EPITOPES ON THE BETA-SUBUNIT OF HUMAN MUSCLE ACETYLCHOLINE-RECEPTOR RECOGNIZED BY CD4-GRAVIS PATIENTS AND HEALTHY-SUBJECTS( CELLS OF MYASTHENIA)

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 subuni t. Since CD4(+) lymphocytes from MG patients' blood did not respond to the peptides, we attempted propagation of beta subunit-specific T lin es from six MG patients and seven healthy controls by cycles of stimul ation of blood lymphocytes with the pooled peptides corresponding to t he S subunit sequence. CD4(+) T lines were obtained from four patients and three controls. They secreted IL-2, not IL-4, suggesting that the y comprised T helper type 1 cells. The T lines from MG patients could be propagated for several months. Three lines were tested with purifie d bovine muscle AChR and cross-reacted well with this antigen. All T l ines 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 patter n of peptides recognition, but three sequence regions (peptides beta 1 81-200, beta 271-290, and the overlapping peptides beta 316-335 and be ta 331-350) were recognized by most MG lines. The beta subunit-specifi c T lines from controls could be propagated for <5 wk. Each line recog nized several peptides, which frequently included the immunodominant r egions listed above.