Enteroviruses and myocarditis: viral pathogenesis through replication, cytokine induction, and immunopathogenicity

Induction of antigen specific peripheral humoral tolerance to cardiac myosin does not prevent CB3-mediated autoimmune myocarditis

Chronic myocarditis often progresses to dilated cardiomyopathy resulting in heart failure or cardiac transplantation. Viral infection is the most common cause of myocarditis and coxsackie B viruses (CBV) are the most frequently cited etiologic agents associated with myocarditis and cardiomyopathy. Additionally, CBV infections of genetically susceptible mice induce autoimmune myocarditis resembling human disease, including the development of autoantibodies to cardiac myosin. Herein, we describe experiments in which peripheral tolerance to cardiac myosin was induced by administration of antigen-coupled antigen presenting cells. While the antibody response to cardiac myosin following CB3 infection was reduced, the viral induction of clinical autoimmune myocarditis was not affected. Additionally, viral replication was unaffected by the reduced humoral response to cardiac myosin. Therefore, the humoral response to cardiac myosin is not required for the development of autoimmunity following infection of NOD mice. This work demonstrates the difficulty in using antigen specific tolerance as a course of treatment to prevent multivalent autoimmune disorders.

Inhibition of coxsackievirus B3 replication by small interfering RNAs requires perfect sequence match in the central region of the viral positive strand

Coxsackievirus B3 (CVB3) is the most common causal agent of viral myocarditis, but existing drug therapies are of limited value. Application of small interfering RNA (siRNA) in knockdown of gene expression is an emerging technology in antiviral gene therapy. To investigate whether RNA interference (RNAi) can protect against CVB3 infection, we evaluated the effects of RNAi on viral replication in HeLa cells and murine cardiomyocytes by using five CVB3-specific siRNAs targeting distinct regions of the viral genome. The most effective one is siRNA-4, targeting the viral protease 2A, achieving a 92% inhibition of CVB3 replication. The specific RNAi effects could last at least 48 h, and cell viability assay revealed that 90% of siRNA-4-pretreated cells were still alive and lacked detectable viral protein expression 48 h postinfection. Moreover, administration of siRNAs after viral infection could also effectively inhibit viral replication, indicating its therapeutic potential. Further evaluation by combination found that no enhanced inhibitory effects were observed when siRNA-4 was cotransfected with each of the other four candidates. In mutational analysis of the mechanisms of siRNA action, we found that siRNA functions by targeting the positive strand of virus and requires a perfect sequence match in the central region of the target, but mismatches were more tolerated near the 3' end than the 5' end of the antisense strand. These findings reveal an effective target for CVB3 silencing and provide a new possibility for antiviral intervention.

Viruses as adjuvants for autoimmunity: evidence from Coxsackievirus-induced myocarditis

Adjuvants historically are considered to stimulate immune responses 'non-specifically'. Recently, a renewed understanding of the critical role of innate immunity in influencing the development of an adaptive immune response has led researchers to a better understanding of 'the adjuvant effect'. Although innate immune cells do not respond to specific antigenic epitopes on pathogens, they do produce restricted responses to particular classes of pathogens via pattern recognition receptors such as Toll-like receptors (TLR). Coxsackievirus infection was found to upregulate TLR4 on mast cells and macrophages immediately following infection. Although both susceptible and resistant mice produce a mixture of Th1 and Th2 cytokines, susceptible mice have increased levels of key proinflammatory cytokines, increased numbers of mast cells, and go on to develop chronic autoimmune heart disease. TLR4 signalling also increases acute myocarditis and proinflammatory cytokines in the heart. Many similarities are described in the pathogenesis of Coxsackievirus and the adjuvant-induced model of myocarditis including upregulation of particular TLRs and cytokines soon after inoculation. Recent findings suggest that mast cell activation by viruses or adjuvants may be important in initiating autoimmune disease.

Dual functions of murine gammadelta cells in inflammation and autoimmunity in coxsackievirus B3-induced myocarditis: role of Vgamma1+ and Vgamma4+ cells

Coxsackieviruses are a cause of clinical myocarditis. Both virus replication and host defense mechanisms, including virus-induced autoimmunity, mediate heart injury and cardiac dysfunction. Vgamma4+ cells kill infected cardiocytes and virus-specific CD4+ Th2 cells through Fas-dependent apoptosis and CD1d. The CD4+ Th1 response is necessary for activation of the autoimmune CD8+ T cells, which kill uninfected cardiocytes through perforin-dependent mechanisms.

