Blockade of interleukin-17A protects against coxsackievirus B3-induced myocarditis by increasing COX-2/PGE2 production in the heart

Prostaglandin E2 and myocarditis; friend or foe?

This review article summarizes the role of prostaglandin E2 (PGE2) and its receptors (EP1-EP4) as it relates to the inflammatory cardiomyopathy, myocarditis. During the COVID-19 pandemic, the onset of myocarditis in a subset of patients prompted a debate on the use of nonsteroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, which act to inhibit the actions of prostaglandins. This review aims to further understanding of the role of PGE2 in the pathogenesis or protection of the myocardium in myocarditis. Inflammatory cardiomyopathies encompass a broad spectrum of disorders, all characterized by cardiac inflammation. Therefore, for the purpose of this review, the authors have placed particular emphasis on etiologies of myocarditis where effects of PGE2 have been documented.

The role of IL17 and IL17RA polymorphisms in lethal pandemic acute viral pneumonia (Influenza A virus H1N1 subtype)

Background

The cytokines play an essential role in acute inflammatory processes, and the IL-17 may be responsible for ambiguous aspects, and the correlation with genetic polymorphisms could improve the search for this critical biomarker. Thus, this study aimed to evaluate the IL-17A and IL-17RA tissue expression and the polymorphisms that codified these proteins in a population that died of pandemic Influenza A virus H1N1 subtype compared to a non-pandemic Influenza virus population.

Methods

Necropsy lung samples immunohistochemistry was performed to assess the presence of IL-17A and IL-17RA in the pulmonary tissue. Eight single nucleotide polymorphisms were genotyped using TaqMan® technology.

Results

The Influenza A H1N1 pandemic group had higher tissue expression of IL-17A, higher neutrophil recruitment and shorter survival time between admission and death. Three single nucleotide polymorphisms conferred risk for pandemic influenza A H1N1, the AA genotype of rs3819025 G/A, the CC genotype of rs2241044 A/C, and the TT genotype of rs 2,241,043 C/T.

Conclusions

One IL17A polymorphism (rs381905) and two IL17RA polymorphisms (rs2241044 and rs2241043) represented biomarkers of worse prognosis in the population infected with pandemic influenza A H1N1. The greater tissue expression of IL-17A shows a Th17 polarization and highlights the aggressiveness of the pandemic influenza virus with its duality in the protection and pathogenesis of the pulmonary infectious process.

Candida albicans-enteric viral interactions-The prostaglandin E2 connection and host immune responses

The human microbiome comprises trillions of microorganisms residing within different mucosal cavities and across the body surface. The gut microbiota modulates host susceptibility to viral infections in several ways, and microbial interkingdom interactions increase viral infectivity within the gut. Candida albicans, a frequently encountered fungal species in the gut, produces highly structured biofilms and eicosanoids such as prostaglandin E₂ (PGE₂), which aid in viral protection and replication. These biofilms encompass viruses and provide a shield from antiviral drugs or the immune system. PGE₂ is a key modulator of active inflammation with the potential to regulate interferon signaling upon microbial invasion or viral infections. In this review, we raise the perspective of gut interkingdom interactions involving C. albicans and enteric viruses, with a special focus on biofilms, PGE₂, and viral replication. Ultimately, we discuss the possible implications of C. albicans-enteric virus associations on host immune responses, particularly the interferon signaling pathway.

