HLA and beta-myosin heavy chain do not influence susceptibility to Chagas disease cardiomyopathy

Cytokine Networks as Targets for Preventing and Controlling Chagas Heart Disease

Chagas disease, a neglected disease caused by the protozoan Trypanosoma cruzi, is endemic in 21 Latin American countries, affecting 6-8 million people. Increasing numbers of Chagas disease cases have also been reported in non-endemic countries due to migration, contamination via blood transfusions or organ transplantation, characterizing Chagas as an emerging disease in such regions. While most individuals in the chronic phase of Chagas disease remain in an asymptomatic clinical form named indeterminate, approximately 30% of the patients develop a cardiomyopathy that is amongst the deadliest cardiopathies known. The clinical distinctions between the indeterminate and the cardiac clinical forms are associated with different immune responses mediated by innate and adaptive cells. In this review, we present a collection of studies focusing on the human disease, discussing several aspects that demonstrate the association between chemokines, cytokines, and cytotoxic molecules with the distinct clinical outcomes of human infection with Trypanosoma cruzi. In addition, we discuss the role of gene polymorphisms in the transcriptional control of these immunoregulatory molecules. Finally, we discuss the potential application of cytokine expression and gene polymorphisms as markers of susceptibility to developing the severe form of Chagas disease, and as targets for disease control.

A Specific IL6 Polymorphic Genotype Modulates the Risk of Trypanosoma cruzi Parasitemia While IL18, IL17A, and IL1B Variant Profiles and HIV Infection Protect Against Cardiomyopathy in Chagas Disease

Background

Chagas disease caused by Trypanosoma cruzi (T. cruzi) affects approximately six million individuals worldwide. Clinical manifestations are expected to occur due to the parasite persistence and host immune response. Herein we investigated potential associations between IL1B, IL6, IL17A, or IL18 polymorphism profiles and cardiomyopathy or T. cruzi parasitemia, as well as the impact of HIV infection on cardiopathy.

Methods

Two hundred twenty-six patients and 90 control individuals were analyzed. IL1B rs1143627 T>C, IL6 rs1800795 C>G, IL17A rs2275913 G>A, IL18 rs187238 C>G, and IL18 rs1946518 C>A SNVs were analyzed by real-time PCR and T. cruzi parasitemia by PCR.

Results

Our data revealed association between a cytokine gene polymorphism and parasitemia never previously reported. The IL6 rs1800795 CG genotype lowered the risk of positive parasitemia (OR = 0.45, 95% CI 0.24–0.86, P = 0.015). Original findings included associations between IL17A rs2275913 AA and IL18 s1946518 AA genotypes with decreased risk of developing cardiomyopathy (OR = 0.27, 95% CI 0.07–0.97, P = 0.044; and OR = 0.35, 95% CI 0.14–0.87, P = 0.023, respectively). IL18 rs1946518 AA and IL1B rs1143627 TC were associated with reduced risk for cardiomyopathy severity, including NYHA (New York Heart Association) class ≥ 2 (OR = 0.21, 95% CI 0.06–0.68, P = 0.009; and OR = 0.48, 95% CI 0.24–0.95, P = 0.036, respectively) and LVEF (left ventricular ejection fraction) <45% for IL18 rs1946518 AA (OR = 0.22, 95% CI 0.05–0.89, P = 0.034). A novel, unexpected protective effect of HIV infection against development/progression of cardiomyopathy was identified, based on a lower risk of developing cardiopathy (OR = 0.48, 95% CI 0.23–0.96, P = 0.039), NYHA class ≥ 2 (OR = 0.15, 95% CI 0.06–0.39, P < 0.001), and LVEF < 45% (OR = 0.03, 95% CI 0.00–0.25, P = 0.001). Digestive involvement was negatively associated with NYHA ≥ 2 and LVEF < 45% (OR = 0.20, 95% CI 0.09–0.47, P < 0.001; and OR = 0.24, 95% CI 0.09–0.62, P = 0.004, respectively).

