenous retroviruses and healthy carriage of infections is the rule, we propose to focus on understanding the mechanisms of this healthy carrier state and what changes its configurations to infectious syndromes, to the restoration of health, or to the sustaining of illness into a chronic state and/or autoimmune disease. It seems that in the development of this healthy carriage state, the infection or colonization in early stages of ontogenesis with key microorganisms, also called ‘old friends’ (lactobacilli, bifidobacteria among others), are important for the healthy living and for the protection from infectious and autoimmune syndromes.

Chagas heart disease pathogenesis: one mechanism or many?

Chagas heart disease (CHD), caused by the protozoan parasite Trypanosoma cruzi, is the leading cause of infectious myocarditis in the world. The etiology of CHD is unclear and multiple mechanisms have been proposed to explain the pathogenesis of the disease. This review describes the proposed mechanisms of CHD pathogenesis and evaluates the historical significance and evidence supporting each. Although the majority of CHD-related pathologies are currently attributed to parasite persistence in the myocardium and autoimmunity, there is strong evidence that CHD develops as a result of additive and even synergistic effects of several distinct mechanisms rather than one factor.

Human autoantibodies specific for neurotrophin receptors TrkA, TrkB, and TrkC protect against lethal Trypanosoma cruzi infection in mice

Patients with Chagas' disease remain asymptomatic for many years, presumably by keeping the etiological agent Trypanosoma cruzi in check through protective immunity against. Recently, we found that T. cruzi uses TrkA, a receptor tyrosine kinase responsive to neurotrophin nerve growth factor in vertebrate nervous systems, to invade cells. We also found that TrkA, TrkB, and TrkC, but not T. cruzi, are targets of specific autoantibodies present in the sera of patients with chronic Chagas' disease. Here we show that TrkA-, TrkB-, and TrkC-specific autoantibodies isolated from the sera of four individuals with chronic indeterminate (asymptomatic) Chagas' disease potently blocked invasion of Trk-bearing neuronal PC12 cells, neuroglial astrocytes, enteroglial cells, and Schwann cells and Trk-expressing non-neural smooth muscle and dendritic cells. However, these autoantibodies did not inhibit T. cruzi invasion of mutant PC12 cells lacking TrkA or of normal cells lacking Trk receptors, suggesting that autoantibodies interfered with parasite/Trk cross talk to access the intracellular milieu. Passive immunization of susceptible and resistant mouse strains with very small doses of these autoantibodies reduced parasitemia and transferred resistance to an otherwise lethal trypanosome infection. Hence, this exquisitely sensitive and unique regulatory immunity against the host (instead of parasite) could benefit infected individuals by blocking cellular invasion of the obligatory intracellular pathogen, resulting in attenuation of tissue infection and clinical manifestations. Such action is contrary to the horror autotoxicus frequently associated with microbe-related autoimmune responses.

Rationale and design of a randomized placebo-controlled trial assessing the effects of etiologic treatment in Chagas' cardiomyopathy: the BENznidazole Evaluation For Interrupting Trypanosomiasis (BENEFIT)

BACKGROUND

Benznidazole is effective for treating acute and chronic (recently acquired) Trypanosoma cruzi infection (Chagas' disease). Recent data indicate that parasite persistence plays a pivotal role in the pathogenesis of chronic Chagas' cardiomyopathy. However, the efficacy of trypanocidal therapy in preventing clinical complications in patients with preexisting cardiac disease is unknown.

STUDY DESIGN

BENEFIT is a multicenter, randomized, double-blind, placebo-controlled clinical trial of 3,000 patients with Chagas' cardiomyopathy in Latin America. Patients are randomized to receive benznidazole (5 mg/kg per day) or matched placebo, for 60 days. The primary outcome is the composite of death; resuscitated cardiac arrest; sustained ventricular tachycardia; insertion of pacemaker or cardiac defibrillator; cardiac transplantation; and development of new heart failure, stroke, or systemic or pulmonary thromboembolic events. The average follow-up time will be 5 years, and the trial has a 90% power to detect a 25% relative risk reduction. The BENEFIT program also comprises a substudy evaluating the effects of benznidazole on parasite clearance and an echo substudy exploring the impact of etiologic treatment on left ventricular function. Recruitment started in November 2004, and >1,000 patients have been enrolled in 35 centers from Argentina, Brazil, and Colombia to date.

CONCLUSION

This is the largest trial yet conducted in Chagas' disease. BENEFIT will clarify the role of trypanocidal therapy in preventing cardiac disease progression and death.

Auto-antibodies to receptor tyrosine kinases TrkA, TrkB and TrkC in patients with chronic Chagas' disease

The Chagas' disease parasite Trypanosoma cruzi promotes survival and differentiation of neurones by binding and activating nerve growth factor (NGF) receptor TrkA. The functional mimic of NGF in T. cruzi is a surface-bound and shed immunogenic protein [neurotrophic factor/trans-sialidase (TS)], which raised the possibility that immune response to T. cruzi in general and to neurotrophic factor/TS in particular leads to loss of immunological tolerance to host NGF and/or the NGF-binding partner TrkA. In testing this hypothesis, we found that sera of individuals with chronic Chagas' disease bear unique IgG2 autoantibodies that bind TrkA and TrkA family members TrkB and TrkC (ATA). Binding of ATA to Trk receptors is specific because the autoantibodies did not cross-react with five other growth factor receptors, NGF and other neurotrophins, and T. cruzi. Thus, individuals with chronic Chagas' disease produce unique antibodies that react with pan-Trk receptors, one of which (TrkA) T. cruzi exploits to inhibit host cell apoptosis and to promote cellular invasion.

