IL-33 independently induces eosinophilic pericarditis and cardiac dilation: ST2 improves cardiac function

The protective role of GATA6+ pericardial macrophages in pericardial inflammation

Prior research has suggested that GATA6+ pericardial macrophages may traffic to the myocardium to prevent interstitial fibrosis after myocardial infarction (MI), while subsequent literature claims that they do not. We demonstrate that GATA6+ pericardial macrophages are critical for preventing IL-33 induced pericarditis and attenuate trafficking of inflammatory monocytes and granulocytes to the pericardial cavity after MI. However, absence of GATA6+ macrophages did not affect myocardial inflammation due to MI or coxsackievirus-B3 induced myocarditis, or late-stage cardiac fibrosis and cardiac function post MI. GATA6+ macrophages are significantly less transcriptionally active following stimulation in vitro compared to bone marrow-derived macrophages and do not induce upregulation of inflammatory markers in fibroblasts. This suggests that GATA6+ pericardial macrophages attenuate inflammation through their interactions with surrounding cells. We therefore conclude that GATA6+ pericardial macrophages are critical in modulating pericardial inflammation, but do not play a significant role in controlling myocardial inflammation or fibrosis.

Autoimmune Myocarditis, Old Dogs and New Tricks

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

Innate and adaptive immunity in acute myocarditis

Acute myocarditis is an acute inflammatory cardiomyopathy associated with cardiac damage triggered by a virus or a pathological immune activation. It may present with a wide range of clinical presentations, ranging from mild symptoms to severe forms like fulminant myocarditis, characterized by hemodynamic compromise and cardiogenic shock. The immune system plays a central role in the pathogenesis of myocarditis. In fact, while its function is primarily protective, aberrant responses can be detrimental. In this context, both innate and adaptive immunity play pivotal roles; notably, the innate system offers a non-specific and immediate defense, while the adaptive provides specialized protection with immunological memory. However, dysregulation in these systems can misidentify cardiac tissue, triggering autoimmune reactions and possibly leading to significant cardiac tissue damage. This review highlights the importance of innate and adaptive immune responses in the progression and treatment of acute myocarditis.

Impact of Concurrent Ischaemic Stroke on Unfavourable Outcomes in Men and Women with Dilated Cardiomyopathy

Background

Growing evidence suggests that concurrent ischaemic stroke (IS) exacerbates the prognosis of patients with dilated cardiomyopathy (DCM) and that this effect may be further influenced by sex. However, the exact effect of sex remains unclear. This study aimed to explore the effects of the relevant risk factors on the prognosis of patients with DCM and concurrent IS. Considering the sex differences in DCM, this study further investigated the impact of concurrent IS on the prognosis of men and women with DCM.

Methods

A total of 632 patients with DCM enrolled between 2016 and 2021 were included in this study. Clinical data were obtained from medical records, and all participants were followed up in the outpatient clinic or by telephone for at least 1 year. A Cox proportional hazards model and Kaplan-Meier curves were used to evaluate the effects of concurrent IS on the prognosis of patients with DCM.

Results

Patients with DCM complicated with IS (DCM-IS) had significantly lower cumulative survival rates than patients with DCM without IS (non-IS) (74.6% vs. 84.2%, χ 2 = 6.85, p = 0.009). Additionally, IS was associated with greater risks of death and heart transplantation (HTx) in men (75.8% vs. 85.1%, χ 2 = 5.02, p = 0.025), but not in women (71.0% vs. 81.5%, χ 2 = 1.91, p = 0.167).

Conclusions

This large-scale multicentre prospective cohort study demonstrated a poorer prognosis in patients with concurrent DCM and IS, particularly among men. Patients with DCM should not be overlooked in IS screening, emphasis should be placed on the occurrence of IS in patients with DCM. Early and proactive secondary prevention of cerebrovascular diseases might improve the prognosis of DCM patients. More intervention studies focusing on men with DCM complicated with IS should be prioritised.

Identification of endocrine-disrupting chemicals targeting key DCM-associated genes via bioinformatics and machine learning

Dilated cardiomyopathy (DCM) is a primary cause of heart failure (HF), with the incidence of HF increasing consistently in recent years. DCM pathogenesis involves a combination of inherited predisposition and environmental factors. Endocrine-disrupting chemicals (EDCs) are exogenous chemicals that interfere with endogenous hormone action and are capable of targeting various organs, including the heart. However, the impact of these disruptors on heart disease through their effects on genes remains underexplored. In this study, we aimed to explore key DCM-related genes using machine learning (ML) and the construction of a predictive model. Using the Gene Expression Omnibus (GEO) database, we screened differentially expressed genes (DEGs) and performed enrichment analyses of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to DCM. Through ML techniques combining maximum relevance minimum redundancy (mRMR) and least absolute shrinkage and selection operator (LASSO) logistic regression, we identified key genes for predicting DCM (IL1RL1, SEZ6L, SFRP4, COL22A1, RNASE2, HB). Based on these key genes, 79 EDCs with the potential to affect DCM were identified, among which 4 (3,4-dichloroaniline, fenitrothion, pyrene, and isoproturon) have not been previously associated with DCM. These findings establish a novel relationship between the EDCs mediated by key genes and the development of DCM.

Role of immune cells in the pathogenesis of myocarditis

Myocarditis is an inflammatory heart disease that mostly affects young people. Myocarditis involves a complex immune network; however, its detailed pathogenesis is currently unclear. The diversity and plasticity of immune cells, either in the peripheral blood or in the heart, have been partially revealed in a number of previous studies involving patients and several kinds of animal models with myocarditis. It is the complexity of immune cells, rather than one cell type that is the culprit. Thus, recognizing the individual intricacies within immune cells in the context of myocarditis pathogenesis and finding the key intersection of the immune network may help in the diagnosis and treatment of this condition. With the vast amount of cell data gained on myocarditis and the recent application of single-cell sequencing, we summarize the multiple functions of currently recognized key immune cells in the pathogenesis of myocarditis to provide an immune background for subsequent investigations.

Reconstituted Extracellular Vesicles from Human Platelets Decrease Viral Myocarditis in Mice

Patients with viral myocarditis are at risk of sudden death and may progress to dilated cardiomyopathy (DCM). Currently, no disease-specific therapies exist to treat viral myocarditis. Here it is examined whether reconstituted, lyophilized extracellular vesicles (EVs) from platelets from healthy men and women reduce acute or chronic myocarditis in male mice. Human-platelet-derived EVs (PEV) do not cause toxicity, damage, or inflammation in naïve mice. PEV administered during the innate immune response significantly reduces myocarditis with fewer epidermal growth factor (EGF)-like module-containing mucin-like hormone receptor-like 1 (F4/80) macrophages, T cells (cluster of differentiation molecules 4 and 8, CD4 and CD8), and mast cells, and improved cardiac function. Innate immune mediators known to increase myocarditis are decreased by innate PEV treatment including Toll-like receptor (TLR)4 and complement. PEV also significantly reduces perivascular fibrosis and remodeling including interleukin 1 beta (IL-1β), transforming growth factor-beta 1, matrix metalloproteinase, collagen genes, and mast cell degranulation. PEV given at days 7-9 after infection reduces myocarditis and improves cardiac function. MicroRNA (miR) sequencing reveals that PEV contains miRs that decrease viral replication, TLR4 signaling, and T-cell activation. These data show that EVs from the platelets of healthy individuals can significantly reduce myocarditis and improve cardiac function.

