A possible role for complement in the pathogenesis of chronic chagasic cardiomyopathy

Role of the Complement System in the Modulation of T-Cell Responses in Chronic Chagas Disease

Chagas disease, caused by the intracellular pathogen Trypanosoma cruzi, is the parasitic disease with the greatest impact in Latin America and the most common cause of infectious myocarditis in the world. The immune system plays a central role in the control of T. cruzi infection but at the same time needs to be controlled to prevent the development of pathology in the host. It has been shown that persistent infection with T. cruzi induces exhaustion of parasite-specific T cell responses in subjects with chronic Chagas disease. The continuous inflammatory reaction due to parasite persistence in the heart also leads to necrosis and fibrosis. The complement system is a key element of the innate immune system, but recent findings have also shown that the interaction between its components and immune cell receptors might modulate several functions of the adaptive immune system. Moreover, the findings that most of immune cells can produce complement proteins and express their receptors have led to the notion that the complement system also has non canonical functions in the T cell. During human infection by T. cruzi, complement activation might play a dual role in the acute and chronic phases of Chagas disease; it is initially crucial in controlling parasitemia and might later contributes to the development of symptomatic forms of Chagas disease due to its role in T-cell regulation. Herein, we will discuss the putative role of effector complement molecules on T-cell immune exhaustion during chronic human T. cruzi infection.

Ficolin-3 in chronic Chagas disease: Low serum levels associated with the risk of cardiac insufficiency

AIMS

To investigate whether FCN3 polymorphisms and circulating ficolin-3 levels were associated with clinical forms of chronic Chagas disease (CD) and to assess their potential use as biomarkers for the disease or its severity.

METHODS AND RESULTS

FCN3 polymorphisms (g.1637delC (rs532781899) in exon 5; g.3524_3532insTATTTGGCC (rs28362807) in intron 5 and g.4473C > A) (rs4494157) in intron 7) were determined in 178 chronic CD patients (65 asymptomatic, 68 cardiac, 21 digestive and 24 cardiodigestive), and 285 healthy controls by sequence-specific PCR. Ficolin-3 serum levels, measured by ELISA in 80 patients and 80 controls, did not differ between groups. On the other hand, ficolin-3 levels were positively correlated with left ventricular ejection fraction (P = .002; r = .5), with lower levels associated with increased risk of cardiac insufficiency (P = .033; OR 7.21, 95%IC 1.17-44.4). Ficolin-3 levels were positively correlated with ficolin-2 (P = .021; r = .63), and negatively with MBL (P = .002; r = -.36) and pentraxin-3 (P = .04; r = -.32) levels. No significant results were observed for the investigated FCN3 polymorphisms and CD. The g.1637del/1637C heterozygotes presented lower ficolin-3 levels than g.1637C/1637C homozygotes in the control group (P = .023).

CONCLUSION

Low ficolin-3 levels may play a role in the pathophysiology of cardiac insufficiency associated with CD.

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

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

Binding capacity of mannose-binding lectin (MBL) is associated with the severity of chronic Chagas cardiomyopathy

Chagas disease (CD) is a global problem. Currently, it affects approximately 15 million individuals in Latin America. It is well know that the human immune response is related to different clinical manifestations. Mannose binding lectin (MBL) plays an important role in innate immunity, and it mediates the phagocytosis and complement-mediated destruction of pathogens. The binding capacity is enhanced by the oligomerization of MBL. In this study, we evaluated the serum concentration and the binding capacity of MBL in patients with chronic chagasic cardiomyopathy. A total of 77 patients with chronic CD were included with indeterminate (n = 19), mild cardiac (n = 29) and severe cardiac (n = 29) forms. The serum concentration and the binding capacity were measured using enzyme-linked immunosorbent assays (ELISA). There was no significant difference in the serum MBL levels between the groups of patients. However, we found a relationship between the binding capacity and the groups studied. Our results suggest that binding capacity of MBL could be an indicator of clinical manifestation in Chronic Chagas cardiomyopathy. Furthermore, combined with the Mannose Binding Index results in a useful clinical tool for management of Chronic Chagas Patients.

