Incidence and reactivity patterns of skeletal and heart (SH) reactive autoantibodies in the sera of patients with myasthenia gravis

Serum from patients with myasthenia gravis (MG) contain antibodies to numerous skeletal muscle components in addition to the acetylcholine receptor (AChR). Certain non-AChR skeletal muscle autoantibodies have been shown by absorption to cross-react with cardiac muscle, leading to the designation of ‘skeletal and heart’ or SH antibodies. This study describes a new procedure for the extraction of human cardiac muscle which allows direct determination of SH antibody reactivity. Serologic evaluation of 17 patients with MG revealed 9 17 (53%) were seropositive for SH antibody to cardiac muscle. Absorption of selected MG serum samples with cardiac muscle extracts, reduced or eliminated reactivity to skeletal muscle in all cases, confirming the presence of cross-reactive antibodies. Immunoblot analysis of cardiac muscle extracts demonstrated several distinct antigenic components, which were unrelated to the acetylcholine receptor or to previously identified striatonal muscle proteins. Serum samples from individual MG patients displayed different immunoblot reactivity patterns to the antigens in cardiac muscle extracts, providing the first evidence of multiple heart-reactive SH antibodies in MG.