Pathogenesis Of Viral Myocarditis Research Articles

Expression of IL-1β and TNF-α in MCMV myocarditis and its role

In order to study the expression of IL-1beta and TNF-alpha in the myocardium of MCMV myocarditis and their role in the myocardial damages, 60 BALB/C mice of 4 weeks were randomly divided into two groups: 36 were injected intraperitoneally with MCMV and 24 served as control group. Immunohistochemistry was used to detect IL-1beta and TNF-alpha expression in the myocardium, and myocardial lesions were observed histopathologically. Histopathological study on the myocardium from infected mice revealed focal or diffuse lesions characterized by inflammatory cells and degeneration or necrosis of myocytes. The myocardial lesion score showed the degree of inflammatory cell infiltration was slight in MCMV myocarditis. The positive staining signals for IL-1beta and TNF-alpha proteins which mainly located in the infiltrating inflammatory cells and degenerative or necrotic myocytes were markedly detectable whereas there were no positive findings in the myocardium of control mice. IL-1beta and TNF-alpha was expressed in the myocardium of viral myocarditis murine model induced by MCMV. IL-1beta and TNF-alpha may play an important role in the pathogenesis of viral myocarditis.

Roles of mast cells in the pathogenesis of viral myocarditis; reconstitution of mast cells to their deficient mice

Background and Study Objectives: Mast cells (MC) are increased in numbers at atherosclerotic and various cardiovascular diseases. We found that stem cell factor (SCF), MC growth factor, and MC density were significantly increased in the heart of mice with encephalomyocarditis virus (EMCV) myocarditis. Furthermore, MC-deficient mice had less prominent histopathologic lesions of viral myocarditis than controls (7.6 ± 3.5%vs.29.3 ± 15.6% area for infiltration; P < 0.01;7.6 ± 3.5%vs.30.0 ± 17.2% area for necrosis; P < 0.01,n = 10). In this study, MC were reconstituted to deficient mice, and the histopathology and gene expression of mouse MC protease (mMCP) and MMP-9 as markers of remodeling were examined in the hearts of MC-reconstituted mice with myocarditis. Methods and Results: MC were reconstituted in WBB6F1-Kit W/Kit W-v(W/W V) mice (which have a mutation of c-kit, SCF receptor) by transplantation of bone marrow-derived MC c-kit+. MC-reconstituted W/W V mice was then inoculated with 10 pfu of EMCV i.p. On day7, myocardial necrosis and cellular infiltration were more prominent in reconstituted than in non-reconstituted mice (W/W V mice:15.9 ± 5.0%vs.8.2 ± 4.9% area for infiltration; P < 0.01,6.9 ± 3.7%vs.4.1 ± 1.6% area for necrosis; P < 0.05, n = 10). The gene expressions of mMCP-4,-5 (MC chymase) and MMP-9 were higher in the reconstituted W/W V mice than in control W/W V mice. Furthermore, the gene expressions of mMCP-4,-5 and MMP-9 were correlated. Conclusions: In viral myocarditis, MC exert deleterious effects. The fibrogenic process that they mediate begins in the acute phase of disease, and inhibition of their activation may be therapeutic.

Local Expression of Interleukin-1 Receptor Antagonist by Plasmid DNA Improves Mortality and Decreases Myocardial Inflammation in Experimental Coxsackieviral Myocarditis

