Persistence of replicating coxsackievirus B3 in the athymic murine heart is associated with development of myocarditic lesions

Soluble coxsackievirus B3 3C protease inhibitor prevents cardiomyopathy in an experimental chronic myocarditis murine model

BACKGROUND

Coxsackievirus B3 (CVB3) is a common cause of myocarditis and dilated cardiomyopathy. CVB3 3C protease (3CP) cleaves the viral polyprotein during replication. We tested whether a water soluble 3CP inhibitor (3CPI) had antiviral effects in a chronic myocarditis model.

METHODS

Chronic myocarditis was established using DBA/2 strain mice. Starting on post-infection (p.i) day 3, CVB3-infected mice (n=41) were treated with 3CPI by daily intraperitoneal (i.p.) injection at a concentration of 50 μM (1.7 mg/kg/day) per day for 3 consecutive days. Additional mice (n=49) were injected with PBS as a control.

RESULTS

The 5-week survival rate was significantly higher with 3CPI treatment (82.3% versus 47.9%; P<0.05). Organ virus titers at day 3 and 7 and myocardial damage were significantly lower in 3CPI-treated mice. Echocardiography at day 31 indicated strong protection of heart function by 3CPI (FS, 51.2±1.5 versus 26.1±1.5%; P<0.001). Hemodynamic measurements indicated that 3CPI treatment markedly reduced CVB3-induced LV dysfunction on day 31 (dP/dTmax, 5302±352 versus 4103±408 mmHg/s, P<0.05; dP/dTmin, -3798±212 versus -2814±206 mmHg/s, P<0.01).

CONCLUSIONS

Water soluble 3CPI was delivered through i.p. injection after CVB3 infection. This agent preserved heart function and decreased organ viral titers and myocardial damage. Soluble 3CPI may be beneficial in the treatment of cardiomyopathy associated with enterovirus infection.

Type B coxsackieviruses and their interactions with the innate and adaptive immune systems

Coxsackieviruses are important human pathogens, and their interactions with the innate and adaptive immune systems are of particular interest. Many viruses evade some aspects of the innate response, but coxsackieviruses go a step further by actively inducing, and then exploiting, some features of the host cell response. Furthermore, while most viruses encode proteins that hinder the effector functions of adaptive immunity, coxsackieviruses and their cousins demonstrate a unique capacity to almost completely evade the attention of naive CD8(+) T cells. In this artcle, we discuss the above phenomena, describe the current status of research in the field, and present several testable hypotheses regarding possible links between virus infection, innate immune sensing and disease.

Copper deficiency increases the virulence of amyocarditic and myocarditic strains of coxsackievirus B3 in mice

Deficiency in several trace elements, including copper and selenium, is associated with increased levels of oxidative stress. Copper deficiency also has been shown to impair immune function. Previous work by others demonstrated that passage of an amyocarditic or myocarditic strain of coxsackievirus B3 (CVB3) through selenium- or vitamin E-deficient mice led to increased cardiac pathology. To determine whether a copper deficiency would similarly alter the pathogenesis of CVB3 infections, Swiss outbred dams and their litters were fed copper-deficient diets from birth and received either deionized water or water with 0.315 mmol/L copper as copper sulfate. At 4 wk of age, copper-adequate or -deficient male and female offspring were infected with an amyocarditic or myocarditic strain of CVB3. Heart titers were elevated at d 3 and 7 postinfection in copper-deficient mice infected with the myocarditic CVB3 strain (CVB3/20) but only at d 7 in deficient mice infected with the amyocarditic CVB3 strain (CVB3/0) compared with copper-adequate controls. Copper-deficient mice infected with either strain of CVB3 had increased cardiac pathology compared with copper-adequate controls. Genomic sequences of viruses isolated from copper-adequate and -deficient mice were identical. Heart cytokine expression was elevated in copper-deficient CVB3-infected mice compared with infected controls. Circulating CVB3-specific IgG2a but not IgM levels were decreased in copper-deficient mice. Thus, copper deficiency is associated with an increased inflammatory response but decreased acquired immune response to CVB3 infection that results in increased cardiac pathology, presumably due to increased viral load.

Coxsackievirus myocarditis: interplay between virus and host in the pathogenesis of heart disease

Coxsackievirus (CVB) infection is a significant cause of myocarditis and dilated cardiomyopathy (DCM). Heart disease may be caused by direct cytopathic effects of the virus, a pathologic immune response to persistent virus, or autoimmunity triggered by the viral infection. CVB interacts with its host at multiple stages during disease development. Signaling through viral receptors may alter the intracellular environment in addition to facilitating virus entry. Viral genetic determinants that encode cardiovirulence have been mapped and may change depending on the nutritional status of the host. Virus persistence is directly associated with pathology, and recent work demonstrates that CVB evolves into a slowly replicating form capable of establishing a low-grade infection in the heart. The innate immune response to CVB has taken on increasing importance because of its role in shaping the development of the adaptive immune response that is responsible for cardiac pathology. Studies of T cell responsiveness and the development of autoimmunity at the molecular level are beginning to clarify the mechanisms through which CVB infection causes inflammatory heart disease.

