Autoimmunity in viral myocarditis.

PURPOSE OF REVIEW: To review how autoimmunity is induced in viral myocarditis. RECENT
FINDINGS: Clinical and experimental myocarditis follows microbial infections, but autoimmunity to cardiac antigens leads to heart failure since infected myocytes are sparse and virus clearance is rapid. In mice, CD4+ T cells specific for cardiac alpha myosin heavy chain (αMYHC) cause myocarditis and mice tolerized to αMYHC are protected from virus challenge proving pathogenesis depends upon autoimmunity. Most importantly, multiple microbes share the same mimicking epitope with αMYHC. Serial infections with very different microbes could result in memory responses to the shared epitope leading to aggressive and severe heart failure. A similar phenomenon may explain autoimmune diseases with suspected infectious causes, where specific pathogens have not been identified. Production of the relevant cardiac epitope for antigen presentation requires more than myosin release from dead myocytes. Otherwise, myocarditis would commonly follow myocardial infarcts. The inherent nature of the innate immune response associated with viral infections in the heart is crucial to cardiac epitope expression.
SUMMARY: Antigenic mimicry between microbes and cardiac proteins causes autoimmunity in myocarditis. Characteristics of innate immunity associated with cardiac infection determine relevant epitope expression (cryptic epitopes).