Genetically Determined MBL Deficiency Is Associated with Protection against Chronic Cardiomyopathy in Chagas Disease

Chagas disease (CD) is caused by Trypanosoma cruzi, whose sugar moieties are recognized by mannan binding lectin (MBL), a soluble pattern-recognition molecule that activates the lectin pathway of complement. MBL levels and protein activity are affected by polymorphisms in the MBL2 gene. We sequenced the MBL2 promoter and exon 1 in 196 chronic CD patients and 202 controls. The MBL2*C allele, which causes MBL deficiency, was associated with protection against CD (P = 0.007, OR = 0.32). Compared with controls, genotypes with this allele were completely absent in patients with the cardiac form of the disease (P = 0.003). Furthermore, cardiac patients with genotypes causing MBL deficiency presented less heart damage (P = 0.003, OR = 0.23), compared with cardiac patients having the XA haplotype causing low MBL levels, but fully capable of activating complement (P = 0.005, OR = 7.07). Among the patients, those with alleles causing MBL deficiency presented lower levels of cytokines and chemokines possibly implicated in symptom development (IL9, p = 0.013; PDGFB, p = 0.036 and RANTES, p = 0.031). These findings suggest a protective effect of genetically determined MBL deficiency against the development and progression of chronic CD cardiomyopathy.

Chagas disease is considered an important neglected tropical disease, affecting approximately ten million people in Latin America. Although most infected individuals remain asymptomatic, one third of patients develop a chronic heart disease, with progressive inflammation, increase of myocardium, arrhythmia, cardiac insufficiency and heart failure. To date, there is no available marker to indicate the progression neither to determinate the severity of heart damage. Mannan binding lectin (MBL) is an important protein of the immune system able to recognize specific regions on the microorganism surfaces (including Trypanosoma cruzi, the causal agent of Chagas disease) which activate the complement system, a crucial mechanism of the effector immunity. MBL levels and protein activity are affected by genetic differences, named polymorphisms, in the MBL2 gene. This is the first Brazilian study with MBL2 polymorphisms in chronic Chagas disease. We sequenced two regions of MBL2 gene in 196 patients and 202 controls. We found that a polymorphism associated with deficient complement activation protects against Chagas disease and patients with deficiency-associated genotypes presented less echocardiographic alterations. Among the patients, those with alleles causing MBL deficiency presented lower levels of cytokines and chemokines possibly implicated in symptom development (IL9, p = 0.013; PDGFB, p = 0.036 and RANTES, p = 0.031). These findings lead us to suggest that genetically determined MBL deficiency plays a protective role against the development and progression of chronic Chagas disease.

MBL-associated serine proteases (MASPs) and infectious diseases

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MASP-1 and MASP-2 are central players of the lectin pathway of complement.

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MASP1 and MASP2 gene polymorphisms regulate protein serum levels and activity.

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MASP deficiencies are associated with increased infection susceptibility.

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MASP polymorphisms and serum levels are associated with disease progression.

The lectin pathway of the complement system has a pivotal role in the defense against infectious organisms. After binding of mannan-binding lectin (MBL), ficolins or collectin 11 to carbohydrates or acetylated residues on pathogen surfaces, dimers of MBL-associated serine proteases 1 and 2 (MASP-1 and MASP-2) activate a proteolytic cascade, which culminates in the formation of the membrane attack complex and pathogen lysis. Alternative splicing of the pre-mRNA encoding MASP-1 results in two other products, MASP-3 and MAp44, which regulate activation of the cascade. A similar mechanism allows the gene encoding MASP-2 to produce the truncated MAp19 protein. Polymorphisms in MASP1 and MASP2 genes are associated with protein serum levels and functional activity. Since the first report of a MASP deficiency in 2003, deficiencies in lectin pathway proteins have been associated with recurrent infections and several polymorphisms were associated with the susceptibility or protection to infectious diseases. In this review, we summarize the findings on the role of MASP polymorphisms and serum levels in bacterial, viral and protozoan infectious diseases.

A vital role for complement in heart disease

Heart diseases are common and significant contributors to worldwide mortality and morbidity. During recent years complement mediated inflammation has been shown to be an important player in a variety of heart diseases. Despite some negative results from clinical trials using complement inhibitors, emerging evidence points to an association between the complement system and heart diseases. Thus, complement seems to be important in coronary heart disease as well as in heart failure, where several studies underscore the prognostic importance of complement activation. Furthermore, patients with atrial fibrillation often share risk factors both with coronary heart disease and heart failure, and there is some evidence implicating complement activation in atrial fibrillation. Moreover, Chagas heart disease, a protozoal infection, is an important cause of heart failure in Latin America, and the complement system is crucial for the protozoa-host interaction. Thus, complement activation appears to be involved in the pathophysiology of a diverse range of cardiac conditions. Determination of the exact role of complement in the various heart diseases will hopefully help to identify patients that might benefit from therapeutic complement intervention.