Conclusions

Our data support a protective role of IL17A AA, IL18 AA, and IL1B TC genotypes against development/progression of cardiomyopathy and a modulatory effect of the IL6 CG genotype on the risk of parasitemia in Chagas disease. Notably, HIV infection was shown to protect against development/progression of cardiopathy, potentially associated with a synergistic effect of HIV and highly active antiretroviral therapy (HAART), attenuating a Th1-mediated response in the myocardium. This proposed hypothesis requires confirmation, however, in larger and more comprehensive future studies.

Genetic Polymorphisms of IL17 and Chagas Disease in the South and Southeast of Brazil

The aim of this study was to investigate possible associations between genetic polymorphisms of IL17A G197A (rs2275913) and IL17F T7488C (rs763780) with Chagas Disease (CD) and/or the severity of left ventricular systolic dysfunction (LVSD) in patients with chronic Chagas cardiomyopathy (CCC). The study with 260 patients and 150 controls was conducted in the South and Southeast regions of Brazil. The genotyping was performed by PCR-RFLP. The A allele and A/A genotype of IL17A were significantly increased in patients and their subgroups (patients with CCC; patients with CCC and LVSD; and patients with CCC and severe LVSD) when compared to the control group. The analysis according to the gender showed that the A/A genotype of IL17A was more frequent in female with LVSD and mild to moderate LVSD and also in male patients with LVSD. The frequency of IL17F T/C genotype was higher in male patients with CCC and severe LVSD and in female with mild to moderate LVSD. The results suggest the possible involvement of the polymorphisms of IL17A and IL17F in the susceptibility to chronic Chagas disease and in development and progression of cardiomyopathy.

Chagas disease cardiomyopathy: immunopathology and genetics

Chagas disease, caused by the protozoan Trypanosoma cruzi, is endemic in Latin America and affects ca. 10 million people worldwide. About 30% of Chagas disease patients develop chronic Chagas disease cardiomyopathy (CCC), a particularly lethal inflammatory cardiomyopathy that occurs decades after the initial infection, while most patients remain asymptomatic. Mortality rate is higher than that of noninflammatory cardiomyopathy. CCC heart lesions present a Th1 T-cell-rich myocarditis, with cardiomyocyte hypertrophy and prominent fibrosis. Data suggest that the myocarditis plays a major pathogenetic role in disease progression. Major unmet goals include the thorough understanding of disease pathogenesis and therapeutic targets and identification of prognostic genetic factors. Chagas disease thus remains a neglected disease, with no vaccines or antiparasitic drugs proven efficient in chronically infected adults, when most patients are diagnosed. Both familial aggregation of CCC cases and the fact that only 30% of infected patients develop CCC suggest there might be a genetic component to disease susceptibility. Moreover, previous case-control studies have identified some genes associated to human susceptibility to CCC. In this paper, we will review the immunopathogenesis and genetics of Chagas disease, highlighting studies that shed light on the differential progression of Chagas disease patients to CCC.

Polymorphism in the alpha cardiac muscle actin 1 gene is associated to susceptibility to chronic inflammatory cardiomyopathy

Aims

Chagas disease, caused by the protozoan Trypanosoma cruzi is endemic in Latin America, and may lead to a life-threatening inflammatory dilated, chronic Chagas cardiomyopathy (CCC). One third of T. cruzi-infected individuals progress to CCC while the others remain asymptomatic (ASY). A possible genetic component to disease progression was suggested by familial aggregation of cases and the association of markers of innate and adaptive immunity genes with CCC development. Since mutations in multiple sarcomeric genes, including alpha-cardiac actin (ACTC1) have been involved in hereditary dilated cardiomyopathy, we investigated the involvement of the ACTC1 gene in CCC pathogenesis.

Methods and Results

We conducted a proteomic and genetic study on a Brazilian study population. The genetic study was done on a main cohort including 118 seropositive asymptomatic subjects and 315 cases and the replication was done on 36 asymptomatic and 102 CCC cases. ACTC1 protein and mRNA levels were lower in myocardial tissue from patients with end-stage CCC than those found in hearts from organ donors. Genotyping a case-control cohort of CCC and ASY subjects for all informative single nucleotide polymorphism (SNP) in the ACTC1 gene identified rs640249 SNP, located at the 5’ region, as associated to CCC. Associations are borderline after correction for multiple testing. Correlation and haplotype analysis led to the identification of a susceptibility haplotype. Functional assays have shown that the rs640249A/C polymorphism affects the binding of transcriptional factors in the promoter regions of the ACTC1 gene. Confirmation of the detected association on a larger independent replication cohort will be useful.