Diabetes acceleration or prevention by a coxsackievirus B4 infection: critical requirements for both interleukin-4 and gamma interferon

Type 1 diabetes acceleration in nonobese diabetic (NOD) mice through coxsackievirus B4 (CVB4) infection requires a preexisting critical mass of autoreactive T cells in pancreatic islets, and in the absence of this insulitic threshold, CVB4 infection leads to long-term disease protection. To understand this acceleration and protection process, we challenged 8- and 12-week-old NOD mice containing a disruption in interleukin-4 (IL-4) or gamma interferon (IFN-gamma) genes (NOD IL-4-/- and NOD IFN-gamma-/-, respectively) with a diabetogenic, pancreatropic Edwards strain of CVB4. The elimination of IL-4 did not alter the rate of insulitis or diabetes development in NOD mice, while the elimination of IFN-gamma delayed these events several weeks. CVB4 infection in 8-week-old mice only significantly accelerated the onset of diabetes in a subset of standard, but not IL-4- or IFN-gamma-deficient, NOD mice. Long-term diabetes protection was established in standard NOD mice as well as in the NOD IFN-gamma-/- mice that did not rapidly develop disease following CVB4 infection at 8 weeks of age. When mice were infected at 12 weeks of age, the onset of diabetes was accelerated in NOD IL-4-/- mice, while neither acceleration nor long-term protection was elicited in NOD IFN-gamma-/- mice. No differences were observed in the kinetics of CVB4 clearance in pancreases from NOD, NOD IL-4-/-, and NOD IFN-gamma-/- mice. Collectively, these results suggest that at the insulitis threshold at which CVB4 infection can first accelerate the onset of diabetes in NOD mice, IL-4 as well as IFN-gamma contributes to this pathogenic process. The protective mechanism against diabetes elicited in NOD mice infected with CVB4 prior to the development of a critical threshold level of insulitis requires neither IL-4 nor IFN-gamma.

Caspase inhibition protects against reovirus-induced myocardial injury in vitro and in vivo

Viral myocarditis is a disease with a high morbidity and mortality. The pathogenesis of this disease remains poorly characterized, with components of both direct virus-mediated and secondary inflammatory and immune responses contributing to disease. Apoptosis has increasingly been viewed as an important mechanism of myocardial injury in noninfectious models of cardiac disease, including ischemia and failure. Using a reovirus murine model of viral myocarditis, we characterized and targeted apoptosis as a key mechanism of virus-associated myocardial injury in vitro and in vivo. We demonstrated caspase-3 activation, in conjunction with terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling and annexin binding, in cardiac myocytes after myocarditic viral infection in vitro. We also demonstrated a tight temporal and geographical correlation between caspase-3 activation, histologic injury, and viral load in cardiac tissue after myocarditic viral infection in vivo. Two pharmacologic agents that broadly inhibit caspase activity, Q-VD-OPH and Z-VAD(OMe)-FMK, effectively inhibited virus-induced cellular death in vitro. The inhibition of caspase activity in vivo by the use of pharmacologic agents as well as genetic manipulation reduced virus-induced myocardial injury by 40 to 60% and dramatically improved survival in infected caspase-3-deficient animals. This study indicates that apoptosis plays a critical role in mediating cardiac injury in the setting of viral myocarditis and is the first demonstration that caspase inhibition may serve as a novel therapeutic strategy for this devastating disease.

Cryptic epitope identified in rat and human cardiac myosin S2 region induces myocarditis in the Lewis rat

Myocarditis is a common cause of dilated cardiomyopathy leading to heart failure. Chronic stages of myocarditis may be initiated by autoimmune responses to exposed cardiac Ags after myocyte damage. Cardiac myosin, a heart autoantigen, induced experimental autoimmune myocarditis (EAM) in susceptible animals. Although cardiac myosin-induced myocarditis has been reported in Lewis rats, the main pathogenic epitope has not been identified. Using overlapping synthetic peptides of the S2 region of human cardiac myosin, we identified an amino acid sequence, S2-16 (residues 1052-1076), that induced severe myocarditis in Lewis rats. The myocarditic epitope was localized to a truncated S2-16 peptide (residues 1052-1073), which contained a sequence identical in human and rat cardiac myosin. The S2-16 peptide was not myocarditic for three other strains of rats, in which the lack of myocarditis was accompanied by the absence of strong S2-16-specific lymphocyte responses in vitro. For Lewis rats, S2-16 was characterized as a cryptic epitope of cardiac myosin because it did not recall lymphocyte and Ab responses after immunization with cardiac myosin. Lymphocytes from S2-16 immunized rats recognized not only S2-16, but also peptides in the S2-28 region. Furthermore, peptide S2-28 was the dominant epitope recognized by T cells from cardiac myosin immunized rats. S2-16 was presented by Lewis rat MHC class II molecules, and myocarditis induction was associated with an up-regulation of inflammatory cytokine production. S2-16-induced EAM provides a defined animal model to investigate mechanisms of EAM and modulation of immune responses to prevent autoimmune myocarditis.

Anti-Oxidant Effects of Coenzyme Q10 on Experimental Viral Myocarditis in Mice

We studied the effects of coenzyme Q10 (CoQ10) on mice with acute myocarditis inoculated with the encephalomyocarditis (EMC) virus with the analysis of indices of effects of oxidative injury and DNA damage in the myocardium. The mice were treated as follows: CoQ10 group (n = 118); CoQ10 1.0 mg (0.1 mL) x 2/d (0.1 mg/g/d), control group (n = 128); sham-liquid 0.1 mL x 2/d. The mice were injected intraperitoneally 1 day before and daily for 12 days after EMC virus inoculation. The expression of thioredoxin, a marker of oxidative stress overload, as well as 8-hydroxy-2'-deoxyguanosine, an established marker of DNA damage, in the myocardium was investigated. The survival rate was significantly higher (P < 0.01) in the CoQ10 group (46.8%, 29/62) than in the control group (14.3%, 10/70). There were significant increases of CoQ9 and CoQ10 in the heart, which are the biologically active forms of CoQ in mice, and significant decrease of serum creatine kinase (CK)-MB in the CoQ10 group as compared with the control group. Histologic examination showed that the severity of myocarditis was less severe (P < 0.01) in the CoQ10 group than in the control group. In addition, the up-regulation of myocardial thioredoxin with DNA damage, which was induced by the inflammatory stimuli by the virus, was suppressed by the CoQ10 treatment, which may reflect the anti-oxidant effects of CoQ10 treatment. Thus, pretreatment with CoQ10 may reduce the severity of viral myocarditis in mice associated with decreasing oxidative stress in the condition.

