Profile of the regions on the alpha-chain of human acetylcholine receptor recognized by autoantibodies in myasthenia gravis.

Eighteen synthetic overlapping peptides encompassing the entire extracellular part (residues alpha 1-210) of the alpha-chain of human acetylcholine receptor (AChR) and a 19th peptide (residues alpha 262-276) corresponding to an extracellular connection between two transmembrane regions were prepared and used for the measurement, by solid-phase radioimmunoassay, of the binding of autoantibodies in plasma from myasthenia gravis (MG) patients. Autoantibodies were found to recognize only a limited number of the synthetic peptides. The regions recognized resided predominantly within the areas alpha 10-30, alpha 111-145 and alpha 175-198 and, less frequently, region alpha 45-77. Differences in the recognition profile of the peptides from patient to patient indicated that the autoantibody responses were under genetic control. However, by using a mixture of the appropriate peptides, it was possible to determine autoantibodies in all 15 myasthenia sera and to distinguish between these, normal human sera and other neurological or autoimmune diseases. The mapping of the continuous antigenic regions recognized by autoantibodies on the alpha-chain of human AChR has permitted a comparison of the regions recognized by autoantibodies and autoimmune T-cells from the same donor. It also provided a peptide-based direct antibody binding method for diagnosis of MG.