Autoimmunity to alpha myosin in a subset of patients with idiopathic dilated cardiomyopathy

Autoimmune Myocarditis, Old Dogs and New Tricks

Autoimmunity significantly contributes to the pathogenesis of myocarditis, underscored by its increased frequency in autoimmune diseases such as systemic lupus erythematosus and polymyositis. Even in cases of myocarditis caused by viral infections, dysregulated immune responses contribute to pathogenesis. However, whether triggered by existing autoimmune conditions or viral infections, the precise antigens and immunologic pathways driving myocarditis remain incompletely understood. The emergence of myocarditis associated with immune checkpoint inhibitor therapy, commonly used for treating cancer, has afforded an opportunity to understand autoimmune mechanisms in myocarditis, with autoreactive T cells specific for cardiac myosin playing a pivotal role. Despite their self-antigen recognition, cardiac myosin-specific T cells can be present in healthy individuals due to bypassing the thymic selection stage. In recent studies, novel modalities in suppressing the activity of pathogenic T cells including cardiac myosin-specific T cells have proven effective in treating autoimmune myocarditis. This review offers an overview of the current understanding of heart antigens, autoantibodies, and immune cells as the autoimmune mechanisms underlying various forms of myocarditis, along with the latest updates on clinical management and prospects for future research.

β1 Adrenergic Receptor Autoantibodies and IgG Subclasses: Current Status and Unsolved Issues

A wide range of anti-myocardial autoantibodies have been reported since the 1970s. Among them, autoantibodies against the β1-adrenergic receptor (β1AR-AAb) have been the most thoroughly investigated, especially in dilated cardiomyopathy (DCM). Β1AR-Aabs have agonist effects inducing desensitization of β1AR, cardiomyocyte apoptosis, and sustained calcium influx which lead to cardiac dysfunction and arrhythmias. Β1AR-Aab has been reported to be detected in approximately 40% of patients with DCM, and the presence of the antibody has been associated with worse clinical outcomes. The removal of anti-myocardial autoantibodies including β1AR-AAb by immunoadsorption is beneficial for the improvement of cardiac function for DCM patients. However, several studies have suggested that its efficacy depended on the removal of AAbs belonging to the IgG3 subclass, not total IgG. IgG subclasses differ in the structure of the Fc region, suggesting that the mechanism of action of β1AR-AAb differs depending on the IgG subclasses. Our previous clinical research demonstrated that the patients with β1AR-AAb better responded to β-blocker therapy, but the following studies found that its response also differed among IgG subclasses. Further studies are needed to elucidate the possible pathogenic role of IgG subclasses of β1AR-AAbs in DCM, and the broad spectrum of cardiovascular diseases including HF with preserved ejection fraction.

Autoantibodies and Cardiomyopathy: Focus on Beta-1 Adrenergic Receptor Autoantibodies

ABSTRACT

Antibody response to self-antigens leads to autoimmune response that plays a determinant role in cardiovascular disease outcomes including dilated cardiomyopathy (DCM). Although the origins of the self-reactive endogenous autoantibodies are not well-characterized, it is believed to be triggered by tissue injury or dysregulated humoral response. Autoantibodies that recognize G protein-coupled receptors are considered consequential because they act as modulators of downstream receptor signaling displaying a wide range of unique pharmacological properties. These wide range of pharmacological properties exhibited by autoantibodies has cellular consequences that is associated with progression of disease including DCM. Increase in autoantibodies recognizing beta-1 adrenergic receptor (β1AR), a G protein-coupled receptor critical for cardiac function, is observed in patients with DCM. Cellular and animal model studies have indicated pathological roles for the β1AR autoantibodies but less is understood about the molecular basis of their modulatory effects. Despite the recognition that β1AR autoantibodies could mediate deleterious outcomes, emerging evidence suggests that not all β1AR autoantibodies are deleterious. Recent clinical studies show that β1AR autoantibodies belonging to the IgG3 subclass is associated with beneficial cardiac outcomes in patients. This suggests that our understanding on the roles the β1AR autoantibodies play in mediating outcomes is not well-understood. Technological advances including structural determinants of antibody binding could provide insights on the modulatory capabilities of β1AR autoantibodies in turn, reflecting their diversity in mediating β1AR signaling response. In this study, we discuss the significance of the diversity in signaling and its implications in pathology.

Regulatory Role of CD4+ T Cells in Myocarditis

Myocarditis is an important cause of heart failure in young patients. Autoreactive, most often, infection-triggered CD4⁺ T cells were confirmed to be critical for myocarditis induction. Due to a defect in clonal deletion of heart-reactive CD4⁺ T cells in the thymus of mice and humans, significant numbers of heart-specific autoreactive CD4⁺ T cells circulate in the blood. Normally, regulatory T cells maintain peripheral tolerance and prevent spontaneous myocarditis development. In the presence of tissue damage and innate immune activation, however, activated self-antigen-loaded dendritic cells promote CD4⁺ effector T cell expansion and myocarditis. So far, a direct pathogenic role has been described for both activated Th17 and Th1 effector CD4⁺ T cell subsets, though Th1 effector T cell-derived interferon-gamma was shown to limit myocarditis severity and prevent transition to inflammatory dilated cardiomyopathy. Interestingly, recent observations point out that various CD4⁺ T cell subsets demonstrate high plasticity in maintaining immune homeostasis and modulating disease phenotypes in myocarditis. These subsets include Th1 and Th17 effector cells and regulatory T cells, despite the fact that there are still sparse and controversial data on the specific role of FOXP3-expressing Treg in myocarditis. Understanding the specific roles of these T cell populations at different stages of the disease progression might provide a key for the development of successful therapeutic strategies.

Significance of Anti-Myosin Antibody Formation in Patients With Myocardial Infarction: A Prospective Observational Study

BACKGROUND

Anti-myosin antibodies (AMAs) are often formed in response to myocardial infarction (MI) and have been implicated in maladaptive cardiac remodelling. We aimed to: (1) compare AMA formation in patients with Non-ST-Elevation MI (NSTEMI) and ST-Elevation MI (STEMI); (2) evaluate factors predicting autoantibody formation; and, (3) explore their functional significance.

