Viral Myocarditis Mice Research Articles

Effects of Free Immunoglobulin Light Chains on Viral Myocarditis

In recent work, we have demonstrated a crucial role of mast cells in the development of viral myocarditis. Viral infection could lead to increased synthesis of free immunoglobulin light chains (FLC) and our earlier work showed that FLC can trigger mast cell activation. We studied the possible involvement of FLC in the pathogenesis of viral myocarditis, and therapeutic effects of FLC using an animal model of viral myocarditis. DBA/2 mice were inoculated intraperitoneally with encephalomyocarditis (EMC) virus. Serum levels and concentrations in the heart of kappa FLC on day 14 in mice inoculated with EMC virus were significantly increased compared with controls. Myocardial viral concentration was significantly inhibited, the area of myocardial lesions was smaller in mice treated with kappa or lambda FLC, and survival of mice given FLC significantly improved. In contrast, an FLC antagonist deteriorated myocarditis. kappa and lambda FLC chains inhibited EMC viral replication in human amnion cells in vitro. lambda FLC significantly increased the gene expression of interleukin-10 in the heart which was previously shown to improve viral myocarditis when given exogenously. FLC also tended to increase the gene expressions of interferon-alpha and -gamma in the heart mice. FLC have antiviral and antiinflammatory effects and improved viral myocarditis in mice. FLC may be promising agents for the treatment of viral myocarditis.

Cetirizine a histamine H1 receptor antagonist improves viral myocarditis

BackgroundWe showed that mast cells played a critical role in the progression of heart failure induced by pressure overload and viral myocarditis in mice. In this study, we investigated the effect of cetirizine, a selective H1 receptor antagonist, on experimental viral myocarditis induced by encephalomyocarditis (EMC) virus.MethodsFour-week-old inbred male DBA/2 mice were inoculated intraperitoneally with 10 plaque-forming units (pfu) of the EMC virus. Cetirizine was administered orally at a dose of 1 or 10 mg/kg per day for the survival study, and 1 mg/kg for the histologic and gene expression studies, beginning on the day of viral inoculation.ResultsCetirizine improved survival dose dependently. Heart weight to body weight ratio was significantly decreased in mice treated with cetirizine. The area of myocardial necrosis was significantly smaller in the hearts of mice treated with cetirizine compared with controls. Gene expressions of tumor necrosis factor, interleukin 6, and metalloproteinase 2 were significantly suppressed in the hearts of mice treated with cetirizine.ConclusionThese results suggest that cetirizine exerts its beneficial effects on viral myocarditis by suppressing expression of pro-inflammatory cytokines, genes related to cardiac remodeling in the hearts of mice.

Coxsackievirus B3 infection induced viral myocarditis by regulating the expression pattern of chemokines in cardiac myocytes.

Viral myocarditis is a common cardiovascular disease, which has greatly threatened human health. However, up to now, the pathogenesis of viral myocarditis has been unclear, which leads to the lack of its effective treatments. To investigate the role of chemokines in pathogenesis of viral myocarditis, mRNA expression for a panel of 19 chemokines detected by RT-PCR in myocardial tissue of BALB/c mice that were inoculated intraperitoneally with coxsackievirus B3. Moreover primary cultured cardiac myocytes were infected with coxsackievirus B3 following extraction of RNA, from myocytes the expression of 19 chemokines was detected by by RT-PCR. Our results showed that there was much difference in the expression pattern of chemokines in myocardial tissue between infected mice with viral myocarditis and uninfected control mice. The expression of chemokines was varied significantly in clusters in myocardium post coxsackievirus B3 infection. There were also complexity and imbalance in the change of the expression of chemokines. In the meantime, Coxsackievirus B3 infection also influenced the expression pattern of chemokines in cardiac myocytes in vitro. However the expression of monocyte chemoattractant protein-1 alone was upregulated in cardiac myocytes post coxsackievirus B3 infection in the 19 detected chemokines. The chemokine expression pattern changed in complexity and imbalance manner both in myocardium and in primary cultured cardiac myocytes after coxsackievirus B3 infection. Coxsackievirus B3 infection may start viral myocarditis by regulating the expression pattern of chemokines in cardiac myocytes. MCP-1 may be one of key chemokines in the initial stage of viral myocarditis.

