Acquired canine myasthenia gravis: immunocytochemical localization of immune complexes at neuromuscular junctions.

In the acquired form of myasthenia gravis in dogs, there are circulating antibodies to acetylcholine receptors (AChRs) and a reduction in the number of AChRs in the postsynaptic membrane. In this study, immune complexes were localized at the neuromuscular junctions in biopsy samples from 10 myasthenic dogs by immunocytochemical means employing conjugates of staphylococcal protein A and horseradish peroxidase. Immune complexes were observed in approximately 70% of the neuromuscular junctions studied in both type 1 and type 2 myofibers. Thus, acquired canine myasthenia gravis appears to involve immune-mediated mechanisms that destroy AChRs in a manner similar to myasthenia gravis in humans. Protein A was also observed to bind principally to elastic fibers in small arteries and arterioles of some myasthenic and control dogs; however, the significance of that localization is unknown.