METHODS

Immunoglobulin M (IgM) and Immunoglobulin G (IgG) AMA titres were determined in serum samples collected at admission, 3 and 6 months post MI. The relationship between demographic and clinical data, and antibody formation, was investigated to determine factors predicting antibody formation and functional significance.

RESULTS

Forty-three (43) patients were consecutively recruited; 74.4% were positive for IgM at admission, compared with 23.3% for IgG. Mean IgG levels increased by 1.24% (±0.28) at 3 months, and 13.55% (±0.13) at 6 months post MI. Mean antibody levels were significantly higher in the NSTEMI cohort at both follow-up time points for IgG (p<0.001, p<0.0001), but not IgM (p=0.910, p=0.066). A moderately positive correlation between infarct size and increase in mean IgM concentration was observed at 3 months (r(98)=0.455; p=0.015). Anti-myosin antibody formation was not associated with an unfavourable outcome at follow-up.

CONCLUSIONS

Anti-myosin antibodies are formed in a significant proportion of patients following MI, particularly among those with NSTEMI. While IgM levels fall after infarction, IgG levels increase and persist beyond 6 months of follow-up. This raises the possibility that they may contribute to long-term myocardial damage and dysfunction. Future research should focus on the specific epitopes that are targeted by these antibodies, and their functional significance. This may result in the emergence of novel therapies to attenuate cardiac dysfunction in MI patients.

Cardiomyopathy - An approach to the autoimmune background

Autoimmunity is increasingly accepted as the origin or amplifier of various diseases. In contrast to classic autoantibodies (AABs), which induce immune responses resulting in the destruction of the affected tissue, an additional class of AABs is directed against G-protein-coupled receptors (GPCRs; GPCR-AABs). GPCR-AABs functionally affect their related GPCRs for activation of receptor mediated signal cascades. Diseases which are characterized by the presence of GPCR-AABs with evidence for disease-specific pathogenic activity could be named "functional autoantibody disease". We briefly summarize here the historical view on autoimmunity in cardiomyopathy, followed by an approach to the mechanistic autoimmunity background. Furthermore, autoantibodies with outstanding importance for cardiomyopathies as a functional autoantibody disease, such as GPCR-AABs, and mainly those directed against the beta1-adrenergic and muscarinic 2 receptor autoantibodies, are introduced. Anti-cardiac myosin and anti-cardiac troponin autoantibodies, as further potential players in autoimmune cardiomyopathy, are additionally taken into account. The basic view on the autoantibodies, their related receptor interactions and pathogenic consequences are presented. Focused specifically on GPCR-AABs, "pros and cons" of assays such as indirect assays (functional changes of cell preparations are monitored after GPCR-AAB receptor binding) and direct assays based on the ELISA technologies (GPCR epitope mimics for GPCR-AAB binding) are critically discussed. Last but not least, treatment strategies for "functional autoantibody disease", such as for GPCR-AAB removal (therapeutic plasma exchange, immunoadsorption) and in vivo GPCR-AAB attack such as intravenous IgG treatment (IVIG), B-cell depletion and GPCR-AAB binding and neutralization, are critically reflected with respect to their patient benefits.

The role of anti-myosin antibodies in perpetuating cardiac damage following myocardial infarction

Recent improvements in the medical and surgical management of myocardial infarction mean that many patients are now surviving with greater impairment of cardiac function. Despite appropriate management, some of these patients subsequently develop pathological ventricular remodelling, which compounds their contractile dysfunction and can lead to congestive cardiac failure (CCF). The pathophysiological mechanism underpinning this process remains incompletely understood. One hypothesis suggests that a post-infarction autoimmune response, directed against constituents of cardiac myocytes, including cardiac myosin, may make an important contribution. Our review summarises the current literature related to the formation and clinical relevance of anti-myosin antibodies (AMAs) in patients with myocardial infarction. This discussion is supplemented with reference to a number of important animal studies, which provide evidence of the potential mechanisms underlying AMA formation and autoantibody mediated cardiac dysfunction.

Autoantibodies and cardiovascular dysfunction: cause or consequence?

There has been a long history of the exploration into autoimmunity as a possible pathogenic factor of cardiovascular diseases from unknown cause represented by dilated cardiomyopathy (DCM). Autoantibodies (AAbs) have emerged either as humoral responses provoked by the release of "self-antigens" due to tissue damage or dysregulated humoral immunity itself. The pathogenic roles of some AAbs have been suggested by the findings from basic research using in vitro and in vivo disease models as well as clinical studies including immunoadsorption studies removing AAbs from patients with DCM. In this context, the importance of AAbs belonging to IgG3 subclass has also been implicated. In this review article, we summarize the findings accumulated to date regarding AAbs which have been considered to be involved in the pathology of DCM or pregnancy-related cardiovascular disease. Furthermore, we discuss the significance of AAbs as a possible cause of DCM and their potential roles as a novel therapeutic target.

Current state of knowledge on aetiology, diagnosis, management, and therapy of myocarditis: a position statement of the European Society of Cardiology Working Group on Myocardial and Pericardial Diseases

In this position statement of the ESC Working Group on Myocardial and Pericardial Diseases an expert consensus group reviews the current knowledge on clinical presentation, diagnosis and treatment of myocarditis, and proposes new diagnostic criteria for clinically suspected myocarditis and its distinct biopsy-proven pathogenetic forms. The aims are to bridge the gap between clinical and tissue-based diagnosis, to improve management and provide a common reference point for future registries and multicentre randomised controlled trials of aetiology-driven treatment in inflammatory heart muscle disease.

