Inhibition of experimental autoimmune myasthenia gravis by major histocompatibility complex class II competitor peptides results not only in a suppressed but also in an altered immune response

To assess the capacity of major histocompatibility complex (MHC) class II-binding competitor peptides in inhibiting antibody-mediated disease processes, we studied experimental autoimmune myasthenia gravis in Lewis rats. Experimental autoimmune myasthenia gravis, a disease model mediated by T cell-dependent autoantibodies against acetylcholine receptors, was induced by immunization with Torpedo californica acetylcholine receptor emulsified in complete Freund's adjuvant. The immunodominant acetylcholine receptor T cell epitope was recognized by T cells in the context of MHC class II RT1.B^L. The disease inhibitory capacity of RT1.B^L-binding peptides not related to the acetylcholine receptor was determined upon co-immunization with Torpedo acetylcholine receptor. Co-immunization of peptide OVA323–339, a strong RT1.B^L-binding competitor peptide, resulted in complete disease inhibition. Although, the priming of the anti-acetylcholine receptor T cell response was not fully inhibited, the kinetics of the response was changed. Moreover, besides a drastic reduction of the anti-Torpedo acetylcholine receptor antibody titers, a shift in isotype distribution was found. These findings indicate that antibody-mediated autoimmune processes can be suppressed by MHC class II competitor peptides. Furthermore, the administration of such peptides in vivo not only passively inhibits T cell activation, but also functionally alters the immune response.