The effects of NK4 on viral myocarditis mice

NK4 may be a promising agent to inhibit tumor invasion and metastasis. To observe the effects of NK4 on the cardiovascular system with pathological injury and to discuss the mechanism, we established an experimental model of viral myocarditis (VCM) by coxsackievirus B3 infection in Balb/c mice on Day 0 and administered NK4 twice daily to the VCM and control mice from Day 20 to Day 45. We then evaluated the cardiac function by means of ultrasonic inspection. Hepatocyte growth factor, TNF (tumor necrosis factor)-alpha, and angiotensin II levels in the myocardial tissue were measured with enzyme-linked immunosorbent assay. Myocardium histopathology was examined with hematoxylin and eosin stain. Collagen deposition of the myocardium was detected through Masson staining. Microvessel staining with the RECA antibody and apoptosis detection with terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling were performed in the myocardium. The changes in MMP3 (matrix metalloproteinase 3), MMP9, TIMP1 (tissue inhibitor of metalloproteinase 1), and TGF (transforming growth factor)-beta1 expression in the myocardium were measured by reverse-transcriptase polymerase chain reaction. We found that NK4 intervention increased TGF-beta and angiotensin II expression, suppressed MMPs, improved the activities of TIMPs, and then promoted collagen deposition in the myocardium. NK4 intervention also decreased the microvessels' density and increased the apoptotic cell count in the myocardia of VCM mice. However, we did not observe the obvious changes in the myocardia of control mice after NK4 intervention. These data suggest that NK4 made negative impacts on the restoration of cardiac function and the recovery from VCM in the experimental mice.

Response to Letter Regarding Article, “Ablation of Matrix Metalloproteinase-9 Increases Severity of Viral Myocarditis in Mice”

It is now clear that release of metalloproteinase–9 (MMP-9)2 inhibition by tissue inhibitor of MMP-1 (TIMP-1)1 is beneficial during the acute phase of CVB3 myocarditis, but chronic MMP activation is detrimental3 after infection has been cleared. We investigated the course of coxsackievirus B3 (CVB3)–induced viral myocarditis within a murine MMP-9 knockout model.2 On accumulating initial data, it was clear that a detailed study was required to support our observation that MMP-9 was protective during acute CVB3 infection and myocarditis. We noted that CVB3 infection within the pancreas and liver was also higher in the MMP-9 …

Letter by Pinto and Heymans Regarding Article, “Ablation of Matrix Metalloproteinase-9 Increases Severity of Viral Myocarditis in Mice”

To the Editor: We have read with great interest the recent article by Cheung et al,1 revealing that matrix metalloproteinase-9 (MMP-9)–deficient mice had increased coxsackievirus B3 (CVB3) replication and resulting inflammation and injury in CVB3-induced myocarditis.1 These findings were to some extent unexpected considering our previous findings that systemic overexpression of the tissue inhibitor of MMPs (TIMP-1) reduced cardiac inflammation and prevented adverse remodeling and dysfunction in CVB3 myocarditis.2 To make it even more complicated, inhibition of TIMP-1 significantly decreased inflammation and injury in CVB3-induced myocarditis, despite lack of differences in viral load or T-cell function.3 What to learn from these seemingly paradoxical …

Ablation of Matrix Metalloproteinase-9 Increases Severity of Viral Myocarditis in Mice