Conclusions

Genetic variations at the ACTC1 gene may contribute to progression to chronic Chagas Cardiomyopathy among T. cruzi-infected patients, possibly by modulating transcription factor binding to ACTC1 promoter regions.

Genetic susceptibility to Chagas disease cardiomyopathy: involvement of several genes of the innate immunity and chemokine-dependent migration pathways

BACKGROUND

Chagas disease, caused by the protozoan Trypanosoma cruzi is endemic in Latin America. Thirty percent of infected individuals develop chronic Chagas cardiomyopathy (CCC), an inflammatory dilated cardiomyopathy that is, by far, the most important clinical consequence of T. cruzi infection. The others remain asymptomatic (ASY). A possible genetic component to disease progression was suggested by familial aggregation of cases and the association of markers of innate and adaptive immunity genes with CCC development. Migration of Th1-type T cells play a major role in myocardial damage.

METHODS

Our genetic analysis focused on CCR5, CCL2 and MAL/TIRAP genes. We used the Tag SNPs based approach, defined to catch all the genetic information from each gene. The study was conducted on a large Brazilian population including 315 CCC cases and 118 ASY subjects.

RESULTS

The CCL2rs2530797A/A and TIRAPrs8177376A/A were associated to an increase susceptibility whereas the CCR5rs3176763C/C genotype is associated to protection to CCC. These associations were confirmed when we restricted the analysis to severe CCC, characterized by a left ventricular ejection fraction under 40%.

CONCLUSIONS

Our data show that polymorphisms affecting key molecules involved in several immune parameters (innate immunity signal transduction and T cell/monocyte migration) play a role in genetic susceptibility to CCC development. This also points out to the multigenic character of CCC, each polymorphism imparting a small contribution. The identification of genetic markers for CCC will provide information for pathogenesis as well as therapeutic targets.

Genetic susceptibility to Chagas disease: an overview about the infection and about the association between disease and the immune response genes

Chagas disease, which is caused by the flagellate parasite Trypanosoma cruzi, affects 8-10 million people in Latin America. The disease is endemic and is characterised by acute and chronic phases that develop in the indeterminate, cardiac, and/or gastrointestinal forms. The immune response during human T. cruzi infection is not completely understood, despite its role in driving the development of distinct clinical manifestations of chronic infection. Polymorphisms in genes involved in the innate and specific immune response are being widely studied in order to clarify their possible role in the occurrence or severity of disease. Here we review the role of classic and nonclassic MHC, KIR, and cytokine host genetic factors on the infection by T. cruzi and the clinical course of Chagas disease.

Evidence for T Cell Help in the IgG Response against Tandemly Repetitive Trypanosoma cruzi B13 Protein in Chronic Chagas Disease Patients

The tandemly repetitive Trypanosoma cruzi B13 protein is an immunodominant antigen among Chagas disease patients. Such repetitive domains may behave as T-independent antigens. However, T cells can recognize B13 epitopes in an HLA class II-restricted fashion and could potentially provide cognate T cell help and boost antibody titers. We assessed whether the presence of HLA class II molecules able to present B13 epitopes to T cells could affect anti-B13 IgG levels in a cognate fashion, in both major clinical forms of chronic Chagas disease. We found no difference between anti-B13 IgG antibody levels between patients carrying HLA class II molecules associated to T cell responses or other alleles. The predominant anti-B13 IgG subclass was IgG1, with negligible IgG2, suggesting a T-dependent, noncognate help for antibody production. In addition, the finding of increased anti-B13 IgG levels in sera from CCC patients indicates that clinical presentation is associated with increased anti-B13 antibody levels.

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.

Protective human leucocyte antigen haplotype, HLA-DRB1*01-B*14, against chronic Chagas disease in Bolivia

BACKGROUND

Chagas disease, caused by the flagellate parasite Trypanosoma cruzi affects 8-10 million people in Latin America. The mechanisms that underlie the development of complications of chronic Chagas disease, characterized primarily by pathology of the heart and digestive system, are not currently understood. To identify possible host genetic factors that may influence the clinical course of Chagas disease, Human Leucocyte Antigen (HLA) regional gene polymorphism was analyzed in patients presenting with differing clinical symptoms.