The inflammatory cytokines have an important role in the pathogenesis of viral myocarditis. Inerleukin-1 (IL-1) is one of the major cytokines that modulate the outcome of viral infection. Among the methods for in vivo gene transfer, direct injection of plasmid DNA is one that is simple and feasible. In this study, we expressed human IL-1 receptor antagonist (hIL-1Ra) in the mouse heart by direct injection of a novel plasmid vector and evaluated its effects on coxsackieviral (CVB3) myocarditis. A plasmid vector expressing hIL-1Ra (total 40 microg/mouse) was injected into the heart apex of 8-week-old inbred female Balb/C mice (day 3). On day 0, mice (IL-1Ra-CVB3, n=35) were infected intraperitoneally with 10(4) PFU of CVB3; control mice (pCK-CVB3, n=15) were injected with empty vector on day -3 and infected on day 0. hIL-1Ra was expressed in the heart, reached its peak on day 5, and persisted for 2 weeks. The 14-day survival rate of IL-1Ra-CVB3 was higher (77%) than that of controls (30%, P<0.01). Myocardial virus titers on day 3 were lower in IL-1Ra-CVB3 mice. Myocardial inflammation on day 7 and fibrosis on day 14 were markedly decreased in IL-1Ra-CVB3. These results showed that direct injection of the expression plasmid vector into the heart was an effective method to transfer the cytokine gene in vivo, and expressed IL-1Ra in the heart can modulate the deleterious effect of the host immune response in viral myocarditis.

The study on intramyocardial calcium overload and apoptosis induced by coxsackievirus B3.

The isolated cardiac myocytes of rats were immediately infected by cosackievirus B3 (CVB3) to investigate the effects of such procedure on the cell cycle, apoptosis and intracellular ionized calcium (Ca2+ i) of cardiac myocytes. Newborn Balb/c murine cardiac myocytes were cultivated, then infected by CVB3. Intracellular Ca2+ i was measured by flow cytometer. The calcium in the medium for culturing cardiac myocytes was detected by using atom absorb spectrum test. It was found that CVB3 could markedly inhibit the differentiation and proliferation of the infected cardiac myocytes and induce the apoptosis. The intracellular Ca2+ i level in the infected group was significantly higher than in the control group (P < 0.01). The calcium concentration in the medium for culturing cardiac myocytes in the infected group was significantly lower than in the control group (P < 0.05). It was suggested that the apoptosis and intracellular calcium overload of the CVB3-affected cardiac myocytes are likely to play an important role in the pathogenesis of viral 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.

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.

Expression of costimulatory molecule CD40 in murine heart with acute myocarditis and reduction of inflammation by treatment with anti-CD40L/B7-1 monoclonal antibodies.

Evidence has accumulated that antigen-specific T cells infiltrate the heart and play an important role in the pathogenesis of viral myocarditis. Costimulatory molecules such as B7s and CD40 expressed on antigen-presenting cells are known to play a critical role for antigen-specific T-cell activation to occur. To investigate the role for a costimulatory molecule, CD40, in the development of acute viral myocarditis, we first analyzed the expression of CD40 in the hearts of mice with acute viral myocarditis induced by Coxsackievirus B3. We also evaluated the induction of CD40 in cultured cardiac myocytes treated with interferon gamma in vitro. Second, we analyzed the cytokine production by cultured cardiac myocytes by stimulation with anti-CD40 monoclonal antibody (mAb) in vitro. Third, we examined the effects of in vivo administration of anti-CD40L/B7-1 mAbs on the development of acute viral myocarditis. We found that Coxsackievirus B3-induced murine acute myocarditis results in enhanced expression of CD40 on cardiac myocytes. The expression of CD40 on cardiac myocytes could be induced by interferon gamma in vitro. We also found that the production of interleukin-6 by cardiac myocytes was stimulated with anti-CD40 mAb and that in vivo anti-CD40L/B7-1 mAb treatment significantly decreased the myocardial inflammation. Our findings strongly suggest that CD40 plays an important role in the development of acute viral myocarditis and raise the possibility of immunotherapy with anti-CD40L/B7-1 mAbs to prevent T cell-mediated myocardial damage in viral myocarditis.

Enhanced expression of superoxide dismutase messenger RNA in viral myocarditis. An SH-dependent reduction of its expression and myocardial injury.

