Anti-pyruvate dehydrogenase complex-E2 antibody immunoglobulin class switch from IgM to IgG in long-term follow-up patients with primary biliary cirrhosis.

Antibody immunoglobulin class switching from IgM to IgG is usually observed in acute viral infections. However, in autoimmune diseases, the autoantibody immunoglobulin class switch from IgM to IgG has been observed only rarely, and the clinical relevance of this immune phenomenon remains unclear. In this report, anti-pyruvate dehydrogenase complex (PDC)-E2 antibody immunoglobulin class switching was followed in two patients with primary biliary cirrhosis (PBC). IgG and IgM anti-PDC-E2 antibodies were examined by an originally enzyme-linked immunosorbent assay and by immunoblot using human recombinant PDC-E2 protein. In both patients, serum IgG and IgM anti-PDC-E2 antibodies could not be detected at initial admission. However, IgM antibody was subsequently detected, and IgG antibody appeared several years thereafter.