METHODOLOGY

Two hundred and twenty nine chronic Chagas disease patients in Santa Cruz, Bolivia, were examined by serological tests, electrocardiogram (ECG), and Barium enema colon X-ray. 31.4% of the examinees showed ECG alterations, 15.7% megacolon and 58.1% showed neither of them. A further 62 seropositive megacolon patients who had undergone colonectomy due to acute abdomen were recruited. We analyzed their HLA genetic polymorphisms (HLA-A, HLA-B, MICA, MICB, DRB1 and TNF-alpha promoter region) mainly through Sequence based and LABType SSO typing test using LUMINEX Technology.

PRINCIPAL FINDINGS

The frequencies of HLA-DRB1*01 and HLA-B*14:02 were significantly lower in patients suffering from megacolon as well as in those with ECG alteration and/or megacolon compared with a group of patients with indeterminate symptoms. The DRB1*0102, B*1402 and MICA*011 alleles were in strong Linkage Disequilibrium (LD), and the HLA-DRB1*01-B*14-MICA*011 haplotype was associated with resistance against chronic Chagas disease.

CONCLUSIONS

This is the first report of HLA haplotype association with resistance to chronic Chagas disease.

Trypanosoma cruzi maxicircle heterogeneity in Chagas disease patients from Brazil

The majority of individuals in the chronic phase of Chagas disease are asymptomatic (indeterminate form, IF). Each year, approximately 3% of them develop lesions in the heart or gastrointestinal tract. Cardiomyopathy (CCHD) is the most severe manifestation of Chagas disease. The factors that determine the outcome of the infection are unknown, but certainly depend on complex interactions amongst the genetic make-up of the parasite, the host immunogenetic background and environment. In a previous study we verified that the maxicircle gene NADH dehydrogenase (mitochondrial complex I) subunit 7 (ND7) from IF isolates had a 455 bp deletion compared with the wild type (WT) ND7 gene from CCHD strains. We proposed that ND7 could constitute a valuable target for PCR assays in the differential diagnosis of the infective strain. In the present study we evaluated this hypothesis by examination of ND7 structure in parasites from 75 patients with defined pathologies, from Southeast Brazil. We also analysed the structure of additional mitochondrial genes (ND4/CR4, COIII and COII) since the maxicircle is used for clustering Trypanosoma cruzi strains into three clades/haplogroups. We conclude that maxicircle genes do not discriminate parasite populations which induce IF or CCHD forms. Interestingly, the great majority of the analysed isolates belong to T. cruzi II (discrete typing unit, (DTU) IIb) genotype. This scenario is at variance with the prevalence of hybrid (DTU IId) human isolates in Bolivia, Chile and Argentina. The distribution of WT and deleted ND7 and ND4 genes in T. cruzi strains suggests that mutations in the two genes occurred in different ancestrals in the T. cruzi II cluster, allowing the identification of at least three mitochondrial sub-lineages within this group. The observation that T. cruzi strains accumulate mutations in several genes coding for complex I subunits favours the hypothesis that complex I may have a limited activity in this parasite.

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.

Immunological and non-immunological effects of cytokines and chemokines in the pathogenesis of chronic Chagas disease cardiomyopathy

The pathogenesis of Chagas disease cardiomyopathy (CCC) is not well understood. Since studies show that myocarditis is more frequent during the advanced stages of the disease, and the prognosis of CCC is worse than that of other dilated cardiomyopathies of non-inflammatory aetiology, which suggest that the inflammatory infiltrate plays a major role in myocardial damage. In the last decade, increasing evidence has shown that inflammatory cytokines and chemokines play a role in the generation of the inflammatory infiltrate and tissue damage. CCC patients have an increased peripheral production of the inflammatory Th1 cytokines IFN-gamma and TNF-alpha when compared to patients with the asymptomatic/indeterminate form. Moreover, Th1-T cells are the main producers of IFN-gamma and TNF-alpha and are frequently found in CCC myocardial inflammatory infiltrate. Over the past several years, our group has collected evidence that shows several cytokines and chemokines produced in the CCC myocardium may also have a non-immunological pathogenic effect via modulation of gene and protein expression in cardiomyocytes and other myocardial cell types. Furthermore, genetic polymorphisms of cytokine, chemokine and innate immune response genes have been associated with disease progression. We will review the molecular and immunological mechanisms of myocardial damage in human CCC in light of recent findings.

