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

Frequency of autoantibodies and their associated clinical characteristics and outcomes in patients with dilated cardiomyopathy: A systematic review and meta-analysis

BACKGROUND

Dilated cardiomyopathy (DCM) is a prevalent myocardial disorder characterized by impaired cardiac function affecting either the left ventricle or both ventricles. Accumulating evidence suggests that autoimmunity represents a key mechanism implicated in its pathogenesis, as several abundant autoantibodies have been identified in patients with the condition. However, the prevalence of these antibodies (Abs) in patients with DCM compared to that in both healthy controls (HCs) and those with ischemic cardiomyopathy (ICM), as well as their potential association with DCM, remains unclear. This study aimed to elucidate the prevalence of certain autoantibodies in patients with DCM compared to that in HCs and patients with ICM, as well as to evaluate their correlation with clinical characteristics and outcomes.

METHODS

A comprehensive literature search of the PubMed, Web of Science, EMBASE, the Cochrane Library, and Scopus was conducted up to March 26, 2024, and any article that fulfilled our inclusion criteria was reviewed. A meta-analysis was then conducted, using both random- and fixed-effects models.

RESULTS

A total of 38 studies met the inclusion criteria and were pulled for this analysis. Significantly higher prevalence rates of autoantibodies targeting the anti-β1 adrenergic receptor (β1-AR; odds ratio [OR] = 4.96, p = 0.000), M2 muscarinic receptor (M2-R; OR = 4.07, p = 0.000), adenine nucleotide translocator (ANT; OR = 21.18, p = 0.001) and myosin (OR = 12.26, p = 0.000) were observed in patients with DCM compared to HCs. Moreover, patients with DCM exhibited a significantly higher frequency of positive ANT Abs (OR = 34.52, p = 0.005) compared to those with ICM. Regarding clinical characteristics and outcomes, seropositivity for β1-AR Abs was found to be significantly correlated with New York Heart Association (NYHA) classification (standardized mean difference [SMD] = 0.78, p = 0.006), left ventricular ejection fraction (LVEF) (SMD = -1.38, p = 0.001), and heart rate (HR) (SMD = 1.505, p = 0.022). Seropositivity for anti‑calcium channel Abs was significantly associated with sudden cardiac death (SCD; OR = 3.17, p = 0.000) and all-cause mortality (OR = 2.06, p = 0.008), while anti-troponin I (TnI) Abs were associated with atrial fibrillation (OR = 0.21, p = 0.042). In terms of Ab prevalence rates, significant heterogeneity in the frequency of anti-β1-AR Abs between studies investigating DCM and ICM may be partially explained by the detection methods used and the mean ages of the patients. Meta-regression analysis suggested that the patients' ages may partially explain the observed heterogeneity between studies regarding β1-AR Ab seropositivity and HR. However, the heterogeneity observed in the studies comparing the prevalences of Abs in patients with DCM vs HCs and ICM, as well as their associated clinical characteristics, could not be explained by subgroup analyses or demographic factors such as age and sex-nor by cardiac function.

CONCLUSIONS

Patients with DCM are more likely to have elevated levels of anti- β1-AR, M2-R, ANT and myosin autoantibodies compared to HCs, as well as higher levels of ANT Abs compared to patients with ICM. Anti-β1-AR, calcium channel, and TnI Abs may play an essential role in DCM severity and poor prognosis. This study represents the first comprehensive meta-analysis regarding autoantibody prevalence and DCM and may thus potentially guide the clinical management of such patients. However, further research is warranted to evaluate the accuracy of this presumed role of autoantibodies in DCM, owing to the small number of the studies included and their high degree of heterogeneity.

Cellular Immunology of Myocarditis: Lights and Shades-A Literature Review

Myocarditis is an inflammatory disease of the myocardium with heterogeneous etiology, clinical presentation, and prognosis; when it is associated with myocardial dysfunction, this identifies the entity of inflammatory cardiomyopathy. In the last few decades, the relevance of the immune system in myocarditis onset and progression has become evident, thus having crucial clinical relevance in terms of treatment and prognostic stratification. In fact, the advances in cardiac immunology have led to a better characterization of the cellular subtypes involved in the pathogenesis of inflammatory cardiomyopathy, whether the etiology is infectious or autoimmune/immune-mediated. The difference in the clinical course between spontaneous recovery to acute, subacute, or chronic progression to end-stage heart failure may be explained not only by classical prognostic markers but also through immune-pathological mechanisms at a cellular level. Nevertheless, much still needs to be clarified in terms of immune characterization and molecular mechanisms especially in biopsy-proven myocarditis. The aims of this review are to (1) describe inflammatory cardiomyopathy etiology, especially immune-mediated/autoimmune forms, (2) analyze recent findings on the role of different immune cells subtypes in myocarditis, (3) illustrate the potential clinical relevance of such findings, and (4) highlight the need of further studies in pivotal areas of myocarditis cellular immunology.