Myocardial Immune Cells: The Basis of Cardiac Immunology

The mammalian heart is characterized by the presence of striated myocytes, which allow continuous rhythmic contraction from early embryonic development until the last moments of life. However, the myocardium contains a significant contingent of leukocytes from every major class. This leukocyte pool includes both resident and nonresident immune cells. Over recent decades, it has become increasingly apparent that the heart is intimately sensitive to immune signaling and that myocardial leukocytes exhibit an array of critical functions, both in homeostasis and in the context of cardiac adaptation to injury. Here, we systematically review current knowledge of all major leukocyte classes in the heart, discussing their functions in health and disease. We also highlight the connection between the myocardium, immune cells, lymphoid organs, and both local and systemic immune responses.

Sex and gender differences in myocarditis and dilated cardiomyopathy: An update

In the past decade there has been a growing interest in understanding sex and gender differences in myocarditis and dilated cardiomyopathy (DCM), and the purpose of this review is to provide an update on this topic including epidemiology, pathogenesis and clinical presentation, diagnosis and management. Recently, many clinical studies have been conducted examining sex differences in myocarditis. Studies consistently report that myocarditis occurs more often in men than women with a sex ratio ranging from 1:2-4 female to male. Studies reveal that DCM also has a sex ratio of around 1:3 women to men and this is also true for familial/genetic forms of DCM. Animal models have demonstrated that DCM develops after myocarditis in susceptible mouse strains and evidence exists for this progress clinically as well. A consistent finding is that myocarditis occurs primarily in men under 50 years of age, but in women after age 50 or post-menopause. In contrast, DCM typically occurs after age 50, although the age that post-myocarditis DCM occurs has not been investigated. In a small study, more men with myocarditis presented with symptoms of chest pain while women presented with dyspnea. Men with myocarditis have been found to have higher levels of heart failure biomarkers soluble ST2, creatine kinase, myoglobin and T helper 17-associated cytokines while women develop a better regulatory immune response. Studies of the pathogenesis of disease have found that Toll-like receptor (TLR)2 and TLR4 signaling pathways play a central role in increasing inflammation during myocarditis and in promoting remodeling and fibrosis that leads to DCM, and all of these pathways are elevated in males. Management of myocarditis follows heart failure guidelines and there are currently no disease-specific therapies. Research on standard heart failure medications reveal important sex differences. Overall, many advances in our understanding of the effect of biologic sex on myocarditis and DCM have occurred over the past decade, but many gaps in our understanding remain. A better understanding of sex and gender effects are needed to develop disease-targeted and individualized medicine approaches in the future.

Unveiling IL-33/ST2 Pathway Unbalance in Cardiac Remodeling Due to Obesity in Zucker Fatty Rats

Obesity is an epidemic condition linked to cardiovascular disease severity and mortality. Fat localization and type represent cardiovascular risk estimators. Importantly, visceral fat secretes adipokines known to promote low-grade inflammation that, in turn, modulate its secretome and cardiac metabolism. In this regard, IL-33 regulates the functions of various immune cells through ST2 binding and-following its role as an immune sensor to infection and stress-is involved in the pro-fibrotic remodeling of the myocardium. Here we further investigated the IL-33/ST2 effects on cardiac remodeling in obesity, focusing on molecular pathways linking adipose-derived IL-33 to the development of fibrosis or hypertrophy. We analyzed the Zucker Fatty rat model, and we developed in vitro models to mimic the adipose and myocardial relationship. We demonstrated a dysregulation of IL-33/ST2 signaling in both adipose and cardiac tissue, where they affected Epac proteins and myocardial gene expression, linked to pro-fibrotic signatures. In Zucker rats, pro-fibrotic effects were counteracted by ghrelin-induced IL-33 secretion, whose release influenced transcription factor expression and ST2 isoforms balance regulation. Finally, the effect of IL-33 signaling is dependent on several factors, such as cell types' origin and the balancing of ST2 isoforms. Noteworthy, it is reasonable to state that considering IL-33 to have a unique protective role should be considered over-simplistic.

Sex and age differences in sST2 in cardiovascular disease

Aims

The goal of this study was to determine whether sex and age differences exist for soluble ST2 (sST2) for several cardiovascular diseases (CVDs).

Methods

We examined sST2 levels using an ELISA kit for myocarditis (n = 303), cardiomyopathy (n = 293), coronary artery disease (CAD) (n = 239), myocardial infarct (MI) (n = 159), and congestive heart failure (CHF) (n = 286) and compared them to controls that did not have CVDs (n = 234).

Results

Myocarditis occurred in this study in relatively young patients around age 40 while the other CVDs occurred more often in older individuals around age 60. We observed a sex difference in sST2 by age only in myocarditis patients (men aged 38, women 46, p = 0.0002), but not for other CVDs. Sera sST2 levels were significantly elevated compared to age-matched controls for all CVDs: myocarditis (p ≤ 0.0001), cardiomyopathy (p = 0.0009), CAD (p = 0.03), MI (p = 0.034), and CHF (p < 0.0001) driven by elevated sST2 levels in females for all CVDs except myocarditis, which was elevated in both females (p = 0.002) and males (p ≤ 0.0001). Sex differences in sST2 levels were found for myocarditis and cardiomyopathy but no other CVDs and were higher in males (myocarditis p = 0.0035; cardiomyopathy p = 0.0047). sST2 levels were higher in women with myocarditis over 50 years of age compared to men (p = 0.0004) or women under 50 years of age (p = 0.015). In cardiomyopathy and MI patients, men over 50 had significantly higher levels of sST2 than women (p = 0.012 and p = 0.043, respectively) but sex and age differences were not detected in other CVDs. However, women with cardiomyopathy that experienced early menopause had higher sST2 levels than those who underwent menopause at a natural age range (p = 0.02).

Conclusion

We found that sex and age differences in sera sST2 exist for myocarditis, cardiomyopathy, and MI, but were not observed in other CVDs including CAD and CHF. These initial findings in patients with self-reported CVDs indicate that more research is needed into sex and age differences in sST2 levels in individual CVDs.

Progress of Research into the Interleukin-1 Family in Cardiovascular Disease

Inflammatory factors, such as the IL-1 family, are generally acknowledged to be involved in systemic diseases and IL-1α and IL-1β, in particular, have been linked to cardiovascular disease with IL-18, IL-33, IL-36, IL-37 and IL-38 yet to be explored. The current review aims to summarize mechanisms of IL-18, IL-33, IL-36, IL-37 and IL-38 in myocardial infarction, hypertension, arrhythmia, valvular disease and aneurysm and to explore the potential for cardiovascular disease treatment strategies and discuss future directions for prevention and treatment.

