What lessons can be learned from animal model studies in viral heart disease?
Several well-defined coxsackievirus B3 (CVB3)-murine models of inflammatory heart disease are providing information about mechanisms which contribute to myocyte necrosis. Severity of disease induced and mechanisms responsible depend upon unresolved molecular activities of the viral genome, nonspecific defenses of the mouse at time of infection and immune responses of the mouse at the time of infection. Most important are the capabilities and directed responses of each mouse to infection which are determined by age and genetic background of the host. In addition to virus-induced contributions to tissue pathology during primary infection, persistence of viral genomes for week to months in some strains of mice forecast whether the acute disease will resolve or continue as chronic disease with sustained inflammatory reactions in the myocardium. Persistent infections can contribute to nascent cardiopathologic alterations by chronic induction of inflammatory events through expression of viral genes and altered expression of host genes during nonlytic infections. Products of these expressions include viral proteins and nonhomeostatic levels of cytokines and arachidonic acid cascade intermediates and final metabolites. Molecular mimicry via shared epitopes between virion capsid proteins and normal cell molecules/structures located on or within heart tissue cells may be the mechanism by which immune systems in certain strains of mice are persistently stimulated. The products of these immune responses, i.e. antibodies and cytotoxic T lymphocytes, may provide initial protection via termination of infection and virus clearance during acute disease but subsequently these autoreactive processes could contribute to chronic disease. The immune effector products (antibodies and T lymphocytes) have potential pro-inflammatory reactivities, capacity for exacerbating ongoing CVB3-induced disease and/or can induce disease in normal animals. In further support of the hypothesis that autoimmune reactions contribute to sustained inflammation of the heart, non-viral models of myocarditis have been developed. Cell constituents such as myosin and adenosine nucleotide translocator protein can induce cardiopathologic alterations in normal mice of strains known to develop CVB3-induced chronic disease. Thus host genetic background determines whether a mouse survives the initial infection, resolves the acute disease or inadvertently contributes to sustained inflammatory heart disease. Finally, shared epitopes among the enteroviruses may play a role in repeated episodes of disease during sequential infections by different serotypes.