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

Up to 18 million of individuals are infected by the protozoan parasite Trypanosoma cruzi in Latin America, one third of whom will develop chronic Chagas disease cardiomyopathy (CCC) up to 30 years after infection. Cardiomyocyte destruction is associated with a T cell-rich inflammatory infiltrate and fibrosis. The presence of such lesions in the relative scarcity of parasites in the heart, suggested that CCC might be due, in part, to a postinfectious autoimmune process. Over the last two decades, a significant amount of reports of autoimmune and molecular mimicry phenomena have been described in CCC. The authors will review the evidence in support of an autoimmune basis for CCC pathogenesis in humans and experimental animals, with a special emphasis on molecular mimicry as a fundamental mechanism of autoimmunity.

Association of the macrophage migration inhibitory factor -173G/C polymorphism with Chagas disease

Our aim was to evaluate the association of functional polymorphism of macrophage migration inhibitory factor (MIF) gene with Chagas disease. Our study includes two independent cohorts: 240 chagasic patients and 199 controls from Colombia; and 74 chagasic patients and 85 controls from Peru. The single nucleotide polymorphism (SNP) -173 G/C of MIF gene was determined using a polymerase chain reaction (PCR) system with pre-developed TaqMan assay. We observed a statistically significant difference in the distribution of -173*C allele of MIF gene between patients and controls in the Colombian cohort (OR = 1.6, 95% CI = 1.12-2.18, p = 0.006). Similar association was found in the Peruvian cohort (OR = 2.4, 95% CI = 1.31-4.38, p = 0.003). A meta-analysis of the Colombian and Peruvian cohorts demonstrated that the -173 C allele confers a risk effect in chagasic patients (pooled OR = 1.75, 95% CI = 1.30-2.33, p = 0.0002). In addition, a gene dose of the MIF -173 C allele was observed (pooled OR = 4.01, 95% CI = 1.25-12.85, p = 0.004). Our results suggest that the MIF -173G/C polymorphism confers susceptibility to Chagas disease in the populations under study.

The MHC gene region of murine hosts influences the differential tissue tropism of infecting Trypanosoma cruzi strains

We have previously demonstrated that both parasite genetic variability and host genetic background were important in determining the differential tissue distribution of the Col1.7G2 and JG T. cruzi monoclonal strains after artificial infections in mice. We observed that the JG strain was most prevalent in hearts of mouse lineages with the MHC haplotype H-2^d (BALB/c and DBA2), while Col1.7G2 was predominant in hearts from C57BL/6 mice, which have the H-2^b haplotype. To assess whether the MHC gene region indeed influenced tissue tropism of T. cruzi, we used the same two parasite strains to infect C57BL/6 (H-2^b) and C57BLKS/J (H-2^d) mice; the latter strain results from the introgression of DBA2 MHC region into the C57BL/6 background. We also performed ex vivo infections of cardiac explants from four congenic mice lineages with the H-2^b and H-2^d haplotypes arranged in two different genetic backgrounds: C57BLKS/J (H-2^d) versus C57BL/6 (H-2^b) and BALB/c (H-2^d) versus BALB/B10-H2^b (H-2^b). In agreement with our former observations, Col1.7G2 was predominant in hearts from C57BL/6 mice (H-2^b), but we observed a clear predominance of the JG strain in hearts from C57BLKS/J animals (H-2^d). In the ex vivo experiments Col1.7G2 also prevailed in explants from H-2^b animals while no predominance of any of the strains was observed in H-2^d mice explants, regardless of the genetic background. These observations clearly demonstrate that the MHC region influences the differential tissue distribution pattern of infecting T. cruzi strains, which by its turn may be in a human infection the determinant for the clinical forms of the Chagas disease.

