Epitopes on the β subunit of human muscle acetylcholine receptor recognized by CD4⁺ cells of myasthenia gravis patients and healthy subjects

We investigated the sequence regions of the human muscle acetylcholine receptor (AChR) β subunit forming epitopes recognized by T helper cells in myasthenia gravis (MG), using overlapping synthetic peptides, 20 residues long, which screened the sequence of the AChR β subunit. Since CD4⁺ lymphocytes from MG patients' blood did not respond to the peptides, we attempted propagation of β subunit-specific T lines from six MG patients and seven healthy controls by cycles of stimulation of blood lymphocytes with the pooled peptides corresponding to the β subunit sequence. CD4⁺ T lines were obtained from four patients and three controls. They secreted IL-2, not IL- 4, suggesting that they comprised T helper type 1 cells. The T lines from MG patients could be propagated for several months. Three lines were tested with purified bovine muscle AChR and cross-reacted well with this antigen. All T lines were tested with the individual synthetic peptides present in the pool corresponding to the β subunit sequence. Several β subunit peptide sequences were recognized. Each line had an individual pattern of peptides recognition, but three sequence regions (peptides β181-200, β271-290, and the overlapping peptides β316-335 and β331-350) were recognized by most MG lines. The β subunit-specific T lines from controls could be propagated for < 5 wk. Each line recognized several peptides, which frequently included the immunodominant regions listed above.