Dissecting the cellular landscape and transcriptome network in viral myocarditis by single-cell RNA sequencing

Coxsackievirus B3 (CVB3)-induced myocarditis is commonly employed to study viral pathogenesis in mice. Chronically affected mice may develop dilated cardiomyopathy, which may involve the mediation of immune and nonimmune cells. To dissect this complexity, we performed single-cell RNA sequencing on heart cells from healthy and myocarditic mice, leading us to note significant proportions of myeloid cells, T cells, and fibroblasts. Although the transcriptomes of myeloid cells were mainly of M2 phenotype, the Th17 cells, CTLs, and Treg cells had signatures critical for cytotoxic functions. Fibroblasts were heterogeneous expressing genes important in fibrosis and regulation of inflammation and immune responses. The intercellular communication networks revealed unique interactions and signaling pathways in the cardiac cellulome, whereas myeloid cells and T cells had upregulated unique transcription factors modulating cardiac remodeling functions. Together, our data suggest that M2 cells, T cells, and fibroblasts may cooperatively or independently participate in the pathogenesis of viral myocarditis.

Neutralization of interleukin-38 exacerbates coxsackievirus B3-induced acute myocarditis in mice

Background

Interleukin (IL)-38, a novel member of the IL-1 family, has been reported to be involved in several diseases associated with viral infection. However, the expression and functional role of IL-38 in acute viral myocarditis (AVMC) have not been investigated.

Methods

Male BALB/c mice were treated with intraperitoneal (i.p.) injection of coxsackievirus B3 (CVB3) for establishing AVMC models. On day 7 post-injection, the expression of IL-38 and IL-36R (IL-36 receptor) were measured. Mice were then treated with i.p. injection of mouse Anti-IL-38 Antibodies (Abs) for neutralization of IL-38. The survival, bodyweight loss, cardiac function, and myocarditis severity of mice were recorded. The percentages of splenic Th1 and Th17 cells, the expression levels of Th1/Th17-related master transcription factors (T-bet and RORγt) and cytokines were determined by flow cytometry, RT-qPCR, and ELISA, respectively. Cardiac viral replication was further detected.

Results

The mRNA and protein expression levels of IL-38 in myocardium and serum, as well as cardiac IL-36R mRNA levels were significantly elevated in mice with AVMC. Increased IL-38 levels were negatively correlated with the severity of AVMC. Neutralization of IL-38 exacerbated CVB3-induced AVMC, as verified by the lower survival rate, impaired cardiac function, continuous bodyweight loss, and higher values of HW/BW and cardiac pathological scores. In addition, neutralization of IL-38 suppressed Th1 cells differentiation while promoted Th17 cells differentiation, accompanied by decreased T-bet mRNA expression and increased RORγt expression. Down-regulation of IFN-γ and up-regulation of IL-17, TNF-α, and IL-6 mRNA and protein expression levels in myocardium and serum were also observed in the IL-38 neutralization group. Furthermore, neutralization of IL-38 markedly promoted cardiac viral replication.

Conclusions

Neutralization of IL-38 exacerbates CVB3-induced AVMC in mice, which may be attributable to the imbalance of Th1/Th17 cells and increased CVB3 replication. Thus, IL-38 can be considered as a potential therapeutic target for AVMC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01687-w.

Lipid droplets and lipid mediators in viral infection and immunity

Lipid droplets (LDs) contribute to key pathways important for the physiology and pathophysiology of cells. In a homeostatic view, LDs regulate the storage of neutral lipids, protein sequestration, removal of toxic lipids and cellular communication; however, recent advancements in the field show these organelles as essential for various cellular stress response mechanisms, including inflammation and immunity, with LDs acting as hubs that integrate metabolic and inflammatory processes. The accumulation of LDs has become a hallmark of infection, and is often thought to be virally driven; however, recent evidence is pointing to a role for the upregulation of LDs in the production of a successful immune response to viral infection. The fatty acids housed in LDs are also gaining interest due to the role that these lipid species play during viral infection, and their link to the synthesis of bioactive lipid mediators that have been found to have a very complex role in viral infection. This review explores the role of LDs and their subsequent lipid mediators during viral infections and poses a paradigm shift in thinking in the field, whereby LDs may play pivotal roles in protecting the host against viral infection.