Characterisation of murine cytomegalovirus myocarditis: cellular infiltration of the heart and virus persistence

Myocarditis triggered by a viral infection has integral viral and immunological aspects associated with the pathogenesis of disease. The present study was performed to analyse the cellular inflammatory response in the heart and cytomegalovirus replication during the development of myocarditis in vivo. We examined murine cytomegalovirus in an animal model of myocarditis using both susceptible BALB/c and resistant C57BL/6 mice. The heart infiltrating cells of BALB/c mice were found to comprise predominantly CD8+ T cells, with other cells of the CD4+ T cell, macrophage, B cell and neutrophil phenotype. Infectious MCMV titres in the heart were low and replicative virus could not be isolated beyond the first week post-infection (p.i.). Direct viral lysis of myocytes in vitro and apoptosis of cardiac cells in vivo was observed. Furthermore, viral DNA was detected in the heart of both mouse strains throughout the development of chronic disease. Viral gB RNA was detected during the first 35 days p.i. However, viral transcript for ie1 RNA but not gB RNA was found in the heart during the late stage of disease, suggesting latent viral infection of the heart. Our findings suggest that maintenance of the chronic phase of myocarditis involving post-viral immunological responses can occur in the presence of little infectious virus replication in the heart.

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.

Ganciclovir and cidofovir treatment of cytomegalovirus-induced myocarditis in mice

The cardiovascular disease myocarditis is characterized by inflammation and necrosis of cardiac muscle. This disease has been associated with various viral etiologies, including cytomegalovirus (CMV). Murine CMV (MCMV) infection of adult BALB/c mice produces a disease with acute and chronic phases similar to that found in humans. In our murine model, we have investigated the therapeutic efficacy of antiviral drug administration on myocarditis. Two drugs commonly used for CMV treatment, ganciclovir and cidofovir, were subjected to trials, with both drugs showing potent antiviral activity against MCMV both in vitro and in vivo. The acute phase of myocarditis was significantly reduced when antiviral therapy commenced 24 h postinfection. Such treatment also reduced the severity of the chronic phase of myocarditis. In contrast, antiviral treatment commencing after the acute phase had no effect on chronic myocarditis. Reinfection of mice with MCMV caused exacerbation of myocardial inflammation. Such an increase in severity of myocarditis could be prevented with either ganciclovir or cidofovir treatment, but the preexisting inflammation and necrosis of the myocardium persisted. These data highlight possible therapeutic uses of antiviral drugs in viral myocarditis as well as further elucidating the pathogenic nature of the disease.

The role of B lymphocytes in coxsackievirus B3 infection

Coxsackieviruses are important human pathogens, frequently causing myocarditis, pancreatitis, and a variety of less severe diseases. B lymphocytes appear central to the interaction between these viruses and their mammalian hosts, because agammaglobulinemic humans, genetically incapable of antibody production, are susceptible to chronic infections by coxsackieviruses and related enteroviruses, such as poliovirus and echovirus. However, recent studies show that Type B coxsackievirus (CVB) infects B lymphocytes soon after infection, suggesting the possibility that these cells may play some role in virus dissemination and/or that the virus may be able to modulate the host immune response. We analyzed the role of B lymphocytes in CVB infection and confirmed that CVB infects B lymphocytes, and extended these findings to show that this is a productive infection involving approximately 1 to 10% of the cells; however, infectious center assays show that other splenocytes are infected at approximately the same frequency. Virus is readily detectable by in situ hybridization in the spleen of immunocompetent mice but is difficult to detect in mice deficient in B cells (BcKO mice), consistent with much of the splenic signal being the result of B cell infection. Surprisingly, given the extent of their infection, B cells express barely detectable levels of the murine coxsackievirus-adenovirus receptor (mCAR), suggesting that another means of cell entry may be used. We found no evidence of B cell depletion following CVB infection, indicating that this is not the explanation for the transient immunosuppression previously reported. Virus replication and dissemination are slightly delayed in BcKO mice, consistent with B cells' playing a role as an important early target of infection and/or a means to distribute the virus to many tissues. In addition, we show that BcKO mice recapitulate a central feature of human agammaglobulinemia: CVB establishes chronic infection in a variety of organs (heart, liver, brain, kidney, lung, pancreas, spleen). In most of these tissues the viral titers remain high (10(5)-10(8) plaque forming units (pfu) per gram of tissue) for the life of the mouse, and in several there is severe pathology, particularly severe myocardial fibrosis with ventricular dilation, reminiscent of the dilated cardiomyopathy seen in humans with chronic enteroviral myocarditis. Transfer of B and/or T cells from non-immune mice had no discernible effect, whereas equivalent transfers from immune mice often resulted in transient or permanent disappearance of detectable CVB.