An engineered human cardiac tissue model reveals contributions of systemic lupus erythematosus autoantibodies to myocardial injury

Systemic lupus erythematosus (SLE) is a heterogenous autoimmune disease that affects multiple organs, including the heart. The mechanisms of myocardial injury in SLE remain poorly understood. In this study, we engineered human cardiac tissues and cultured them with IgG from patients with SLE, with and without myocardial involvement. IgG from patients with elevated myocardial inflammation exhibited increased binding to apoptotic cells within cardiac tissues subjected to stress, whereas IgG from patients with systolic dysfunction exhibited enhanced binding to the surface of live cardiomyocytes. Functional assays and RNA sequencing revealed that, in the absence of immune cells, IgG from patients with systolic dysfunction altered cellular composition, respiration and calcium handling. Phage immunoprecipitation sequencing (PhIP-seq) confirmed distinctive IgG profiles between patient subgroups. Coupling IgG profiling with cell surfaceome analysis identified four potential pathogenic autoantibodies that may directly affect the myocardium. Overall, these insights may improve patient risk stratification and inform the development of new therapeutic strategies.

The Role of the Immune System in Pathobiology and Therapy of Myocarditis: A Review

The role of the immune system in myocarditis onset and progression involves a range of complex cellular and molecular pathways. Both innate and adaptive immunity contribute to myocarditis pathogenesis, regardless of its infectious or non-infectious nature and across different histological and clinical subtypes. The heterogeneity of myocarditis etiologies and molecular effectors is one of the determinants of its clinical variability, manifesting as a spectrum of disease phenotype and progression. This spectrum ranges from a fulminant presentation with spontaneous recovery to a slowly progressing, refractory heart failure with ventricular dysfunction, to arrhythmic storm and sudden cardiac death. In this review, we first examine the updated definition and classification of myocarditis at clinical, biomolecular and histopathological levels. We then discuss recent insights on the role of specific immune cell populations in myocarditis pathogenesis, with particular emphasis on established or potential therapeutic applications. Besides the well-known immunosuppressive agents, whose efficacy has been already demonstrated in human clinical trials, we discuss the immunomodulatory effects of other drugs commonly used in clinical practice for myocarditis management. The immunological complexity of myocarditis, while presenting a challenge to simplistic understanding, also represents an opportunity for the development of different therapeutic approaches with promising results.

An engineered human cardiac tissue model reveals contributions of systemic lupus erythematosus autoantibodies to myocardial injury

Systemic lupus erythematosus (SLE) is a highly heterogenous autoimmune disease that affects multiple organs, including the heart. The mechanisms by which myocardial injury develops in SLE, however, remain poorly understood. Here we engineered human cardiac tissues and cultured them with IgG fractions containing autoantibodies from SLE patients with and without myocardial involvement. We observed unique binding patterns of IgG from two patient subgroups: (i) patients with severe myocardial inflammation exhibited enhanced binding to apoptotic cells within cardiac tissues subjected to stress, and (ii) patients with systolic dysfunction exhibited enhanced binding to the surfaces of viable cardiomyocytes. Functional assays and RNA sequencing (RNA-seq) revealed that IgGs from patients with systolic dysfunction exerted direct effects on engineered tissues in the absence of immune cells, altering tissue cellular composition, respiration and calcium handling. Autoantibody target characterization by phage immunoprecipitation sequencing (PhIP-seq) confirmed distinctive IgG profiles between patient subgroups. By coupling IgG profiling with cell surface protein analyses, we identified four pathogenic autoantibody candidates that may directly alter the function of cells within the myocardium. Taken together, these observations provide insights into the cellular processes of myocardial injury in SLE that have the potential to improve patient risk stratification and inform the development of novel therapeutic strategies.

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.

The role of B cells in heart failure and implications for future immunomodulatory treatment strategies

Despite numerous demonstrations that the immune system is activated in heart failure, negatively affecting patients' outcomes, no definitive treatment strategy exists directed to modulate the immune system. In this review, we present the evidence that B cells contribute to the development of hypertrophy, inflammation, and maladaptive tissue remodelling. B cells produce antibodies that interfere with cardiomyocyte function, which culminates as the result of recruitment and activation of a variety of innate and structural cell populations, including neutrophils, macrophages, fibroblasts, and T cells. As B cells appear as active players in heart failure, we propose here novel immunomodulatory therapeutic strategies that target B cells and their products.