Coxsackievirus B3 (CVB3) causes human myocarditis, which can result in cardiac damage, maladaptive remodeling, and heart failure. Matrix metalloproteinases (MMP)-8 and -9 have been identified in virus-infected myocardium, but their particular roles and underlying mechanisms of effect are unknown. For the first time, we examine the severity of CVB3-induced myocarditis in MMP-8-and MMP-9-deficient mice. CVB3-infected MMP-8 and MMP-9 knockout (KO) mice and corresponding wild-type (WT) mice were euthanized and harvested at 9 days after infection. Expression of MMP-2, -8, -12, and -13 and tissue inhibitors of MMPs was assessed by zymography or immunoblotting on harvested hearts, and in situ hybridization was performed to detect active infection. Infected MMP-9 KO mice had greater myocardial injury and foci of infection than WT mice despite similar pancreatic infection. Increased fibrosis (10.6+/-2.7% versus 7.1+/-2.6%, P=0.04), viral titer, as well as decreased cardiac output, were evident in MMP-9 KO compared with WT mice as assessed by picrosirius red staining, plaque assay, and echocardiography, respectively. Immune infiltration was also greatly increased in MMP-9 KO compared with WT mice (15.2+/-12.6% versus 2.0+/-3.0%, P<0.002). Myocardial interferon-beta1, interferon-gamma, interleukin-6, interleukin-10, and macrophage inflammatory protein-1alpha expression was elevated in MMP-9 KO mice as measured by quantitative real-time polymerase chain reaction and ELISA. In contrast, MMP-8 KO mice had the same degree of cardiac injury, fibrosis, and viral infection as their WT counterparts. During acute CVB3 infection, MMP-9 appears necessary to halt virus propagation in the heart, promote proper immune infiltration and remodeling, and preserve cardiac output.

Mao-to Prolongs the Survival of and Reduces TNF-α Expression in Mice with Viral Myocarditis

Goal of this study was to evaluate effects of Mao-to on development of myocarditis induced by encephalomyocarditis (EMC) virus in mice. Mice were randomly divided into five groups. Group N included uninfected controls (n = 18), while group A, B and C underwent intraperitoneal injection of EMC virus. Group A was administered oral saline from day 0 to day 4. Group B was administered oral Mao-to (500 mg−1 kg−1 day−1) from day 0 to day 4. Group C was administered Mao-to from day 2 to day 6. Group D was administered Mao-to from day 5 to day 10. Treated mice were followed for survival rates during 2 weeks after infection. Body weight (BW) and organ weights including heart (HW), lungs, thymus and spleen were examined on days 4, 6 and 14. Survival rate of group C (36.4%) was significantly improved compared with group A, B or D (0% of each, P < 0.05). HW and HW/BW ratio in group C was significantly (P < 0.05) lower than those in group A, B or D. Viral titers of hearts were significantly different among groups A, B and C. Cardiac expression in tumor necrosis factor-α (TNF-α) was significantly reduced in group C in comparison with group A, B or D on day 6 by immunohistochemical study. Administration of Mao-to starting on day 2 improves mortality resulting from viral myocarditis in mice with reduced expression of cardiac TNF-α. These findings suggest that timing of Mao-to is crucial for preventing cardiac damage in mice with viral myocarditis.

French Maritime Pine Bark Extract Inhibits Viral Replication and Prevents Development of Viral Myocarditis

Background French maritime pine bark extract (Pycnogenol) revealed diverse anti-inflammatory actions by an inhibition of NF-κB–dependent gene expression. The aim of this study was to determine whether Pycnogenol had a beneficial effect on viral myocarditis in mice. Methods and Materials Four-week-old inbred male DBA/2 mice were inoculated intraperitoneally with 10 plaque-forming units (pfu) of the encephalomyocarditis (EMC) virus. Pycnogenol was administered orally at a dose of 1 or 10 mg/kg per day for the histologic study, and 10 or 100 mg/kg for the gene expression study, beginning on the day of viral inoculation. Results The area of myocardial infiltration and necrosis on day 7 was significantly smaller in the hearts of mice treated with Pycnogenol 10 mg/kg (16.2 ± 8.9% and 19.2 ± 9.7%, respectively, n = 10, mean ± SEM) compared with controls (27.6 ± 15.0% and 30.1 ± 15.7%, respectively, n = 10, P < .05). There was a nonsignificant trend for less myocardial infiltration in the Pycnogenol 1 mg/kg group. Myocardial virus concentration on day 7 was 8.4 ± 0.3 × 10 3 pfu/mg in mice treated with 1 mg/kg of Pycnogenol, and 2.7 ± 0.6 × 10 4 pfu/mg in control mice, and the difference was statistically significant ( P < .05). Gene expressions of tumor necrosis factor, type-I procollagen, stem cell factor, and mast cell tryptase were significantly suppressed in the hearts of mice treated with Pycnogenol 100 mg/kg. Conclusions These results suggest that Pycnogenol exerts its beneficial effects on viral myocarditis by decreasing virus replication, and by suppressing expression of pro-inflammatory cytokines, genes related to cardiac remodeling, and mast cell–related genes in the hearts of mice.

