Immunohistochemical Demonstration of IgG and Fab Fragments at Motor Endplates of Passively Transferred Mice

Interaction between the circulating receptor antibodies and the nicotinic acetylcholine receptor (nAChR) at the neuromuscular junction is probably the main cause of the impaired neuromuscular transmission in myasthenia gravis (MG) (for review see, e.g. 6). It has been demonstrated that by passive transfer of human myasthenic immunoglobulins to recipient mice many of the features of MG can be reproduced: reduced amplitudes of miniature endplate potentials (MEPP), a decreased number of available nAChR:s (α- bungarotoxin binding sites), decremental response to repetitive nerve stimulation and occasionally clinical weakness. Increased degradation of nAChR has also been observed in mice treated with myasthenic immunoglobulins (10). Using muscle cell cultures, evidence has been obtained that native receptor antibodies or bivalent F(ab’)2 fragments are needed to induce accelerated degradation of nAChR, since monovalent Fab fragments were inactive in this respect (1).