Epitopes on the Beta 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) beta 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 beta subunit. Since CD4+ lymphocytes from MG patients' blood did not respond to the peptides, we attempted propagation of beta 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 beta 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 beta subunit sequence. Several beta subunit peptide sequences were recognized. Each line had an individual pattern of peptides recognition, but three sequence regions (peptides beta 181-200, beta 271-290, and the overlapping peptides beta 316-335 and beta 331-350) were recognized by most MG lines. The beta 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.