Passive transfer of experimental myasthenia gravis via antigenic modulation of acetylcholine receptor

Antigenic modulation of acetylcholine receptor (AChR) is considered to contribute to the reduction of endplate AChR in myasthenia gravis (MG). Yet, the pathogenic significance of this mechanism is unclear. To investigate the in vivo role of AChR antigenic modulation we examined the ability of bivalent F(ab')2 and monovalent Fab fragments of monoclonal antibody (mAb) 35 to passively transfer experimental autoimmune MG (EAMG) in rats. mAb 35 which binds at the main immunogenic region (MIR) of the AChR causes severe EAMG without being involved in channel function. Compared to the intact mAb, F(ab')2 35 proved to be less potent but still capable of inducing moderate EAMG, whereas Fab 35 were totally ineffective. Furthermore, both intact and F(ab')2 35 induced mild EAMG in complement-depleted rats. These results (a) provide evidence that antigenic modulation of endplate AChR is sufficient to generate passive transfer of EAMG and (b) further support the pathogenic potential of the anti-MIR antibodies in MG.