Expansion of specific alphabeta+ T-cell subsets in the myocardium of patients with myocarditis and idiopathic dilated cardiomyopathy associated with Coxsackievirus B infection

Idiopathic dilated cardiomyopathy (IDC) is one of the major causes of death in humans and has been linked to Coxsackievirus B (CVB) infection. The aim of this study was to analyze phenotypes of heart-infiltrating immune cells in patients suffering from myocarditis and IDC associated with CVB infections. We found that the myocardium of these patients was infiltrated by CD4(+) and CD8(+) T lymphocytes as well as macrophages. Evidence of CVB3/4 infections was also found. In the majority of patients, the T-cell receptor repertoire (TCR) of the infiltrating lymphocytes was restricted, with a polyclonal expansion of the Vbeta7 gene family. We also found that human leukocyte antigen (HLA) class II alleles associated with susceptibility to type 1 diabetes (HLA-DR4 and HLA-DQA1*04/05/06 alleles) were remarkably infrequent in IDC patients (p < 0.005), thus suggesting that they might confer protection against IDC. Finally, mRNA for interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha was detected in the cardiac specimens, although at a lower level compared with specimens from hearts without signs of viral infections. We conclude that CVB infection of the human myocardium is associated with a selective, yet polyclonal activation of different T-cell subsets in genetically susceptible individuals. This immune response may play a critical role in modulating disease progression after viral infections.

Myocarditis

Myocarditis and its sequela, dilated cardiomyopathy (DCM), cause substantial morbidity and mortality, especially in children and young adults. Physicians should include myocarditis in the differential diagnosis of all patients who have new symptoms of heart failure, arrhythmia, or chest pain syndromes of unclear cause, and should strongly consider performing endomyocardial biopsy (EMB) to establish the diagnosis. It may be necessary to perform multiple or serial biopsies to increase sensitivity. Patients with myocarditis and symptomatic heart failure, chest pain, or arrhythmias need hospitalization for evaluation and treatment. Patients with symptomatic left ventricular dysfunction should be treated with conventional heart failure therapy, including angiotensin-converting enzyme (ACE) inhibitors, digitalis, diuretics, and beta-blockers. Patients with arrhythmias or syncope may require electrophysiologic evaluation. In addition to conventional therapy, physicians should consider a course of immunosuppressive therapy in selected patients. The clinical course, response to therapy, and left ventricular function need close monitoring. Patients with myocarditis and rapidly progressive heart failure or cardiogenic shock should be referred early to an advanced heart failure center for implantation of a ventricular assist device and consideration for cardiac transplantation.

Vgamma4(+) T cells promote autoimmune CD8(+) cytolytic T-lymphocyte activation in coxsackievirus B3-induced myocarditis in mice: role for CD4(+) Th1 cells

T cells expressing the Vgamma4 T-cell receptor (TCR) promote myocarditis in coxsackievirus B3 (CVB3)-infected BALB/c mice. CD1, a major histocompatibility complex (MHC) class I-like molecule, is required for activation of Vgamma4(+) cells. Once activated, Vgamma4(+) cells initiate myocarditis through gamma interferon (IFN-gamma)-mediated induction of CD4(+) T helper type 1 (Th1) cells in the infected animal. These CD4(+) Th1 cells are required for activation of an autoimmune CD8(+) alphabeta TCR(+) effector, which is the predominant pathogenic agent in this model of CVB3-induced myocarditis. Activated Vgamma4(+) cells can adoptively transfer myocarditis into BALB/c mice infected with a nonmyocarditic variant of CVB3 (H310A1) but cannot transfer myocarditis into either uninfected or CD1(-/-) recipients, demonstrating the need for both infection and CD1 expression for Vgamma4(+) cell function. In contrast, CD8(+) alphabeta TCR(+) cells transfer myocarditis into either infected CD1(-/-) or uninfected recipients, showing that once activated, the CD8(+) alphabeta TCR(+) effectors function independently of both virus and CD1. Vgamma4(+) cells given to mice lacking CD4(+) T cells minimally activate the CD8(+) alphabeta TCR(+) cells. These studies show that Vgamma4(+) cells determine CVB3 pathogenicity by their ability to influence both the CD4(+) and CD8(+) adaptive immune response. Vgamma4(+) cells enhance CD4(+) Th1 (IFN-gamma(+)) cell activation through IFN-gamma- and CD1-dependent mechanisms. CD4(+) Th1 cells promote activation of the autoimmune CD8(+) alphabeta TCR(+) effectors.