Cardiac troponins and autoimmunity: their role in the pathogenesis of myocarditis and of heart failure

Despite the widespread use of cardiac troponins as biomarkers for the diagnosis and quantitation of cardiac injury, the effect of troponin release and a possible autoimmune response to the troponins is unknown. Other investigators reported that programmed cell death-1 (PD-1)-receptor deficient mice developed severe cardiomyopathy with autoantibodies to troponin I. We found that immunization of genetically susceptible mice with troponin I but not troponin T induced a robust autoimmune response leading to marked inflammation and fibrosis in the myocardium. At later times, antibodies to cardiac myosin were detected in troponin-immunized mice. The severity of inflammation correlated with expression of chemokines RANTES, MIP-2, IP-10 and MCP-1 in the myocardium. Prior immunization with troponin I increased the severity of experimental infarctions, indicating that an autoimmune response to troponin I aggravates acute cardiac damage. Cardiac inflammation, fibrosis and functional impairment were transferred from immunized to naive recipients by CD4+ T cells, and the cytokine profile suggested both Th2 and Th17 profiles in A/J mice. Finally we identified an 18-mer of troponin I containing an immuno-dominant epitope.

Anti-heart autoantibodies in familial dilated cardiomyopathy

Familial aggregation is a feature of myocarditis and dilated cardiomyopathy (DCM). Myocarditis, a clinically polymorphic inflammatory disease of the myocardium, is diagnosed by endomyocardial biopsy (EMB) and may lead to DCM. Mutations in several genes encoding myocyte structural proteins are known monogenic DCM causes, but because of high etiologic and genetic heterogeneity, the gene defects identified so far account for a minority of cases. In the last decade, it has been discovered that autoimmunity plays a pivotal role in myocarditis and DCM that are thought to represent different stages of an organ-specific autoimmune disease in genetically predisposed individuals. None of the available genetic studies in familial DCM has taken into account the autoimmune phenotype markers in the characterization of index patients and relatives, thus it is not known whether or not the described gene defects are involved in the autoimmune form of the disease. In animal models autoimmune myocarditis/DCM can be induced by viral infection, immunization with heart-specific autoantigens, or develop spontaneously in genetically predisposed strains. It may be cell or antibody-mediated; susceptibility is based upon multiple MHC and non-MHC genes. In patients, the diagnosis of autoimmune myocarditis/DCM requires exclusion of viral genome on EMB and detection of serum heart-reactive autoantibodies. They are found in index patients and relatives from about 60% of both familial and non-familial pedigrees and predict DCM development among healthy relatives. Some antibodies have functional effects on cardiac myocytes in vitro, in animal models and possibly in a DCM subset without inflammation, responsive to extracorporeal immunoadsorption. Cardiac-specific autoantibodies, which are shown to be disease-specific for myocarditis/DCM, can be used as biomarkers for identifying patients in whom, in the absence of active infection of the myocardium, immunosuppression and/or immunomodulation may be beneficial and their relatives at risk. Future studies should clarify genetic basis of human autoimmune myocarditis/DCM as well as genotype/immune phenotype correlations.

Recombinant cardiac myosin fragment induces experimental autoimmune myocarditis via activation of Th1 and Th17 immunity

The specificity and function of T helper (Th) immune responses underlying the induction, progression, and resolution of experimental autoimmune myocarditis (EAM) in A/J mice are unclear. Published data suggest involvement of both Th1 and Th2 responses in EAM; however, the previous inability to assess antigen-specific in vivo and in vitro T-cell responses in cardiac myosin-immunized animals has confounded our understanding of this important model of autoimmune myocarditis. The goal of our study was to develop an alternative model of EAM based on a recombinant fragment of cardiac myosin, in hopes that the recombinant protein will permit measurement of functional T-cell responses that is not possible with purified native protein. A/J mice immunized with a recombinant fragment of cardiac myosin spanning amino acids 1074-1646, termed Myo4, developed severe myocarditis characterized by cardiac hypertrophy, massive mononuclear cell infiltration and fibrosis, three weeks post-immunization. The mice also developed an IgG1 dominant humoral immune response specific for both Myo4 and purified cardiac myosin. The in vitro stimulation of splenocytes harvested from Myo4-immunized animals with Myo4 resulted in cellular proliferation with preferential production of the Th1- and Th17-associated cytokines, IFN-gamma, IL-17, and IL-6, respectively. Production of IL-4 was negligible by comparison. This study describes a new model of EAM, inducible by immunization with a specific fragment of cardiac myosin, from which antigen-specific analyses reveal an importance for both Th1 and Th17 immunity.

Genetically determined myocarditis: clinical presentation and immunological characteristics

PURPOSE OF REVIEW

Myocarditis is a clinically heterogeneous myocardial inflammatory disease, diagnosed by endomyocardial biopsy; it may be idiopathic, infectious, or autoimmune and may lead to dilated cardiomyopathy. Myocarditis and dilated cardiomyopathy represent different stages of an organ-specific autoimmune disease in genetically predisposed individuals.

RECENT FINDINGS

In animal models, cell-mediated or antibody-mediated autoimmune myocarditis/dilated cardiomyopathy can be induced by viral infection or immunization with heart-specific autoantigens, or can develop spontaneously in genetically predisposed strains. Susceptibility is based on multiple major histocompatibility complex and nonmajor histocompatibility complex genes. In patients the diagnosis of autoimmune myocarditis/dilated cardiomyopathy requires exclusion of viral genome on endomyocardial biopsy and detection of serum heart-reactive autoantibodies. They are directed against multiple antigens that are found in patients and relatives from about 60% of familial and nonfamilial pedigrees. They predict dilated cardiomyopathy development among relatives, years before disease. Some antibodies have functional effects on cardiac myocytes in vitro, in animals and possibly in a dilated cardiomyopathy subset, responsive to extracorporeal immunoadsorption.

SUMMARY

In myocarditis/dilated cardiomyopathy, cardiac-specific and disease-specific antibodies of IgG class are potential biomarkers for identifying 'at risk' relatives as well as those patients in whom, in the absence of active infection of the myocardium, immunosuppression, and/or immunomodulation may be beneficial. Future studies should better define the genetic basis of human autoimmune myocarditis/dilated cardiomyopathy.