Immunomodulatory Effects of Rhinovirus and Enterovirus Infections During the First Year of Life

Early childhood infections have been implicated in the development of immune-mediated diseases, such as allergies, asthma, and type 1 diabetes. We set out to investigate the immunomodulatory effects of early viral infections experienced before the age of one year on the peripheral regulatory T cell population (Treg) and circulating cytokines in a birth-cohort study of Estonian and Finnish infants. We show here a temporal association of virus infection with the expression of FOXP3 in regulatory T cells. Infants with rhinovirus infection during the preceding 30 days had a higher FOXP3 expression in Treg cells and decreased levels of several cytokines related to Th1 and Th2 responses in comparison to the children without infections. In contrast, FOXP3 expression was significantly decreased in highly activated (CD4+CD127-/loCD25+FOXP3high) regulatory T cells (TregFOXP3high) in the infants who had enterovirus infection during the preceding 30 or 60 days. After enterovirus infections, the cytokine profile showed an upregulation of Th1- and Th17-related cytokines and a decreased activation of CCL22, which is a chemokine derived from dendritic cells and associated with Th2 deviation. Our results reveal that immunoregulatory mechanisms are up-regulated after rhinovirus infections, while enterovirus infections are associated with activation of proinflammatory pathways and decreased immune regulation.

Advancement of Mechanisms of Coxsackie Virus B3-Induced Myocarditis Pathogenesis and the Potential Therapeutic Targets

Viral myocarditis is a cardiac disease caused by Group B Coxsackie virus of Enterovirus genus in the Picorna viridae family. It causes heart failure in children, young and adults. Ten Percent (10%) of acute heart failure and 12% of sudden deaths in young and adults who are less than 40 years is due to this viral myocarditis. If treatment action is not taken earlier, the viral disease can develop into chronic myocarditis and Dilated Cardiomyopathy which lead to congestive heart failure. And these eventually result in a reduced cardiac function which finally brings the victim to death. The only treatment option of the disease is heart transplantation once the acute stage of disease develops to chronic and Dilated Cardiomyopathy. Currently, there is a limitation in daily clinical treatments and even some available treatment options are ineffective. Therefore, focusing on search for treatment options through investigation is imperative. Recent studies have reported that biological molecules show a promising role. But their mechanism of pathogenesis is still unclear. A detailed study on identifying the role of biological molecules involved in Coxsackie B3 virus induced myocarditis and their mechanisms of pathogenesis; compiling and disseminating the findings of the investigation to the scientific communities contribute one step forward to the solution. Therefore, this review is aimed at compiling information from findings of current studies on the potential therapeutic role of micro RNA, cytokines and chemokines on the mechanism of pathogenesis of Coxsackie virus B3- induced myocarditis to give brief information for scholars to conduct a detailed study in the area.

CARD9 mediates T cell inflammatory response in Coxsackievirus B3-induced acute myocarditis

Cardiac inflammation in Coxsackievirus B3 (CVB3)-induced myocarditis is a consequence of viral-related cardiac injury and immune response. Caspase-associated recruitment domain 9 (CARD9) is a critical adaptor protein involved in transduction of signals from various innate pattern recognition receptors. In this study, the role of CARD9 in acute viral myocarditis was evaluated. CARD9^-/- and C57BL/6 mice were infected with CVB3. On day 7 postinfection, myocardial tissue and blood samples were collected and examined. After CARD9 knockout, mRNA and protein levels of transforming growth factor-β(TGF-β), interleukin-17A(IL-17A), and CARD domain of B-cell CLL/lymphoma 10(BCL-10) in the myocardium were markedly lower in CARD9^-/- mice than in C57BL/6 mice with CVB3-induced viral myocarditis. This trend was similar for the pathological scores for inflammation and serum levels of cytokines interleukin-6(IL-6), interleukin-10(IL-10), interferon -γ(IFN-γ), TGF-β, and IL-17A. These results suggest that the CARD9-mediated secretion of pro-inflammatory cytokines plays an important role in the immune response to acute viral myocarditis.

