The concept of autoimmunity in the pathogenesis of
myocarditis or
dilated cardiomyopathy is gaining impetus. Since systolic functional impairment and subsequent recovery are frequently observed in
myocarditis, we reasoned that the development of autoimmunity to cardiac
sarcoplasmic reticulum calcium ATPase (SR-
Ca2+ ATPase), which could interfere with intracellular
calcium regulation and therefore affect myocardial contractility, should lead to immune-mediated
myocarditis in experimental animals. Murine
monoclonal antibody 4C11-20.21 (
IgM class) generated against canine cardiac SR-
Ca2+ ATPase inhibits the cardiac but not the skeletal
ATPase activity. Immunization of CAF1/J mice with 4C11-20.21-affinity-column-purified cardiac SR-
ATPase produced a time-dependent induction of myocardial injury consistent with the diagnosis of
myocarditis. Furthermore, the antibody 4C11-20.21 alone can induce myo-
necrosis in
severe combined immunodeficiency (SCID) mice indicating a mechanism of
cardiomyopathy independent of the cytotoxic T-cell mediated autoimmunopathy. Administration of 4C11-20.21 into immunocompetent CAF1/J mice resulted in minimal myocardial abnormality (40% with perivascular and/or interstitial mononuclear lymphoplasmacytoid aggregates, 10% with borderline
myocarditis and 10% with lesions consistent with focal
myocarditis). All control animals had normal hearts. Immunoperoxidase electron microscopic examination of the involved cardiac tissues showed antibody localization in the subsarcolemmal myotubular system and focal staining of the immediately adjacent sarcolemma in mice injected with 4C11-20.21 but not with 2C12.1B5. The time-dependent association between cardiac SR-
Ca2+ ATPase administration and development of myocardial lesions, as well as potentiated induction of myonecrosis with anti-cardiac SR-
Ca2+ ATPase antibody in SCID relative to immunocompetent mice, suggest a potential autoimmunopathogenic role of cardiac SR-
Ca2+ ATPase in experimental
myocarditis.