Th cell differentiation in chronic stage of viral myocarditis in mice and interference of Qingxin-Ⅱ Recipe

To investigate part mechanisms of Th cell differentiation, and to observe the interference effect of Qingxin-II Recipe in the chronic stage of viral myocarditis (VMC), so as to provide some experimental evidences for illuminating the pathogenesis of VMC and treatment mechanisms of Qingxin-II Recipe. According to 20%-40% death rate of experiment in advance, 100 BALB/c male mice (4 weeks old and weighing 12-15 g) were used. Twenty mice were randomly assigned to normal control group, and the other 80 mice were intraperitoneally injected with 0.1 ml normal saline containing coxsackie virus B3 at the 1st, 4th and 28th day (the virus densities were 1:2000, 1:1000 and 1:500 respectively) to induce chronic VMC. At the 42nd day, the surviving mice were randomly divided into untreated group and treatment group, with 20 mice in each group. Mice in the treatment group were orally administered with 0.2 ml Qingxin-II Recipe every day, while mice in the normal control group and the untreated group were administered with 0.2 ml normal saline. All the mice were sacrificed after 45 days, and the sera, heart and spleen cells were collected. Then the myocardial pathological changes were observed by using a light microscope, and the levels of IL-4, IL-10 and IFN-gamma in serum were detected by enzyme linked immunosorbent assay (ELISA). And the Th cell differentiation was observed by flow cytometry. No obvious myocardial pathological changes were observed in mice of the normal control group. Myocardial pathological changes in the treatment group were slighter than those in the untreated group. The difference of serum IL-10 level between the normal control group and the untreated group showed no significance (P>0.05), and the levels of IFN-gamma and IL-4 of the untreated group were higher than those of the normal control group (P<0.05 or P<0.01). There was no statistical difference in IL-10 level between the treatment group and the untreated group (P>0.05), while the serum levels of IL-4 and IFN-gamma of the treatment group were lower than those of the untreated group (P<0.05 or P<0.01). There was no significant difference of the Th1 cell responder between the treatment group and the untreated group (P>0.05), while the Th2 cell responder was inhibited significantly in the treatment group (P<0.05). Qingxin-II Recipe can restore the balance of Thl and Th2 cells through inhibiting the reaction of Th2.

Complex genetic control of host susceptibility to coxsackievirus B3-induced myocarditis

The pathogenesis of viral myocarditis is a multifactorial process involving host genetics, viral genetics and the environment in which they interact. We have used a model of infection with coxsackievirus B3 (CVB3) to characterize the contribution of host genetics to viral myocarditis in mice of different genetic backgrounds but with a common H2 haplotype: A/J and B10.A-H2(a). Here we have used Evans blue dye as a quantitative biomarker for susceptibility to CVB3-induced myocarditis in addition to histopathological semiquantitative measures. We have found evidence of linkage between susceptibility to viral myocarditis and three loci. A locus on chromosome 1 centered on D1Mit200 was linked to sarcolemmal disruption in males (P=0.00005), a second locus on chromosome 4 centered on D4Mit81 was also linked to sarcolemmal disruption in males (P=0.0022). A third locus on distal chromosome 3 centered on D3Mit19 was linked to myocardial infiltration, with a logarithm of odds (LOD) score of 4.7 (P=0.0045), as well as sarcolemmal disruption in females (P=0.0015). These results provide strong evidence for the presence of loci contributing to the susceptibility of mice to viral myocarditis.

