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

Repurposing of rituximab biosimilars to treat B cell mediated autoimmune diseases

Rituximab, the first monoclonal antibody approved for the treatment of lymphoma, eventually became one of the most popular and versatile drugs ever in terms of clinical application and revenue. Since its patent expiration, and consequently, the loss of exclusivity of the original biologic, its repurposing as an off-label drug has increased dramatically, propelled by the development and commercialization of its many biosimilars. Currently, rituximab is prescribed worldwide to treat a vast range of autoimmune diseases mediated by B cells. Here, we present a comprehensive overview of rituximab repurposing in 115 autoimmune diseases across 17 medical specialties, sourced from over 1530 publications. Our work highlights the extent of its off-label use and clinical benefits, underlining the success of rituximab repurposing for both common and orphan immune-related diseases. We discuss the scientific mechanism associated with its clinical efficacy and provide additional indications for which rituximab could be investigated. Our study presents rituximab as a flagship example of drug repurposing owing to its central role in targeting cluster of differentiate 20 positive (CD20) B cells in 115 autoimmune diseases.

Case report: Systemic lupus erythematosus combined with myocardial hypertrophy

OBJECTIVE

Systemic lupus erythematosus (SLE) is a multisystem-involved, highly heterogeneous autoimmune disease with diverse clinical manifestations. We report an extremely rare case of SLE with severe diffuse myocardial hypertrophy.

METHODS

The patient's echocardiography and cardiac magnetic resonance imaging (CMR) results indicated diffuse myocardial hypertrophy. After excluding coronary atherosclerosis, hypertensive cardiomyopathy, drug toxicity, and other causes, the patient was diagnosed with SLE-specific cardiomyopathy. Medications such as hormones, antimalarials, immunosuppressants, and biologics were administered.

RESULTS

Ancillary test results were as follows: hs-cTnI: 0.054 ng/mL (0-0.016); NTproBNP: 1594.0 pg/mL (<150); A contrast-enhanced CMR revealed the diffuse thickening of the left ventricular wall with multiple abnormal enhancements, reduced left ventricular systolic and diastolic function, and moderate amount of pericardial effusion. Endomyocardial myocardial biopsy was performed, showing cardiomyocyte hypertrophy and degeneration, and no changes in myocarditis or amyloidosis. The pathology viewed by electron microscopy showed increased intracellular glycogen in the myocardium, and no hydroxychloroquine-associated damage in the myocardium. The 24-h ambulatory blood pressure and contrast-enhanced computed tomography of coronary arteries were normal. The diagnosis of SLE-specific cardiomyopathy was clear. The myocardial hypertrophy showed reversible alleviation following treatment with high-dose corticosteroids. CMR results before and after treatment were as follows: interventricular septum, pretreatment (28) versus post-treatment (22) mm; left ventricular inferior wall, pretreatment (18-21) versus post-treatment (12-14) mm; left ventricular lateral wall, pretreatment (17-18) versus post-treatment (10-12) mm; pericardial effusion (left ventricular lateral wall), pretreatment (25) versus post-treatment (12) mm; left ventricular ejection fraction, pretreatment (38.9%) versus post-treatment (66%).

CONCLUSION

Myocardial hypertrophy may be an important sign of active and prognostic assessment in SLE diagnosis and management. Similarly, when encountering cases of myocardial hypertrophy, the possibility of autoimmune disease should be considered in addition to common causes.

Immune checkpoint inhibitors break whose heart? Perspectives from cardio-immuno-oncology

Immune checkpoint inhibitors (ICIs) are monoclonal antibody antagonists, which can block cytotoxic T lymphocyte antigen-4 (CTLA-4), programmed death-1/ligand-1 (PD-1/PD-L1) pathways, and other molecules exploited by tumor cells to evade T cell-mediated immune response. ICIs have transformed the treatment landscape for various cancers due to their amazing efficacy. Many anti-tumor therapies, including targeted therapy, radiotherapy, and chemotherapy, combine ICIs to make the treatment more effective. However, the off-target immune activation caused by ICIs may lead to a broad spectrum of immune-related adverse events (irAEs) affecting multiple organ systems. Among irAEs, cardiotoxicity induced by ICIs, uncommon but fatal, has greatly offset survival benefits from ICIs, which is heartbreaking for both patients and clinicians. Consequently, such cardiotoxicity requires special vigilance, and it has become a common challenge both for patients and clinicians. This article reviewed the clinical manifestations and influence of cardiotoxicity from the view of patients and clinicians, elaborated on the underlying mechanisms in conjunction with animal studies, and then attempted to propose management strategies from a cardio-immuno-oncology multidisciplinary perspective.

Adjuvants in COVID-19 vaccines: innocent bystanders or culpable abettors for stirring up COVID-heart syndrome

COVID-19 infection is a multi-system clinical disorder that was associated with increased morbidity and mortality. Even though antiviral therapies such as Remdesvir offered modest efficacy in reducing the mortality and morbidity, they were not efficacious in reducing the risk of future infections. So, FDA approved COVID-19 vaccines which are widely administered in the general population worldwide. These COVID-19 vaccines offered a safety net against future infections and re-infections. Most of these vaccines contain inactivated virus or spike protein mRNA that are primarily responsible for inducing innate and adaptive immunity. These vaccines were also formulated to contain supplementary adjuvants that are beneficial in boosting the immune response. During the pandemic, clinicians all over the world witnessed an uprise in the incidence and prevalence of cardiovascular diseases (COVID-Heart Syndrome) in patients with and without cardiovascular risk factors. Clinical researchers were not certain about the underlying reason for the upsurge of cardiovascular disorders with some blaming them on COVID-19 infections while others blaming them on COVID-19 vaccines. Based on the literature review, we hypothesize that adjuvants included in the COVID-19 vaccines are the real culprits for causation of cardiovascular disorders. Operation of various pathological signaling events under the influence of these adjuvants including autoimmunity, bystander effect, direct toxicity, anti-phospholipid syndrome (APS), anaphylaxis, hypersensitivity, genetic susceptibility, epitope spreading, and anti-idiotypic antibodies were partially responsible for stirring up the onset of cardiovascular disorders. With these mechanisms in place, a minor contribution from COVID-19 virus itself cannot be ruled out. With that being said, we strongly advocate for careful selection of vaccine adjuvants included in COVID-19 vaccines so that future adverse cardiac disorders can be averted.

Myocarditis and Autoimmunity

INTRODUCTION

Autoimmune myocarditis may develop due to heterogeneous causes. Myocarditis is often caused by viral infections, but it can also be caused by systemic autoimmune diseases. Immune checkpoint inhibitors and virus vaccines induce immune activation, and they can cause the development of myocarditis, as well as several immune-related adverse events. The development of myocarditis is dependent on the genetic factors of the host, and the major histocompatibility complex (MHC) may be an important determinant of the type and severity of the disease. However, non-MHC immunoregulatory genes may also play a role in determining susceptibility.

AREA COVERED

This review summarizes the current knowledge of the etiology, pathogenesis, diagnosis and treatment of autoimmune myocarditis with a particular focus on viral infection and autoimmunity, and biomarkers of myocarditis.

EXPERT OPINION

An endomyocardial biopsy may not be the gold standard for the diagnosis of myocarditis. Cardiac magnetic resonance imaging is useful in diagnosing autoimmune myocarditis. Recently identified biomarkers of inflammation and myocyte injury are promising for the diagnosis of myocarditis when measured simultaneously. Future treatments should focus on the appropriate diagnosis of the etiologic agent, as well as on the specific stage of the evolution of immune and inflammatory processes.