Circulating autoantibodies to troponin I in Emery-Dreifuss muscular dystrophy

The pathogenesis of dilated cardiomyopathy in Emery- Dreifuss muscular dystrophy (EDMD) is still unknown. Autoimmune mechanisms have recently been taken into account. The aim of this investigation was to determine whether the level of circulating antibodies to heart proteins which were previously detected, correlates with disease progression. Troponin I was chosen as the target. Ten patients with EDMD and 10 age-matched normal controls were tested. An enzyme linked immunoassay (ELISA) technique was used to determine the possible relation between the level of anti-troponin I antibodies at diagnosis and at followup. Autoantibodies against troponin I were detected in all EDMD patients. At diagnosis the level was higher in the X-linked EDMD form (X-EDMD), as compared to the autosomal dominant form (AD-EDMD). At follow-up the elevated level of the autoantibodies persisted in all the EDMD cases. However, in the AD-EDMD form, the level was found to be significantly rising with disease progression, in the X-EDMD form, on the other hand, it was declining. No clear-cut relationship between the level of the circulating antibodies and cardiac symptomatology was present. Detection of anti-troponin I antibodies may provide a non-invasive marker of early stages of dilated cardiomyopathy in EDMD.

Clinical implications of anti-heart autoantibodies in myocarditis and dilated cardiomyopathy

Dilated cardiomyopathy (DCM), a leading cause of heart failure and heart transplantation in younger adults, is characterized by dilatation and impaired contraction of the left or both ventricles; it may be idiopathic, familial/genetic (20-30%), viral, and/or immune. On endomyocardial biopsy there is chronic inflammation in 30-40% of cases. Mutations in genes encoding myocyte structural proteins, cardiotoxic noxae and infectious agents are known causes; due to high aetiologic and genetic heterogeneity, the gene defects identified so far account for a tiny proportion of the familial cases. In at least two thirds of patients, DCM remains idiopathic. Myocarditis may be idiopathic, infectious or autoimmune and may heal or lead to DCM. Circulating heart-reactive autoantibodies are found in myocarditis/DCM patients and symptom-free relatives at higher frequency than in normal or noninflammatory heart disease control groups. These autoantibodies are directed against multiple antigens, some of which are expressed only in the heart (organ-specific); some autoantibodies have functional effects on cardiac myocytes in vitro as well as in animal models. Depletion of nonantigen-specific antibodies by extracorporeal immunoadsorption is associated with improved ventricular function and reduced cardiac symptoms in some DCM patients, suggesting that autoantibodies may also have a functional role in humans. Immunosuppression seems beneficial in patients who are virus-negative and cardiac autoantibody positive. Prospective family studies have shown that cardiac-specific autoantibodies are present in at least 60% of both familial and non familial pedigrees and predict DCM development among asymptomatic relatives, years before clinical and echocardiographic evidence of disease. Animal models have shown that autoimmune myocarditis/DCM can be induced by virus as well as reproduced by immunization with a well-characterized autoantigen, cardiac myosin. Thus, in a substantial proportion of patients, myocarditis and DCM represent different stages of an organ-specific autoimmune disease, that represents the final common pathogenetic pathway of infectious and noninfectious myocardial injuries in genetically predisposed individuals.

Human cardiac myosin autoantibodies impair myocyte contractility: a cause‐and‐effect relationship

The functional relevance of autoantibodies (Abs) against cardiac myosin (CM) in clinical idiopathic dilated cardiomyopathy (DCM) remains controversial. The study sought to determine effects of human Abs affinity-purified (AF) by immunoaffinity column chromotography on excitation-contraction coupling in isolated myocytes. Effects of CM-Abs from heart failure patients with DCM (n=19) and ischemic heart disease (IHD, n=19) on contractility, L-type Ca2+ current, and Ca2+ transients in continuously perfused rat ventricular myocytes were studied. Immunofluorescence studies using confocal microscopy were carried out to determine whether Abs were internalized. AF-Abs from either group did not differ in IgG titer but differed in their elution profiles. The IgG3 subclass response was higher in AF fractions from DCM (21%) than IHD (5%) patients. The Abs reduced the capacity of field-stimulated myocytes to contract in a dose-dependent manner. Inhibition of contraction, as a percentage of untreated cells, was greater with DCM than IHD-Abs (P=0.004), and the effect was independent of Ab titer. An increase in frequency of the beating myocytes (0.2 to 3.0 Hz) raised peak systolic and diastolic levels of [Ca2+]i of cells treated with DCM but not IHD-Abs (P<0.005). The AF-Abs were not internalized by myocytes and had no effect on L-type Ca2+ currents. The altered sensitivity of the myofilaments to [Ca2+]i by CM-Abs may represent a potential mechanism of autoantibody-mediated impairment in clinical DCM.

Clinical implications of anti-cardiac immunity in dilated cardiomyopathy

Criteria of organ-specific autoimmunity are fulfilled in a subset of patients with myocarditis/dilated cardiomyopathy (DCM). In particular, circulating heart-reactive autoantibodies are found in such patients and symptom-free relatives. These autoantibodies are directed against multiple antigens, some of which are expressed in the heart (organ-specific), others in heart and some skeletal muscle fibres (partially heart-specific) or in heart and skeletal muscle (muscle-specific). Distinct autoantibodies have different frequency in disease and normal controls. Different techniques detect one or more antibodies, thus they cannot be used interchangeably for screening. It is unknown whether the same patients produce more antibodies or different patient groups develop autoimmunity to distinct antigens. IgG antibodies, shown to be cardiac- and disease-specific for myocarditis/DCM, can be used as autoimmune markers for relatives at risk as well as for identifying patients in whom immunosuppression may be beneficial. Some autoantibodies may also have a functional role, but further work is needed.