Relevance of inflammatory cell infiltrates for complete atrioventricular block in experimental murine myocarditis

There are few systemic pathologic studies on myocarditis. This study aimed to clarify the pathologic characteristics of murine myocarditis. We recorded serial electrocardiograms in experimental viral myocarditis in mice and then examined their cardiac pathology. After taking baseline electrocardiograms, we inoculated the mice intraperitoneally with the encephalomyocarditis virus. Electrocardiograms were serially recorded until 220 days after the virus inoculation. Serial electrocardiograms revealed ectopic beats, low voltage of the QRS complex, and the appearance of complete atrioventricular (AV) block. Corresponding myocardial lesions were found in the hearts of mice with these ectopic beats. Mononuclear cell infiltrations into the His bundle were most frequently found in mice with complete AV block. Inflammatory change with cellular infiltrations was the most common pathologic finding in mice with complete AV block. In clinical settings, anti-inflammatory therapy might be recommended for patients with myocarditis complicated with conduction disturbances.

283 u-PA-inactivation or TIMP-1-overexpression prevents cardiac injury and dysfunction during acute viral myocarditis in mice

283 u-PA-inactivation or TIMP-1-overexpression prevents cardiac injury and dysfunction during acute viral myocarditis in mice

Embryonic Stem Cells Attenuate Viral Myocarditis in Murine Model

We used mice to test our hypothesis that in response to viral invasion, stem cells may migrate into the heart and attenuate the effect of viral myocarditis. Male BALB/c mice were divided into three groups: mouse embryonic stem (ES) cell control, encephalomyocarditis virus (EMCV), and EMCV + ES cells. After administration of ES cells via tail vein, mice were immediately inoculated with EMCV. Mice were sacrificed at different days after EMCV inoculation. Mortality was recorded. Inflammatory cell infiltration and necrosis (major pathological changes of viral myocarditis) were evaluated by hematoxylin-eosin staining. ES cell migration and differentiation were identified by immunofluorescence. The survival rate in the EMCV + ES cell group (80%) was significantly increased (p < 0.05) over the EMCV-alone group (64%). Also, the incidence of inflammatory cell infiltration and myocardial lesions was lower in the EMCV + ES cell mice. Furthermore, the result of green fluorescent protein (GFP) and alpha-actinin analysis indicated that ES cells migrated into the heart and differentiated into myocytes after virus inoculation. In conclusion, ES cells significantly increased the survival of viral myocarditis mice and also decreased the necrosis and infiltration of inflammatory cells. These results demonstrated the ability of stem cells to mitigate the effects of viral infection on the heart and illustrated their potential therapeutic application to other mammalian species, including humans.

Oral administration of L-arginine prevents congestive heart failure in murine viral myocarditis.

It was previously demonstrated that administration of the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) aggravated viral myocarditis in mice. In the current study, the effects of l-arginine, a precursor of nitric oxide, on congestive heart failure (CHF) in myocarditis were evaluated. Dietary l-arginine and l-arginine plus l-NAME (l-arginine + l-NAME group) were administered to encephalomyocarditis virus-infected BALB/c mice over 4 weeks (experiment I) and to encephalomyocarditis virus-infected DBA/2 mice from the 4th through 12th weeks after the virus inoculation (experiment II). An infected control was prepared in each experiment. In experiment I, survival was higher in the l-arginine group compared with the other two groups, and cardiac damage was less, as was incidence of CHF. In addition, extravasated fibrin was less prominent in the l-arginine group. Plasma concentrations of l-arginine and nitric oxide were elevated in the l-arginine group. In experiment II, plasma cardiomyopathic lesions in the l-arginine group were less prominent and were associated with lower plasma catecholamine and lower myocardial collagen concentrations compared with the other two groups. l-arginine treatment may be effective in preventing the development of CHF in viral myocarditis by modifying postmyocarditic architectural remodeling.