Association of L-ficolin levels and FCN2 genotypes with chronic Chagas disease

BACKGROUND

L-ficolin (encoded by FCN2) binds to acetylated sugar moieties of many pathogens, including Trypanosoma cruzi, promoting their phagocytosis and lysis by the complement system.

METHODS

We investigated L-ficolin levels in 160 T. cruzi infected patients with chronic Chagas disease and 71 healthy individuals, and FCN2 polymorphisms (-986 G>A, -602 G>A, and -4 A>G in the promoter and A258S in exon 8) in 243 patients, being 88 indeterminate (asymptomatic), 96 with cardiac, 23 with digestive and 33 with cardiodigestive manifestations (two were unspecified) and 305 controls (135 for A258S).

RESULTS

Patients presented lower L-ficolin plasma levels than controls (p<0.0001). Among the different groups of cardiac commitment, individuals with moderate forms had higher L-ficolin levels than the severe forms (P = 0.039). Lower L-ficolin levels were found associated with the 258S variant in the patients (P = 0.034). We found less -4A/G heterozygotes in the cardiac patients, than in the controls (OR = 0.56 [95% CI = 0.33-0.94], P = 0.034). Heterozygote -4A/G genotypes with the 258S variant and 258SS homozygotes were nevertheless more frequent among cardiodigestive patients than in controls (OR = 14.1 [95% CI = 3.5-56.8], P = 0.0001) and in indeterminate patients (OR = 3.2 [95% CI = 1.1-9.4], P = 0.037). We also found an association of the allelic frequency of the 258S variant with cardiodigestive Chagas disease compared to controls (OR = 2.24 [95% CI = 1.1-4.5], P = 0.037). Thus, decreased patient levels of L-ficolin reflect not only protein consumption due to the disease process, but also the higher frequency of the 258S variant in patients with cardiodigestive symptoms.

CONCLUSION

The very first study on Brazilian cohort associates both L-ficolin plasma levels and FCN2 variants to Chagas disease and subsequent disease progression. The prognostic value of L-ficolin levels and the FCN2*A258S polymorphism should be further evaluated in other settings.

MASP2 haplotypes are associated with high risk of cardiomyopathy in chronic Chagas disease

Mannose-binding lectin (MBL) initiates complement on Trypanosoma cruzi through the MBL-associated serine protease 2 (MASP2). We haplotyped six MASP2 polymorphisms in 208 chronic chagasic patients, being 81 indeterminate and 123 symptomatic (76 with cardiac, 19 with digestive and 28 with cardiodigestive forms) and 300 healthy individuals from Southern Brazil, using PCR with sequence-specific primers. The g.1961795C, p.371D diplotype (short CD) occurred at a higher frequency among symptomatic patients, compared with the indeterminate group (P(Bf)=0.012, OR=3.11), as well as genotypes with CD, but not with the g.1945560A in the promoter in cardiac patients (P(Bf)=0.012, OR=13.54). CD haplotypes linked to the p.P126L and p.V377A variants were associated with reduced MASP-2 levels (P<0.0001) but not reduced MBL/MASP-2/C4 complexes. MASP2*CD genotypes, most of them generating low MASP-2 levels, are associated with high risk of chagasic cardiomyopathy. Rapid MASP2 genotyping might be used to predict the risk of symptomatic disease.

Autoimmunity

The scarcity of Trypanosoma cruzi in inflammatory lesions of chronic Chagas disease led early investigators to suggest that tissue damage had an autoimmune nature. In spite of parasite persistence in chronic Chagas disease, several reports indicate that inflammatory tissue damage may not be correlated to the local presence of T. cruzi. A significant number of reports have described autoantibodies and self-reactive T cells, often cross-reactive with T. cruzi antigens, both in patients and in animal models. Evidence for a direct pathogenetic role of autoimmunity was suggested by the development of lesions after immunization with T. cruzi antigens or passive transfer of lymphocytes from infected animals, and the amelioration of chronic myocarditis in animals made tolerant to myocardial antigens. Autoimmune and T. cruzi-specific innate or adaptative responses are not incompatible or mutually exclusive, and it is likely that a combination of both is involved in the pathogenesis of chronic Chagas disease cardiomyopathy. The association between persistent infection and autoimmune diseases-such as multiple sclerosis or diabetes mellitus-suggests that post-infectious autoimmunity may be a frequent finding. Here, we critically review evidence for autoimmune phenomena and their possible pathogenetic role in human Chagas disease and animal models, with a focus on chronic Chagas disease cardiomyopathy.