Comparison of COVID-19 Vaccine-Associated Myocarditis and Viral Myocarditis Pathology

The COVID-19 pandemic has led to significant loss of life and severe disability, justifying the expedited testing and approval of messenger RNA (mRNA) vaccines. While found to be safe and effective, there have been increasing reports of myocarditis after COVID-19 mRNA vaccine administration. The acute events have been severe enough to require admission to the intensive care unit in some, but most patients fully recover with only rare deaths reported. The pathways involved in the development of vaccine-associated myocarditis are highly dependent on the specific vaccine. COVID-19 vaccine-associated myocarditis is believed to be primarily caused by uncontrolled cytokine-mediated inflammation with possible genetic components in the interleukin-6 signaling pathway. There is also a potential autoimmune component via molecular mimicry. Many of these pathways are similar to those seen in viral myocarditis, indicating a common pathophysiology. There is concern for residual cardiac fibrosis and increased risk for the development of cardiomyopathies later in life. This is of particular interest for patients with congenital heart defects who are already at increased risk for fibrotic cardiomyopathies. Though the risk for vaccine-associated myocarditis is important to consider, the risk of viral myocarditis and other injury is far greater with COVID-19 infection. Considering these relative risks, it is still recommended that the general public receive vaccination against COVID-19, and it is particularly important for congenital heart defect patients to receive vaccination for COVID-19.

Proteome-wide analysis of lysine β-hydroxybutyrylation in the myocardium of diabetic rat model with cardiomyopathy

Lysine ß-hydroxybutyrylation (kbhb), a novel modification of lysine residues with the ß-hydroxybuty group, is associated with ketone metabolism in numerous species. However, its potential role in diabetes, especially in diabetic cardiomyopathy (DCM), remains largely unexplored. In this study, using affinity enrichment and liquid chromatography-mass spectrometry (LC-MS/MS) method, we quantitatively analyze the kbhb residues on heart tissues of a DCM model rat. A total of 3,520 kbhb sites in 1,089 proteins were identified in this study. Further analysis showed that 336 kbhb sites in 143 proteins were differentially expressed between the heart tissues of DCM and wild-type rats. Among them, 284 kbhb sites in 96 proteins were upregulated, while 52 kbhb sites in 47 proteins were downregulated. Bioinformatic analysis of the proteomic results revealed that these kbhb-modified proteins were widely distributed in various components and involved in a wide range of cellular functions and biological processes (BPs). Functional analysis showed that the kbhb-modified proteins were involved in the tricarboxylic acid cycle, oxidative phosphorylation, and propanoate metabolism. Our findings demonstrated how kbhb is related to many metabolic pathways and is mainly involved in energy metabolism. These results provide the first global investigation of the kbhb profile in DCM progression and can be an essential resource to explore DCM's pathogenesis further.

Viral myocarditis involves the generation of autoreactive T cells with multiple antigen specificities that localize in lymphoid and non-lymphoid organs in the mouse model of CVB3 infection

Autoreactive T cells may contribute to post-viral myocarditis induced with Coxsackievirus B3 (CVB3), but the underlying mechanisms of their generation are unclear. Here, we have comprehensively analyzed the generation of antigen-specific, autoreactive T cells in the mouse model of CVB3 infection for antigens implicated in patients with myocarditis/dilated cardiomyopathy. First, comparative analysis of CVB3 proteome with five autoantigens led us to identify three mimicry epitopes, one each from adenine nucleotide translocator 1 (ANT), sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) and cardiac troponin I. None of these induced cross-reactive T cell responses. Next, we generated major histocompatibility complex (MHC) class II dextramers to enumerate the frequencies of antigen-specific T cells to determine whether T cells with multiple antigen specificities are generated by CVB3 infection. These analyses revealed appearance of CD4 T cells positive for SERCA2a 971-990, and cardiac myosin heavy chain-α (Myhc) 334-352 dextramers, both in the periphery and also in the hearts of CVB3-infected animals. While ANT 21-40 dextramer⁺ T cells were inconsistently detected, the β1-adrenergic receptor 181-200/211-230 or branched chain α-ketoacid dehydrogenase kinase 111-130 dextramer⁺ cells were absent. Interestingly, SERCA2a 971-990, Myhc 334-352 and ANT 21-40 dextramer⁺ cells were also detected in the liver indicating that they may have a pathogenic role. Finally, we demonstrate that the SERCA2a 971-990-reactive T cells generated in CVB3 infection could transfer disease to naïve mice. The data suggest that CVB3 infection can lead to the generation of autoreactive T cells for multiple antigens indicating a possibility that the autoreactive T cells localized in the liver can potentially circulate and contribute to the development of viral myocarditis.

Predictors for In-hospital Mortality in Pediatric Patients with Acute Myocarditis – a Retrospective Study

Background: Acute myocarditis, a primary inflammatory cardiac disease commonly caused by viral infection, is an important cause of morbidity and mortality in children. Data obtained from forensic studies found an incidence of 15–33% for acute myocarditis in sudden deaths in the pediatric age group. Currently, there is a lack of data regarding the incidence and factors associated with short-term outcomes in pediatric patients admitted for acute myocarditis.

The aim of the study was to identify predictors for in-hospital mortality in a pediatric population admitted with acute myocarditis.

Material and methods: We conducted a retrospective observational cohort study that included 21 patients admitted for acute myocarditis. Clinical, laboratory, ECG, and imaging data acquired via 2D transthoracic echocardiography and cardiac magnetic resonance imaging were collected from the medical charts of each included patient. The primary end-point of the study was all-cause mortality occurring during hospitalization (period ranging from 10 to 14 days). The study population was divided into 2 groups according to the occurrence of the primary end-point.

Results: The mean age of the study population was 99.62 ± 77.25 months, and 61.90% (n = 13) of the patients were males. The in-hospital mortality rate was 23.9% (n = 5). Patients in the deceased group were significantly younger than the survivors (55.60 ± 56.18 months vs. 113.4 ± 78.50 months, p = 0.039). Patients that had deceased presented a significantly higher level of LDH (365 ± 21.38 U/L vs. 234.4 ± 63.30 U/L, p = 0.0002) and a significantly higher rate of ventricular extrasystolic dysrhythmias (60% vs. 6.25%, p = 0.02, OR: 22.5, 95% CI: 1.5–335) compared to survivors. The 2D echocardiography showed that patients that had deceased presented more frequently an impaired left ventricular ejection fraction (<30%) (p = 0.001) and a significantly higher rate of severe mitral regurgitation (p = 0.001) compared to survivors.

Conclusions: The most powerful predictors for in-hospital mortality in pediatric patients admitted for acute myocarditis were the presence of ventricular extrasystolic dysrhythmias on the 24h Holter ECG monitoring, impaired left ventricular systolic function (LVEF <30%), the presence of severe mitral regurgitation, and confirmed infection with Mycoplasma pneumoniae.

Non-invasive contrast enhanced ultrasound molecular imaging of inflammation in autoimmune myocarditis for prediction of left ventricular fibrosis and remodeling

Background

Myocarditis can lead to myocyte loss and myocardial fibrosis resulting in dilated cardiomyopathy (DCMP). Currently employed methods for assessing the risk for development of DCMP are inaccurate or rely on invasive myocardial biopsies. We hypothesized that molecular imaging of tissue inflammation with contrast enhanced ultrasound during peak inflammation in myocarditis could predict development of fibrosis and impaired left ventricular function.

Methods and results

Experimental autoimmune myocarditis (EAM) was induced in Balbc mice by injection of the α-myosin heavy chain peptide. Contrast enhanced ultrasound (CEU) using microbubbles targeted to leukocytes (MB_Lc), to CD4+ lymphocytes (MB_CD4), and to the endothelial cell adhesion molecule P-selectin (MB_PSel) was performed during the expected EAM peak inflammatory activity 21 days after induction. High resolution ultrasound, invasive hemodynamic measurements and fibrosis quantification were done 63 days after EAM assessment. All tested microbubbles correlated to fibrosis (MB_Lc spearman r 0.28, p 0.047, MB_CD4 r 0.44, p 0.01, MB_PSel r 0.73, p 0.02), however, correlations were weak overall and the spread of data was considerable. Also, targeted CEU data on day 21 did not correlate to hemodynamic and functional data on day 63.