Pathogenic Role of an IL-23/γδT17/Neutrophil Axis in Coxsackievirus B3-Induced Pancreatitis

Coxsackievirus B is a common cause of viral myocarditis and pancreatitis. IL-17A is intensively involved in the pathogenesis of viral myocarditis. Whether IL-17A plays a role in Coxsackievirus B-induced pancreatitis, characterized by acinar cell destruction and immune infiltration, remains largely unknown. We found a significant, but transient, increase of IL-17A expression and γδT influx in the pancreas of C57BL/6J mice within 3 d following CVB3 infection. The pancreatic IL-17A was mainly produced by Vγ4 γδ T cells, to a lesser extent by CD4⁺ Th17 cells. IL-17A^-/- and TCRδ^-/- mice both reduced their susceptibility to CVB3 infection and pancreatitis severity when compared with the wild-type mice, without altering viral load. mAb depletion of Vγ4γδ T cells significantly improved mice survival and pancreatic pathology via decreasing Th17 expansion and neutrophil influx into the pancreas compared with isotype-treated mice. Transfer of Vγ4γδ T cells from wild-type, but not IL-17^-/-, mice reconstituted TCRδ^-/- mice to produce IL-17 and develop pancreatitis to the level of wild-type mice during CVB3 infection, indicating γδ T IL-17A is required for the onset of viral pancreatitis. IL-23 was robustly induced in the pancreas within the first day of infection. Administration of exogenous rIL-23 to mice increased CVB3 pancreatitis through in vivo expansion of IL-17⁺γδT17 cells at 12 h postinfection. Our findings reveal a key pathogenic role for early-activated γδT17 cells in viral pancreatitis via promoting neutrophil infiltration and Th17 induction. This IL-23/γδT17/neutrophil axis is critically involved in the onset of CVB3 pancreatitis and represents a potential treating target for the disease.

Progranulin ameliorates coxsackievirus-B3-induced viral myocarditis by downregulating Th1 and Th17 cells

Viral myocarditis, which is caused by Coxsackievirus B3 (CVB3) infection, is a leading reason of sudden cardiac death in young adults. Progranulin (PGRN), a pleiotropic growth factor, has been shown to exert anti-inflammatory function in a variety of inflammatory diseases. However, the expression and function of PGRN in the pathogenesis of viral myocarditis remain largely unknown. In this study, we found that PGRN levels in plasma and cardiac tissues were significantly upregulated post CVB3 infection, and negative correlated with disease severity. PGRN deficiency significantly exacerbated, whereas recombinant PGRN treatment attenuated CVB3-induced myocarditis in mice. PGRN downregulated Th1 and Th17 cell responses and cytokine production in vitro and in vivo, whereas its effect on viral myocarditis was Treg cell independent. Furthermore, PGRN regulated Th1 and Th17 cells differentiation through inhibition of the JAK/STAT pathway. Therefore, our findings reveal a critical role for PGRN in reducing CVB3-induced myocarditis and suggest that PGRN maybe a novel therapeutic treatment for viral myocarditis.

Role of gene polymorphisms/haplotypes and serum levels of interleukin-17A in susceptibility to viral myocarditis