Do Archaea and bacteria co-infection have a role in the pathogenesis of chronic chagasic cardiopathy?

Chronic cardiopathy (CC) in Chagas disease is a fibrotic myocarditis with C5b-9 complement deposition. Mycoplasma and Chlamydia may interfere with the complement response. Proteolytic enzymes and archaeal genes that have been described in Trypanosoma cruzi may increase its virulence. Here we tested the hypothesis that different ratios of Mycoplasma, Chlamydia and archaeal organisms, which are frequent symbionts, may be associated with chagasic clinical forms.

MATERIALS AND METHODS

eight indeterminate form (IF) and 20 CC chagasic endomyocardial biopsies were submitted to in situ hybridization, electron and immunoelectron microscopy and PCR techniques for detection of Mycoplasma pneumoniae (MP), Chlamydia pneumoniae(CP), C5b-9 and archaeal-like bodies.

RESULTS

MP and CP-DNA were always present at lower levels in CC than in IF (p < 0.001) and were correlated with each other only in CC. Electron microscopy revealed Mycoplasma, Chlamydia and two types of archaeal-like bodies. One had electron dense lipid content (EDL) and was mainly present in IF. The other had electron lucent content (ELC) and was mainly present in CC. In this group, ELC correlated negatively with the other microbes and EDL and positively with C5b-9. The CC group was positive for Archaea and T. cruzi DNA. In conclusion, different amounts of Mycoplasma, Chlamydia and archaeal organisms may be implicated in complement activation and may have a role in Chagas disease outcome.

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.

Dynamic expression of the membrane attack complex (MAC) of the complement system in failing human myocardium

Inflammatory cytokine-mediated pathways are activated in heart failure and participate in the pathogenesis and progression of the disease. Another major response to inflammation is mediated through the complement system with the production of the membrane attack complex (MAC), a protein known to cause cell lysis and mediate apoptosis. It was postulated that the complement system is activated in patients with heart failure, and this study investigated whether hemodynamic conditions regulate this pathway. The expression of the MAC was assessed in myocardial biopsy samples of normal and failing hearts by immunohistochemistry and Western blot analysis. Myocardial samples from failing hearts were obtained before and after left ventricular assist device implantation. Immunohistochemical staining and Western blot analysis identified increased MAC expression in failing but not normal myocardium. After hemodynamic unloading with left ventricular assist device support, MAC expression returned to levels found in normal controls. In failing hearts, MAC expression did not differ between ischemic and nonischemic causes of heart failure. In conclusion, increased MAC expression in failing human hearts indicates that the complement system is activated in the heart failure milieu. Its removal after hemodynamic normalization is evidence of dynamic regulation, suggesting a pathogenic role for the MAC. These findings identify the complement system as part of a novel pathophysiologic path in heart failure that can potentially be targeted by future therapy.

Cardiac involvement in non-human primates infected with the Lyme disease spirochete Borrelia burgdorferi

To investigate cardiac involvement in the non-human primate (NHP) model of Lyme disease, we inoculated 39 adult Macaca mulatta with Borrelia burgdorferi sensu stricto strains N40 (BbN40) by needle (N=22, 14 immunocompetent (IC), seven permanently immunosuppressed (IS), and four transiently immunosuppressed (TISP)) or by tick-bite (N=4, all TISP) or strain 297 (Bb297) by needle (N=2 IS), or with B. garinii strains Pbi (N=4, 2 TISP and 2 IS), 793 (N=2, TISP) or Pli (N=2, TISP). Five uninfected NHPs were used as controls. Infection and inflammation was studied in the hearts and the aorta removed at necropsy 2-32 months after inoculation by (1) H&E and trichrome-staining; (2) immunohistochemistry and digital image analysis; (3) Western blot densitometry; and (4) TaqMan RT-PCR. All NHPs inoculated with BbN40 became infected and showed carditis at necropsy. The predominant cells were T cells, plasma cells, and macrophages. There was increased IgG and IgM in the heart independent of immunosuppression. The B-cell chemokine BLC was significantly increased in IS-NHPs. There was increased deposition of the complement membrane attack complex (MAC) in TISP and IS-NHPs. The spirochetal load was very high in all BbN40-inoculated IS-NHPs but minimal if any in IC or TISP NHPs. Double-immunostaining revealed that many spirochetes in the heart of BbN40-IS NHPs had MAC on their membranes. We conclude that carditis in NHPs infected with B. burgdorferi is frequent and can persist for years but is mild unless they are immunosupressed.

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.