Variants in the promoter region of IKBL/NFKBIL1 gene may mark susceptibility to the development of chronic Chagas' cardiomyopathy among Trypanosoma cruzi-infected individuals

Chagas' disease, caused by Trypanosoma cruzi, is an inflammatory disorder leading to chronic Chagas cardiomyopathy (CCC). Only one third of T. cruzi-infected individuals progress to CCC while the others are considered asymptomatic (ASY). The human inhibitory kappaB-like gene (IKBL/NFKBIL1), homologous to the IkappaB family of proteins that regulate the NFkappaB family of transcription factors, is suggested as a putative inhibitor of NFkappaB. We investigated two functional polymorphisms, -62A/T and -262A/G, in the promoter of IKBL by PCR-RFLP analysis in 169 patients with CCC and 76 ASY. Genotype distributions for both -62A/T and -262A/G differed between the CCC and ASY (chi2=7.3; P=0.025 and chi2=6.8; P=0.03, respectively). Subjects, homozygous for the -62A allele, had three-fold risk of developing CCC compared with those carrying the TT genotype (P=0.0095; Odds Ratio [OR]=2.9; [95% CI 1.2-7.3]). Similar trend was observed for the -262A homozygotes (P=0.005; OR=2.7 [95% CI 1.3-6.0]. The haplotype -262A -62A was prevalent in patients with CCC (40% versus 24%; OR 2.1 [95% CI 1.4-3.3]; Pc=0.0014). The IKBL locus itself or another critical gene in this region may confer susceptibility to the development of CCC.

Lack of association of tumor necrosis factor-α polymorphisms with Chagas disease in Brazilian patients

One third of Trypanosoma cruzi-infected individuals develop chronic Chagas disease cardiomyopathy (CCC) while the majority remains asymptomatic (ASY). About 30% of CCC patients develop heart failure due to end-stage inflammatory dilated cardiomyopathy. Increased production of tumor necrosis factor (TNF)-alpha has been described in all clinical forms of Chagas disease, and the highest levels are detected in CCC patients with severe ventricular dysfunction. Genetic susceptibility may play a role in the clinical outcome of Chagas disease. We investigated TNF as a candidate gene for susceptibility to development and/or progression of CCC. We analyzed the TNFa microsatellite and the -308 TNF promoter polymorphisms, in 166 CCC compared to 80 ASY geographically and age-matched patients in an association study. To analyze the association of TNF polymorphisms with progression of the cardiomyopathy, CCC patients were also grouped in three categories according to degree of left ventricular (LV) dysfunction into severe (n=57), mild to moderate (n=21) and absent (n=88). Our results show no significant differences either between CCC and ASY patients, or among CCC patients according to severity of cardiomyopathy with respect to TNFa or -308 TNF promoter polymorphisms. These results indicate that TNF polymorphisms are associated neither to CCC development nor to progression to more severe forms of cardiomyopathy in Brazilian Chagas disease patients.

Human Genetic Diversity and the Epidemiology of Parasitic and Other Transmissible Diseases

This paper aims to review human genetic studies that are generally poorly known by parasitologists and scientists working on other pathogenic agents. The key proposals of this paper are as follows: (i) human susceptibility to transmissible diseases may often have a complex, multigenic background; (ii) recent discoveries indicate that major genomic rearrangements may be involved, possibly more so than DNA sequence; (iii) it is crucial to have a general population genetics framework of the human species based on neutral/historical markers to analyse reliably genetic susceptibility to infectious diseases; and (iv) the population level is a key factor. Ethnic diversity, a highly adaptive genetically driven phenotypic diversity, is possibly a valuable source for exploring human genetic susceptibility to transmissible diseases, since different populations have been exposed to drastically different geographic/climatic environments and different pathogens and vectors for tens of thousands of years. Studies dealing with human genetic susceptibility to transmissible diseases have mostly been based on the hypothesis that this factor is driven by only one or a few genes, and considered the individual more than the population level. Two different approaches have been developed for identifying the genes involved: (i) candidate genes and (ii) blind association studies (linkage analysis), screening the genome with a large number of high-resolution markers. Some loci involved in susceptibility to leishmaniosis, malaria and schistosomosis, for example, have already been identified. South American trypanosomosis (Chagas disease) is reviewed in detail to show the methodological problems of this classical approach. Current knowledge on the general impact of transmissible diseases on human genetic diversity, mainly HLA polymorphism, and the hopes raised by recent major international programmes such as the Human Genome Project (HGP), Human Genome Diversity Project (HGDP), International Human Haplotype Map Project (Hap Map) and extended databases, networks and networks of networks will also be reviewed.