Conclusions

Ultrasound molecular imaging using targeted microbubbles during the peak inflammatory activity of myocarditis correlates weakly with later development of fibrosis but not with hemodynamic or left ventricular functional parameters.

Use of Cardiac Biomarkers for Monitoring Improvement of Left Ventricular Function by Immunoadsorption Treatment in Dilated Cardiomyopathy

Immunoadsorption and subsequent administration of intravenous immunoglobulin (IVIG) have shown beneficial effects on cardiac function and symptoms in patients with dilated cardiomyopathy. Biomarkers play an emerging role in disease monitoring and outcome prediction of heart failure (HF) patients. We aimed to analyze cardiac biomarkers as predictor for improvement of left ventricular (LV) function after immunoadsorption treatment in dilated cardiomyopathy (DCM). Thirty-one patients with dilated cardiomyopathy on optimized HF pharmacotherapy received a single cycle of immunoadsorption for five days followed by IVIG administration. Left ventricular ejection fraction (LVEF) and heart failure biomarkers (hs troponin T, hs troponin I, NT-proBNP and sST2) were evaluated before treatment, after the last cycle of immunoadsorption and during a median follow-up of 30.5 months. We correlated HF biomarkers before immunoadsorption and acute changes of HF biomarkers by immunoadsorption with LV improvement during the long-term follow-up. LV function improved significantly after immunoadsorption from 28.0 to 42.0% during the long-term follow-up (p < 0.0001). Evaluation of biomarker levels showed a significant decrease for hs troponin I (from 9.2 to 5.5 ng/L, p < 0.05) and NT-proBNP (from 789.6 to 281.2 pg/mL, p < 0.005). Correlation of biomarker levels before immunoadsorption and LVEF at the long-term follow-up show good results for hs troponin T (r = −0.40, r² = 0.16, p < 0.05), hs troponin I (r = −0.41, r² = 0.17, p < 0.05) and sST2 (r = −0.46, r² = 0.19, p < 0.05). Correlation of biomarker levels before immunoadsorption and the individual increase in LV function was significant for hs troponin T (r = −0.52, r² = 0.27, p < 0.005) and hs troponin I (r = −0.53, r² = 0.29, p < 0.005). To imply a tool for monitoring outcome immediately after immunoadsorption treatment, we investigated the correlation of acute changes of biomarker levels by immunoadsorption treatment and individual increase in LV function. A drop in hs troponin T (r = −0.41, r² = 0.17, p < 0.05) and hs troponin I (r = −0.53, r² = 0.28, p < 0.005) levels demonstrate a good correlation to improvement in LVEF during the long-term follow-up. Conclusion: Hs troponin T and I levels correlate with LV function improvement during long-term follow-up. Acute decrease of troponins by immunoadsorption treatment is paralleled by individual improvement of LVEF at the long-term follow-up. Thus, troponins could serve as a monitoring tool for the improvement of LV function after immunoadsorption treatment in dilated cardiomyopathy.

Humoral Immunity in Heart Failure

Cardiovascular Disease (CVD) is a class of diseases that involve disorders of heart and blood vessels, including hypertension, coronary heart disease, cerebrovascular disease, peripheral vascular disease, which finally lead to Heart Failure (HF). There are several treatments available all over the world, but still, CVD and heart failure became the number one problem causing death every year worldwide. Both experimental and clinical studies have shown a role for inflammation in the pathogenesis of heart failure. This seems related to an imbalance between pro-inflammatory and anti-inflammatory cytokines. Cardiac inflammation is a major pathophysiological mechanism operating in the failing heart, regardless of HF aetiology. Disturbances of the cellular and humoral immune system are frequently observed in heart failure. This review describes how B-cells play a specific role in the heart failure states. There is an urgent need to identify novel therapeutic targets and develop advanced therapeutic strategies to combat the syndrome of HF. Understanding and describing the elements of the humoral immunity function are essential and may suggest potential new treatment strategies.

Add-on Immunoadsorption Shortly-after Optimal Medical Treatment Further Significantly and Persistently Improves Cardiac Function and Symptoms in Recent-Onset Heart Failure-A Single Center Experience

Background: Immunoadsorption and intravenous immunoglobulin (IVIG) administration may have beneficial effects in patients with dilated cardiomyopathy with end-stage heart failure. We investigated the effect of immunoadsorption with subsequent IVIG administration on cardiac function and symptoms in patients on optimal medical treatment (OMT) for heart failure (HF) with recent-onset cardiomyopathy during long-term follow-up. Methods: Thirty-five patients with recent-onset of HF symptoms received intensive guideline-recommended medical HF therapy for 5.2 months. Subsequently, all patients received a single cycle of immunoadsorption for five days followed by IVIG administration. During the 29-month follow-up period, New York Heart Association (NYHA) functional class, left ventricular ejection fraction (LVEF) and N-terminal pro brain natriuretic peptide (NT-proBNP) were evaluated. Changes in quality of life (QoL) were assessed using the Minnesota Living with HF Questionnaire. Results: Three months after immunoadsorption, NYHA functional class improved from 2.0 to 1.5 (p < 0.005) and LVEF significantly increased from 27.0% to 39.0% (p < 0.0001). Long-term follow-up of 29 months showed stable NYHA functional class and a further moderate increase in LVEF from 39.0% to 42.0% (p < 0.0001) accompanied by a significant improvement in NT-proBNP and QoL scores. Conclusion: Immunoadsorption followed by IVIG administration further enhances LVEF, HF symptoms, QoL and biomarkers in patients with recent-onset HF on OMT.

New Paradigms in Cell Therapy: Repeated Dosing, Intravenous Delivery, Immunomodulatory Actions, and New Cell Types

Perhaps the most important advance in the field of cell therapy for heart disease has been the recognition that all stem/progenitor cells (both adult and embryonic) fail to engraft in the heart to a significant extent and thus work via paracrine mechanisms. This fundamental advance has led to 4 new paradigms that are discussed in this review and that may importantly shape, or even revolutionize, the future of the field: (1) repeated cell therapy, (2) intravenous cell therapy, (3) immunomodulatory actions of cell therapy, and (4) new cell types. Because virtually all of our current knowledge of cell therapy is predicated on the effects of a single cell dose, the idea that the full therapeutic effects of a cell product require repeated doses is disruptive and has far-reaching implications. For example, inadequate dosing (single-dose protocols) may be responsible, at least in part, for the borderline or disappointing results obtained to date in clinical trials; furthermore, future studies (both preclinical and clinical) may need to incorporate repeated cell administrations. Another disruptive idea, supported by emerging preclinical and clinical evidence, is that intravenously injected cells can produce beneficial effects on the heart, presumably via release of paracrine factors in extracardiac organs or endocrine factors into the systemic circulation. Intravenous administration would obviate the need for direct delivery of cells to the heart, making cell therapy simpler, cheaper, safer, more scalable, and more broadly available, even on an outpatient basis. Although the mechanism of action of cell therapy remains elusive, there is compelling in vitro evidence that transplanted cells modulate the function of various immune cell types via release of paracrine factors, such as extracellular vesicles, although in vivo evidence is still limited. Investigation of the new paradigms reviewed herein should be a top priority because it may profoundly transform cell therapy and finally make it a reality.

Cardiac Non-Human Leukocyte Antigen Identification: Techniques and Troubles

Historically efforts have focused on the human leukocyte antigen (HLA) as the major cause for acute and chronic rejection following cardiac transplantation. However, rising evidence indicates that non-HLA antibodies can be both primary initiators and modifiers of antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV). The purpose of this review is to assess currently available technologies for non-HLA identification and leveraging such responses toward antibody quantification. Several techniques have been used to identify antigenic determinants of recipient graft-specific non-HLA humoral immune responses, but each comes with its own set of benefits and caveats. Improving our ability to detect non-HLA humoral immune response will aid in our understanding of the underlying antigenic determinants of AMR and CAV, as well as improve patient outcomes.