Cocaine enhances myocarditis induced by encephalomyocarditis virus in murine model.

This study was designed to investigate whether cocaine can exacerbate viral myocarditis and increase its incidence. Recent clinical evidence suggests that cocaine abuse increases the incidence of myocarditis. However, it has not been directly demonstrated that cocaine exposure enhances murine myocarditis. BALB/c mice were divided into eight groups: saline control, encephalomyocarditis virus (EMCV), 10 mg/kg cocaine (Coc-10), 30 mg/kg cocaine (Coc-30), 50 mg/kg cocaine (Coc-50), EMCV+Coc-10, EMCV+Coc-30, EMCV+Coc-50. After inoculation with EMCV, the mice were treated daily with either cocaine or saline for 90 days. Mice were euthanized at different days after EMCV inoculation. Mortality was recorded and myocarditis severity was evaluated. The mortality of the myocarditis mice treated with cocaine increased significantly, from 22% (EMCV) to 25.7% (Coc-10+EMCV), 41.4% (Coc-30+EMCV), and 51.4% (Coc-50+EMCV) (P < 0.05), respectively. The incidence and severity of inflammatory cell infiltration and myocardial lesions was higher in infected mice exposed to cocaine. Cocaine administered only before infection did not exacerbate myocarditis. Norepinephrine (NE) assay showed that cocaine exposure significantly increased myocardial NE concentration but this increase was partially inhibited in infected animals. Adrenalectomy abolished the effect of cocaine on mortality. Furthermore, propranolol, a beta-blocker, significantly decreased the enhancing effects of cocaine on myocarditis mice. In conclusion, cocaine increases the severity and mortality of viral myocarditis in mice. Increased catecholamines may be a major factor responsible for this effect.

Reduction of cardiac endothelin-1 by angiotensin II type1 receptor antagonist in viral myocarditis of mice

Renin angiotensin system contributes to activation of circulating endothelin in congestive heart failure. To investigate the effects of angiotensin II receptor antagonist and angiotensin converting enzyme inhibitors (ACEI) on the levels of endothelin-1 (ET-1), we administered orally angiotensin II type1 receptor (AT1) antagonist, L-158,809 (ATA) (6, 1.2 and 0.12 mg/kg/day), enalapril (1 mg/kg/day) and captopril (7.5 mg/kg/day) for 14 days to mice with viral myocarditis, beginning 7 days after encephalomyocarditis virus (500 pfu/mouse) inoculation. Plasma ET-1, cardiac ET-1, heart weight (HW) and HW/ body weight (BW) ratio were examined and compared with infected untreated mice. Moreover, the HW (mg) and HW/BW (×10 −3) ratio were significantly (P<0.05) reduced in mice treated with ATA and ACEIs in comparison with infected control. ACEIs and higher dosed of ATA reduced myofiber hypertrophy. Both of plasma and cardiac ET-1 proteins were significantly elevated in infected control compared with uninfected normal mice. Plasma ET-1 was significantly (P<0.01) reduced in mice with three different concentrations of ATA but were not decreased in mice with captopril or enalapril compared with infected control. The expression of endothelin-1 mRNA was significantly reduced in mice with ATA in comparison with infected untreated mice by competitive RT-PCR. ATA reduced ET-1 protein and mRNA in the myocardium of mice with myocarditis, improving congestive heart failure and myofiber hypertrophy. We suggest the effect of ATA on the reduction of endothelin has a different pathway from angiotensin converting inhibitor and that ATA seems to be a useful agents for congestive heart failure due to viral myocarditis.