Genes from Chagas susceptibility loci that are differentially expressed in T. cruzi-resistant mice are candidates accounting for impaired immunity

Variation between inbred mice of susceptibility to experimental Trypanosoma cruzi infection has frequently been described, but the immunogenetic background is poorly understood. The outcross of the susceptible parental mouse strains C57BL/6 (B6) and DBA/2 (D2), B6D2F1 (F1) mice, is highly resistant to this parasite. In the present study we show by quantitative PCR that the increase of tissue parasitism during the early phase of infection is comparable up to day 11 between susceptible B6 and resistant F1 mice. A reduction of splenic parasite burdens occurs thereafter in both strains but is comparatively retarded in susceptible mice. Splenic microarchitecture is progressively disrupted with loss of follicles and B lymphocytes in B6 mice, but not in F1 mice. By genotyping of additional backcross offspring we corroborate our earlier findings that susceptibility maps to three loci on Chromosomes 5, 13 and 17. Analysis of gene expression of spleen cells from infected B6 and F1 mice with microarrays identifies about 0.3% of transcripts that are differentially expressed. Assuming that differential susceptibility is mediated by altered gene expression, we propose that the following differentially expressed transcripts from these loci are strong candidates for the observed phenotypic variation: H2-Eα, H2-D1, Ng23, Msh5 and Tubb5 from Chromosome 17; and Cxcl11, Bmp2k and Spp1 from Chromosome 5. Our results indicate that innate mechanisms are not of primary relevance to resistance of F1 mice to T. cruzi infection, and that differential susceptibility to experimental infection with this protozoan pathogen is not paralleled by extensive variation of the transcriptome.

Differential transcription profiles in Trypanosoma cruzi associated with clinical forms of Chagas disease: Maxicircle NADH dehydrogenase subunit 7 gene truncation in asymptomatic patient isolates

The majority of individuals in the chronic phase of Chagas disease are asymptomatic (indeterminate form). Every year 2-3% of these individuals develop severe clinical manifestations (cardiac and digestive forms). In this study a Trypanosoma cruzi DNA microarray was used to compare the transcript profiles of six human isolates: three from asymptomatic and three from cardiac patients. Seven signals were expressed differentially between the two classes of isolates, including tryparedoxin, surface protease GP63, cyclophilin, some hypothetical proteins and the pre-edited maxicircle gene NADH dehydrogenase subunit 7 (ND7). The approximately 30-fold greater signal in cardiac strains for ND7 was the most pronounced of the group, and differential levels of pre-edited ND7 transcript confirmed the microarray analysis. The ND7 gene from asymptomatic isolates showed a deletion of 455bp from nt 222 to nt 677 relative to ND7 of the CL Brener reference strain. The ND7 gene structure correlated with disease manifestation for 20 isolates from clinically characterised, chronic phase patients. The ND7 lesion produces a truncated product that could impair the function of mitochondrial complex I. Possible links between the integrity of the electron transport chain and symptom presentation are discussed. We propose that ND7 and other genes of the pathway constitute valuable targets for PCR assays in the differential diagnosis of the infective T. cruzi strain. While this hypothesis requires validation by the examination of additional recent parasite isolates from patients with defined pathologies, the identification of specific molecular markers represents a promising advance in the association between parasite genetics and disease pathology.