The transition from viral to autoimmune myocarditis

Myocarditis offers a unique opportunity to study the factors contributing to its transition from a viral infection to an autoimmune disease. In this article, we review recent studies on the role of nitric oxide (NO), gamma interferon (IFN-gamma) and interleukin 12 (IL-12) in the progression from early (viral) to late (autoimmune) phases of myocarditis induced by Coxsackievirus B3 (CB3) in highly susceptible (A.CA) and moderately susceptible (B10.M) mice. NO plays a paradoxical role, being protective in early stages but detrimental later in the course of disease. Treatment with antibody to IFN-gamma reduced early disease, but had little effect on the severity of cardiac lesions at later times. Treatment with recombinant (r) IL-12 significantly reduced the autoimmune cardiac lesions in moderately susceptible B10.M mice, but had no measurable effect in highly susceptible A.CA animals. These studies provide evidence that the profile of inflammatory mediators produced early in the course of viral infection determines the later development of autoimmune disease.

Antibody-mediated immune enhancement in coxsackievirus B3 myocarditis

The aim of the present study was to explore the contribution of antibody-mediated immune enhancement in coxsackievirus B3(CB3) infection. Murine macrophage-like P388D1 cells were exposed to various concentrations of anti-CB3 immunoglobulin G (anti-CB3 IgG) or the Fab fragment of anti-CB3 IgG, and were infected with CB3 in Experiment I. High concentrations of anti-CB3 IgG showed a virus-neutralizing activity; however, a subneutralizing antibody concentration of IgG significantly enhanced virus replication. This infectious enhancement was blocked not only by the pretreatment of heat-aggregated gamma-globulin but by a specific Fc receptor (Fc gamma III/II receptor) antibody treatment. In contrast, the Fab fragment of anti-CB3 IgG did not enhance CB3 infection, but showed a rational neutralizing activity to CB3. These findings suggest the presence of Fc receptor mediated enhancement of CB3 infection in vitro. In Experiment II, C(3)H/He mice were inoculated with various amounts of an amyocarditic variant of CB3 followed 15 days later by myocarditic CB3. By this rechallenge, myocarditis was not induced in the mice with high neutralizing antibody titers. There was an inverse relationship between preexisting neutralizing antibody titers and the severity of myocarditis. The severity of myocarditis and myocardial CB3 titers, however, were markedly enhanced in the mice with a subneutralizing level of immunity compared to those with no immunity. The distribution of myocardial Fc receptor-bearing cells and serum macrophage inflammatory protein-2 levels paralleled the severity of myocarditis. By another virus rechallenge in Experiment III, enhanced infection of CB3 was not observed in vivo. These findings suggest that antibody-mediated immune enhancement might be involved in the pathogenesis of CB3 myocarditis.

Induction of myocarditis and valvulitis in lewis rats by different epitopes of cardiac myosin and its implications in rheumatic carditis

Immune responses against cardiac myosin and group A streptococcal M protein have been implicated in the pathogenesis of rheumatic heart disease. Although cardiac myosin is known to produce myocarditis in susceptible animals, it has never been investigated for its role in production of valvular heart disease, the most serious sequelae of group A streptococcal infection in acute rheumatic fever. In our study, cardiac myosin induced valvulitis in the Lewis rat, and epitopes responsible for production of valvulitis were located in the rod region. Human and rat cardiac myosins induced severe myocarditis in the Lewis rats as expected. A purified S2 fragment (amino acid sequences 842 to 1295) produced the most severe myocarditis as well as valvulitis. Different regions of light meromyosin produced valvulitis (residues 1685 to 1936) or myocarditis (residues 1529 to 1611). Because streptococcal M proteins produced valvular heart disease in Lewis rats and have been linked to anti-cardiac myosin responses, we reacted myosin-sensitized lymphocytes isolated from the hearts of Lewis rats with peptides of streptococcal M5 protein in tritiated thymidine assays. Infiltrating lymphocytes responded most strongly to peptides within the B repeat region of streptococcal M protein. These data show direct evidence that immune responses against cardiac myosin lead to valvular heart disease and the infiltration of the heart by streptococcal M protein reactive T lymphocytes.

Persistent expression of cytokines in the chronic stage of CVB3-induced myocarditis in NMRI mice

Coxsackievirus B3 (CVB3)-induced myocarditis in NMRI mice represents a model for studying the pathogenesis of this chronic heart disease. Previously, we reported on specific cytokine patterns during the acute stage of myocarditis since cytokines are thought to play the important role in this cardiomyopathy. In this study, the expression of various cytokine mRNAs and CVB3-RNA kinetics was examined with particular emphasis on the late phase of myocarditis, by using reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemistry (IHC). In addition, replicating and persisting CVB3-RNAs were semiquantified by PCR-ELISA. Distinct histopathological changes responsible for ongoing heart disease were found and characterized by increased fibrosis, persistent cellular infiltration and degenerated necrotic myocytes. One of the most important findings of this study was that the mRNA-expression of TNF- alpha, IL-1 alpha, interferon- gamma, IL-10, IL-18, macrophage inflammatory protein-1 alpha (MIP-1 alpha), transforming growth factor- beta (TGF- beta) and inducible nitric oxide synthase (iNOS) persisted as long as 98 days after the virus infection. The induction of IL-10 as well as IFN- gamma mRNAs was also verified by ISH and IHC at days 28 and 98 p.i. The clearly apparent persistence of the viral genomes in the myocardium of infected mice was confirmed by seminested PCR, ISH, and PCR-enzyme linked immunoabsorbent assay (ELISA), showing the highest amount of viral RNA in myocardial cells at day 7 after infection. These data indicate that the persistence of viral RNA is associated with persistently high levels of cytokine mRNAs which, when translated, could severely contribute to pathological changes and injury of connective tissue in the chronic stage of myocarditis.