Role of Trypanosoma cruzi autoreactive T cells in the generation of cardiac pathology

Chagas disease, caused by Trypanosoma cruzi, affects several million people in Central and South America. About 30% of chronic patients develop cardiomyopathy probably caused by parasite persistence and/or autoimmunity. While several cross-reactive antibodies generated during mammal T. cruzi infection have been described, very few cross-reactive T cells have been identified. We performed adoptive transfer experiments of T cells isolated from chronically infected mice. The results showed the generation of cardiac pathology in the absence of parasites. We also transferred cross-reactive SAPA-specific T cells and observed unspecific alterations in heart repolarization, cardiac inflammatory infiltration, and tissue damage.

Etiological treatment of chronic Chagas disease: neglected 'evidence' by evidence-based medicine

No randomized clinical trials regarding the etiological treatment of chronic Chagas disease can be found in the medical literature. However, other 'evidence' sustaining the use of anti-Trypanosoma cruzi drugs for adult individuals with Chagas disease will be analyzed along with the limitations in evaluating the treatment efficacy. Today, the hypothesis of T. cruzi persistence in the target organs giving rise to the chronic inflammatory response is sustained. In addition, several experimental, pathological, nonrandomized clinical studies and studies based on the response or serological evolution (besides the clinical experience) demonstrate the role of T. cruzi in the pathogenesis of the chronic stage and the efficacy of etiological treatment to reduce the titers of antibodies and the progression of chronic Chagas heart disease. All of this supports the recommendation of treatment for every patient diagnosed with Chagas disease. The interpretation of this sum of evidence is not considered from the perspective of evidence-based medicine.

Trypanosoma cruzi infection from the view of CD8+ T cell immunity--an infection model for developing T cell vaccine

Chagas' disease is caused by Trypanosoma cruzi (T. cruzi) which was once prevalent in Central and South America. Although the recent success in Triatoma vector control has made the disease being possibly "extinct" in the near future, the development of effective preventive and therapeutic vaccines is still necessary to prevent the resurgence of the neglected infection. In addition to the importance for containing the disease, T. cruzi infection presents unique features for elucidating hosts' immune responses against intracellular infectious agents. Due to its biological capacity for invading into principally any types of cells and for causing systemic infection which damages particularly muscle and neural cells, T cell immunity is critical for resolving its infection. Although T cell-mediated immune responses have been, so far, extensively investigated in viral and bacterial infections, parasitic infection such as malaria has presented epoch-making discovery in T cell immunity. Recent advances in the analyses of T cell-mediated immune responses against T. cruzi infection now make this infectious disease potentially more suitable for detecting subtle immunological changes in hosts' immune defense upon modifying immune system. The current review focuses on the usefulness of T. cruzi infection as a model for developing effective CD8(+) T cell-mediated vaccine against intracellular infectious agents.

TNF blockade aggravates experimental chronic Chagas disease cardiomyopathy

Chronic Chagas disease cardiomyopathy (CCC), caused by Trypanosoma cruzi, is an inflammatory dilated cardiomyopathy associated with increased circulating levels of TNF-alpha. We investigate whether TNF blockade with Etanercept during the chronic phase of T. cruzi infection could attenuate experimental CCC development. The effect of Etanercept was evaluated after 11 months of T. cruzi infection on survival, parasitism, left ventricular function, intensity of myocarditis, fibrosis, and left ventricular mRNA expression of cytokines and TNF-alpha-induced genes. Left ventricular function was significantly reduced in treated animals as compared to infected untreated animals. Blood and cardiac parasitism as well as survival rate were not altered with Etanercept treatment. Inflammatory infiltrates were located predominantly in the subendocardic region in treated animals, whereas in untreated animals inflammation was scattered throughout the myocardium. Left ventricular mRNA IL-10 expression was significantly higher, and iNOS, significantly lower in treated than in untreated animals. mRNA expression of TNF-alpha, IFN-gamma, TGF-beta, A20 and ANP was similar in both groups. Our results suggest that TNF-alpha/LT-alpha blockade with Etanercept enhances left ventricular dysfunction in T. cruzi-induced chronic cardiomyopathy and the absence of TNF signaling may be deleterious to the failing heart in Chagas disease cardiomyopathy.

Pathogenesis of chronic Chagas heart disease

BACKGROUND

Chagas disease remains a significant public health issue and a major cause of morbidity and mortality in Latin America. Despite nearly 1 century of research, the pathogenesis of chronic Chagas cardiomyopathy is incompletely understood, the most intriguing challenge of which is the complex host-parasite interaction.

METHODS AND RESULTS

A systematic review of the literature found in MEDLINE, EMBASE, BIREME, LILACS, and SCIELO was performed to search for relevant references on pathogenesis and pathophysiology of Chagas disease. Evidence from studies in animal models and in anima nobile points to 4 main pathogenetic mechanisms to explain the development of chronic Chagas heart disease: autonomic nervous system derangements, microvascular disturbances, parasite-dependent myocardial aggression, and immune-mediated myocardial injury. Despite its prominent peculiarities, the role of autonomic derangements and microcirculatory disturbances is probably ancillary among causes of chronic myocardial damage. The pathogenesis of chronic Chagas heart disease is dependent on a low-grade but incessant systemic infection with documented immune-adverse reaction. Parasite persistence and immunological mechanisms are inextricably related in the myocardial aggression in the chronic phase of Chagas heart disease.

CONCLUSIONS

Most clinical studies have been performed in very small number of patients. Future research should explore the clinical potential implications and therapeutic opportunities of these 2 fundamental underlying pathogenetic mechanisms.