Meeting the Challenges of Myocarditis: New Opportunities for Prevention, Detection, and Intervention—A Report from the 2021 National Heart, Lung, and Blood Institute Workshop

The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop of international experts to discuss new research opportunities for the prevention, detection, and intervention of myocarditis in May 2021. These experts reviewed the current state of science and identified key gaps and opportunities in basic, diagnostic, translational, and therapeutic frontiers to guide future research in myocarditis. In addition to addressing community-acquired myocarditis, the workshop also focused on emerging causes of myocarditis including immune checkpoint inhibitors and SARS-CoV-2 related myocardial injuries and considered the use of systems biology and artificial intelligence methodologies to define workflows to identify novel mechanisms of disease and new therapeutic targets. A new priority is the investigation of the relationship between social determinants of health (SDoH), including race and economic status, and inflammatory response and outcomes in myocarditis. The result is a proposal for the reclassification of myocarditis that integrates the latest knowledge of immunological pathogenesis to refine estimates of prognosis and target pathway-specific treatments.

Interrelationship and Sequencing of Interleukins4, 13, 31, and 33 - An Integrated Systematic Review: Dermatological and Multidisciplinary Perspectives

The interrelations and sequencing of interleukins are complex (inter)actions where each interleukin can stimulate the secretion of its preceding interleukin. In this paper, we attempt to summarize the currently known roles of IL-4, IL-13, IL-31, and IL-33 from a multi-disciplinary perspective. In order to conduct a comprehensive review of the current literature, a search was conducted using PubMed, Google Scholar, Medscape, UpToDate, and Key Elsevier for keywords. The results were compiled from case reports, case series, letters, and literature review papers, and analyzed by a panel of multi-disciplinary specialist physicians for relevance. Based on 173 results, we compiled the following review of interleukin signaling and its clinical significance across a multitude of medical specialties. Interleukins are at the bed rock of a multitude of pathologies across different organ systems and understanding their role will likely lead to novel treatments and better outcomes for our patients. New interleukins are being described, and the role of this inflammatory cascade is still coming to light. We hope this multi-discipline review on the role interleukins play in current pathology assists in this scope.

Transcriptome analysis uncovers the autophagy-mediated regulatory patterns of the immune microenvironment in dilated cardiomyopathy

The relationship between autophagy and immunity has been well studied. However, little is known about the role of autophagy in the immune microenvironment during the progression of dilated cardiomyopathy (DCM). Therefore, this study aims to uncover the effect of autophagy on the immune microenvironment in the context of DCM. By investigating the autophagy gene expression differences between healthy donors and DCM samples, 23 dysregulated autophagy genes were identified. Using a series of bioinformatics methods, 13 DCM‐related autophagy genes were screened and used to construct a risk prediction model, which can well distinguish DCM and healthy samples. Then, the connections between autophagy and immune responses including infiltrated immunocytes, immune reaction gene‐sets and human leukocyte antigen (HLA) genes were systematically evaluated. In addition, two autophagy‐mediated expression patterns in DCM were determined via the unsupervised consensus clustering analysis, and the immune characteristics of different patterns were revealed. In conclusion, our study revealed the strong effect of autophagy on the DCM immune microenvironment and provided new insights to understand the pathogenesis and treatment of DCM.

Increased Interleukin 18-Dependent Immune Responses Are Associated With Myopericarditis After COVID-19 mRNA Vaccination

Myocarditis and myopericarditis may occur after COVID-19 vaccination with an incidence of two to twenty cases per 100,000 individuals, but underlying mechanisms related to disease onset and progression remain unclear. Here, we report a case of myopericarditis following the first dose of the mRNA-1273 COVID-19 vaccine in a young man who had a history of mild COVID-19 three months before vaccination. The patient presented with chest pain, elevated troponin I level, and electrocardiogram abnormality. His endomyocardial biopsy revealed diffuse CD68⁺ cell infiltration. We characterized the immune profile of the patient using multiplex cytokine assay and flow cytometry analysis. Sex-matched vaccinated individuals and healthy individuals were used as controls. IL-18 and IL-27, Th1-type cytokines, were highly increased in the patient with COVID-19 vaccine-related myopericarditis compared with vaccinated controls who experienced no cardiac complications. In the patient, circulating NK cells and T cells showed an activated phenotype and mRNA profile, and monocytes expressed increased levels of IL-18 and its upstream NLRP3 inflammasome. We found that recombinant IL-18 administration into mice caused mild cardiac dysfunction and activation of NK cells and T cells in the hearts, similar to the findings in the patient with myopericarditis after COVID-19 mRNA vaccination. Collectively, myopericarditis following COVID-19 mRNA vaccination may be associated with increased IL-18-mediated immune responses and cardiotoxicity.

Trpc6 Promotes Doxorubicin-Induced Cardiomyopathy in Male Mice With Pleiotropic Differences Between Males and Females

Background: Doxorubicin is a widely used and effective chemotherapy, but the major limiting side effect is cardiomyopathy which in some patients leads to congestive heart failure. Genetic variants in TRPC6 have been associated with the development of doxorubicin-induced cardiotoxicity, suggesting that TRPC6 may be a therapeutic target for cardioprotection in cancer patients. Methods: Assessment of Trpc6 deficiency to prevent doxorubicin-induced cardiac damage and function was conducted in male and female B6.129 and Trpc6 knock-out mice. Mice were treated with doxorubicin intraperitoneally every other day for a total of 6 injections (4 mg/kg/dose, cumulative dose 24 mg/kg). Cardiac damage was measured in heart sections by quantification of vacuolation and fibrosis, and in heart tissue by gene expression of Tnni3 and Myh7. Cardiac function was determined by echocardiography. Results: When treated with doxorubicin, male Trpc6-deficient mice showed improvement in markers of cardiac damage with significantly reduced vacuolation, fibrosis and Myh7 expression and increased Tnni3 expression in the heart compared to wild-type controls. Similarly, male Trpc6-deficient mice treated with doxorubicin had improved LVEF, fractional shortening, cardiac output and stroke volume. Female mice were less susceptible to doxorubicin-induced cardiac damage and functional changes than males, but Trpc6-deficient females had improved vacuolation with doxorubicin treatment. Sex differences were observed in wild-type and Trpc6-deficient mice in body-weight and expression of Trpc1, Trpc3 and Rcan1 in response to doxorubicin. Conclusions: Trpc6 promotes cardiac damage following treatment with doxorubicin resulting in cardiomyopathy in male mice. Female mice are less susceptible to cardiotoxicity with more robust ability to modulate other Trpc channels and Rcan1 expression.

