Acetylcholine Receptor Antibodies in Primary Biliary Cirrhosis: Characterization of Antigen and Idiotypic Specificity

Auto‐antibodies against the acetylcholine receptor of skeletal muscle are considered to be the cause of the neuromuscular dysfunction in myasthenia gravis. However, such auto‐anlibodies also occur in disease states not accompanied by neuromuscular symptoms. Patients with primary biliary cirrhosis have a high prevalence of different auto‐antibodies, including antibodies against the acetylcholine receptor. In primary biliary cirrhosis, these anti‐receptor antibodies are predominantly of IgM isotype. The IgM antibodies show a broader reactivity with receptors from other species than antibodies from myasthenic patients, Immunoglobulins from patients with primary biliary cirrhosis bear the same receptor antibody‐associated idiotypes, but ihe repertoire is quantitatively different from that found in myasthenia gravis patients. The IgM receptor antibody activity in a serum from a patient with primary biliary cirrhosis could be inhibited by cardiolipin, poly [dT], poly[I], and ssDN A, whereas this antibody activity in serum from a patient with myasthenia gravis was slightly reduced only by cardiolipin. Generally, IgM antibodies from patients with primary biliary cirrhosis had a broader reactivity with polynucleotides and phospholipids than IgG antibodies and antibodies from patients with myasthenia gravis. These results indicate a difference in the fine specificity between acetylcholine receptor antibodies in primary biliary cirrhosis and in myasthenia gravis.