The viral genetic background determines the outcome of coxsackievirus B3 infection in outbred NMRI mice

The reasons for the different outcome of coxsackievirus B3 (CVB3)-induced heart disease in humans are not well understood. Since there are no experimental data on the course of disease after infection with genetically different CVB3 in a natural variable population until now, we studied the outcome of virus infection in outbred NMRI mice after inoculation of genetically different CVB3 variants. Adult male mice were inoculated with seven closely related CVB3 variants. The histopathological changes of heart and pancreas tissue, antibody induction, virus titers, and persistence of viral positive- as well as negative-strand RNA in spleen and heart tissue were compared at day 7 or day 28 after infection to detect prerequisites and predictive factors for chronic myocarditis. Six CVB3 variants infected NMRI mice. CVB3 infection (i) did not induce detectable myocardial injury, (ii) caused signs of healing up acute myocarditis or (iii) ongoing chronic myocarditis. Neither IgG antibody responses nor the extent of destruction of exocrine pancreatic tissue or viral RNA load in spleen did correlate with myocardial histopathology. In contrast, a high persistent viral RNA load in heart tissue specimens was characteristic for mice developing chronic myocarditis. The results of the present study corroborate high viral load in the acute stage of myocarditis and high amounts of persisting CVB3 RNA in heart tissue as predictive marker of chronic myocarditis. The outcome of CVB3-induced heart disease in outbred NMRI mice depends strongly on the viral genetic background. In particular an important role of viral capsid proteins is suggested.

Alternative methods for validation of cell culture infection with duck hepatitis B virus

Hepatitis B virus (HBV) is an important virus used in disinfection procedures for blood spillage. However, validation of HBV inactivation is difficult, since there are no feasible infectivity assays. In some countries, the duck HBV (DHBV) is recognized as a suitable model for testing antiviral activity of chemical biocides against HBV. Currently, DHBV-infected ducks are required for preparation of the test virus as well as eggs from DHBV-free flocks for testing DHBV infectivity. To improve the practicality of the system, we suggested to use commercially available embryonated duck eggs for preparation of DHBV-susceptible hepatocyte cultures and to exclude infected hepatocytes by pre-screening with qualitative detection of DHBV DNA using polymerase chain reaction (PCR). A standardized DHBV test virus was prepared from the DHBV DNA-transfected hepatoma cell line D2, which contained 10(11)DHBV DNA molecules per mL detected by light cycler real-time PCR. Infection of cell cultures was most efficient 4 days after plating. The best identification of infected cultures was possible 6 days after infection with immunofluorescence using an antiserum against DHBV surface antigen.

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.

Cytokine profiles in heart, spleen, and thymus during the acute stage of experimental coxsackievirus B3-induced chronic myocarditis

Since cytokines play an important role in the pathogenesis of virus-induced chronic heart diseases, cytokine mRNA expression was studied in coxsackievirus B3-infected NMRI mice during the acute phase of myocarditis until the onset of chronic cardiac disease. Virus replication, cytokine induction, inflammatory cell infiltration and myocardial damage were studied by titer determination, reverse transcription-polymerase chain reaction (RT-PCR), and histopathology. To investigate whether the coxsackievirus B3-induced cytokine mRNA accumulation was only limited to the heart or generalized, spleen and thymus specimens were also included. Surprisingly, interleukin (IL)-10 as a deactivator of T cell and macrophage functions was transcribed in the myocardium nearly in parallel with virus replication from Day 1 through Day 14. At Day 3 p.i., the mRNA of IL-1alpha, tumor necrosis factor (TNF)-alpha, IL-6, and interferon (IFN)-beta accumulated. At Days 4, 7, and 14, IL-12-specific mRNA was produced. Furthermore, increasing amounts of IFN-gamma mRNA were found, whereas IL-2 and IL-4 mRNA remained undetectable. TNF-alpha, IL-1alpha, IL-10, IL-12, and IFN-gamma mRNA persisted into the late stage of myocarditis. In the spleen a closely correlated expression of virus and IL-10-specific mRNAs was also found, and in addition, IFN-beta, TNF-alpha, and IL-6 were detected. In striking contrast to heart and spleen tissue, the distinct expression of viral RNA in the thymus was not accompanied by an increased cytokine mRNA production. These data provide evidence for a unique coxsackievirus B3-induced cytokine pattern in the myocardium and spleen and suggest that persistently expressed IL-10 may play a leading role in acute and chronic myocarditis by subverting the immune response.