Role of Adaptive Immunity in the Development and Progression of Heart Failure: New Evidence

Heart failure (HF) is considered the endpoint of a variety of cardiac diseases, which are the leading cause of death in adults and considered a growing pandemic worldwide. Independent of the initial form of cardiac injury, there is evidence linking the involvement of the immune system. In HF there is evidence of the participation of T_H1, and T_H17 cells, which account for sustained pathological chronic inflammation, cell migration, and the induction of specific pathological phenotypes of mononuclear cells. Of equal or even higher relevance are the B lymphocyte activation mechanisms that include production of pro-inflammatory cytokines, chemokines, and cardiac autoantibodies with or without activation of the complement proteins. Both of these unbalanced T- and B-cell pathways of the adaptive immune system are associated with cardiomyocyte death and tissue remodeling by fibrosis leading to a dysfunctional heart. At this time, therapy with neutralizing antibodies and the use of anti-cytokine immunomodulators to counteract the immune system effects have reached a plateau of mixed results in clinical trials. Nevertheless, recent evidence showed promising results in animal models that suggest that modulation of the adaptive immune system cells more than some of their effector molecules could have benefits in HF patients. This review summarizes the role of the adaptive immunity cells in HF, considering the sustained activation of adaptive immune system as a potential contributor to disease progression in humans and experimental models where its regulation provides a new therapeutic target.

Branched chain α-ketoacid dehydrogenase kinase 111-130, a T cell epitope that induces both autoimmune myocarditis and hepatitis in A/J mice

INTRODUCTION

Organ-specific autoimmune diseases are believed to result from immune responses generated against self-antigens specific to each organ. However, when such responses target antigens expressed promiscuously in multiple tissues, then the immune-mediated damage may be wide spread.

METHODS

In this report, we describe a mitochondrial protein, branched chain α-ketoacid dehydrogenase kinase (BCKD_k ) that can act as a target autoantigen in the development of autoimmune inflammatory reactions in both heart and liver.

RESULTS

We demonstrate that BCKD_k protein contains at least nine immunodominant epitopes, three of which, BCKD_k 71-90, BCKD_k 111-130 and BCKD_k 141-160, were found to induce varying degrees of myocarditis in immunized mice. One of these, BCKD_k 111-130, could also induce hepatitis without affecting lungs, kidneys, skeletal muscles, and brain. In immunogenicity testing, all three peptides induced antigen-specific T cell responses, as verified by proliferation assay and/or major histocompatibility complex class II/IA^k dextramer staining. Finally, the disease-inducing abilities of BCKD_k peptides were correlated with the production of interferon-γ, and the activated T cells could transfer disease to naive recipients.

CONCLUSIONS

The disease induced by BCKD_k peptides could serve as a useful model to study the autoimmune events of inflammatory heart and liver diseases.

Cardiac Autoimmunity: Myocarditis

Myocarditis is the inflammation of the muscle tissues of the heart (myocardium). After a pathologic cardiac-specific inflammatory process, it may progress to chronic damage and dilated cardiomyopathy. The latter is characterized by systolic dysfunction, whose clinical correlate is heart failure. Nevertheless, other acute complications may arise as consequence of tissue damage and electrophysiologic disturbances. Different etiologies are involved in triggering myocarditis. In some cases, such as giant cell myocarditis or eosinophilic necrotizing myocarditis, it is an autoimmune process. Several factors predispose the development of autoimmune myocarditis such as systemic/local primary autoimmunity, viral infection, HLA and gender bias, exposure of cryptic antigens, mimicry, and deficient thymic training/Treg induction. Once the anti-myocardium autoimmune process is triggered, several components of the immune response orchestrate a sustained attack toward myocardial tissues with particular timing and immunopathogenic features. Innate response mediated by monocytes/macrophages, neutrophils, and eosinophils parallels the adaptive response, playing a final effector role and not only a priming function. Stromal cells like fibroblast are also involved in the process through specific cytokines. Furthermore, adaptive T cell responses have anti-paradigmatic features, as Th17 response is dispensable for acute myocarditis but is the main driver of the process leading to dilated cardiomyopathy. Humoral response, thought to be a bystander, is important in the appearance of late-stage hemodynamic complications. The complexity of that process, as well as the unspecific and variable clinical presentation, had generated difficulties for diagnosis and treatment, which remain suboptimal. In this chapter, we will discuss the most relevant immunopathogenic findings from a basic science and clinical perspective.

The Quest for New Approaches in Myocarditis and Inflammatory Cardiomyopathy

Myocarditis is a diverse group of heart-specific immune processes classified by clinical and histopathological manifestations. Up to 40% of dilated cardiomyopathy is associated with inflammation or viral infection. Recent experimental studies revealed complex regulatory roles for several microribonucleic acids and T-cell and macrophage subtypes. Although the prevalence of myocarditis remained stable between 1990 and 2013 at about 22 per 100,000 people, overall mortality from cardiomyopathy and myocarditis has decreased since 2005. The diagnostic and prognostic value of cardiac magnetic resonance has increased with new, higher-sensitivity sequences. Positron emission tomography has emerged as a useful tool for diagnosis of cardiac sarcoidosis. The sensitivity of endomyocardial biopsy may be increased, especially in suspected sarcoidosis, by the use of electrogram guidance to target regions of abnormal signal. Investigational treatments on the basis of mechanistic advances are entering clinical trials. Revised management recommendations regarding athletic participation after acute myocarditis have heightened the importance of early diagnosis.

Targeting of anti-citrullinated protein/peptide antibodies in rheumatoid arthritis using peptides mimicking endogenously citrullinated fibrinogen antigens

INTRODUCTION

We have previously identified endogenously citrullinated peptides derived from fibrinogen in rheumatoid arthritis (RA) synovial tissues. In this study, we have investigated the auto-antigenicity of four of those citrullinated peptides, and explored their feasibility to target anti-citrullinated protein/peptide antibodies (ACPA).

METHODS

The autoantigenic potential of the fibrinogen peptides was investigated by screening 927 serum samples from the Epidemiological Investigation of RA (EIRA) cohort on a peptide microarray based on the ImmunoCAP ISAC® system. In order to assay for ACPA blocking, two independent pools of purified ACPA were incubated with the respective targeting peptide prior to binding to cyclic citrullinated peptide (CCP)2 using the CCPlus® ELISA kit.

RESULTS

Two peptides derived from the fibrinogen α chain, Arg573Cit (563-583) and Arg591Cit (580-600), referred to as Cit573 and Cit591, and two peptides from the fibrinogen β chain, Arg72Cit (62-81) and Arg74Cit (62-81) (Cit72 and Cit74), displayed 65%, 15%, 35%, and 53% of immune reactivity among CCP2-positive RA sera, respectively. In CCP2-negative RA sera, a positive reactivity was detected in 5% (Cit573), 6% (Cit591), 8% (Cit72), and 4% (Cit74). In the competition assay, Cit573 and Cit591 peptides reduced ACPA binding to CCP2 by a maximum of 84% and 63% respectively. An additive effect was observed when these peptides were combined. In contrast, Cit74 and Cit72 were less effective. Cyclization of the peptide structure containing Cit573 significantly increased the blocking efficiency.

CONCLUSIONS

Here we demonstrate extensive autoantibody reactivity against in vivo citrullinated fibrinogen epitopes, and further show the potential use of these peptides for antagonizing ACPA.

Inhibition of autoimmune Chagas-like heart disease by bone marrow transplantation

BACKGROUND

Infection with the protozoan Trypanosoma cruzi manifests in mammals as Chagas heart disease. The treatment available for chagasic cardiomyopathy is unsatisfactory.