Altered mRNA Expression of Interleukin-1 Receptors in Myocardial Tissue of Patients with Left Ventricular Assist Device Support

Serum levels of cytokines interleukin 1 beta ( IL-1β) and interleukin 33 (IL-33) are highly abnormal in heart failure and remain elevated after mechanical circulatory support (MCS). However, local cytokine signaling induction remains elusive. Left (LV) and right ventricular (RV) myocardial tissue specimens of end-stage heart failure (HF) patients without (n = 24) and with MCS (n = 39; 594 ± 57 days) were analyzed for cytokine mRNA expression level of IL-1B, interleukin 1 receptor 1/2 (IL-1R1/2), interleukin 1 receptor-like 1 (IL-1RL1), IL-33 and interleukin-1 receptor accessory protein (IL-1RaP). MCS patients showed significantly elevated IL-1B expression levels (LV: 2.0 fold, p = 0.0058; RV: 3.3 fold, p < 0.0001). Moreover, IL-1R1, IL-1RaP and IL-33 expression levels strongly correlated with each other. IL-1RL1 and IL-1R2 expression levels were significantly higher in RV myocardial tissue (RV/LV ratio IL-1R2 HF: 4.400 ± 1.359; MCS: 4.657 ± 0.655; IL-1RL1 HF: 3.697 ± 0.876; MCS: 4.529 ± 0.5839). In addition, IL1-RaP and IL-33 RV expression levels were significantly elevated in MCS. Furthermore, IL-33 expression correlates with C-reactive protein (CRP) plasma levels in HF, but not in MCS patients. Increased expression of IL-1B and altered correlation patterns of IL-1 receptors indicate enhanced IL-1β signaling in MCS patients. Correlation of IL-1 receptor expression with IL-33 may hint towards a link between both pathways. Moreover, diverging expression in LV and RV suggests specific regulation of local cytokine signaling.

Interleukin-33 alleviates diabetic cardiomyopathy through regulation of endoplasmic reticulum stress and autophagy via insulin-like growth factor-binding protein 3

Prolonged endoplasmic reticulum (ER) stress is the key driving force behind diabetic cardiomyopathy (DCM). Autophagy is extensively implicated in adaptive mechanisms for cell survival. Interleukin-33 (IL-33) is known to be a potent cardiac protector, but its roles in DCM, ER stress, and autophagy are currently unknown. We aimed to explore the effects of IL-33 on DCM and characterize the roles that ER stress and autophagy play in DCM. The effects of IL-33 on DCM, ER stress, and autophagy were characterized both in db/db mice and in palmitic acid (PA)-treated cardiomyocytes. The manipulators of ER stress and autophagy were used to clarify their roles in DCM remittance conferred by IL-33. Gene expression analysis was used to identify IL-33-dependent regulators of ER stress and autophagy. Both db/db mice and PA-treated cells presented with enhanced levels of ER stress, apoptosis, and lipid deposition, as well as impaired autophagy, all of which could be reversed by IL-33. Treatment with IL-33 improved the cardiac diastolic function of diabetic mice. Nonselective autophagy inhibitors, such as 3-methyladenine (3-MA) or wortmannin, abolished the protective effects of IL-33, resulting in an increase in both ER stress and apoptosis. Strikingly, insulin-like growth factor-binding protein 3 (IGFBP3) was identified as the gene most significantly differentially expressed between IL-33 and control groups. Knockdown of IGFBP3 expression, similar to the effect of nonselective autophagy inhibitors, resulted in high levels of ER stress, impaired autophagy, and apoptosis that were not rescued upon treatment with IL-33. IL-33 abates DCM by alleviating ER stress and promoting autophagy. IGFBP3 is essential for IL-33-induced ER stress resolution and autophagic enhancement during DCM.

Sex Differences, Genetic and Environmental Influences on Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is characterized by dilatation of the left ventricle and impaired systolic function and is the second most common cause of heart failure after coronary heart disease. The etiology of DCM is diverse including genetic pathogenic variants, infection, inflammation, autoimmune diseases, exposure to chemicals/toxins as well as endocrine and neuromuscular causes. DCM is inherited in 20–50% of cases where more than 30 genes have been implicated in the development of DCM with pathogenic variants in TTN (Titin) most frequently associated with disease. Even though male sex is a risk factor for heart failure, few studies have examined sex differences in the pathogenesis of DCM. We searched the literature for studies examining idiopathic or familial/genetic DCM that reported data by sex in order to determine the sex ratio of disease. We found 31 studies that reported data by sex for non-genetic DCM with an average overall sex ratio of 2.5:1 male to female and 7 studies for familial/genetic DCM with an overall average sex ratio of 1.7:1 male to female. No manuscripts that we found had more females than males in their studies. We describe basic and clinical research findings that may explain the increase in DCM in males over females based on sex differences in basic physiology and the immune and fibrotic response to damage caused by mutations, infections, chemotherapy agents and autoimmune responses.

Innate Lymphoid Cells Play a Pathogenic Role in Pericarditis

We find that cardiac group 2 innate lymphoid cells (ILC2s) are essential for the development of IL-33-induced eosinophilic pericarditis. We show a pathogenic role for ILC2s in cardiac inflammation, in which ILC2s activated by IL-33 drive the development of eosinophilic pericarditis in collaboration with cardiac fibroblasts. ILCs, not T and B cells, are required for the development of pericarditis. ILC2s transferred to the heart of Rag2^-/-Il2rg^-/- mice restore their susceptibility to eosinophil infiltration. Moreover, ILC2s direct cardiac fibroblasts to produce eotaxin-1. We also find that eosinophils reside in the mediastinal cavity and that eosinophils transferred to the mediastinal cavity of eosinophil-deficient ΔdblGATA1 mice following IL-33 treatment migrate to the heart. Thus, the serous cavities may serve as a reservoir of cardiac-infiltrating eosinophils. In humans, patients with pericarditis show higher amounts of ILCs in pericardial fluid than do healthy controls and patients with other cardiac diseases. We demonstrate that ILCs play a critical role in pericarditis.

Friend or foe of innate lymphoid cells in inflammation-associated cardiovascular disease

As a distinctive population of leucocytes, innate lymphoid cells (ILCs) participate in immune-mediated diseases and play crucial roles in tissue remodelling after injury. ILC lineages can be divided into helper ILCs and cytotoxic ILCs. Most helper ILCs are integrated into the fabric of tissues and produce different types of cytokines involving in the pathogenesis of many kinds of cardiovascular disease and form intricate response circuits with adaptive immune cells. However, the specific phenotype and function of helper ILC subsets in cardiovascular diseases are still poorly understood. In this review, we firstly highlight the distribution of helper ILCs in cardiovascular system and further discuss the potential contribution of helper ILCs in inflammation-associated cardiovascular disease.

IL-33 induces type-2-cytokine phenotype but exacerbates cardiac remodeling post-myocardial infarction with eosinophil recruitment, worsened systolic dysfunction, and ventricular wall rupture

Myocardial infarction (MI) is the leading cause of mortality worldwide. Interleukin (IL)-33 (IL-33) is a cytokine present in most cardiac cells and is secreted on necrosis where it acts as a functional ligand for the ST2 receptor. Although IL-33/ST2 axis is protective against various forms of cardiovascular diseases, some studies suggest potential detrimental roles for IL-33 signaling. The aim of the present study was to examine the effect of IL-33 administration on cardiac function post-MI in mice. MI was induced by coronary artery ligation. Mice were treated with IL-33 (1 μg/day) or vehicle for 4 and 7 days. Functional and molecular changes of the left ventricle (LV) were assessed. Single cell suspensions were obtained from bone marrow, heart, spleen, and peripheral blood to assess the immune cells using flow cytometry at 1, 3, and 7 days post-MI in IL-33 or vehicle-treated animals. The results of the present study suggest that IL-33 is effective in activating a type 2 cytokine milieu in the damaged heart, consistent with reduced early inflammatory and pro-fibrotic response. However, IL-33 administration was associated with worsened cardiac function and adverse cardiac remodeling in the MI mouse model. IL-33 administration increased infarct size, LV hypertrophy, cardiomyocyte death, and overall mortality rate due to cardiac rupture. Moreover, IL-33-treated MI mice displayed a significant myocardial eosinophil infiltration at 7 days post-MI when compared with vehicle-treated MI mice. The present study reveals that although IL-33 administration is associated with a reparative phenotype following MI, it worsens cardiac remodeling and promotes heart failure.