Expression of inducible nitric oxide synthase in experimental viral myocarditis

Nitric oxide (NO) is an important bioactive molecule with regulatory, cytotoxic or cytoprotective properties. In virus-induced myocarditis, NO mediates host defense mechanisms against the infection or causes cardiac dysfunctions. NO is synthesized from L-arginine by the enzyme nitric oxide synthase (NOS). The expression of the inducible form of the nitric oxide synthase (iNOS) is regulated by cytokines, involved in the complex myocardial immune response to enterovirus infections. The present study was undertaken to characterize the role of iNOS and NO in the murine model of viral myocarditis induced by coxsackievirus B3 (CVB3). In response to CVB3 infection we investigated the time course of iNOS induction in correlation with cytokine mRNA expression (TNF-alpha, IL-1 alpha, IFN-gamma, TGF-beta) in the heart of NMRI mice by RT-PCR. Positive PCR signals for viral RNA were found in the acute and chronic stage of disease by seminested PCR, indicating the persistence of viral genome. We found distinct expression of iNOS at all time points (1, 2, 3, 4, 7, 14, 28, 56, 98 days post infection [p.i.]). Higher iNOS mRNA levels were identified between days 4 until 28 p.i. in comparison to day 56 and 98 p.i. using densitometric values. The mRNA of the inflammatory cytokines TNF-alpha, IL-1 alpha, IFN-gamma appeared at days 1, 4, and 7 p.i., peaked at day 7 p.i. and persisted until day 98 p.i. Similar like the iNOS mRNA pattern was the expression profile of TGF-beta. Using in situ hybridization and immunohistochemistry iNOS was localized in infiltrates, vascular endothelial cells, smooth muscle cells, myocytes and throughout the interstitial spaces between myocardial fibers in the heart sections of NMRI mice. Increased levels of NO were measured as total nitrate/nitrite concentration in the sera of mice from day 7 until day 28 p.i.

Coxsackievirus B3-induced chronic myocarditis in outbred NMRI mice

OBJECTIVES

The pathogenesis of coxsackievirus B3 (CVB3)-induced myocarditis was investigated in adult Han:NMRI mice. The outbred model, in comparison with inbred models, represents better the natural variable susceptibility of the human population.

STUDY DESIGN/METHODS

We analyzed the replicating virus titer, the antibody response in the acute and chronic phase of disease, the histology of myocardial injury, and the persistence of viral RNA.

RESULTS

NMRI mice infected with 5000 plaque-forming units (PFU) of the CVB3 variant "P"D, a lytic variant to human fibroblast lines, showed a peak of virus replication at day 14 and developed a severe acute myocarditis. The chronic myocarditis was characterized by progressive fibrosis, small foci of infiltrates, persistent viral RNA in the heart, and detectable anti-CVB3 IgG production and neutralizing antibody response up to day 98 postinfection.

CONCLUSIONS

CVB3"P"D is able to induce chronic myocarditis in NMRI mice. This model provides a method for examining and proving the mechanisms of myocardial pathogenesis and of developing therapeutic strategies.

Coxsackievirus B3-induced myocarditis in MHC class II-deficient mice

OBJECTIVES

The pathogenesis of coxsackievirus B3 (CVB3)-induced myocarditis was investigated in immunocompetent C57BL/6 and MHC class II knockout mice with identical genetic backgrounds.

STUDY DESIGN/METHODS

We analyzed the histology and immunohistology of myocardial injury, the replicating virus titer, and antibody response in the early and late phase of disease.

RESULTS

CVB3-infected C57BL/6 mice showed acute myocarditis, with spontaneous healing, virus elimination, anti-CVB3 IgM/IgG production, and neutralizing antibody response. In contrast, MHC class II knockout mice developed less severe acute myocarditis, persistence of infiltrations and strong fibrosis, virus persistence, and weak IgG response, with absence of virus neutralizing antibodies.

CONCLUSIONS

Immunodeficient organisms are more susceptible to long-term heart muscle injuries after infection with CVB3. The presence of CD4+ T cells are necessary to prevent the development of chronic disease.