Interleukin-17A (IL-17A) has been implicated in the pathogenesis of viral myocarditis (VMC). However, the role of IL-17A polymorphisms in susceptibility to VMC has not been reported to date. The aim of this study was to explore the association between IL-17A variants as well as serum IL-17 levels with VMC. Three single-nucleotide polymorphisms (SNPs) (rs2275913, rs3819025, and rs3748067) were analyzed by the polymerase chain reaction-restriction fragment length polymorphism method in 236 VMC patients and 259 controls from China. Serum IL-17A levels were measured by enzyme-linked immunosorbent assay kits. Multivariable logistic regression analysis that the rs2275913 AA genotype and the haplotype -197A/+45G/+1249G (AGG) were associated with an increased risk of VMC (all P < 0.05). Consistent with these findings, the rs2275913 AA genotype was linked to higher serum IL-17A compared to GG/AG genotype (all P < 0.001). We observed no associations between the other two SNPs and risk of VMC. Serum IL-17A levels were significantly higher in the VMC group than controls (P < 0.001) and gradually increased with the increase of New York Heart Association grade in VMC patients (P < 0.05). Spearman correlation test revealed that the serum IL-17A level was correlated with the cardiac damage and left ventricular systolic functions among VMC patients (all P < 0.05). Our study reveals that IL-17A expression may contribute to the development and severity of VMC. The SNP rs2275913 in the IL-17A gene might exert influence on susceptibility to VMC via linking with the serum IL-17A level.

Prostaglandin E2 As a Modulator of Viral Infections

Viral infections are a major cause of infectious diseases worldwide. Inflammation and the immune system are the major host defenses against these viral infection. Prostaglandin E2 (PGE2), an eicosanoid generated by cyclooxygenases, has been shown to modulate inflammation and the immune system by regulating the expression/concentration of cytokines. The effect of PGE2 on viral infection and replication is cell type- and virus-family-dependent. The host immune system can be modulated by PGE2, with regards to immunosuppression, inhibition of nitrogen oxide (NO) production, inhibition of interferon (IFN) and apoptotic pathways, and inhibition of viral receptor expression. Furthermore, PGE2 can play a role in viral infection directly by increasing the production and release of virions, inhibiting viral binding and replication, and/or stimulating viral gene expression. PGE2 may also have a regulatory role in the induction of autoimmunity and in signaling via Toll-like receptors. In this review the known effects of PGE2 on the pathogenesis of various infections caused by herpes simplex virus, rotavirus, influenza A virus and human immunodeficiency virus as well the therapeutic potential of PGE2 are discussed.

Valproic acid ameliorates coxsackievirus-B3-induced viral myocarditis by modulating Th17/Treg imbalance

Background

Viral myocarditis, which is often caused by coxsackievirus B3 (CVB3), is a serious clinical disorder characterized by excessive myocardial inflammation. Valproic acid (VPA) is described as a histone deacetylase inhibitor that has anti-inflammatory effects in several inflammatory diseases. However, the role and the detailed mechanism of VPA in viral myocarditis remain unclear.

Methods

Experimental CVB3-induced myocarditis was induced in mice by intraperitoneally (i.p.) infected with CVB3. VPA was i.p. administered from day 0 to day 7. The survival, body weight loss, and myocarditis severity of mice were recorded. Th17 and Treg cells in spleen were analyzed by flow cytometry. Th17/Treg cell-related cytokine expressions were quantified by ELISA. The effect of VPA on Th17 and Treg cells differentiation was examined in vitro and in vivo.

Results

Administration of VPA significantly attenuated the clinical severity of myocarditis, and the overall mortality from CVB3-induced myocarditis. The infiltration of Th17 and Treg cells, as well as the serum level of related cytokines (IL-17A and IL-10), were increased in CVB3 infected mice. In addition, VPA decreased the percentage of splenic Th17 cells while increased the percentage of Treg cells. Moreover, VPA downregulated the expression of IL-17A and upregulated IL-10 in serum and heart tissues of CVB3 infected mice. Additionally, VPA directly inhibited the differentiation of Th17 cells and promoted both the differentiation and suppressive function of Treg cells in vitro and in vivo.

Conclusions

Our results suggest that VPA may thus be a promising strategy in the therapy of viral myocarditis.