Graft IL-33 regulates infiltrating macrophages to protect against chronic rejection

Alarmins, sequestered self-molecules containing damage-associated molecular patterns, are released during tissue injury to drive innate immune cell proinflammatory responses. Whether endogenous negative regulators controlling early immune responses are also released at the site of injury is poorly understood. Herein, we establish that the stromal cell-derived alarmin interleukin 33 (IL-33) is a local factor that directly restricts the proinflammatory capacity of graft-infiltrating macrophages early after transplantation. By assessing heart transplant recipient samples and using a mouse heart transplant model, we establish that IL-33 is upregulated in allografts to limit chronic rejection. Mouse cardiac transplants lacking IL-33 displayed dramatically accelerated vascular occlusion and subsequent fibrosis, which was not due to altered systemic immune responses. Instead, a lack of graft IL-33 caused local augmentation of proinflammatory iNOS+ macrophages that accelerated graft loss. IL-33 facilitated a metabolic program in macrophages associated with reparative and regulatory functions, and local delivery of IL-33 prevented the chronic rejection of IL-33-deficient cardiac transplants. Therefore, IL-33 represents what we believe is a novel regulatory alarmin in transplantation that limits chronic rejection by restraining the local activation of proinflammatory macrophages. The local delivery of IL-33 in extracellular matrix-based materials may be a promising biologic for chronic rejection prophylaxis.

Sex-Related Differences in Dilated Cardiomyopathy with a Focus on Cardiac Dysfunction in Oncology

PURPOSE OF REVIEW

The aim of this report is to describe the main aspects of sex-related differences in non-ischemic dilated cardiomyopathies (DCM), focusing on chemotherapy-induced heart failure (HF) and investigating the possible therapeutic implications and clinical management applications in the era of personalized medicine.

RECENT FINDINGS

In cardio-oncology, molecular and multimodality imaging studies confirm that sex differences do exist, affecting the therapeutic cardioprotective strategies and, therefore, the long-term outcomes. Interestingly, compelling evidences suggest that sex-specific characteristics in drug toxicity might predict differences in the therapeutic response, most likely due to the tangled interplay between cancer and HF, which probably share common underlying mechanisms. Cardiovascular diseases show many sex-related differences in prevalence, etiology, phenotype expression, and outcomes. Complex molecular mechanisms underlie this diverse pathological manifestations, from sex-determined differential gene expression to sex hormone interaction with their receptors in the heart. Non-ischemic DCM is an umbrella definition that incorporates several etiologies, including chemotherapy-induced cardiomyopathies. The role of sex as a risk factor for cardiotoxicity is poorly explored. However, understanding the various features of disease manifestation and outcomes is of paramount importance for a prompt and tailored evaluation.

An overview of the immune mechanisms of viral myocarditis

Viral myocarditis has been identified as a major cause of dilated cardiomyopathy (DCM) that can lead to heart failure. Historically, Coxsackieviruses and adenoviruses have been commonly suspected in myocarditis/DCM patients in North America and Europe. However, this notion is changing as other viruses such as Parvovirus B19 and human herpesvirus-6 are increasingly reported as causes of myocarditis in the United States, with the most recent example being the severe acute respiratory syndrome coronavirus 2, causing the Coronavirus Disease-19. The mouse model of Coxsackievirus B3 (CVB3)-induced myocarditis, which may involve mediation of autoimmunity, is routinely used in the study of immune pathogenesis of viral infections as triggers of DCM. In this review, we discuss the immune mechanisms underlying the development of viral myocarditis with an emphasis on autoimmunity in the development of post-infectious myocarditis induced with CVB3.

ST2 silencing aggravates ventricular remodeling and chronic heart failure in rats by mediating the IL-33/ST2 axis

Heart failure appears to be a severe public health problem affecting millions of people worldwide. Knowledge of the molecular mechanism contributing to ventricular remodeling would allow for earlier prevention of heart failure. Evidence exists reporting the involvement of IL-33 and ST2 and in heart remodeling. Thus, this study aims to delineate the effects of ST2 on chronic heart failure (CHF) via the IL-33/ST2 axis. Coronary artery ligation was employed to simulate CHF in rats, which were characterized by transthoracic echocardiography for cardiac function. After that, ST2 silencing and IL-33 overexpression were induced in rat models to evaluate apoptosis and pathological alterations in myocardial tissues and serum levels of biochemical indices. It was revealed that cardiac function was impaired in response to ST2 silencing. Furthermore, ST2 knockdown suppressed the activities of the mitochondrial respiratory chain and accelerated cardiomyocyte apoptosis via blockade of the IL-33/ST2 axis. These findings suggest an inhibitory role of ST2 silencing on the IL-33/ST2 axis, which consequently increases the risk of cardiac dysfunction, accelerates ventricular remodeling, and aggravates heart failure in rats. This study highlights that ST2 silencing may be a novel potential preventive or therapeutic target for CHF.

Elevated Sera sST2 Is Associated With Heart Failure in Men ≤50 Years Old With Myocarditis

Background

Myocarditis is an important cause of acute and chronic heart failure. Men with myocarditis have worse recovery and an increased need for transplantation compared with women, but the reason for the sex difference remains unclear. Elevated sera soluble (s)ST2 predicts mortality from acute and chronic heart failure, but has not been studied in myocarditis patients.

Methods and Results

Adults with a diagnosis of clinically suspected myocarditis (n=303, 78% male) were identified according to the 2013 European Society of Cardiology position statement. Sera sST2 levels were examined by ELISA in humans and mice and correlated with heart function according to sex and age. Sera sST2 levels were higher in healthy men (P=8×10⁻⁶) and men with myocarditis (P=0.004) compared with women. sST2 levels were elevated in patients with myocarditis and New York Heart Association class III‐IV heart failure (P=0.002), predominantly in men (P=0.0003). Sera sST2 levels were associated with New York Heart Association class in men with myocarditis who were ≤50 years old (r=0.231, P=0.0006), but not in women (r=0.172, P=0.57). Sera sST2 levels were also significantly higher in male mice with myocarditis (P=0.005) where levels were associated with cardiac inflammation. Gonadectomy with hormone replacement showed that testosterone (P<0.001), but not estradiol (P=0.32), increased sera sST2 levels in male mice with myocarditis.