Difference in thioredoxin expression in viral myocarditis in inbred strains of mice

Redox regulating mechanisms may be involved in the pathogenesis of viral myocarditis and thioredoxin (TRX) is a small multifunctional protein that contains a redox active sequence. The present study investigated the histopathology and characteristics of TRX expression in acute coxsackievirus B3 myocarditis in inbred strains of mice (severe myocarditis in DBA/2 mice, moderate myocarditis in BALB/c mice and mild myocarditis in C57BL/6 mice). Thioredoxin was upregulated and its expression correlated with the severity of the disease. In addition, 8-hydroxy-2'-deoxyguanosine, which is an established marker for oxidative stress, was concominantly positive in damaged myocytes. Thus, TRX may be specifically induced by the acute inflammatory stimuli in murine viral myocarditis, and the severity and development of acute viral myocarditis may be regulated by the cellular redox state.

From infection to autoimmunity

We have investigated two models of virally-induced autoimmune myocarditis in mice using widely different infectious agents. Infection of susceptible BALB/c mice with either Coxsackievirus or murine cytomegalovirus results in the development of acute myocarditis from day 7-14 after infection, and chronic myocarditis from day 28 onwards. The chronic phase of myocarditis is associated with mononuclear infiltration of the myocardium and the production of autoantibodies to cardiac myosin, although infectious virus cannot be detected past day 14 of infection. T cells and autoantibodies have been shown to be important for the development of autoimmune myocarditis. Many researchers have investigated the role of molecular mimicry in the development of myocarditis after viral infection. This review explores the 'adjuvant' effect of infection on the innate immune response and how this determines the progression to autoimmune disease. We show that NK cells protect against the development of disease, while complement and complement receptors are involved in the development of autoimmune myocarditis induced by inoculation with virus or cardiac myosin, respectively. Our results suggest that the innate immune response to viral and self-antigens may determine whether susceptible strains of mice progress to chronic autoimmune disease. These findings have broad implications for understanding the role of infection in inducing autoimmune disease.

Picornavirus proteins share antigenic determinants with heat shock proteins 60/65

Immunological cross-reactions between enteroviruses and islet cell autoantigens have been suggested to play a role in the etiopathogenesis of insulin dependent diabetes mellitus (IDDM). In the nonobese diabetic mouse, an autoimmune model of IDDM, one of the reactive beta cell autoantigens is the heat shock protein 60 (HSP60). These studies were prompted by sequence homology discovered between the immunogenic region in HSP60 and two regions in enterovirus capsid proteins, one in the VP1 protein and the other in the VP0, the precursor of VP2 and VP4 proteins. Possible immunological cross-reactions between enterovirus proteins and heat shock proteins were studied by EIA and immunoblotting by using purified virus preparations, viral expression proteins VP1 and VP0, and recombinant HSP60/65 proteins, and corresponding polyclonal antisera. The HSP60/65 family of proteins is highly conserved and there is a striking degree of homology between bacterial and human heat shock proteins. Rabbit antibodies to HSP65 of Mycobacterium bovis that reacted with human HSP60 were also found to recognise capsid protein VP1 of coxsackievirus A9, VP1, and/or VP2 of coxsackievirus B4. Both viruses were also recognised by antisera raised against HSP60 of Chlamydia pneumoniae. In addition to the capsid proteins derived from native virions, antisera to both bacterial HSP proteins recognised expression protein VP1 of coxsackievirus A9. The cross-reactivity was also demonstrated the other way around; antisera to purified virus particles reacted with the HSP 60/65 proteins to some extent. These results suggest that apart from the well-documented sequence homology between the 2C protein of coxsackieviruses and the beta-cell autoantigen glutamic acid decarboxylase, there are other motifs in picornavirus proteins homologous to islet cell autoantigens, which might induce cross-reacting immune responses during picornavirus infections.

V gamma 1+ T cells suppress and V gamma 4+ T cells promote susceptibility to coxsackievirus B3-induced myocarditis in mice