METHODS/PRINCIPAL FINDINGS

To study the disease pathology and its inhibition, we employed a syngeneic chicken model refractory to T. cruzi in which chickens hatched from T. cruzi inoculated eggs retained parasite kDNA (1.4 kb) minicircles. Southern blotting with EcoRI genomic DNA digests revealed main 18 and 20 kb bands by hybridization with a radiolabeled minicircle sequence. Breeding these chickens generated kDNA-mutated F1, F2, and F3 progeny. A targeted-primer TAIL-PCR (tpTAIL-PCR) technique was employed to detect the kDNA integrations. Histocompatible reporter heart grafts were used to detect ongoing inflammatory cardiomyopathy in kDNA-mutated chickens. Fluorochromes were used to label bone marrow CD3+, CD28+, and CD45+ precursors of the thymus-dependent CD8α+ and CD8β+ effector cells that expressed TCRγδ, vβ1 and vβ2 receptors, which infiltrated the adult hearts and the reporter heart grafts.

CONCLUSIONS/SIGNIFICANCE

Genome modifications in kDNA-mutated chickens can be associated with disruption of immune tolerance to compatible heart grafts and with rejection of the adult host's heart and reporter graft, as well as tissue destruction by effector lymphocytes. Autoimmune heart rejection was largely observed in chickens with kDNA mutations in retrotransposons and in coding genes with roles in cell structure, metabolism, growth, and differentiation. Moreover, killing the sick kDNA-mutated bone marrow cells with cytostatic and anti-folate drugs and transplanting healthy marrow cells inhibited heart rejection. We report here for the first time that healthy bone marrow cells inhibited heart pathology in kDNA+ chickens and thus prevented the genetically driven clinical manifestations of the disease.

Learning from myocarditis: mimicry, chaos and black holes

Autoimmune myocarditis and its sequel, dilated cardiomyopathy, are major causes of heart failure, especially in children and young adults. We have developed animal models to investigate their pathogenesis by infecting genetically susceptible mice with coxsackievirus B3 or by immunizing them with cardiac myosin or its immunodominant peptide. A number of valuable lessons have emerged from our study of this paradigm of an infection-induced autoimmune disease. We understand more clearly how natural autoimmunity, as an important component of normal physiology, must be recalibrated regularly due to changes caused by infection or other internal and external stimuli. A new normal homeostatic platform will be established based on its evolutionary fitness. A loss of homeostasis with out-of-control normal autoimmunity leads to autoimmune disease. It is signified early on by a spread of an adaptive autoimmune response to novel epitopes and neighboring antigens. The progression from infection to normal, well-balanced autoimmunity to autoimmune disease and on to irreversible damage is a complex, step-wise process. Yet, chaos theory provides hope that the pattern is potentially predictable. Infection-induced autoimmune disease represents a sequence of events heading for a train wreck at the end of the line. Our aim in autoimmune disease research must be to stop the train before this happens.

Effects of preexisting autoimmunity on heart graft prolongation after donor-specific transfusion and anti-CD154

BACKGROUND

Alloreactive memory T cells prevent costimulatory blockade-induced heart graft survival in mice, but whether and how preexisting autoreactive T cells affect solid-organ transplants under these conditions is unknown.

METHODS

We tested the impact of preexisting cardiac myosin (CM)-specific immunity on murine heart transplant recipients treated with donor-specific transfusion (DST) plus anti-CD154 monoclonal antibody MR1.

RESULTS

Preimmunization with CM but not control ovalbumin abrogated the graft prolonging effects of DST/MR1, whether administered 2 weeks or more than 6 weeks before transplantation. Adoptive transfer of spleen cells from CM-immunized mice into naïve recipients had similar effects. CM-specific immunity did not cross-react with donor antigens and preimmunization with CM had no impact on the survival or histology of DST/MR1-treated syngeneic heart grafts, the latter indicating that persistent autoimmunity is insufficient to cause rejection in the context of costimulatory blockade. We observed that the CM preimmunized mice produced higher frequencies of donor-reactive T cells with higher ratios of CD8/CD4Foxp3 cells, suggesting that the autoreactive memory T cells provide help for activation of alloreactive T cells despite the costimulatory blockade.

CONCLUSIONS

These mechanistic insights linking autoimmunity and alloimmunity in a model of murine heart transplantation have clinical relevance to the known association between autoimmunity and an elevated risk of acute and chronic heart transplant injury in humans.

Insulin promotes T cell recovery in a murine model of autoimmune myocarditis

Glucose-insulin-potassium (GIK) is a useful adjunct to myocarditis. Besides its essential action in energy metabolism, insulin also exerts an anti-inflammatory effect. This study investigated the effect of insulin on myocardial inflammation in experimental autoimmune myocarditis (EAM) in mice and its potential role in T cell regulation. Mice were divided randomly into a normal control group, a saline-treated EAM group and an insulin-treated EAM group. The histopathological changes of myocardium, α-myosin heavy chain (MyHCα)(614-629) antigen-specific autoantibody titre, the serum level of cardiac troponin I (cTnI), mitogen-activated protein kinase (MAPK) family members' activity and content were measured. Furthermore, the phenotype of T lymphocyte subsets in splenocytes was analysed to evaluate the immune status of mice. Insulin reduced serum cTnI of EAM mice on days 14 and 21 (P < 0·05) after immunization, with no changes in blood glucose and autoantibody production. Western blot revealed that extracellular signal-regulated protein kinase (ERK1/2) may be a determining factor in this process. Total ERK1/2 and phospho-ERK1/2 (p-ERK1/2) were both up-regulated in insulin-treated mice after immunization. We also found that insulin treatment promoted T cell recovery without changing the naive-to-memory T-cell ratio; in particular, CD3(+) T cells in insulin-treated mice proliferated more vigorously than in control mice (P < 0·05). We report here for the first time that insulin alleviates myocarditis in the EAM model. These data show that insulin has a direct effect on T cell proliferation in EAM. It is possible that GIK or insulin may assist T cell recovery towards normal in myocarditis, especially for diabetic or hyperglycaemic patients.

Autoimmune myocarditis, valvulitis, and cardiomyopathy

Myocarditis and valvulitis are inflammatory diseases affecting myocardium and valve. Myocarditis, a viral-induced disease of myocardium, may lead to dilated cardiomyopathy and loss of heart function. Valvulitis leads to deformed heart valves and altered blood flow in rheumatic heart disease. Animal models recapitulating these diseases are important in understanding the human condition. Cardiac myosin is a major autoantigen in heart, and antibodies and T cells to cardiac myosin are evident in inflammatory heart diseases. This unit is a practical guide to induction and evaluation of experimental autoimmune myocarditis (EAM) in several mouse strains and the Lewis rat. Purification protocols for cardiac myosin and protocols for induction of EAM by cardiac myosin and its myocarditis-producing peptides, and coxsackievirus CVB3, are defined. Protocols for assessment of myocarditis and valvulitis in humans and animal models provide methods to define functional autoantibodies targeting cardiac myosin, β-adrenergic, and muscarinic receptors, and their deposition in tissues.

Characterization of fibrosis-promoting factors and siRNA-mediated therapies in C-protein-induced experimental autoimmune myocarditis

Due to poor proliferation abilities of cardiomyocytes, the repair process in the heart after insults is often associated with fibrosis formation. In this study, we characterized inflammation and/or fibrosis-related molecules in the heart with experimental autoimmune carditis. Immunohistochemical examinations reveled that expression of tenascin-C (TNC), matrix metalloproteinase-9 (MMP-9), transforming growth factorβ1 (TGF-β1), connective tissue growth factor (CTGF) and α smooth muscle cell actin (αSMA) peaked at 2 weeks post-immunization but only TGF-β1 expression was sustained at 8 weeks. Administration of siRNAs for MMP-2 (siMMP-2) and for MMP-9 (siMMP-9) alone did not modulate inflammation and fibrosis. In contrast, simultaneous administration of siMMP-2 and siMMP-9 significantly reduced inflammation and fibrosis. Of note, siRNA treatment for TGF-β1, which is an anti-inflammatory cytokine, increased inflammation and decreased fibrosis. These findings suggest that in case of diseases characterized by initial inflammation and subsequent fibrosis, immunotherapies should target inflammation, not fibrosis, because the latter therapies exacerbate inflammation.