The oxygen free radical system has been reported to be activated by influenza virus infection in the lungs. However, the involvement of oxygen radicals in viral myocarditis is still unknown. Captopril, an angiotensin-converting enzyme (ACE) inhibitor and potent free radical scavenger with a sulfhydryl group, was effective for the treatment of viral myocarditis, while enalapril, an ACE inhibitor without a sulfhydryl group, was not effective against acute myocarditis. In this study, we investigated the role of oxygen radicals in the pathogenesis of viral myocarditis and the therapeutic effects of agents with a sulfhydryl group. 4-wk-old BALB/c mice were inoculated with the encephalomyocarditis virus, and treated with captopril or N,2-mercapto-propionyl glycine (MPG), a sulfhydryl-containing amino acid derivative without ACE inhibiting property, from days 4 to 14. On day 14, captopril and MPG significantly improved survival of mice and myocardial injury (necrosis, cellular infiltration, and calcification) in a dose-dependent manner compared with the infected control group. Thus, captopril and MPG were effective for the treatment of virus-induced myocarditis. Furthermore, a striking induction of manganese superoxide dismutase (Mn-SOD) and copper/zinc SOD (Cu/Zn-SOD) mRNAs in infected hearts was found (8-13-fold for Mn-SOD and 4-11-fold for Cu/Zn-SOD) when compared with age-matched uninfected mice hearts. MPG completely inhibited the increase of both mRNAs, even when treatment was started on day 4. Thus, oxygen radicals may play an important role in the pathogenesis of viral myocarditis, and a therapeutic approach by eliminating oxygen radicals seems possible.

Expression of intercellular adhesion molecule-1 in murine hearts with acute myocarditis caused by coxsackievirus B3.

A cell-mediated autoimmune mechanism has been strongly implicated in the pathogenesis of viral myocarditis. Using a murine model of myocarditis caused by coxsackievirus B3 (CVB3), we previously reported that the heart is infiltrated first by natural killer cells, which express a cytolytic factor, perforin, and then by activated T cells. This action may play an important role in the pathogenesis of the observed myocardial cell damage. Cell-cell contact and adhesion is required in immune responses, and intercellular adhesion molecule-1 (ICAM-1), which is a ligand for lymphocyte function-associated antigen-1 (LFA-1), plays an important role in this process. To investigate the essential role of the ICAM-1/LFA-1 pathway in the cell-mediated cytotoxicity involved in viral myocarditis, we examined by immunofluorescence the expression of ICAM-1 in murine hearts with acute myocarditis caused by CVB3. We also evaluated the induction of ICAM-1 in cultured cardiac myocytes treated with cytokines by immunofluorescence and Northern blot hybridization. Furthermore, we analyzed the effects of in vivo administration of anti-ICAM-1 mAbs on the inflammation associated with acute viral myocarditis. We found that CVB3-induced murine acute myocarditis resulted in enhanced expression of ICAM-1 in myocardial cells. The expression of ICAM-1 in myocardial cells could be induced in vitro by IFN-gamma and TNF-alpha, which were shown to be synthesized by the infiltrating cells. In vivo treatment with F(ab')2 fragments of an anti-ICAM-1 mAb significantly reduced the myocardial inflammation induced by CVB3. These data strongly suggest that the expression of ICAM-1 in myocardial cells plays a critical role in the cell-mediated cytotoxicity involved in acute viral myocarditis.

Expression of perforin in infiltrating cells in murine hearts with acute myocarditis caused by coxsackievirus B3.