Coxsackievirus B3 infections of C57BL/6 mice, which express the MHC class II IA but not IE Ag, results in virus replication in the heart but minimal myocarditis. In contrast, Bl.Tg.Ealpha mice, which are C57BL/6 mice transgenically induced to express IE Ag, develop significant myocarditis upon Coxsackievirus B3 infection. Despite this difference in inflammatory damage, cardiac virus titers are similar between C57BL/6 and Bl.Tg.Ealpha mice. Removing gammadelta T cells from either strain by genetic manipulation (gammadelta knockout(ko)) changes the disease phenotype. C57BL/6 gammadelta ko mice show increased myocarditis. In contrast, Bl.Tg.Ealpha gammadelta ko mice show decreased cardiac inflammation. Flow cytometry revealed a difference in the gammadelta cell subsets in the two strains, with Vgamma1 dominating in C57BL/6 mice, and Vgamma4 predominating Bl.Tg.Ealpha mice. This suggests that these two Vgamma-defined subsets might have different functions. To test this possibility, we used mAb injection to deplete each subset. Mice depleted of Vgamma1 cells showed enhanced myocarditis, whereas those depleted of Vgamma4 cells suppressed myocarditis. Adoptively transfusing enriched Vgamma4(+) cells to the C57BL/6 and Bl.Tg. Ealpha gammadelta ko strains confirmed that the Vgamma4 subset promoted myocarditis. Th subset analysis suggests that Vgamma1(+) cells biased the CD4(+) T cells to a dominant Th2 cell response, whereas Vgamma4(+) cells biased CD4(+) T cells toward a dominant Th1 cell response.

Myocarditis

Myocarditis and its sequela, dilated cardiomyopathy (DCM), cause substantial morbidity and mortality, especially in children and young adults. Physicians should include myocarditis in the differential diagnosis of all patients who have new symptoms of heart failure, arrhythmia, or chest pain syndromes of unclear cause, and should strongly consider performing endomyocardial biopsy (EMB) to establish the diagnosis. It may be necessary to perform multiple or serial biopsies to increase sensitivity. Patients with myocarditis and symptomatic heart failure, chest pain, or arrhythmias need hospitalization for evaluation and treatment. Patients with symptomatic left ventricular dysfunction should be treated with conventional heart failure therapy, including angiotensin-converting enzyme (ACE) inhibitors, digitalis, diuretics, and beta-blockers. Patients with arrhythmias or syncope may require electrophysiologic evaluation. In addition to conventional therapy, physicians should consider a course of immunosuppressive therapy in selected patients. The clinical course, response to therapy, and left ventricular function need close monitoring. Patients with myocarditis and rapidly progressive heart failure or cardiogenic shock should be referred early to an advanced heart failure center for implantation of a ventricular assist device and consideration for cardiac transplantation.

Special feature for the Olympics: effects of exercise on the immune system: infections and exercise in high-performance athletes

The elite athlete has a potentially increased sensitivity to respiratory infections, rendering protective measures particularly important. Some other infections that may appear in clusters in the sports setting, such as gastroenteritis, leptospirosis, herpes simplex and viral hepatitis, also require special precautionary attention. Strenuous exercise during ongoing infection and fever may be hazardous and should always be avoided. In addition, early symptoms of infection warrant caution until the nature and severity of the infection become apparent. Because myocarditis may or may not be accompanied by fever, malaise or catarrhal symptoms, athletes should be informed about the symptoms suggestive of this disease. Although sudden unexpected death resulting from myocarditis is rare, exercise should be avoided whenever myocarditis is suspected. Guidelines are suggested for the management and counselling of athletes suffering from infections, including recommendations on when to resume training. Acute febrile infections are associated with decreased performance resulting from muscle wasting, circulatory deregulation and impaired motor coordination, which require variable amounts of time to become normalized once the infection is over.

Host gene regulation during coxsackievirus B3 infection in mice: assessment by microarrays

Host genetic responses that characterize enteroviral myocarditis have not yet been determined. The injurious and inflammatory process in heart muscle may reflect host responses of benefit to the virus and ultimately result in congestive heart failure and dilated cardiomyopathy. On the other hand, host responses within the myocardium may secure the host against acute or protracted damage. To investigate the nature of modified gene expression in comparison with normal tissue, mRNA species were assessed in myocardium using cDNA microarray technology at days 3, 9, and 30 after infection. Of 7000 clones initially screened, 169 known genes had a level of expression significantly different at 1 or more postinfection time points as compared with baseline. The known regulated genes were sorted according to their functional groups and normalized expression patterns and, subsequently, interpreted in the context of viremic, inflammatory, and healing phases of the myocarditic process.

Redistribution of accumulated 2,3,7,8-tetrachlorodibenzo-p-dioxin during coxsackievirus B3 infection in the mouse

The tissue redistribution of accumulated 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) during infection was studied in adult male A/J mice using a common human virus coxsackievirus B3. Before infection (day 1), all mice were injected intraperitoneally (i.p.) with 1 microCi 3H-TCDD, corresponding to 0.5 microg TCDD kg(-1). One group was sacrificed before virus inoculation (day 0). Of the remaining mice, one subgroup was inoculated i.p. with CB3 virus while the other subgroup served as a noninfected control. On days 0, 4 and 7, the spleen, thymus, heart, pancreas, liver, white and brown adipose tissue, skeletal muscle, lung, kidney, brain, adrenals, thyroid, testes, epididymis and blood were sampled from infected and noninfected groups. Liquid scintillation was used to determine the 3H-TCDD-content of the tissues. The results showed that the accumulated TCDD was redistributed due to infection. The major changes occurred in the organs involved in the infectious process. In the target organs for coxsackievirus B3 (the pancreas and heart), the TCDD concentration peaked in relation to noninfected control values, concurrent with the development of inflammatory lesions (P<0.001 and 0.01, respectively for the heart and pancreas). The TCDD levels in the thymus increased three-fold during the infection to an estimated 0.5 pmol g(-1) tissue on day 7 of the infection, whereas the levels in noninfected mice did not change markedly (P<0.001). In the brain of infected mice, the TCDD concentration increased significantly with time, at day 7 reaching two-fold levels in comparison with noninfected controls (P<0.001). The findings suggest that a common infection causes redistribution of a previously accumulated environmental pollutant, resulting in increased concentrations and potentially increased toxicity in selected target tissues.