Lymphocytic subsets play distinct roles in heart diseases

Heart diseases are one of the leading causes of death for humans in the world. Increasing evidence has shown that myocardial injury induced innate and adaptive immune responses upon early cellular damage but also during chronic phases post-injury. The immune cells can not only aggravate the injury but also play an essential role in the induction of wound healing responses, which means they play a complex role throughout the acute inflammatory response and reparative response after cardiac injury. This review will summarize the current experimental and clinical evidence of lymphocytes, one of the major types of immune cells, participate in heart diseases and try to explain the possible role of these immune cells following cardiac injury.

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.

Autoimmunity and autoinflammation as the yin and yang of idiopathic recurrent acute pericarditis

Autoimmunity and autoinflammation are generally considered as mutually exclusive mechanisms of diseases but may concur to specific syndromes. Idiopathic recurrent acute pericarditis (IRAP) is defined as the recurrence of pericardial symptoms at any point following the prior cessation of acute pericarditis, and the latency is generally 6 weeks. Manifestations of pericarditis such as pericardial friction rub, electrocardiographic changes, and pericardial effusion are less frequent in the subsequent episodes compared to the index attack, and in some cases the only clinical sign is represented by a suggestive chest pain. Several autoimmune diseases may manifest with pericarditis which is often related to viral infections, while postviral pericarditis may in turn display a nonspecific autoimmune background. Similarly, autoinflammatory syndromes such as familial Mediterranean fever and tumor necrosis factor receptor-associated periodic syndrome are characterized by self-limiting pericardial symptoms. Corticosteroids are generally effective, thus supporting the autoimmune nature of IRAP, but dramatic results are obtained with interleukin-1 blocking agents in corticosteroid-dependent cases, pointing to a pathogenic role for the inflammasome. Based on these observations, we submit that IRAP represents a paradigmatic example of the putative coexistence of autoimmunity and autoinflammation: the main aim of this review is to critically discuss the hypothesis as well as the current understanding of this enigmatic clinical condition.

High proportion of patients with end-stage heart failure regardless of aetiology demonstrates anti-cardiac antibody deposition in failing myocardium: humoral activation, a potential contributor of disease progression

AIMS

Various reports have raised the possibility of humoral immune responses as contributors for the progression of heart failure. Previous studies, however, have focused on the analysis of serum and documented circulating antibodies against a variety of cardiac proteins. However, there is little evidence on whether anti-cardiac antibodies are deposited in end-stage failing myocardium. Our objective was to determine whether or not there was evidence of deposition of anti-cardiac antibodies and/or activated complement components in end-stage failing human myocardium.

METHODS AND RESULTS

Myocardial samples were obtained from 100 end-stage heart failure patients and 40 donor control biopsies. Sections were cut and stained using standard fluorescent immunohistochemistry techniques with anti-human immunoglobulin G (IgG), IgG3, and C3c. Gel electrophoresis and protein identification by mass spectrometry were used to confirm the presence of IgG and its antigen. Immunoglobulin G was localized to the sarcolemma in 71% of patients, 48% of those being positive for the subtype IgG3. The proportion of patients with ischaemic heart disease that was positive for IgG was 65% and among those with non-ischaemic aetiologies was 76%. In a subgroup analysis, the presence of IgG and its subunits were confirmed by mass spectrometry and adenosine triphosphate synthase β subunit identified as an antigen. Complement was activated in 31% of all patients. The presence of IgG, IgG3, and C3c was directly correlated with the length of disease (r = 0.451, P = 0.006).

CONCLUSION

Evidence of anti-cardiac antibodies and complement activation was found in a large number of patients with end-stage cardiomyopathy regardless of the aetiology. Adenosine triphosphate synthase appears to be a new prominent antigenic stimulus; but more interestingly, the simultaneous co-existence of activated complement components suggests that this humoral mechanism may participate in disease progression.

The role of B-cells in heart failure

Heart failure is a complex disease that has great impact on morbidity and mortality in the general population. No recent therapies have proven to be effective; however, the discovery of new potential pathophysiological mechanisms involved in heart failure expression and progression could offer novel therapeutic strategies. A number of studies have shown that the immune system may be a central mediator in the development and progression of heart failure, and here we describe how the B-cell and B-cell-mediated pathways play specific roles in the heart failure state. Therapies aimed at B-cells, either blocking antibody production or inactivating B-cell function, may suggest potential new treatment strategies.

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.

