title: [Pathogenic antibodies in myasthenia gravis].
abstract: Myasthenia gravis (MG) is the most common autoimmune disorder of the neuromuscular junction and is clinically characterized by weakness and muscle fatigue. We have classified MG into 3 types on the basis of the antibody pattern. The first type associated with acetylcholine receptor (AChR) autoantibodies, which predominantly belong to IgG1 subclass and are measured by a conventional radioimmunoprecipitation assay with 125I-alpha-bungarotoxin. This subtype occurs in approximately 80% of patients with MG and leads to the loss of AChR number and function, mainly by complement-mediated destruction of the neuromuscular junction. Approximately 40% of patients with MG who have AChR antibodes have a thymoma as a paraneoplastic neurological syndrome. However, the role of antigen expression by thymomas is unclear. The second type of MG occurs in a proportion of "seronegative" patients who did not have AChR autoantibodies. These patients process IgG autoantibodies to muscle-specific tyrosine kinase (MuSK); these antibodies are predominantly of the IgG4 subclass but are not associated with complement-mediated damage to the neuromuscular junction or with the presence of thymomas. In most patients with MuSK antibodies, the symptoms of MG improve after plasma exchange; these patients show a good response to steroid and immunosuppressive drugs but a poor response to thymectomy. MG not associated with the presence of the 2 abovementioned pathogenic autoantibodies is classified as heterogeneous "double seronegative" MG. Our classification is superior to the present classifications with regard to the mechanism, treatment, and prognosis of the disease.
authors.affiliation: First Department of Clinical Neuroscience and Neurology, Graduate School of Biomedical Sciences, Nagasaki University, 1-7-1 Sakamoto, Nagasaki 852-8501, Japan.
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Motomura
mesh_terms: D001323:Autoantibodies; D006801:Humans; D007074:Immunoglobulin G; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D009157:Myasthenia Gravis / Q000276:immunology / Q000628:therapy; D009469:Neuromuscular Junction; D020361:Paraneoplastic Syndromes, Nervous System; D010951:Plasma Exchange; D011505:Protein-Tyrosine Kinases / Q000276:immunology; D011950:Receptors, Cholinergic / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D007074:Immunoglobulin G; D007166:Immunosuppressive Agents; D011950:Receptors, Cholinergic; D011505:Protein-Tyrosine Kinases