Aloe polymannose enhances anti-coxsackievirus antibody titres in mice

Aloe polymannose (AP), a high mannose biological response modifier (BRM) purified from the Aloe barbadensis Miller plant, was tested for activity in enhancing antibody titres against coxsackievirus B3 (CVB3) and CVB3-induced myocarditis in murine models of the disease. Inoculation of mice with AP over a range of three nontoxic doses and in varying schedules did not reduce virus titres in heart tissues or ameliorate virus-induced cardiopathological alterations during acute disease. However, this BRM was found to significantly enhance titres of anti-CVB3 antibodies produced during acute infection of three strains of mice with CVB3. Simultaneous intraperitoneal inoculation of AP at a dose of 0.5 mg/kg body weight per mouse with purified CVB3 significantly increased ELISA titres of anti-CVB3 antibodies and the proportion of mice with these titres, compared with similar parameters in mice inoculated only with CVB3. The data conclusively show that AP can immunopotentiate antibody production against capsid protein epitopes of a nonenveloped picornavirus and suggest this BRM (AP) might be of benefit in enhancing antibody titres against other enteroviruses during a natural infection and poliovirus vaccine strains.

The shift in the myocardial adenine nucleotide translocator isoform expression pattern is associated with an enteroviral infection in the absence of an active T-cell dependent immune response in human inflammatory heart disease

OBJECTIVES

This study evaluates the relevance of an enteroviral infection and the intramyocardial T-cell immune response for the alteration in the adenine nucleotide translocator isoform transcription pattern (ANTitp) in patients suspected of having myocardial inflammation.

BACKGROUND

The ANT, the only mitochondrial carrier for ADP and ATP, plays a significant role in the energy metabolism and is involved in the apoptosis process. Its function and expression were found to be altered in the myocardium of patients with dilated cardiomyopathy and myocarditis.

METHODS

The ANTitp was analyzed in endomyocardial biopsies from 53 patients with clinically suspected inflammatory heart disease (csIHD). Enteroviral RNA was detected in the biopsies using the reverse transcripted polymerase chain reaction technique. The activation of the cellular immune system was assessed by the quantification of T-lymphocytes employing immunohistochemistry.

RESULTS

The ANTitp was found to be altered in 21 csIHD patients. Enteroviral genome was found in the heart of 71.4% of these patients, but only 37.5% of the patients with a normal ANTitp were virus-positive (p < 0.02). The infiltration with CD3+, CD45R0+ and CD8+ T-cells was substantially lower in myocardial specimens with an altered ANTitp than in biopsies with a normal ANTitp. Combining the data, an altered ANTitp was primarily found in virus-positive heart tissue, which was less infiltrated with lymphocytes or not at all.

CONCLUSIONS

An enteroviral infection is linked to changes in the ANT isoform expression in human heart tissue, which shows little or no evidence of an active T-cell dependent immune response. These results make a contribution to a better understanding of the pathophysiology of enterovirus-induced human inflammatory heart disease.

Apoptosis in coxsackievirus B3-induced myocarditis and dilated cardiomyopathy

Group B coxsackieviruses (CVB), which infect the myocardium, cause myocarditis and dilated cardiomyopathy. However, not all infections of the myocardium result in disease. In the mouse model, CVB infection stimulates autoimmune T cell response to cardiac antigens, and these autoimmune effectors cause myocyte necrosis and cardiomyopathy. Induction of pathogenic autoimmunity depends upon CD4+ Th1 (interferon-gamma positive) cells while Th2 (IL-4 positive) cell responses promote disease resistance. T lymphocytes expressing the gamma-delta T cell receptor (gamma delta +) constitute up to 12% of the inflammatory cells in the heart and are crucial to maintaining a dominant Th1 response phenotype. gamma delta + lymphocytes modulate T cell responses by selectively lysing CD4+ Th2 cells. Th1 cells are not killed by gamma delta + cells. Lysis requires direct cell:cell interaction between the gamma delta + cell and CD4+ Th2 target and is most likely mediated through Fas:FasL interaction. These studies demonstrate a novel mechanism for immune modulation of cytokine responses in vivo.