Autoantibodies in Heart Failure and Cardiac Dysfunction

Human heart failure is a disease with multifactorial causes, considerable morbidity, and high mortality. Several circulating autoantibodies, some of them being heart-specific, play a crucial role in the progression and induction of heart failure. However the precise mechanisms on how these autoantibodies perpetuate or even induce an organ specific autoimmune response are not yet fully understood. Also it is being a matter of current research to elucidate a potential pathophysiological role of the innate immune system in generating auto-reactive antibodies. In this review we will summarize the current available literature on circulating autoantibodies which are related to human heart failure. We will present clinical and animal studies that demonstrate the occurrence and pathophysiological relevance of several autoantibodies in heart failure, as well as point out biological mechanisms on molecular and cellular level. Finally the beneficial therapeutic effects of numerous clinical studies that target the humoral arm of the immune system by using either intravenous immunoglobulins and/or immunoadsorption will be critically discussed.

Presence of circulating anti-myosin antibodies in endomyocardial fibrosis

Background

Endomyocardial Fibrosis (EMF) is a tropical restrictive cardiomyopathy of unknown etiology with high prevalence in Sub-Saharan Africa, for which it is unclear whether the primary target of injury is the endocardial endothelium, the subendocardial fibroblast, the coronary microcirculation or the myocyte. In an attempt to explore the possibility of endocardial lesions being a result of an immune response against the myocyte we assessed the presence and frequency of circulating anti-myocardial antibodies in EMF patients.

Methodology/Principal Findings

EMF classification, assessment of severity and staging was based on echocardiography. We used sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of myocardial proteins followed by western blotting to screen serum samples for antiheart antibodies G and M classes. The degree of serum reactivity was correlated with the severity and activity of EMF. We studied 56 EMF patients and 10 healthy controls. IgG reactivity against myocardial proteins was stronger and more frequent in patients with EMF when compared to controls (30/56; 53.6% vs. 1/10; 10%, respectively). IgM reactivity was weak in both groups, although higher in EMF patients (11/56; 19.6%) when compared to controls (n = 0). EMF patients showed greater frequency and reactivity of IgG antibodies against myocardial proteins of molecular weights 35 kD, 42 kD and 70 kD (p values <0.01, <0.01 and <0.05 respectively).

Conclusions

The presence of antibodies against myocardial proteins was demonstrated in a subset of EMF patients. These immune markers seem to be related with activity and might provide an adjunct tool for diagnosis and classification of EMF, therefore improving its management by identifying patients who may benefit from immunosuppressive therapy. Further research is needed to clarify the role of autoimmunity in the pathogenesis of EMF.

Endomyocardial Fibrosis is a tropical disease in which the heart cannot open properly to receive blood due to a scar that covers its inner layer. It affects mainly children and adolescents, and has a poor prognosis because the cause and mechanisms of scarring are unknown. The conventional treatment is frustrating and does not alter the natural history of the disease. Despite affecting several million people worldwide there has been little investigation on the mechanisms of the disease or drug development to improve its prognosis. In this study we investigate the presence of antibodies against the myocardial cells of African patients with severe and advanced EMF aiming at uncovering new pathways for the disease. Our results reveal that EMF patients have anti-myocardial antibodies in their blood. The reaction of these antibodies with the heart may be one of the mechanisms involved in the genesis of the fibrotic lesions. This knowledge may help in diagnosing the condition and provide alternatives for its management, using drugs that reduce the impact of the circulating antibodies in the cardiac tissue. The significance of these results needs confirmation on studies involving larger number of subjects due to frequent finding of antiheart antibodies in African populations with heart failure of any cause.

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.

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.

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.

Viscum album agglutinin-I induces degradation of cytoskeletal proteins in leukaemia PLB-985 cells differentiated toward neutrophils: cleavage of non-muscle myosin heavy chain-IIA by caspases

The role of the anti-cancer agent Viscum album agglutinin-I (VAA-I) in leukaemia PLB-985 cells differentiated toward a neutrophil-like phenotype by dimethylsulphoxide (PLB-985D) has never been studied. This study investigated whether or not VAA-I can induce cytoskeletal breakdown in PLB-985D cells, as previously observed in undifferentiated PLB-985 cells. VAA-I was found to induce apoptosis in PLB-985D cells, as assessed by cytology and by degradation of gelsolin, an event known to occur via caspase-3 activation. VAA-I induced cytoskeletal breakdown based on the disruption of the F-actin network and cleavage of paxillin, vimentin and lamin B(1). In addition, we demonstrated, for the first time, that non-muscle myosin heavy chain IIA (NMHC-IIA) was cleaved by VAA-I treatment. Degradation of NMHC-IIA was reversed by the pan caspase inhibitor z-VAD-fmk in PLB-985D cells and neutrophils. However, unlike lamin B(1), no NMHC-IIA was detected on the cell surface of apoptotic neutrophils. In conclusion, PLB-985D cells responded in a similar manner to neutrophils regarding the degradation of the tested cytoskeletal. Therefore, PLB-985D cells may provide a suitable substitute for neutrophils in screening experiments, preventing extensive neutrophil cell isolation.