Contractile depression and expression of proinflammatory cytokines and iNOS in viral myocarditis

We assessed two strains of mice [CD-1 and C3H.HeJ (C3H)] with different responses to coxsackievirus B3 (CVB3) infection at 7, 14, and 21 days after inoculation with 10(5) pfu of CVB3. CD-1 mice developed inflammatory lesions at 7 days that nearly recovered by 21 days; C3H mice demonstrated persistence of infiltrates. Although there were differences in the baseline fractional shortening, it was further reduced at 7 and 14 days in both strains. It recovered in CD-1 mice but remained depressed at 21 days in C3H mice. Interleukin-6 and tumor necrosis factor-alpha transcripts were increased in both strains at 7 days. Levels dropped to near control in CD-1 mice at 21 days but remained elevated in C3H mice. Interleukin-1 beta was minimally elevated in CD-1 mice but increased progressively in C3H mice. mRNA for the inducible form of NO synthase (iNOS) was increased at 7 days in the CD-1 mice, returning to baseline by 14 days; it rose progressively in C3H mice, with a fivefold increase at 21 days. We conclude that mice infected with CVB3 show increased expression of proinflammatory cytokines as well as iNOS associated with reduced contractile performance. In more susceptible mice, contractile depression and cytokine and iNOS expression are more pronounced.

Extracellular matrix remodeling in coxsackievirus B3 myocarditis

The connective tissue abnormality in relation to T lymphocytes was investigated in murine myocarditis. Inbred BALB/c-nu/+ (euthymic and normal T cell function) and BALB/c-nu/nu (athymic and T cell deficient) mice were inoculated with coxsackievirus B3 (CB3). Hearts were stained with hematoxylin-eosin, Malloryazan, and silver impregnation, for reticulin fiber abnormalities, and T lymphocyte subsets. In BALB/c-nu/+ mice, active myocardial necrosis appeared parallel with T lymphocyte infiltrates, that is, it was absent on day 0, increased until 14 days, and then decreased with time. In contrast, the abnormal reticulin fiber architecture and interstitial fibrosis increased with time until 60 days, when ventricular remodeling was noted. In the hearts of BALB/c-nu/nu mice, although minimal myocardial necrosis associated with infiltrating immature T lymphocytes was noted earlier, subsequent interstitial fibrosis and reticulin fiber abnormalities were not documented later. The abnormal reticulin fiber architecture seen in BALB/c-nu/+ mice may contribute to the extracellular matrix remodeling in murine CB3 myocarditis in which dilated cardiomyopathy develops later.

Experimental CVB3-induced chronic myocarditis in two murine strains: evidence of interrelationships between virus replication and myocardial damage in persistent cardiac infection

In order to analyse the relationships between enteroviral replication and the myocardial damage at the onset of chronic cardiac infection, 2 mouse strains with different degrees of immunological competence (NMRI nu/nu, DBA/2) were infected by a myocarditic Coxsackie virus B3 (CVB3-M1) variant. At 31 days post-inoculation, plaque-forming assay, polymerase chain reaction (RT-PCR), and immunohistochemistry were carried out for detecting viruses and viral components in the myocardium. The virological findings were related to histopathological changes in the myocardium as well to the dilatation of both cardiac ventricles. Chronic myocardial lesions characterized by large fibrosis areas and interstitial inflammatory infiltrates were detected together with cardiomegalia in 52.6% (10/19) of athymic mice and in 9% (2/22) of euthymic mice. Viral replication foci were located and were found only in myocarditic cells adjacent to myocardial inflammatory lesions by immunostaining myocardial tissue sections with anti-serum to VP1 virus capsid protein. Using PCR followed by microwell capture hybridization assay, a large excess of viral positive strand RNA over negative strand was semiquantified in heart tissue from mice with chronic myocarditis, whereas approximately equal amounts of plus and minus strand RNA were detected in cases of persistent cardiac infection without chronic myocardial injuries. These findings provide evidence of the major role of viral replication in the pathogenesis of chronic murine CVB3-induced cardiomyopathy. The results indicate that the cardiac persistence of enteroviral RNAs can be observed without chronic cardiomyopathy, which could be explained by a defective viral positive RNA replication.

Susceptibility of human bone marrow cells and hematopoietic cell lines to coxsackievirus B3 infection

Viremia is commonly observed in association with enterovirus infections, and during this phase viruses can be transmitted to secondary target organs in the body. It is not known, however, whether blood cells play a role in the pathogenesis of enterovirus infection supporting virus replication. Our earlier work (T. Vuorinen, R. Vainionpää, H. Kettinen, and T. Hyypiä, Blood 84:823-829, 1994) demonstrated that coxsackievirus B3 is able to replicate in representatives of B- and T-cell lines but not in a monocytic cell line or peripheral blood mononuclear cells, indicating that virus replication may depend on the differentiation and maturation stages of the cells. Therefore, we have broaden our studies and analyzed the susceptibility of granulocyte-macrophage CFU and hematopoietic cell lines with various differentiation and maturation stages to coxsackievirus B3 infection. Virus replication was detected in B- and T-cell lines with no direct correlation to the maturation stage. Granulocyte-macrophage CFU were also able to support virus multiplication.