Autoimmune myocarditis and dilated cardiomyopathy: focus on cardiac autoantibodies

Criteria of organ-specific autoimmunity are fulfilled in a subset of patients with myocarditis/dilated cardiomyopathy (DCM). In particular, circulating heart-reactive autoantibodies are found in patients and symptom-free relatives. These autoantibodies are directed against multiple antigens, some of which are expressed in the heart (organ-specific), others in heart and some skeletal muscle fibres (partially-heart specific) or in heart and skeletal muscle (muscle-specific). Distinct autoantibodies have different frequency in disease and normal controls. Different techniques detect one or more antibodies, thus they cannot be used interchangeably for screening. It is unknown whether the same patients produce more antibodies or different patient groups develop autoimmunity to distinct antigens. IgG antibodies, shown to be cardiac and disease-specific for myocarditis/DCM, can be used as autoimmune markers for identifying patients in whom immunosuppression may be beneficial and relatives at risk. Some autoantibodies may also have a functional role, but further work is needed.

Pre- and post-transplant anti-myosin and anti–heat shock protein antibodies and cardiac transplant outcome

BACKGROUND

The purpose this study was to investigate the relationship of anti-myosin and anti-heat shock protein immunoglobulin G (IgG) serum antibodies to the original heart disease of cardiac transplant recipients, and also to rejection and patient survival after cardiac transplantation.

METHODS

Anti-myosin and anti-heat shock protein (anti-hsp) IgG antibodies were evaluated in pre-transplant sera from 41 adult cardiac allograft recipients and in sequential post-transplant serum samples from 11 recipients, collected at the time of routine endomyocardial biopsies during the first 6 months after transplantation. In addition, the levels of these antibodies were determined from the sera of 28 healthy blood donors.

RESULTS

Higher anti-myosin antibody levels were observed in pre-transplant sera than in sera from normal controls. Moreover, patients with chronic Chagas heart disease showed higher anti-myosin levels than patients with ischemic heart disease, and also higher levels, although not statistically significant, than patients with dilated cardiomyopathy. Higher anti-hsp levels were also observed in patients compared with healthy controls, but no significant differences were detected among the different types of heart diseases. Higher pre-transplant anti-myosin, but not anti-hsp, levels were associated with lower 2-year post-transplant survival. In the post-transplant period, higher anti-myosin IgG levels were detected in sera collected during acute rejection than in sera collected during the rejection-free period, whereas anti-hsp IgG levels showed no difference between these periods.

CONCLUSIONS

The present findings are of interest for post-transplant management and, in addition, suggest a pathogenic role for anti-myosin antibodies in cardiac transplant rejection, as has been proposed in experimental models of cardiac transplantation.

Immunopathogenesis of HIV-related heart muscle disease: current perspectives

As more effective antiretroviral therapies improve survival times, growing numbers of HIV-positive patients are at risk of developing end-organ damage or neoplasia. Heart muscle disease is the most important cardiovascular manifestation of HIV infection and seems set to become increasingly prevalent. This may take the form of either a dilated cardiomyopathy or isolated left or right ventricular dysfunction, is associated with a poor prognosis, and results in symptomatic heart failure in up to 5% of HIV patients. The precise cause of HIV-associated cardiomyopathy remains unclear but is undoubtedly complex, and most probably multifactorial. This report examines our current understanding of the immunopathogenesis of HIV-associated cardiomyopathy.

Cardiac autoantibodies to myosin and other heart-specific autoantigens in myocarditis and dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is characterized by dilation and impaired contraction of the left ventricle or both; it is a relevant cause of heart failure and a common indication for heart transplantation. It may be idiopathic, familial/genetic, viral, autoimmune or immune-mediated, associated with a viral infection. Myocarditis is an inflammatory disease of the myocardium; it may be idiopathic, infectious or autoimmune and may heal or lead to DCM. Thus, in a patient subset, myocarditis and DCM are thought to represent the acute and chronic stages of an organ-specific autoimmune disease of the myocardium. In keeping with this hypothesis, autoimmune features in patients with myocarditis/DCM include: familial aggregation, a weak association with HLA-DR4, abnormal expression of HLA class II on cardiac endothelium on endomyocardial biopsy, detection of organ- and disease-specific cardiac autoantibodies in the sera of affected patients and of symptom-free relatives. The organ-specific cardiac autoantibodies detected by immunofluorescence are directed against multiple antigens. One of these, first identified using immunoblotting and confirmed by ELISA, is the cardiac-specific alpha-myosin isoform. Myosin fulfils the expected criteria for organ-specific autoimmunity, in that immunization with cardiac but not skeletal myosin reproduces, in susceptible mouse strains, the human disease phenotype of myocarditis/DCM; in addition, alpha-myosin is entirely cardiac-specific. The organ-specific cardiac autoantibodies detected by immunofluorescence in symptom-free relatives were associated with echocardiographic features suggestive of early disease. Short-term follow-up is in keeping with this interpretation, although extended follow-up is necessary to define better the role of the antibody as predictor of disease susceptibility in healthy subjects at risk of myocarditis/DCM, such as first-degree relatives.

Circulating cardiac autoantibodies in dilated cardiomyopathy and myocarditis: pathogenetic and clinical significance