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of viral myocarditis. Using a murine model of acute myocarditis caused by coxsackievirus B3, we analyzed the phenotypes and morphology of the infiltrating cells in the hearts by immunofluorescence and electron microscopy. We also examined the expression of a cytolytic factor, perforin, in the infiltrating cells by immunoperoxidase and in situ hybridization. We found that the dominant population of the infiltrating cells were asialo GM1 positive, were negative for T-cell markers, and had electron-dense cytoplasmic granules, which is consistent with a morphology of large granular lymphocytes. Perforin was found in the cytoplasmic granules of the infiltrating cells expressing perforin messenger RNA. These findings provide for the first time the direct evidence that the first wave of cell infiltration in hearts mainly consists of killer cells and strongly suggests that perforin plays, in part, an important role in myocardial cell damage involved in acute viral myocarditis. T-helper cells and cytotoxic T lymphocytes made up the second wave of cell infiltration. As we previously reported, the expression of major histocompatibility complex class I antigen on cardiac myocytes induced by the infiltrating cells, such as killer cells, may facilitate the interaction between cardiac myocytes and cytotoxic T lymphocytes, and may lead to further myocardial cell damage in a later phase.

Expression of major histocompatibility complex class I antigen in murine ventricular myocytes infected with Coxsackievirus B3.

Evidence has accumulated that T cell-mediated autoimmunity plays an important role in the pathogenesis of viral myocarditis. T lymphocytes are known to recognize antigen-presenting cells, such as virus-infected cells, being restricted by syngeneic major histocompatibility complex (MHC) antigens. To clarify in more detail the immunological mechanisms involved, we induced acute viral myocarditis in C3H/He mouse ventricles with coxsackievirus B3 (CVB3) and examined, by immunofluorescence, the expression of MHC class I and II antigens, previously reported not to be expressed by normal cardiac myocytes. Furthermore, to confirm the expression of MHC class I (H-2Kk) antigens at the cellular level, we treated cultured cardiac myocytes with interferon gamma and examined the antigen expression by immunofluorescence and Northern blot hybridization, using an antisense RNA probe for MHC messenger RNA. Our observations demonstrated 1) CVB3-induced myocarditis resulted in the enhanced expression of MHC class I (H-2Kk) gene product on the surface of cardiac myocytes but low or undetectable levels of MHC class II or H-2Dk gene products, and moderate focal transient (days 5-7) expression of both MHC class I (Kk + Dk) region gene products and MHC class II antigens were induced on capillary endothelial cells; 2) murine fetal cardiac myocytes cultured in vitro in the presence of interferon gamma similarly were shown to express marked levels of MHC class I (H-2Kk) but low to undetectable levels of the H-2Dk gene product; however, weak to moderate MHC Class II antigens were expressed by these cultured myocytes; and 3) the expression of MHC antigens in cardiac myocytes was modulated at the transcriptional level.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological changes induced in cardiac myocytes by cytotoxic T lymphocytes.

The "lethal hit" induced by viral specific, sensitized, cytotoxic T lymphocytes (CTL) attacking virus-infected heart cells is important in the pathogenesis of viral myocarditis and reflects the key role of CTL in this immune response. The mechanisms involved are incompletely understood. Studies of the physiological changes induced in mengovirus-infected, cultured, neonatal, rat heart cells by CTL that had been previously sensitized by the same virus are presented. The CTL were obtained from spleens of mengovirus-infected, major histocompatibility complex (MHC) matched adult rats. Cell wall motion was measured by an optical method, action potentials with intracellular microelectrodes, and total exchangeable calcium content by 45Ca tracer measurements after loading the myocytes with 45Ca and then exposing them to CTL. After 50 min (mean time) of exposing mengovirus-infected myocytes to the CTL, the mechanical relaxation of the myocyte was slowed, with a subsequent slowing of beating rate and a reduced amplitude of contraction. Impaired relaxation progressed, and prolonged oscillatory contractions lasting up to several seconds appeared, with accompanying oscillations in the prolonged plateau phase of the action potentials. Arrest of the myocyte contractions appeared 98 min (mean time) after exposure to CTL. These changes in action potentials and contractions were reversible either by washout with the normal medium or by the addition of verapamil. The amount of total exchangeable calcium in the cultured myocytes, 1 h after exposure to CTL, was significantly increased. This increase was prevented by pretreatment with verapamil. (ABSTRACT TRUNCATED AT 250 WORDS)