Immune modulation in heart failure: past challenges and future hopes

Immune-modulation therapy has had great success in various inflammatory diseases. Despite the promising results of preliminary studies in anti-tumor necrosis factor-α therapies, large randomized studies have lacked positive clinical outcomes in patients with heart failure. These results have led to the idea that therapies directed toward specific inflammatory mediators may not be the answer and lead us toward the development of novel anti-inflammatory strategies that may involve a broader spectrum of inflammatory mediators. Therapeutic plasma exchange has been demonstrated as a safe treatment, and preliminary outcomes led us to develop new treatment schemes.

Effects of protein A immunoadsorption in patients with chronic dilated cardiomyopathy

OBJECTIVES

The objective of this study was to investigate functional effects of immunoadsorption (IA) in patients with chronic nonfamilial dilated cardiomyopathy (DCM) regarding clinical and humoral markers of heart failure.

BACKGROUND

IA has been shown to induce early hemodynamic improvement in patients with nonfamilial dilated cardiomyopathy (DCM).

METHODS

We performed IA using protein A agarose columns on five consecutive days in 51 patients with chronic DCM, congestive heart failure of NYHA class ≥ II, left ventricular ejection fraction ≤50%, and mean time since initial diagnosis of 5.0 ± 5.8 years.

RESULTS

Immediately after IA, immunoglobulin G (IgG) decreased by 89.4% and IgG3 by 66.7% (both P < 0.0001). Median NT-pro BNP was reduced from 1230.0 ng L(-1) at baseline to 829.0 ng L(-1) after 6 months (P < 0.0001). Also mean left ventricular ejection fraction (LVEF) was significantly improved (26.3% ± 9.4% to 28.7% ± 11.4% after 6 months, P = 0.016) and LVEF improved ≥5% (absolute) in 21 of 51 (41.2%) patients. After 6 months, bicycle spiroergometry showed a significant increase in exercise capacity from 82.0 ± 30.8 Watts to 93.1 ± 34.3 Watts (P = 0.008) while VO2max rose from 15.0 ± 4.1 to 16.4 ± 4.8 mL min(-1) kg(-1) (P = 0.01).

CONCLUSIONS

In this study, on heart failure patients with nonfamilial DCM, IA therapy significantly improved clinical and humoral markers of heart failure severity. These promising results may be due to the selected study population, with a shorter disease duration and the higher amount of IgG 3 reduction. Future blinded prospective multicenter studies are necessary to identify those patients that benefit most.

Immunoadsorption in dilated cardiomyopathy: long-term reduction of cardiodepressant antibodies

BACKGROUND

Disturbances of humoral immunity have been described in dilated cardiomyopathy (DCM), and a number of antibodies against cardiac cell proteins have been identified. Previous studies showed that immunoadsorption therapy with subsequent IgG substitution (IA/IgG) enhances cardiac function, and that removal of cardiodepressant antibodies may represent one essential mechanism of this therapy. The long-term effect of IA/IgG on the level of cardiodepressant antibodies remains to be elucidated.

METHODS

A total of 17 patients with DCM were observed up to 12 months after IA/IgG. Echocardiographic measurements were performed at baseline, 3, 6 and 12 months after therapy. Cardiodepressant antibodies were detected by incubation of rat cardiomyocytes with purified patients' IgG and recording of contractility and Ca(2+) ratio.

RESULTS

In contrast to patients without cardiodepressant antibodies before IA/IgG, patients with negative inotropic antibodies showed an improvement of left ventricular ejection fraction (LVEF) from 33.8 +/- 1.7% to 44.7 +/- 2.7%; 44.5 +/- 2.3% and 51.8 +/- 1.7% after 3, 6 and 12 months (P < 0.001 vs. baseline, P < 0.05 vs. LVEF of non-cardiodepressant group). Immediately after IA/IgG therapy, no cardiodepressant effects of patients' IgG on isolated cardiomyocytes were detectable, and this effect remained diminished until 6 months after IA/IgG (P < 0.001 for contractility and Ca(2+) ratio). Compared with the levels after 3 and 6 months, cardiodepressant antibodies reoccured after 12 months (P = 0.067 for contractility, P < 0.05 for Ca(2+) ratio vs. 6 months after IA/IgG). However, the negative inotropic reaction is still diminished compared with the reaction before IA/IgG.

CONCLUSION

IA/IgG therapy induces long-term reduction of negative inotropic antibodies. After 12 months, however, re-increase of negative inotropic antibodies cannot be excluded.

Impaired activation of IFN-gamma+CD4+ T cells in peripheral blood of patients with dilated cardiomyopathy

Viral persistence and autoantibodies are pathogenic components in patients with idiopathic dilated cardiomyopathy (DCM). The aim was to evaluate T-cell function in DCM using different flow cytometry based detection techniques. Following stimulation, the frequency of IFN-gamma-producing CD4+ T cells was significantly lower in patients compared with controls. In contrast, the frequency of IL-4 producing CD4+ T cells was no different. In supernatants of cultured PBMC, IFN-gamma and IL-10 were significantly lower in patients. In addition, lymphocyte proliferation was significantly lower in patients compared with controls, whereas major lymphocyte subsets were not different. IFN-gamma and IL-10 are key cytokines in the ability to mount protective immune responses and to maintain self-tolerance. A reduced activation of T-helper 1 (IFN-gamma producing) cells and a decreased capacity to produce IL-10, found in the present study, could explain parts of the autoimmune features seen in patients with DCM.

Myocarditis

Myocarditis is an uncommon, potentially life-threatening disease that presents with a wide range of symptoms in children and adults. Viral infection is the most common cause of myocarditis in developed countries, but other etiologies include bacterial and protozoal infections, toxins, drug reactions, autoimmune diseases, giant cell myocarditis, and sarcoidosis. Acute injury leads to myocyte damage, which in turn activates the innate and humeral immune system, leading to severe inflammation. In most patients, the immune reaction is eventually down-regulated and the myocardium recovers. In select cases, however, persistent myocardial inflammation leads to ongoing myocyte damage and relentless symptomatic heart failure or even death. The diagnosis is usually made based on clinical presentation and noninvasive imaging findings. Most patients respond well to standard heart failure therapy, although in severe cases, mechanical circulatory support or heart transplantation is indicated. Prognosis in acute myocarditis is generally good except in patients with giant cell myocarditis. Persistent, chronic myocarditis usually has a progressive course but may respond to immunosuppression.

Effects of protein A immunoadsorption in patients with advanced chronic dilated cardiomyopathy

OBJECTIVES

The objective of this study was to investigate functional effects of immunoadsorption (IA) in severely limited study patients with chronic nonfamilial dilated cardiomyopathy (DCM), and to analyze the prevalence of Troponin I (TNI) autoantibodies.

BACKGROUND

Immunoadsorption (IA) has been shown to induce early hemodynamic improvement in patients with nonfamilial DCM.

METHODS

We performed IA using Immunosorba columns on five consecutive days in 27 patients with chronic DCM, congestive heart failure of NYHA class >or=II, left ventricular ejection fraction below 40%, and mean time since initial diagnosis of 7.2 +/- 6.8 years.