Dilated cardiomyopathy (DCM) is a relevant cause of heart failure and a common indication for heart transplantation. It may be idiopathic, familial/genetic, viral, autoimmune or immune-mediated associated with a viral infection. Myocarditis is an inflammatory disease of the myocardium; it may be idiopathic, infectious or autoimmune and may heal or lead to DCM. Thus, in a patient subset, myocarditis and DCM are thought to represent the acute and chronic stages of an organ-specific autoimmune disease of the myocardium. In keeping with this hypothesis, autoimmune features in patients with myocarditis/DCM include: familial aggregation; a weak association with HLA-DR4; abnormal expression of HLA class II on cardiac endothelium on endomyocardial biopsy; and detection of organ- and disease-specific cardiac autoantibodies of the IgG class in the sera of affected patients and symptom-free relatives. The cardiac autoantibodies detected by immunofluorescence are directed against multiple antigens. Two of these, first identified using immunoblotting and confirmed by ELISA, are the atrial-specific alpha- and the ventricular and skeletal muscle beta-heavy chain isoform. The alpha-myosin isoform fulfils the expected criteria for organ-specific autoimmunity, in that immunization with cardiac, but not skeletal myosin reproduces, in susceptible mouse strains, the human disease phenotype of myocarditis/DCM; in addition, alpha-myosin is entirely cardiac-specific. Additional antigenic targets of heart-reactive autoantibodies include unknown sarcolemmal proteins, mitochondrial enzymes, beta-adrenergic and muscarinic receptors. For some of these antibodies, there is in vitro evidence for a functional role. The organ-specific cardiac autoantibodies detected by immunofluorescence in symptom-free relatives were associated with echocardiographic features suggestive of early disease. Mid-term follow-up suggests that these antibodies are predictive markers of progression to DCM among symptom-free relatives with or without abnormal echocardiographic findings.

Characterization of anti-myocardial autoantibodies in Japanese patients with dilated cardiomyopathy

Few previous reports have comprehensively screened all the anti-myocardial autoantibodies (AMCA) in relation to other clinical profiles in patients with idiopathic dilated cardiomyopathy (IDC), so the present study used both immunohistochemistry (FITC) and immunoblotting (IB) for screening patients with IDC in order to characterize the clinical significance of AMCA. Sera were collected from 100 patients with IDC and age-matched 100 healthy control subjects (CTL). For FITC, an unfixed frozen section of human myocardium was used for the standard indirect immunofluorescence; for IB, total cardiac homogenates of the same myocardium were blotted to serum at 2 sets of dilution (1:200 and 1:10,000). The positive rates of AMCA detection for each method were as follows (IDC vs CTL); 39% vs 6% for FITC, 38% vs 4% for IB (1:200), and 10% vs 0% for IB (1:10,000). Fifty-nine patients with IDC and 8 CTL were positive for AMCA by either method, and 18 patients with IDC and 2 CTL were positive for AMCA by both methods. IB-positivity at 1:200 was an independent predictor by multiple logistic regression analysis of non-sustained ventricular tachycardias as well as left ventricular end-diastolic diameter and plasma norepinephrine concentration.

Elevated serum levels of soluble interleukin-2 receptor, neopterin and beta-2-microglobulin in idiopathic dilated cardiomyopathy: relation to disease severity and autoimmune pathogenesis

BACKGROUND

It has not been assessed whether high levels of soluble interleukin 2 receptor (sIL-2R), neopterin and beta-2 microglobulin in idiopathic dilated cardiomyopathy reflect heart failure severity and/or an active autoimmune process. The aim of this study was to relate serum levels of these markers to clinical and autoimmune features.

METHODS

We studied 60 patients with idiopathic dilated cardiomyopathy, 67 controls with ischemic heart failure and 34 normals.

RESULTS

Abnormal levels of sIL-2R, but not of neopterin and beta-2 microglobulin, were more frequent in idiopathic dilated cardiomyopathy than in ischemic patients (35% vs. 16%; P=0.02) or in normals (35% vs. 12%, P=0.01); mean sIL-2R levels were, however, similar in idiopathic dilated cardiomyopathy and ischemic heart failure (842+/-75 vs. 762+/-93 U/ml, P=NS). In idiopathic dilated cardiomyopathy abnormal levels of sIL-2R were associated with lower peak oxygen consumption (P=0.008), higher neopterin and HLA class II expression in the myocardium (P=0.02), but were unrelated to cardiac autoantibody status or titer. In addition, abnormal levels of neopterin were associated with adverse prognosis and higher beta-2 microglobulin; abnormal levels of beta-2 microglobulin with lower echocardiographic percent fractional shortening, higher sIL-2R and higher neopterin.

CONCLUSIONS

There is no convincing evidence that abnormal sIL-2R, neopterin and/or beta-2 microglobulin are disease-specific markers of idiopathic dilated cardiomyopathy. The lack of association with cardiac autoantibodies suggests that these abnormalities are mainly related to heart failure severity rather than autoimmune pathogenesis. In keeping with this view, high levels of sIL-2R, neopterin and/or beta-2 microglobulin identified a subset of idiopathic dilated cardiomyopathy patients with advanced disease and poor prognosis.

Enzyme-linked immunosorbent assay for anti-tropomyosin antibodies and its clinical application to various heart diseases

Tropomyosin is one of the key proteins for muscle contraction. We developed an enzyme-linked immunosorbent assay for antibodies to porcine muscle tropomyosin and measured serum anti-tropomyosin antibodies in patients with heart diseases and in normal controls. The mean values of absorbance in the ELISA assay of patients with ischemic heart disease (n=36, P<0.001), dilated cardiomyopathy (n=28, P<0.005), valvular heart disease (n=27, P<0.05), and collagen disease (n=38, P<0.05) were significantly higher than those of normal controls (n=53), but the value in patients with hypertrophic cardiomyopathy (n=19) was not significantly different from that of normal controls. When the cut-off value was fixed at the mean+2 SD of absorbance in normal controls, positive reactions were found in 19.4%, 7.1%, 18.5% and 15.8% of patients with ischemic heart disease, dilated cardiomyopathy, valvular heart disease, and collagen disease, respectively. An inhibition study revealed that anti-tropomyosin antibodies were different from anti-myosin antibodies, but there was a partial cross-reactivity between the two. Thus, there was a weak correlation of the titers of the two types of antibody within the group of heart diseases. These data indicate that measurement of anti-tropomyosin antibodies by ELISA is helpful for detecting autoimmune abnormalities in various heart diseases.

