Myocarditis: Infection Versus Autoimmunity

Myocarditis, which is the inflammation of the heart muscle, remains a vexing therapeutic problem. Many cases are associated with viral infection, and appropriate treatment may depend upon whether the disease is primarily infectious, immune-mediated, or both. The combination of endomyocardial biopsies with newer molecular and immunologic tools holds a promise of distinguishing the different etiologies of myocarditis, thus, guiding future treatments. Nucleic acid hybridization and polymerase chain reaction have been applied to detect viral genome persisting in the heart. Early trials with type 1 interferons have shown a promise in patients with biopsy-proven enteroviral infection. Antibodies to cardiac antigens and increased HLA expression in cardiac biopsies have been used to identify patients, most likely, to benefit from immunosuppression or immunoadsorption. Future advances in the therapy of inflammatory disease of the heart may be based on detailed studies of myocarditis in animal models. Using coxsackievirus B3 infection or cardiac myosin immunization, we have identified some critical steps leading from a self-limited viral myocarditis to chronic autoimmune myocarditis and sometimes, to dilated cardiomyopathy. Myocarditis offers an opportunity to dissect the complex interaction between a viral infection and an autoimmune disease. The lessons learned from investigations in humans and in animal models hold a promise that may lead the way to improved treatments.