Conclusions

We show in a well‐characterized subset of heart failure patients with clinically suspected and biopsy‐confirmed myocarditis that elevated sera sST2 is associated with an increased risk of heart failure based on New York Heart Association class in men ≤50 years old.

Dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a clinical diagnosis characterized by left ventricular or biventricular dilation and impaired contraction that is not explained by abnormal loading conditions (for example, hypertension and valvular heart disease) or coronary artery disease. Mutations in several genes can cause DCM, including genes encoding structural components of the sarcomere and desmosome. Nongenetic forms of DCM can result from different aetiologies, including inflammation of the myocardium due to an infection (mostly viral); exposure to drugs, toxins or allergens; and systemic endocrine or autoimmune diseases. The heterogeneous aetiology and clinical presentation of DCM make a correct and timely diagnosis challenging. Echocardiography and other imaging techniques are required to assess ventricular dysfunction and adverse myocardial remodelling, and immunological and histological analyses of an endomyocardial biopsy sample are indicated when inflammation or infection is suspected. As DCM eventually leads to impaired contractility, standard approaches to prevent or treat heart failure are the first-line treatment for patients with DCM. Cardiac resynchronization therapy and implantable cardioverter-defibrillators may be required to prevent life-threatening arrhythmias. In addition, identifying the probable cause of DCM helps tailor specific therapies to improve prognosis. An improved aetiology-driven personalized approach to clinical care will benefit patients with DCM, as will new diagnostic tools, such as serum biomarkers, that enable early diagnosis and treatment.

Conflicting vascular and metabolic impact of the IL-33/sST2 axis

Interleukin 33 (IL-33), which is expressed by several immune cell types, endothelial and epithelial cells, and fibroblasts, is a cytokine of the IL-1 family that acts both intra- and extracellularly to either enhance or resolve the inflammatory response. Intracellular IL-33 acts in the nucleus as a regulator of transcription. Once released from cells by mechanical stress, inflammatory cytokines, or necrosis, extracellular IL-33 is proteolytically processed to act in an autocrine/paracrine manner as an 'alarmin' on neighbouring or various immune cells expressing the ST2 receptor. Thus, IL-33 may serve an important role in tissue preservation and repair in response to injury; however, the actions of IL-33 are dampened by a soluble form of ST2 (sST2) that acts as a decoy receptor and is produced by endothelial and certain immune cells. Accumulating evidence supports the conclusion that sST2 is a biomarker of vascular health with diagnostic and/or prognostic value in various cardiovascular diseases, including coronary artery disease, myocardial infarction, atherosclerosis, giant-cell arteritis, acute aortic dissection, and ischaemic stroke, as well as obesity and diabetes. Although sST2 levels are positively associated with cardiovascular disease severity, the assumption that IL-33 is always beneficial is naïve. It is increasingly appreciated that the pathophysiological importance of IL-33 is highly dependent on cellular and temporal expression. Although IL-33 is atheroprotective and may prevent obesity and type 2 diabetes by regulating lipid metabolism, IL-33 appears to drive endothelial inflammation. Here, we review the current knowledge of the IL-33/ST2/sST2 signalling network and discuss its pathophysiological and translational implications in cardiovascular diseases.

Established and novel pathophysiological mechanisms of pericardial injury and constrictive pericarditis

This review article aims to: (1) discern from the literature the immune and inflammatory processes occurring in the pericardium following injury; and (2) to delve into the molecular mechanisms which may play a role in the progression to constrictive pericarditis. Pericarditis arises as a result of a wide spectrum of pathologies of both infectious and non-infectious aetiology, which lead to various degrees of fibrogenesis. Current understanding of the sequence of molecular events leading to pathological manifestations of constrictive pericarditis is poor. The identification of key mechanisms and pathways common to most fibrotic events in the pericardium can aid in the design and development of novel interventions for the prevention and management of constriction. We have identified through this review various cellular events and signalling cascades which are likely to contribute to the pathological fibrotic phenotype. An initial classical pattern of inflammation arises as a result of insult to the pericardium and can exacerbate into an exaggerated or prolonged inflammatory state. Whilst the implication of major drivers of inflammation and fibrosis such as tumour necrosis factor and transforming growth factor β were foreseeable, the identification of pericardial deregulation of other mediators (basic fibroblast growth factor, galectin-3 and the tetrapeptide Ac-SDKP) provides important avenues for further research.

Macrophages and cardiac fibroblasts are the main producers of eotaxins and regulate eosinophil trafficking to the heart

Cardiac manifestations are a major cause of morbidity and mortality in patients with eosinophil-associated diseases. Eosinophils are thought to play a pathogenic role in myocarditis. We investigated the pathways that recruit eosinophils to the heart using a model of eosinophilic myocarditis, in which experimental autoimmune myocarditis (EAM) is induced in IFNγ^-/- IL-17A^-/- mice. Two conditions are necessary for efficient eosinophil trafficking to the heart: high eotaxin (CCL11, CCL24) expression in the heart and expression of the eotaxin receptor CCR3 by eosinophils. We identified cardiac fibroblasts as the source of CCL11 in the heart interstitium. CCL24 is produced by F4/80⁺ macrophages localized at inflammatory foci in the heart. Expression of CCL11 and CCL24 is controlled by Th2 cytokines, IL-4 and IL-13. To determine the relevance of this pathway in humans, we analyzed endomyocardial biopsy samples from myocarditis patients. Expression of CCL11 and CCL26 was significantly increased in eosinophilic myocarditis compared to chronic lymphocytic myocarditis and positively correlated with the number of eosinophils. Thus, eosinophil trafficking to the heart is dependent on the eotaxin-CCR3 pathway in a mouse model of EAM and associated with cardiac eotaxin expression in patients with eosinophilic myocarditis. Blocking this pathway may prevent eosinophil-mediated cardiac damage.

Natural killer cells limit cardiac inflammation and fibrosis by halting eosinophil infiltration

Myocarditis is a leading cause of sudden cardiac failure in young adults. Natural killer (NK) cells, a subset of the innate lymphoid cell compartment, are protective in viral myocarditis. Herein, we demonstrated that these protective qualities extend to suppressing autoimmune inflammation. Experimental autoimmune myocarditis (EAM) was initiated in BALB/c mice by immunization with myocarditogenic peptide. During EAM, activated cardiac NK cells secreted interferon γ, perforin, and granzyme B, and expressed CD69, tumor necrosis factor-related apoptosis-inducing ligand treatment, and CD27 on their cell surfaces. The depletion of NK cells during EAM with anti-asialo GM1 antibody significantly increased myocarditis severity, and was accompanied by elevated fibrosis and a 10-fold increase in the percentage of cardiac-infiltrating eosinophils. The resultant influx of eosinophils to the heart was directly responsible for the increased disease severity in the absence of NK cells, because treatment with polyclonal antibody asialogangloside GM-1 did not augment myocarditis severity in eosinophil-deficient ΔdoubleGATA1 mice. We demonstrate that NK cells limit eosinophilic infiltration both indirectly, through altering eosinophil-related chemokine production by cardiac fibroblasts, and directly, by inducing eosinophil apoptosis in vitro. Altogether, we define a new pathway of eosinophilic regulation through interactions with NK cells.