Subclass specificity of autoantibodies against myosin in patients with idiopathic dilated cardiomyopathy: pro-inflammatory antibodies in DCM patients

Detection of antimyosin antibodies in non-inflammatory cardiac disease undermines their disease specificity as a sensitive marker of damage in dilated cardiomyopathy (DCM) patients. Antibody subclass specificity could provide a more sensitive marker of disease and possibly discriminate the humoral autoimmune responses in different cardiac diseases. Frequency and reactivity of autoantibodies against alpha- and beta-isoforms of myosin heavy chain (mhc) were evaluated by ELISA for IgG, IgM, and subclasses IgG1, IgG2, and IgG3 in patients with DCM (NYHA III/IV, n = 82), end stage ischemic heart disease (E-IHD: NYHA III/IV, n = 62), mild ischemic heart disease (NYHA I/II, n = 27), and controls (n = 54). Autoantibodies against atrial and ventricular myosin were raised in heart failure patients compared to mild-IHD and controls but with different antigen affinities. Reactivity in E-IHD was significantly raised against (ventricular) beta-mhc compared with only mild-IHD patients, suggesting a relative increase in ventricular specific antibodies in IHD patients with a higher NYHA class. IgG subclass analysis for IgG1, IgG2, and IgG3 against alpha- and beta-mhc showed statistically raised levels of IgG3 only in DCM patients and a significantly higher reactivity of IgG2 in heart failure patients versus controls. The results demonstrate immunological heterogeneity of antimyosin antibodies developed in different clinical entities. Pro-inflammatory characteristics of IgG3 antibodies in a select group of patients with DCM may contribute to autoimmune mechanisms of injury in these patients.

Nonischemic heart failure: epidemiology, pathophysiology, and progression of disease

The prevalence of nonischemic heart failure including idiopathic dilative cardiomyopathy is not well known. It may vary considerably in different population sub-groups and geographic areas. In ambulatory and hospitalized patients with clinically manifest heart failure primary cardiomyopathy is diagnosed in 2-15%, while in recent large scale therapeutic trials the proportion of patients with nonischemic heart failure ranged from 18% to 53%. There is a relation between sex, age and etiology of chronic heart failure, nonischemic cardiomyopathy being more frequent in women and in younger individuals. In contrast to ischemic heart failure, where the severity usually correlates with the extent of coronary artery lesions, the pathophysiology of cardiomyopathy is less clear. Genetic factors, myocarditis from infectious agents, auto-immune mechanisms, cytokine activation, hormonal and metabolic influences can play a role. The functional consequences of myocardial damage in nonischemic heart failure is a global instead of localized abnormality of ventricular contractility. There is epidemiological evidence that in general the prognosis of nonischemic heart failure is better than in ischemic heart failure. The mortality of patients with ischemic heart failure was usually higher in the placebo groups of recent heart failure trials than in patients with nonischemic etiology. Furthermore, therapeutic responses to angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, amlodipine and amiodarone were also different in some studies. The outcome of nonischemic heart failure is better even in transplant candidates with the most advanced stages of heart failure, they survive longer and respond better to intensified drug regimens than patients with similar clinical severity of ischemic heart failure. Thus, an early and precise diagnosis of the etiology of heart failure should be encouraged not only in clinical trials but also in every day patient management. As more therapeutic options are developed, individualized drug selection for patients with various etiologies of heart failure may become possible.

Etiology and response to drug treatment in heart failure

Clinical trials in heart failure (HF) tend to randomize patients according to demographic characteristics and severity of left ventricular dysfunction, without taking account of the precise diagnosis. This article reviews results from recent trials suggesting that the etiology of HF, and particularly whether it is ischemic or nonischemic, may influence the long-term prognosis and the response to treatment. Some studies, but not all, suggest that nonischemic HF has a better prognosis than ischemic HF. The data on the benefits of angiotensin-converting enzyme inhibitors in ischemic versus nonischemic HF are conflicting. Carvedilol, and recently, bisoprolol have been shown to reduce mortality in ischemic and nonischemic HF, whereas metoprolol has, to date, improved prognosis only in dilated cardiomyopathy. Better responses to digoxin, amlodipine and amiodarone have been reported in non-ischemic HF. There is at present no clear explanation for the apparent therapeutic differences between ischemic and nonischemic HF. Absence of a rigorous definition of "nonischemic HF" in many studies makes interpretation of the results difficult. Further studies to clarify the effects of etiology of HF on the response to treatment could be particularly important for preventing progression to more advanced stages, in which any type of drug therapy may have limited value in prolonging survival. An individualized therapeutic approach, based on etiology of HF and possibly other factors such as plasma drug levels or the levels of neurohormones, could result in major progress in treating HF patients.

Cardiac autoimmunity in HIV related heart muscle disease

OBJECTIVE

To assess the frequency of circulating cardiac specific autoantibodies in HIV positive patients with and without echocardiographic evidence of left ventricular dysfunction.

SUBJECTS

74 HIV positive patients including 28 with echocardiographic evidence of heart muscle disease, 52 HIV negative people at low risk of HIV infection, and 14 HIV negative drug users who had all undergone non-invasive cardiac assessment were studied along with a group of 200 healthy blood donors.

RESULTS

Cardiac autoantibodies detected by indirect immunofluorescence (serum dilution 1/10) were more common in the HIV positive patients (15%), particularly the HIV heart muscle disease group (21%), than in HIV negative controls (3.5%) (both p < 0.001). By ELISA (dilution 1/320), abnormal anti-alpha myosin autoantibody concentrations were found more often in HIV patients with heart muscle disease (43%) than in HIV positive patients with normal hearts (19%) or in HIV negative controls (3%) (p < 0.05 and p < 0.001, respectively). Anti-alpha myosin autoantibody concentrations were greater in HIV positive patients than in HIV negative controls, regardless of cardiac status ((mean SD) 0.253 (0.155) v 0.170 (0.076); p = 0.003). In particular the mean antibody concentration was higher in the HIV heart muscle disease patients (0.291 (0.160) v 0.170 (0.076); p = 0.001) than in HIV negative controls. On follow up, six subjects with normal echocardiograms but raised autoantibody concentrations had died after a median of 298 days, three with left ventricular abnormalities at necropsy. This compared with a median survival of 536 days for 21 HIV positive patients with normal cardiological and immunological results.