Common variants in IL-17A/IL-17RA axis contribute to predisposition to and progression of congestive heart failure

Heart failure is characterized by immune activation leading to production and release of proinflammatory cytokines. Interleukin 17A (IL-17A) is a proinflammatory cytokine and multiple lines of evidence from animal and human studies suggest crucial roles of IL-17A in heart failure. Therefore, we investigated whether common polymorphisms of genes IL17A and IL17RA (coding interleukin 17 receptor A) contribute to genetic predisposition to heart failure and adverse clinical outcomes associated with it.A total of 1713 adult patients with congestive heart failure and 1713 age- and sex-matched controls were genotyped for promoter single nucleotide polymorphisms (SNPs), rs2275913 and rs8193037 in IL17A and rs4819554 in IL17RA, to assess the relationship between individual SNPs and the risk of congestive heart failure. Results showed that rs8193037 in IL17A was associated with the risk of congestive heart failure (odds ratio [OR] = 0.76; 95% confidence interval [CI] 0.63-0.90, adjusted P = 0.002) after adjustment for multiple cardiovascular risk factors including age, sex, smoking status, diabetes, hypertension, and dyslipidemia. This association was evident in both ischemic and nonischemic heart failure (P = 0.005 and P = 0.05, respectively). Furthermore, prospective follow-up of 12.7 months for the occurrence of adverse clinical outcomes showed that rs4819554 in IL17RA was significantly associated with cardiovascular mortality (hazard ratio [HR] = 1.28; 95% CI = 1.02-1.59, adjusted P = 0.03) after adjustments for multiple cardiovascular risk factors and New York Heart Association functional class.This study demonstrated associations of rs8193037 in the promoter of IL17A with the risk of congestive heart failure, and of rs4819554 in the promoter of IL17RA with the risk of cardiovascular mortality in patients with congestive heart failure. These data lend further support to the notion that immune activation and genetic polymorphisms contribute to heart failure pathogenesis and progression.

Ethyl pyruvate attenuated coxsackievirus B3-induced acute viral myocarditis by suppression of HMGB1/RAGE/NF-ΚB pathway

Inflammation plays important roles in the pathogenesis of coxsackievirus B3 (CVB3)-induced acute viral myocarditis (AVMC). Ethyl pyruvate (EP) has been shown to be an anti-inflammatory agent. High mobility group box 1 (HMGB1)/receptor for advanced glycation end product (RAGE)/nuclear factor (NF)-ΚB pathway has close relation with inflammatory responses. Here, we investigated the effects of EP on CVB3-induced AVMC and potential mechanisms. The mice with AVMC were treated with EP (40 or 80 mg/kg/day) from day 5 to day 7 post-infection. EP significantly decreased the mortality of mice with AVMC. H&E staining and immunohistochemistry for HMGB1 demonstrated less inflammatory lesions and fewer abnormal location of HMGB1 in the hearts of AVMC mice receiving EP. Immuoblot showed that EP significantly inhibited the levels of HMGB1, RAGE, phospho(p)-NF-ΚB and p-I-ΚBα, and raised I-ΚBα expression in the hearts of AVMC mice. Furthermore, real-time PCR and Elisa displayed decreased levels of HMGB1, TNF-α, IL-1β, IL-17 and increased levels of IL-10 in the hearts and serum of AVMC mice treated with EP. Our findings suggest that EP protects against CVB3-induced AVMC that is associated with inhibition of HMGB1/RAGE/NF-ΚB pathway.

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

Overexpression of Fgl2 deteriorates the heart function of experimenta l autoimmune myocarditis rats

Studies have demonstrated that fibrinogen-like protein 2 (Fgl2) has been involved in immune and inflammatory responses which might contribute to the pathogenesis of immune-mediated diseases. Experimental autoimmune myocarditis (EAM) provided a model that mimics the pathophysiology of human giant cell myocarditis. We observed that the effect of Fgl2 overexpression on the heart function of autoimmune myocarditis rats using echocardiography and detected the level of inflammatory cytokines using enzyme-linked immunosorbent assay. Fgl2 overexpression decreased the heart function of EAM model rat, increased the inflammatory cell infiltrations, and increased the level of brain natriuretic peptide (BNP). Tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-17 (IL-17). These results indicate that Fgl2 is a potent target for the treatment of EAM. In conclusion, Fgl2 is a potent target to treat inflammatory dysfunctions of the heart.