RESULTS

Immediately after IA, IgG decreased by 87.7% and IgG3 by 58.5%. Median NT-pro BNP was reduced from 1740.0 ng/L at baseline to 1504.0 ng/L after 6 months (P = 0.004). Mean left ventricular ejection fraction (LVEF) was not significantly improved overall (24.1 +/- 7.8% to 25.4 +/- 10.4% after 6 months, P = 0.38), but LVEF improved >or=5% (absolute) in 9 of 27 (33%) patients. Bicycle spiroergometry showed a significant increase in exercise capacity from 73.7 +/- 29.4 Watts to 88.8 +/- 31.1 Watts (P = 0.003) after 6 months while VO2max rose from 13.7 +/- 3.8 to 14.9 +/- 3.0 mL/min kg after 6 months (P = 0.09). Subgroup analysis revealed a higher NT-pro BNP reduction in patients with shorter disease duration (P = 0.03) and without TNI autoantibodies at baseline (P = 0.05). All 9 patients with an absolute increase of LVEF of >or=5.0% were diabetic (P = 0.0001).

CONCLUSIONS

In this study, on severely limited heart failure patients with nonfamilial DCM, IA therapy moderately improved markers of heart failure severity in a limited subgroup of patients. This may be due to the selected study population with end-stage heart failure patients and the lower reduction of IgG3 compared to previous studies. Future blinded multicenter studies are necessary to identify those patients that benefit most.

Attenuation of experimental autoimmune myocarditis by blocking T cell activation through 4-1BB pathway

4-1BB, a member of the tumor necrosis factor receptor (TNFR) family, binds the 4-1BB ligand (4-1BBL), works as a costimulatory molecule, and regulates T cell-mediated immune responses. Although inflammation is an essential pathological feature of myocarditis, the role of 4-1BB in experimental autoimmune myocarditis (EAM) remains unclear. Lewis rats were immunized on day 0 with purified porcine cardiac myosin to establish EAM. 4-1BB-immunoglobulin (4-1BBIg) was administered intraperitoneally (n=6) a total of 9 times (3 times per week). Rats were killed on day 21 to study effects of 4-1BB/4-1BBL pathway blockade. For controls, isotype-matched human IgG was administered in other EAM rats (n=6). Histologic and echocardiographic examination showed development of EAM attenuated by 4-1BBIg. Suppression of mRNA expression for IL-1alpha, IL-1beta, IL-4, IL-6, and TNF-alpha was noted in the heart tissue treated with 4-1BBIg. Treatment with 4-1BBIg reduced production of Th1-type cytokines, and inhibited T cell proliferation in vitro. In the 4-1BB signaling pathway in splenocytes, 4-1BBIg suppressed JNK, p38, and IkappaB activity but not that of ERK1/2. Blockade of T cell activation through the 4-1BB/4-1BBL pathway regulates development of EAM; therefore, 4-1BB may be an effective target for treating myocarditis.

Consequences of unlocking the cardiac myosin molecule in human myocarditis and cardiomyopathies

Myocarditis, often initiated by viral infection, may progress to autoimmune inflammatory heart disease, dilated cardiomyopathy and heart failure. Although cardiac myosin is a dominant autoantigen in animal models of myocarditis and is released from the heart during viral myocarditis, the characterization, role and significance of anti-cardiac myosin autoantibodies is poorly defined. In our study, we define the human cardiac myosin epitopes in human myocarditis and cardiomyopathies and establish a mechanism to explain how anti-cardiac myosin autoantibodies may contribute to heart disease. We show that autoantibodies to cardiac myosin in sera from myocarditis and dilated cardiomyopathies in humans targeted primarily epitopes in the S2 hinge region of cardiac myosin. In addition, anti-cardiac myosin antibodies in sera or purified IgG from myocarditis and cardiomyopathy targeted the beta-adrenergic receptor and induced antibody-mediated cAMP-dependent protein kinase A (PKA) cell signaling activity in heart cells. Antibody-mediated PKA activity in sera was abrogated by absorption with anti-human IgG. Antibody-mediated cell signaling of PKA was blocked by antigen-specific inhibition by human cardiac myosin or the beta-adrenergic receptor but not the alpha adrenergic receptor or bovine serum albumin. Propranolol, a beta blocker and inhibitor of the beta-adrenergic receptor pathway also blocked the antibody-mediated signaling of the beta-adrenergic receptor and PKA. The data suggest that IgG antibody against human cardiac myosin reacts with the beta-adrenergic receptor and triggers PKA signaling in heart cells. In summary, we have identified a new class of crossreactive autoantibodies against human cardiac myosin and the beta-adrenergic receptor in the heart. In addition, we have defined disease specific peptide epitopes in the human cardiac myosin rod S2 region in human myocarditis and cardiomyopathy as well as a mechanistic role of autoantibody in the pathogenesis of disease.

Potential role of antibodies against cardiac Kv channel-interacting protein 2 in dilated cardiomyopathy

BACKGROUND

Growing evidence suggests participation of autoimmune mechanisms in the pathogenesis of dilated cardiomyopathy (DCM).

METHODS

Patients with heart failure (left ventricular ejection fraction < or =50%) due to DCM (n = 98) or ischemic cardiomyopathy (ICM, n = 49) and controls with normal left ventricular function (n = 98) were included. Immunoglobulin G antibodies were purified from plasma by affinity chromatography and analyzed by surface plasmon resonance analysis. We analyzed the distribution of autoantibodies against Kv channel-interacting protein (KChIP) 2.6, cardiac troponin I (cTnI), and the beta1-adrenergic receptor (second extracellular loop, cardiac beta1-adrenergic receptor [SEL-beta1-AR])-two other known autoantibodies involved in heart failure. Effects of antibodies against KChIP2 on cell death of isolated rat cardiomyocytes were assessed by flow cytometry.

RESULTS

We detected autoantibodies against KChIP2.6 in 14.3% (P < .015 vs controls, P = .286 vs ICM) of the DCM samples, in 8.2% of the ICM samples (P = .304 vs controls), and in 4.1% of the control samples. Virus persistence was significantly associated with detection of autoantibodies against KChIP2.6 in DCM patients (P = .025). Antibodies against SEL-beta1-AR were more frequent in DCM samples (34.7%, P < .001 vs controls, P = .02 vs ICM) and ICM samples (16.3%, P = .083 vs control) than in control samples (7.1%). Antibodies against cTnI were more frequent in DCM samples (20.4%, P < .001 vs controls, P = .769 vs ICM) and in ICM samples (18.4%, P < .01 vs controls) than in control samples (4.1%). Antibodies against rat KChIP2 enhanced cell death in isolated rat cardiomyocytes. Immunofluorescence indicated cell surface expression of KChIP2.

CONCLUSIONS

Autoantibodies against KChIP2.6, SEL-beta1-AR, and cTnI appear to be associated with DCM. Antibodies against KChIP2 may enhance cell death of rat cardiomyocytes.

Autoimmunity in coxsackievirus B3 induced myocarditis

Virus infections are implicated in several autoimmune diseases. Multiple mechanisms of autoimmunity induction have been proposed including antigenic mimicry, production of cryptic epitopes and infection acting as both adjuvant for self-antigens and the mechanism of releasing these cell antigens. Evidence for these mechanisms in coxsackievirus B3 induced myocarditis is discussed.

Characterization of pathogenic T cells and autoantibodies in C-protein-induced autoimmune polymyositis

Although autoimmune processes may take place in human polymyositis, little is known with regard to its pathogenesis due to the lack of appropriate animal models. In the present study, we developed experimental autoimmune myositis (EAM) in Lewis rats by immunization with recombinant skeletal C-protein and examined the role of pathogenic T cells and autoantibodies. Using recombinant proteins and synthetic peptides, we demonstrated that skeletal C-protein Fragment 2 (SC2) has the strongest myositis-inducing ability and that myositis-inducing epitope(s) reside within the residues 334-363 of SC2 (SC2P3). However, immunization with SC2P3 induced only mild EAM compared with SC2 immunization. Characterization of T cells and antisera revealed that SC2P3 and SC2P7 contain the B cell epitope, while the T cell epitope resides in SC2P5. Furthermore, anti-SC2, but not anti-SC2P3, antisera contained antibodies against the conformational epitope(s) in the SC2 molecule. However, SC2P3 or SC2P5 immunization plus anti-SC2 antibody transfer aggravated the disease only slightly. These findings suggest that C-protein-induced EAM is formed by activation of C-protein-specific T cells along with antibodies against conformational epitopes in C-protein but that there are undetermined factors related to the disease progression. Further analysis of C-protein-induced EAM will provide useful information to elucidate the pathomechanisms of human polymyositis.

