Suppression of Experimental Autoimmune Myasthenia Gravis by Epitope-Specific Neonatal Tolerance to Synthetic Region α146-162 of Acetylcholine Receptor

A gene conversion event between Eb^b and Ab^b in the B6.C-H-2^bm12 (bm12) strain, which alters three amino acids in the C-terminal half of the first domain of Ab^b (Ile-67 → Phe; Arg-70 → Gln; Thr-71 → Lys) resulted in resistance to experimental autoimmune myasthenia gravis (EAMG) pathogenesis. To study the effect of bm12 mutation on the T-cell responses to epitopes of acetylcholine receptor (AChR)-α subunit, C57BL6 (B6) and bm12 mice were primed with Torpedo californica AChR, and the profiles of T-lymphocyte proliferation were determined with 18 synthetic overlapping peptides encompassing the entire extracellular portion of the AChR-α subunit. The proliferative responses of AChR-primed bm12 lymphocytes were markedly reduced to two (α146-162 and α182-198) of the three AChR peptides (α111-126, α146-162, and α182-198) that are immunodominant in B6 mice. Thus, the Ab residues encompassing the region 67-71 determine the immunogenicity of two of the AChR-α subunit T-cell epitopes. To test the involvement of AChR-α chain epitopes within peptide α146-162 in EAMG pathogenesis, B6 mice were neonatally tolerized with soluble peptide α146-162, and subsequently immunized with AChR in complete Freund's adjuvant. Neonatal tolerance to AChR or to peptide α146-162 reduced the incidence of clinical myasthenia gravis and suppressed serum anti-AChR antibodies. This indicates the involvement of T-cell epitopes within AChR-α subunit region α146-162 in EAMG pathogenesis. Neonatal tolerance to peptide α146-162 could have caused specific clonal deletion, and/or clonal anergy, and/or recruited suppressor cells to prevent clinical EAMG. Presumably, epitope(s) with AChR α146-162, in the context of Ab encompassing region 67-71, stimulate specific T helper cells which interact with specific B cells to produce pathogenic antibodies, the primary culprit causing the end plate lesion in patients with myasthenia gravis.