The frequency of invariant natural killer T cells correlates with the severity of myocarditis

Invariant natural killer T cells (iNKT) perform different functions in different diseases. The cells were reported to protect myocarditis. However, the detail relationships between iNKT and Coxsackievirus B3 (CVB3)-induced myocarditis remain unclear. In order to investigate the correlation between the severity of CVB3-induced inflammation infiltration and the proportion of iNKT in the spleen and circulating blood, BALB/c mice were grouped into three groups according to the inflammation infiltration area of heart sections. The proportion of iNKT in CD3-positive cells in the spleen correlated negatively with the inflammation area (linear fit; R(2)=0.93) and virus capsid protein VP1 (linear fit; R(2)=0.84) in the myocardial tissue, while the proportion of iNKT in CD3-positive cells in the PBMC positively correlated with the inflammation area (linear fit; R(2)=0.91) and virus capsid protein VP1 (linear fit; R(2)=0.93) in the myocardial tissue. The results imply that iNKT might be used as a parameter for the diagnosis of myocarditis in clinical practice.

Autoimmunity in viral myocarditis

PURPOSE OF REVIEW

To review how autoimmunity is induced in viral myocarditis.

RECENT FINDINGS

Clinical and experimental myocarditis follows microbial infections, but autoimmunity to cardiac antigens leads to heart failure since infected myocytes are sparse and virus clearance is rapid. In mice, CD4+ T cells specific for cardiac alpha myosin heavy chain (αMYHC) cause myocarditis and mice tolerized to αMYHC are protected from virus challenge proving pathogenesis depends upon autoimmunity. Most importantly, multiple microbes share the same mimicking epitope with αMYHC. Serial infections with very different microbes could result in memory responses to the shared epitope leading to aggressive and severe heart failure. A similar phenomenon may explain autoimmune diseases with suspected infectious causes, where specific pathogens have not been identified. Production of the relevant cardiac epitope for antigen presentation requires more than myosin release from dead myocytes. Otherwise, myocarditis would commonly follow myocardial infarcts. The inherent nature of the innate immune response associated with viral infections in the heart is crucial to cardiac epitope expression.

SUMMARY

Antigenic mimicry between microbes and cardiac proteins causes autoimmunity in myocarditis. Characteristics of innate immunity associated with cardiac infection determine relevant epitope expression (cryptic epitopes).

Update on coxsackievirus B3 myocarditis

PURPOSE OF REVIEW

To present recent findings on the pathogenesis of coxsackievirus B3 (CVB3) myocarditis based on animal models, with a focus on the role of T helper (Th) immune responses in disease progression.

RECENT FINDINGS

Acute CVB3 myocarditis is known to be increased by Th1 immune responses, but recent findings indicate that Th1-type immunity protects against acute myocarditis by reducing viral replication and prevents the progression to chronic myocarditis and dilated cardiomyopathy (DCM) by inhibiting Th2 responses. Th2 responses reduce acute myocarditis by inhibiting Th1 responses via regulatory T cells and anti-inflammatory cytokines, but can be deleterious when they induce acute cardiac remodeling leading to chronic myocarditis/DCM. Th2-skewed immune responses allow resistant strains of mice to progress from myocarditis to DCM. In contrast, Th17 responses are elevated during acute and chronic myocarditis and have been found to contribute to cardiac remodeling and DCM.

SUMMARY

Recent data indicate that elevated Th2 and Th17 responses during acute CVB3 myocarditis are critical for the progression from myocarditis to DCM and heart failure because of their ability to induce cardiac remodeling. Th1 responses protect against CVB3 myocarditis by inhibiting Th2 responses and viral replication, but increase acute inflammation.