Characterization of anti-acetylcholine receptor antibody activity in patients with anti-mitochondrial antibodies

Antibodies binding to the acetylcholine receptor of human skeletal muscle were found in patients with different kinds of anti-mitochondrial antibodies. In patients with primary biliary cirrhosis (PBC), the antibody activity was found in monomeric and pentameric IgM as well as in IgG, whereas patients with other kinds of anti-mitochondrial antibodies had anti-receptor antibodies of predominantly IgG class. Mice transfused with immunoglobulins from patients with PBC showed a reduction of skeletal muscle receptors comparable to that found in mice who had received immunoglobulins from myasthenia gravis (MG) patients. The antibody affinity was of the same order of magnitude in MG and PBC but antibodies with multiple affinities were more common in PBC. In PBC, the anti-receptor antibody associated idiotype repertoire was markedly different from that found in MG.