Unresolved issues in theories of autoimmune disease using myocarditis as a framework

Many theories of autoimmune disease have been proposed since the discovery that the immune system can attack the body. These theories include the hidden or cryptic antigen theory, modified antigen theory, T cell bypass, T cell-B cell mismatch, epitope spread or drift, the bystander effect, molecular mimicry, anti-idiotype theory, antigenic complementarity, and dual-affinity T cell receptors. We critically review these theories and relevant mathematical models as they apply to autoimmune myocarditis. All theories share the common assumption that autoimmune diseases are triggered by environmental factors such as infections or chemical exposure. Most, but not all, theories and mathematical models are unifactorial assuming single-agent causation of disease. Experimental and clinical evidence and mathematical models exist to support some aspects of most theories, but evidence/models that support one theory almost invariably supports other theories as well. More importantly, every theory (and every model) lacks the ability to account for some key autoimmune disease phenomena such as the fundamental roles of innate immunity, sex differences in disease susceptibility, the necessity for adjuvants in experimental animal models, and the often paradoxical effect of exposure timing and dose on disease induction. We argue that a more comprehensive and integrated theory of autoimmunity associated with new mathematical models is needed and suggest specific experimental and clinical tests for each major theory that might help to clarify how they relate to clinical disease and reveal how theories are related.

IL-33 is an unconventional Alarmin that stimulates IL-2 secretion by dendritic cells to selectively expand IL-33R/ST2+ regulatory T cells

IL-33 is a recently characterized IL-1 family member that is proposed to function as an alarmin, or endogenous signal of cellular damage, as well as act as a pleiotropic cytokine. The ability of IL-33 to potentiate both Th1 and Th2 immunity supports its role in pathogen clearance and disease immunopathology. Yet, IL-33 restrains experimental colitis and transplant rejection by expanding regulatory T cells (Treg) via an undefined mechanism. We sought to determine the influence of IL-33 on hematopoietic cells that drives Treg expansion and underlies the therapeutic benefit of IL-33 administration. In this study, we identify a feedback loop in which conventional mouse CD11c(+) dendritic cells (DC) stimulated by IL-33 secrete IL-2 to selectively expand IL-33R(ST2(+))- suppressive CD4(+)Foxp3(+) Treg. Interestingly, this occurs in the absence of classical DC maturation, and DC-derived (innate) IL-2 increases ST2 expression on both DC and interacting Treg. ST2(+) Treg represent an activated subset of Foxp3(+) cells, demonstrated to be ICOS(high)CD44(high) compared with their ST2(-) counterparts. Furthermore, although studies have shown that IL-33-exposed DC promote Th2 responses, we reveal that ST2(+) DC are required for IL-33-mediated in vitro and in vivo Treg expansion. Thus, we have uncovered a relationship between IL-33 and innate IL-2 that promotes the selective expansion of ST2(+) Treg over non-Treg. These findings identify a novel regulatory pathway driven by IL-33 in immune cells that may be harnessed for therapeutic benefit or for robust expansion of Treg in vitro and in vivo.

Soluble ST2 and interleukin-33 levels in coronary artery disease: relation to disease activity and adverse outcome

Objectives

ST2 is a receptor for interleukin (IL)-33. We investigated an association of soluble ST2 (sST2) and IL-33 serum levels with different clinical stages of coronary artery disease. We assessed the predictive value of sST2 and IL-33 in patients with stable angina, non-ST elevation myocardial infarction (NSTEMI) and ST elevation myocardial infarction (STEMI).

Methods

We included 373 patients of whom 178 had stable angina, 97 had NSTEMI, and 98 had STEMI. Patients were followed for a mean of 43 months. The control group consisted of 65 individuals without significant stenosis on coronary angiography. Serum levels of sST2 and IL-33 were measured by ELISAs.

Results

sST2 levels were significantly increased in patients with STEMI as compared to patients with NSTEMI and stable angina as well as with controls. IL-33 levels did not differ between the four groups. During follow-up, 37 (10%) patients died and the combined endpoint (all cause death, MI and rehospitalisation for cardiac causes) occurred in 66 (17.6%) patients. sST2 serum levels significantly predicted mortality in the total cohort. When patients were stratified according to their clinical presentation, the highest quintile of sST2 significantly predicted mortality in patients with STEMI, but not with NSTEMI or stable coronary artery disease. sST2 was a significant predictor for the combined endpoint in STEMI patients and in patients with stable angina. Serum levels of IL-33 were not associated with clinical outcome in the total cohort, but the highest quintile of IL-33 predicted mortality in patients with STEMI.

Conclusions

Serum levels of sST2 are increased in patients with acute coronary syndromes as compared to levels in patients with stable coronary artery disease and in individuals without coronary artery disease. sST2 and IL-33 were associated with mortality in patients with STEMI but not in patients with NSTEMI or stable angina.

Cardiomyocyte-specific transforming growth factor β suppression blocks neutrophil infiltration, augments multiple cytoprotective cascades, and reduces early mortality after myocardial infarction

RATIONALE

Wound healing after myocardial infarction involves a highly regulated inflammatory response that is initiated by the appearance of neutrophils to clear out dead cells and matrix debris. Neutrophil infiltration is controlled by multiple secreted factors, including the master regulator transforming growth factor β (TGFβ). Broad inhibition of TGFβ early postinfarction has worsened post-myocardial infarction remodeling; however, this signaling displays potent cell specificity, and targeted suppression particularly in the myocyte could be beneficial.

OBJECTIVE

Our aims were to test the hypothesis that targeted suppression of myocyte TGFβ signaling ameliorates postinfarct remodeling and inflammatory modulation and to identify mechanisms by which this may be achieved.

METHODS AND RESULTS

Mice with TGFβ receptor-coupled signaling genetically suppressed only in cardiac myocytes (conditional TGFβ receptor 1 or 2 knockout) displayed marked declines in neutrophil recruitment and accompanying metalloproteinase 9 activation after infarction and were protected against early-onset mortality due to wall rupture. This is a cell-specific effect, because broader inhibition of TGFβ signaling led to 100% early mortality due to rupture. Rather than by altering fibrosis or reducing the generation of proinflammatory cytokines/chemokines, myocyte-selective TGFβ inhibition augmented the synthesis of a constellation of highly protective cardiokines. These included thrombospondin 4 with associated endoplasmic reticulum stress responses, interleukin-33, follistatin-like 1, and growth and differentiation factor 15, which is an inhibitor of neutrophil integrin activation and tissue migration.

CONCLUSIONS

These data reveal a novel role of myocyte TGFβ signaling as a potent regulator of protective cardiokine and neutrophil-mediated infarct remodeling.

IL-33/ST2 pathway and classical cytokines in end-stage heart failure patients submitted to left ventricular assist device support: a paradoxic role for inflammatory mediators?