Expressional patterns of cytokines in a murine model of acute myocarditis: early expression of cardiotrophin-1

To determine the role of cytokines in acute myocarditis, we examined expressional patterns of cardiotrophin-1 (CT-1), TNF-alpha, and IL-1alpha in a murine model of acute myocarditis. Ten-day-old Institute of Cancer Research mice were injected with Coxsackievirus B3 and killed on Days 1, 2, 3, 4, 5, 7, 10, 14, and 28 of injection. TNF-alpha and IL-1alpha expressions were investigated on histological sections from each heart, and mRNA expression of TNF-alpha, IL-1alpha, and CT-1 in the heart was examined by reverse transcription-polymerase chain reaction and RNase protection assay. To determine myocardial regeneration, cardiomyocytic DNA synthesis was investigated using bromodeoxyuridine on Days 3, 5, 7, and 10, and the labeling index was calculated in each heart. Age-matched uninfected mice were used as controls. TNFalpha and IL-1alpha expression was first detected in the cardiomyocytes on Day 3 and reached the maximum level on Day 7, when inflammatory changes were most prominent. Although an increased expression of TNFalpha and IL-1alpha mRNA was also detected on Day 3, CT-1 mRNA expression was distinctly augmented on Day 2. The labeling indices in the hearts with myocarditis were significantly higher than in those of the controls in all of the time points examined. CT-1 expression preceded TNF-alpha and IL-1alpha expressions and active DNA synthesis in a murine model of acute myocarditis. All CVB3-infected mice with anti-glycoprotein-130 antibody treatment died within 6 days. CT-1 may exert a protective role by modulating cytokine production and by inducing cardiomyocytic proliferation in CVB3-infected murine hearts.

A glyconutritional mixture (Ambrotose®) provides some amelioration to mice with coxsackievirus-induced pancreatitis

Challenge of adolescent male CD-1 mice with a coxsackievirus B3 (CVB3) strain (CVB3m) induces mild to severe destruction of pancreatic acinar cells, but causes no deaths and does not induce hyperglycemia. A weekly parenteral (intraperitoneal) administration of a glyconutritional mixture (Ambrotose® to virus-challenged mice was assessed to determine if there were any benefits to recovery over an eight month period. Virus-challenged mice showed a significant weight loss over the initial five weeks of the experiment, but injection of Ambrotose® to similar virus-challenged mice restored the total body weight to levels found in normal mice. Normal mice given Ambrotose® exhibited a small weight gain. Mice given Ambrotose® showed reduced severity of pancreatitis, as evidenced by significant reductions in percentages of pancreatic acinar cells destroyed and proportion of sections of pancreata with destroyed acinar cells, compared to virus control-mice not injected with Ambrotose®. Statistical analyses of the extent of acinar cell pathology in all virus-challenged mice showed that Ambrotose® contributed significantly to recovery of the acinar cell population in virus-inoculated mice. Anti-viral antibody titers were not affected by Ambrotose® injections. One potential mechanism to explain the benefits derived from Ambrotose® injections came from studies of antioxidant levels of glutathione in splenic macrophages/monocytes. Whereas CVB3 challenge of mice reduced glutathione levels in the latter cells, Ambrotose® injections to virus-challenged mice restored glutathione levels to those found in normal mice. In summary, most but not all mice derived benefits from Ambrotose® injections, i.e. a reduction in pathology in the pancreas and restored levels of the antioxidant glutathione in macrophages/monocytes. Higher doses of Ambrotose® could provide greater benefits for more mice, a study for the future.

Estradiol prevents and testosterone promotes Fas-dependent apoptosis in CD4+ Th2 cells by altering Bcl 2 expression

Coxsackievirus B3 (CVB3) induces myocarditis in male BALB/c mice. Female mice are resistant to viral myocarditis, except in the third trimester of pregnancy and postpartum. Cardiac damage is mediated by T lymphocytes activated during virus infection. Th1 (interferon-gamma+) cell responses promote cardiac injury, while disease resistance correlates to preferential activation of Th2 (interleukin-4+) cell responses. CVB3-specific Th1 and Th2 cell clones were established, treated with between 0 and 100 ng/ml 17beta estradiol and 4-androsten-17beta-ol-one (testosterone) for two days, 51Cr-labeled and cultured on FasL-transfected 3T3 cells to determine susceptibility to Fas-dependent apoptosis. Testosterone treatment enhanced Th2 cell lysis while estradiol treatment was protective. Staining of Th2 cells for Bcl 2, an anti-apoptotic factor, indicates that Bcl 2 expression increased in these cells with estradiol but decreased with testosterone exposure. Hormone-induced changes in Bcl 2 expression likely explain the selective survival of Th2 cells in females and prevention of viral myocarditis.

Viruses, host responses, and autoimmunity

Conceptually, the initiation of autoimmune disease can be described as a three-stage process involving both genetic and environmental influences. This process begins with the development of an autoimmune cellular repertoire, followed by activation of these autoreactive cells in response to a localized target and, finally, the immune system's failure to regulate these self-reactive constituents. Viruses have long been associated with inciting autoimmune disorders. Two mechanisms have been proposed to explain how a viral infection can overcome immunological tolerance to self-components and initiate an organ-specific autoreactive process; these mechanisms are molecular mimicry and bystander activation. Both pathways, as discussed here, could play pivotal roles in the development of autoimmunity without necessarily excluding each other. Transgene technology has allowed us and others to examine more closely the roles of these mechanisms in mice and to dissect the requirements for initiating disease. These results demonstrate that bystander activation is the most likely explanation for disease development. Additional evidence suggests a further role for viruses in the reactivation and chronicity of autoimmune diseases. In this scenario, a second invasion by a previously infecting virus may restimulate already existing autoreactive lymphocytes, and thereby contribute to the diversity of the immune response.