CONCLUSIONS

There is an increased frequency of circulating cardiac specific autoantibodies in HIV positive individuals, particularly those with heart muscle disease. The data support a role for cardiac autoimmunity in the pathogenesis of HIV related heart muscle disease, and suggest that cardiac autoantibodies may be markers of the development of left ventricular dysfunction in HIV positive patients with normal hearts.

Human chagasic disease is not associated with an antiheart humoral response

An inflammatory cardiomyopathy occurs in humans with chronic Trypanosoma cruzi infection (Chagas' disease). This study finds that T. cruzi infection is not associated with the production of cardiac-specific autoantibodies in humans with cardiac manifestations.

Cardiac autoantibodies in dilated cardiomyopathy become undetectable with disease progression

OBJECTIVE

To determine the relation of cardiac autoantibody and disease status in a consecutive series of patients with dilated cardiomyopathy by prospective antibody testing at diagnosis and at follow up.

METHODS

Antibody status was assessed by indirect immunofluorescence in 110 patients with dilated cardiomyopathy (85 male, mean (SD) age 44 (13) years) at diagnosis and at follow up (mean (SD) 14 (12) months); in 57 of them cardiac specific anti-alpha myosin antibody titres were also measured by an enzyme-linked immunosorbent assay (ELISA). Patients underwent complete evaluation at diagnosis and clinical and non-invasive assessment at follow up, including exercise testing with maximal oxygen consumption measurements.

RESULTS

The frequency of cardiac specific antibodies by immunofluorescence was lower at follow up than at diagnosis (28 (25%) v 11 (10%), P = 0.002). Mean (SEM) anti-alpha myosin antibody titres at follow up were also lower than at diagnosis (0.24 (0.02) v 0.30 (0.02), P = 0.038); 24% of patients at diagnosis and 14% at follow up had an abnormal ELISA result. None of the patients who were negative by immunofluorescence or ELISA at diagnosis became positive at follow up. Presence of antibody at diagnosis was associated with milder symptoms and greater exercise capacity at follow up and persistence of antibody at follow up was associated with stable disease and milder symptoms at diagnosis.

CONCLUSIONS

Cardiac specific autoantibodies in dilated cardiomyopathy become undetectable with disease progression; this is a recognised feature of other autoimmune conditions, such as type 1 diabetes. Detection of these antibodies at diagnosis and at follow up may provide a non-invasive marker of early dilated cardiomyopathy.

Recognition and optimum management of myocarditis

Myocarditis is a poorly understood condition and its prevalence is largely underestimated. A significant proportion of cases may be subclinical and chronic, leading to dilated cardiomyopathy, which represents the first cause of heart transplantation worldwide. Although inflammation of the myocardium can be associated with various causes, particularly viruses, myocarditis is usually idiopathic. Present evidence suggests that some 'idiopathic' and chronic 'postviral' myocarditis cases may be autoimmune, whereas others with acute self-limited disease or with persisting pathogenic virus by molecular methods may represent viral myocarditis. The major obstacle in identifying a specific therapy in myocarditis lies in the difficulty of a thorough clinical characterisation of individual patients in relation to viral and autoimmune involvement. This also explains the inconclusive results of trials of immunosuppressive drugs in myocarditis/dilated cardiomyopathy. Diagnosis is based upon endomyocardial biopsy. Management of myocarditis requires avoidance of agents that exacerbate myocarditis or depress myocardial function, and conventional therapy for heart failure (diuretics, ACE inhibitors and, if indicated, digoxin) and arrhythmias. Although at present the use of immunosuppressive therapy cannot be recommended on a routine basis, the recent Myocarditis Treatment Trial, where an aetiologically heterogeneous patient population was treated without significant adverse effects, provides some rationale for applying the same immunosuppression protocol to selected patients, e.g. those with active biopsy-proven myocarditis, unresponsive to conventional therapy, prior to transplantation, and those with idiopathic giant cell myocarditis.

Evidence for autoimmunity to myosin and other heart-specific autoantigens in patients with dilated cardiomyopathy and their relatives

Autoimmune disease is characterised by the presence of circulating autoantibodies in the affected patients and in a proportion of their relatives. These antibodies are generally not pathogenic but are reliable markers of immune-mediated tissue damage. In organ-specific autoimmune disease, the destruction process is largely restricted to one organ within the body and the autoantibodies react with autoantigens which are unique to the diseased target organ. At least in a patient subset, myocarditis and dilated cardiomyopathy (DCM) may represent the acute and chronic stages of a progressive organ-specific autoimmune disease of the myocardium. Autoimmune features in patients with myocarditis/DCM include: familial aggregation, a weak association with HLA-DR4, abnormal expression of HLA class II on cardiac endothelium on endomyocardial biopsy, and detection of organ- and disease-specific cardiac autoantibodies, by immunofluorescence and absorption techniques, in the affected patients and in a proportion of their symptom-free relatives from both familial and non-familial DCM pedigrees. The organ-specific cardiac autoantibodies detected by immunofluorescence are directed against multiple antigens. One of these, first identified using immunoblotting and confirmed by ELISA, is the cardiac-specific alpha-myosin isoform. Myosin fulfils the expected criteria for organ-specific autoimmunity, in that immunisation with cardiac but not skeletal myosin reproduces, in susceptible mouse strains, the human disease phenotype of DCM; in addition, alpha-myosin is entirely cardiac-specific and is only expressed in the myocardium. Using ELISA, high titer organ- and disease-specific anti alpha-myosin antibodies have been found in 16% of the symptom-free relatives of DCM patients and in 38% of the pedigrees of the same cohort of relatives studied by immunofluorescence. The ELISA results provide additional evidence for autoimmunity in a subset of DCM families, and emphasise the importance of alpha-myosin as a target antigen.