Autoimmunological features in inflammatory cardiomyopathy

During recent years, increasing evidence has been obtained that cellular as well as humoral autoimmunity is involved in the pathogenesis of dilated cardiomyopathy (DCM). The immune system is generally activated by viral infections with the objective of virus elimination from the myocardium. However, a relevant number of patients demonstrate viral persistence and/or chronic inflammation in the myocardium. This chronic myocardial inflammation, defined by chronic inflammation, is termed "inflammatory cardiomyopathy" according to the WHO classification of cardiomyopathies. Chronic inflammation is frequently followed by the development of autoimmunity. A breakdown in the control mechanisms protecting against autoimmune reactions by both presentation of normally not accessible self-antigens and bystander- activation, induced by the pathogen, leads to the formation of autoreactive antibodies and T cells. The auto-reactive antibodies interact directly with heart tissue resulting in altered signal transduction or complement activation, whereas the T cell-mediated mechanisms include direct attack by cytotoxic T cells or indirect effects of cytotoxic cytokines released by stimulated T cells or macrophages.

Molecular mapping of autoimmune B cell responses in experimental myocarditis

Autoimmune responses directed against heart-specific antigens most likely play a key role in the pathogenesis of myocarditis. Although autoantibodies against cardiac determinants are frequently detected both in human patients and mice suffering from myocarditis, the immunological mechanisms for their induction have not yet been fully explored. We used here the SEREX approach (serological identification of recombinantly expressed proteins) to molecularly dissect heart-specific autoimmune B cell responses that develop in the course of experimentally induced myocarditis. Screening of a heart cDNA library with sera of cardiac myosin heavy chain alpha (myhcalpha) peptide-immunized BALB/c mice revealed a strong focusing of the B cell response on the myhcalpha protein. The vast majority of the myhcalpha transcripts coded for regions other than the sequence of the immunogenic myhcalpha peptide, indicating extensive intramolecular epitope spreading. Importantly, we found that the infection with cardiotropic viruses such as MCMV and Coxsackievirus B3 elicited specific autoantibody pattern with a particular skewing to the myhcalpha protein. The induction of myhcalpha peptide-specific Th cells in the course of both infections suggests that infection-associated determinant spreading on the Th cell level paves the way for a focused and dominant anti-myhcalpha B cell response.

Microarray analysis reveals the role of matrix metalloproteinases in mouse experimental autoimmune myocarditis induced by cardiac myosin peptides

Autoimmune myocarditis develops after the presentation of heart-specific antigens to autoaggressive CD4(+) T cells and after inflammation has infiltrated the tissues. To shed light on global changes in the gene expression of autoimmune myocarditis and to gain further insight into the molecular mechanisms underlying the genesis of myocarditis, we conducted a comprehensive microarray analysis of mRNA using an experimental mouse autoimmune myocarditis model via immunization with alpha-myosin heavy chain-derived peptides. Of over 39,000 transcripts on a high density oligonucleotide microarray, 466 were under-expressed and 241 over-expressed by >or= 1.5-fold compared with the controls in BALB/C mouse with autoimmune myocarditis. In this paper, we list the top 50 up-regulated genes related to the immune response. These altered genes encode for leukocyte-specific markers and receptors, the histocompatibility complex, cytokines/receptors, chemokines/receptors, adhesion molecules, components of the complement cascade, and signal transduction-related molecules. Interestingly, matrix metalloproteinases (MMPs) such as MMP-3 and MMP-9 were up-regulated, as further revealed by the reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry assays. This indicates that MMPs may act as major regulators of the cytokine profile. Together, these findings provide new insight into the molecular events associated with the mechanism of the autoimmune genesis of myocarditis.

Mimicry and Antibody-Mediated Cell Signaling in Autoimmune Myocarditis

The mechanisms by which autoantibodies against cardiac myosin (CM) may lead to heart dysfunction is unknown. We show that autoantibodies to CM in anti-CM sera and mAbs derived from experimental autoimmune myocarditis targeted the heart cell surface and induced Ab-mediated cAMP-dependent protein kinase A activity. Ab-mediated cell signaling of protein kinase A was blocked by CM, anti-IgG, or by specific inhibitors of the beta-adrenergic receptor (beta-AR) pathway. mAbs confirmed mimicry between CM and the beta-AR. Passive transfer of purified Ab (IgG) from CM-immunized rats resulted in IgG deposition and apoptosis in the heart, leading to a cardiomyopathic heart disease phenotype in recipients. Our novel findings link anti-CM Ab with the beta-AR and subsequent Ab-mediated cell signaling in the heart.

Critical role for monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha in induction of experimental autoimmune myocarditis and effective anti-monocyte chemoattractant protein-1 gene therapy

BACKGROUND

Autoimmune myocarditis is a principal cause of heart failure among young adults and is often a precursor of dilated cardiomyopathy. Monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1alpha (MIP-1alpha) are potent chemotactic factors for mononuclear cells. The inflammatory infiltrate observed in myocardial lesions of myocarditis consists of >70% mononuclear cells. To determine their critical role in the pathogenesis of myocarditis, we inhibited mononuclear cell activation and migration to see if it would affect disease severity and disease prevalence in experimental autoimmune myocarditis (EAM).

METHODS AND RESULTS

In this report, we demonstrated that blockade of MCP-1 or MIP-1alpha with monoclonal antibodies significantly reduced severity of myocarditis in BALB/c mice immunized with cardiac myosin. Similar results were obtained when CCR2-/- and CCR5-/- mice were used. In CCR2-/- mice, not only disease severity but also disease prevalence was reduced. To further inhibit mononuclear cell activation and migration, we transfected the mice before inducing EAM with a dominant-negative inhibitor of MCP-1 gene (7ND). This transfection significantly reduced the disease severity, decreased mRNA expression levels, especially of the chemokines RANTES, MIP-2, IP-10, MCP-1, T-cell activation gene 3, and eotaxin in the myocardium, and resulted in a reduction in cardiac myosin-induced interleukin-1 and interleukin-4 and in an increase in interferon-gamma and interleukin-10 cytokine production by splenocytes.

CONCLUSIONS

Overall, these findings suggest that the chemokines MCP-1 and MIP-1alpha, acting through their receptors CCR2 and CCR5, are important in the induction of EAM and that inhibition of MCP-1 with 7ND gene transfection significantly reduced disease severity. This strategy may be a new feasible form of gene therapy against autoimmune myocarditis.

The significance of autoimmunity in myocarditis

A growing body of evidence supports the view that some forms of human myocarditis and dilated cardiomyopathy result from a pathogenic autoimmune response. The evidence is based first on the presence of heart-specific antibodies in many patients with these diseases, including antibodies with demonstrated functional effects. These antibodies may be present before the onset of dilated cardiomyopathy and may be predictive of the course of disease in terms of deterioration of cardiac function. Depletion of the heart-specific antibodies by extracorporeal immunoadsorption may result in amelioration of disease in some patients, often continuing for long periods of time. Clinical investigations show that a subpopulation of patients with dilated cardiomyopathy benefit from immunosuppressive treatment. In one report, this subpopulation was identified as autoantibody-positive and virus-negative. Finally, animal experiments have shown that autoimmune myocarditis can be induced by viral infection and that this autoimmune response can be duplicated by immunization with a well-characterized antigen, cardiac myosin. Based on this evidence, we propose that some forms of dilated cardiomyopathy and myocarditis result from pathogenic autoimmune responses that represent the final common pathogenetic pathway of various infectious and even non-infectious injuries.