TNF gene polymorphisms are associated with reduced survival in severe Chagas' disease cardiomyopathy patients

Chronic Chagas' disease cardiomyopathy (CCC) is the most important clinical outcome of infection by the parasite Trypanosoma cruzi, affecting 18 million individuals in Latin America. One-third of CCC patients develop heart failure due to end-stage dilated cardiomyopathy, and their survival is reduced by 50% compared to patients with other cardiomyopathies. Genetic susceptibility may play a role in the differential survival of severe CCC patients. Given the role of TNF-alpha in the progression of heart failure, and the increased TNF-alpha plasma and heart tissue levels observed in these patients, we chose TNF as a candidate gene for increased mortality in severe CCC patients. We typed the TNFa microsatellite and the -308 TNF promoter polymorphism and then analyzed the survival curves of 42 patients with severe ventricular dysfunction (left ventricular ejection fraction<or=40%) according to the presence of the TNF2 promoter allele or the TNFa2 microsatellite allele, both previously associated with high TNF-alpha production. Multivariate regression analysis (Cox proportional hazards model) revealed the TNF genotype and age of onset of severe CCC as independent predictors of mortality in severe CCC. We showed that patients positive for TNF2 or TNFa2 alleles display a significantly shorter survival time compared to those carrying other alleles; the median survival times were 2.9 and 8 months, respectively (HR(adj)=2.28, p=0.020). We have identified for the first time a genetic factor related to reduced survival in severe Chagas' disease cardiomyopathy. The association of TNF genotype with earlier death in CCC should be taken into account when planning therapeutic intervention.

The clinical immunology of human Chagas disease

Human infection with the protozoan parasite Trypanosoma cruzi leads to Chagas disease, which affects approximately 17 million people in Latin America. A significant percentage of the infected population will develop clinical symptoms or present changes in laboratory and/or image evaluation. The existence of a large spectrum of clinical manifestations--with patients ranging from asymptomatic to severe cardiac involvement--emphasizes the need to use standardized and well-defined clinical criteria among different research groups. In this article, we carry out a systematic review of the immunology in human Chagas disease, discussing recent findings in the context of a clinical perspective.

Complement C3 F and BF S allotypes are risk factors for Chagas disease cardiomyopathy

The heterogeneity in the clinical expression of Chagas disease gives strong evidences for the involvement of genetic factors on its pathogenesis. Several studies have indicated different markers of genetic susceptibility to Chagas cardiomyopathy. In the present study, we present evidence of association between complement C3 and BF allotypes, and the susceptibility to Chagas disease and the development of cardiomyopathy. C3, BF, C4A, C4B and C2 polymorphism were determined in 100 seropositive Chagasic patients [cardiomyopathic (CARD), n = 57; asymptomatic indetermined (IND), n = 43] and in 100 non-related seronegative healthy controls. Patients and controls were matched according to their ethnic and geographical origin. A significantly increased frequency of C3F was observed in patients with the CARD form (8/57 14.03%), when compared with those presenting the IND form (0/43, 0%; RR 7.0) and with the healthy controls (5/100, 5%; RR 3.1). A negative association of the BF S allotype was observed in the CARD patients (19/57 33.33%) and in the Chagas total (38/100 38.0%), when compared with the controls (55/100, 55.0%; RR 0.4). All other C3, BF, C4A, C4B and C2 alleles showed no significant differences. These results suggest the allele C3F as a susceptible marker for the progression of the CARD form. On the other hand, BF S may represent a protective role against severe CARD disease. These results corroborate the importance of the alternative pathway in Trypanosoma cruzi infection and indicate possible genetic markers of Chagas cardiomyopathy.

Chronic murine Chagas' disease: the impact of host and parasite genotypes

Chagas' disease is a protozoan infection caused by the flagellate Trypanosoma cruzi. Herein we utilise experimental infections of different mouse and parasite strains to investigate the relative importance of the host and parasite genotype, respectively, in causing Chagas' disease in mice. CBA/J and BALB/c mice infected with the Tulahuen strain of T. cruzi develop a severe acute disease characterised by transient parasitaemia and a high rate of mortality. While the acute phases in these mice are indistinguishable, they display differential outcomes of the infection since CBA/J mice eventually develop polymyositis and mild myocarditis whereas BALB/c mice are resistant to chronic disease. In contrast, BALB/c mice infected with the CA-1 clone of T. cruzi exhibit a mild acute phase, develop no polymyositis but do develop severe myocarditis. Thus both the parasite and host genotype, but not the severity of the acute phase, are important in determining the eventual outcome of T. cruzi infection. We also present a murine model suitable for investigating which host factors may be necessary to induce a chronic inflammatory disease after T. cruzi infection.