Background. Inflammation is a critical process contributing to heart failure (HF). We hypothesized that IL-33/ST2 pathway, a new mechanism regulated during cardiac stress, may be involved in the functional worsening of end-stage HF patients, candidates for left ventricular assist device (LVAD) implantation, and potentially responsible for their outcome. Methods. IL-33, ST2, and conventional cytokines (IL-6, IL-8, and TNF-α) were determined in cardiac biopsies and plasma of 22 patients submitted to LVAD implantation (pre-LVAD) and compared with (1) control stable chronic HF patients on medical therapy at the moment of heart transplantation without prior circulatory support (HT); (2) patients supported by LVAD at the moment of LVAD weaning (post-LVAD). Results. Cardiac expression of ST2/IL-33 and cytokines was lower in the pre-LVAD than in the HT group. LVAD determined an increase of inflammatory mediators comparable to levels of the HT group. Only ST2 correlated with outcome indices after LVAD implantation. Conclusions. IL-33/ST2 and traditional cytokines were involved in decline of cardiac function of ESHF patients as well as in hemodynamic recovery induced by LVAD. IL-33/ST2 pathway was also associated to severity of clinical course. Thus, a better understanding of inflammation is the key to achieving more favorable outcome by new specific therapies.

Fatal eosinophilic myocarditis develops in the absence of IFN-γ and IL-17A

CD4(+) T cells play a central role in inflammatory heart disease, implicating a cytokine product associated with Th cell effector function as a necessary mediator of this pathophysiology. IFN-γ-deficient mice developed severe experimental autoimmune myocarditis (EAM), in which mice are immunized with cardiac myosin peptide, whereas IL-17A-deficient mice were protected from progression to dilated cardiomyopathy. We generated IFN-γ(-/-)IL-17A(-/-) mice to assess whether IL-17 signaling was responsible for the severe EAM of IFN-γ(-/-) mice. Surprisingly, IFN-γ(-/-)IL-17A(-/-) mice developed a rapidly fatal EAM. Eosinophils constituted a third of infiltrating leukocytes, qualifying this disease as eosinophilic myocarditis. We found increased cardiac production of CCL11/eotaxin, as well as Th2 deviation, among heart-infiltrating CD4(+) cells. Ablation of eosinophil development improved survival of IFN-γ(-/-)IL-17A(-/-) mice, demonstrating the necessity of eosinophils in fatal heart failure. The severe and rapidly fatal autoimmune inflammation that developed in the combined absence of IFN-γ and IL-17A constitutes a novel model of eosinophilic heart disease in humans. This is also, to our knowledge, the first demonstration that eosinophils have the capacity to act as necessary mediators of morbidity in an autoimmune process.

Control of inflammatory heart disease by CD4+ T cells

This review focuses on autoimmune myocarditis and its sequela, inflammatory dilated cardiomyopathy (DCMI), and the inflammatory and immune mechanisms underlying the pathogenesis of these diseases. Several mouse models of myocarditis and DCMI have improved our knowledge of the pathogenesis of these diseases, informing more general problems of cardiac remodeling and heart failure. CD4(+) T cells are critical in driving the pathogenesis of myocarditis. We discuss in detail the role of T helper cell subtypes in the pathogenesis of myocarditis, the biology of T cell-derived effector cytokines, and the participation of other leukocytic effectors in mediating disease pathophysiology. We discuss interactions between these subsets in both suppressive and collaborative fashions. These findings indicate that cardiac inflammatory disease, and autoimmunity in general, may be more diverse in divergent effector mechanisms than has previously been appreciated.

Sex and gender differences in myocarditis and dilated cardiomyopathy

Heart failure due to nonischemic dilated cardiomyopathy (DCM) contributes significantly to the global burden of cardiovascular disease. Myocarditis is, in turn, a major cause of acute DCM in both men and women. However, recent clinical and experimental evidence suggests that the pathogenesis and prognosis of DCM differ between the sexes. This seminar provides a contemporary perspective on the immune mediators of myocarditis, including interdependent elements of the innate and adaptive immune response. The heart's acute response to injury is influenced by sex hormones that appear to determine the subsequent risk of chronic DCM. Preliminary data suggest additional genetic variations may account for some of the differences in epidemiology, left ventricular recovery, and survival between men and women. We highlight the gaps in our knowledge regarding the management of women with acute DCM and discuss emerging therapies, including bromocriptine for the treatment of peripartum cardiomyopathy.

Implications for Interleukin-33 in solid organ transplantation

Interleukin(IL)-33 is a member of the IL-1 cytokine family that has been attributed T helper (Th) type 2 immunity-promoting capacity. However, new studies indicate that IL-33 is a multifunctional protein that acts as transcriptional/signaling repressor, functions as an alarmin alerting the immune system to necrosis, as well as serves as a cytokine that targets cells expressing ST2, the IL-33 receptor. Interestingly, IL-33 is also emerging as a pleiotropic cytokine. Depending on the innate or adaptive immune cells targeted by IL-33, it can not only promote type 2, but also IFN-γ dominated type 1 immunity. In addition, IL-33 expands regulatory T cells. In this review, we assimilate the current knowledge of IL-33 immunobiology and discuss how IL-33 may mediate such diverse roles in the immune response to pathogens and development of immune-mediated pathologies. The function of IL-33 in shaping alloimmune responses to transplanted organs is poorly explored, but a particularly beneficial role of IL-33 in experimental heart transplant models is summarized. Finally, given the implication of IL-33 in pathologies of the lung and intestine, we discuss how IL-33 may contribute to the comparatively poor outcomes following transplantation of these two organs.

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.

TLR3 deficiency induces chronic inflammatory cardiomyopathy in resistant mice following coxsackievirus B3 infection: role for IL-4

Recent findings indicate that TLR3 polymorphisms increase susceptibility to enteroviral myocarditis and inflammatory dilated cardiomyopathy (iDCM) in patients. TLR3 signaling has been found to inhibit coxsackievirus B3 (CVB3) replication and acute myocarditis in mouse models, but its role in the progression from myocarditis to iDCM has not been previously investigated. In this study we found that TLR3 deficiency increased acute (P = 5.9 × 10(-9)) and chronic (P = 6.0 × 10(-7)) myocarditis compared with WT B6.129, a mouse strain that is resistant to chronic myocarditis and iDCM. Using left ventricular in vivo hemodynamic assessment, we found that TLR3-deficient mice developed progressively worse chronic cardiomyopathy. TLR3 deficiency significantly increased viral replication in the heart during acute myocarditis from day 3 through day 12 after infection, but infectious virus was not detected in the heart during chronic disease. TLR3 deficiency increased cytokines associated with a T helper (Th)2 response, including IL-4 (P = 0.03), IL-10 (P = 0.008), IL-13 (P = 0.002), and TGF-β(1) (P = 0.005), and induced a shift to an immunoregulatory phenotype in the heart. However, IL-4-deficient mice had improved heart function during acute CVB3 myocarditis by echocardiography and in vivo hemodynamic assessment compared with wild-type mice, indicating that IL-4 impairs cardiac function during myocarditis. IL-4 deficiency increased regulatory T-cell and macrophage populations, including FoxP3(+) T cells (P = 0.005) and Tim-3(+) macrophages (P = 0.004). Thus, TLR3 prevents the progression from myocarditis to iDCM following CVB3 infection by reducing acute viral replication and IL-4 levels in the heart.