Effects of astragaloside in treating myocardial injury and myocardial sarco/endoplasmic ca2+ -atpase of viral myocarditis mice

To investigate the effects on myocardial injury and sarcoplasmic reticulum (SR) Ca(2+)-ATPase of viral myocarditis mice treated with Astragaloside (AS) and Astragalus Injection (AI). Viral myocarditis model was created by intraperitoneal inoculation with coxsackievirus B3m (CVB3m) solution and were divided into model, AS, AI and normal control groups. The mortality, myocardial pathological changes, serum cardiac troponin I (cTnI) and the activity of myocardial Sarco/Endoplasmic Ca(2+)-ATPase (SERCA) were observed. The mortality of model was higher than that of the normal control (P = 0.0042), AS and AI (P < 0.05). The serum level of cTnI of model was significantly higher than that of the normal control (P < 0.001), AS (P < 0.025) and AI (P < 0.05). The myocardial necrosis and inflammatory changes of AS and AI groups were alleviated than that of model (P < 0.01). The activity of myocardial SERCA of model were significantly lower than that of normal control (P < 0.001), AS (P < 0.01) and AI (P < 0.05). AS and AI have some protecting effects on myocardial injury of viral myocarditis mice. AS is the effective component of Astragalus membranaceus in treating viral myocarditis. One of the mechanisms of Astragalus membranaceus and AS for viral myocarditis mice depriving of the myocardial injury may be due to improve the activity of myocardial SERCA in the mice.

Interferon regulatory factor 3 is required for viral induction of beta interferon in primary cardiac myocyte cultures.

Viral myocarditis affects an estimated 5 to 20% of the human population. The antiviral cytokine beta interferon (IFN-beta) is critical for protection against viral myocarditis in mice. That is, nonmyocarditic reoviruses induce myocarditis in mice that lack IFN-alpha/beta, and nonmyocarditic reoviruses both induce more IFN-beta and are more sensitive to the antiviral effects of IFN-beta than myocarditic reoviruses in primary cardiac myocyte cultures. Induction of IFN-beta in certain cell types involves viral activation of the transcription factor interferon regulatory factor 3 (IRF-3). To address whether IRF-3 can induce IFN-beta in cardiac myocytes, primary cardiac myocyte cultures and control L929 cells were transfected with a plasmid constitutively expressing IRF-3. Overexpression of IRF-3 resulted in induction of IFN-beta in the absence of viral infection in both cell types. To address whether IRF-3 is required for viral induction of IFN-beta, cell cultures were transfected with a plasmid constitutively expressing a dominant negative IRF-3 protein. The dominant negative IRF-3 reduced reovirus induction of IFN-beta in control L929 cells and completely eliminated induction in primary cardiac myocyte cultures. This provides the first identification of a cardiac cellular factor required for viral induction of IFN-beta and the first report of any cell type requiring IRF-3 for this response.

Increased severity of viral myocarditis in mice lacking lymphocyte maturation

The role of lymphocytes in the pathogenesis of viral myocarditis is controversial. To better understand how lymphocyte maturation controls a virus-induced myocarditic process, a murine model of viral myocarditis was utilized. Encephalomyocarditis virus (EMCV) was inoculated intraperitoneally into three kinds of mice; virus-susceptible C57BL/6, virus-resistant 129/SV and recombination activity gene (RAG)-2 knockout 129/SV mice. The RAG2 participate in the maturity of T and B lymphocytes. Survival rate, heart weight (HW), HW to body weight (BW) ratio, viral genome, cardiac inflammation and myocardial necrosis were evaluated after EMCV (500 plaque forming unit/mouse) inoculation. On post-inoculation day 10, the survival rate of C57BL/6, 129/SV and RAG2 knockout mice were 42, 90 and 0%, respectively. Myocardial viral titer was significantly ( P<0.05) higher in C57BL/6 and RAG2 knockout mice than in 129/SV mice. In situ hybridization demonstrated the EMCV genome in the myocardium of RAG2 knockout and C57BL/6 mice, but not in 129/SV mice. At day 8, HW and HW/BW ratios were elevated ( P<0.05) in RAG2 knockout mice as well as C57BL/6 mice compared with 129/SV mice. Myocardial necroses were more severe in RAG2 knockout mice than in wild-type 129/SV mice. In conclusion, matured lymphocytes protect the development of viral myocarditis which includes viral replication and myocardial apoptosis.