An assessment of radioimmunoassay procedures for determination of anti-acetylcholine receptor antibodies in the sera of patients with myasthenia gravis

An ELISA for the detection of anti-acetylcholine receptor antibodies using biotinylated alpha-bungarotoxin

An antibody-capture enzyme immunoassay has been developed for the detection of anti-acetylcholine receptor (AChR) antibodies in tissue culture supernatants using biotinylated alpha-bungarotoxin (B alpha BGT). Immunoglobulins in culture supernatants were bound indirectly to microtitre plates via an anti-globulin antibody already coupled to polyvinyl plates. Anti-AChR antibodies were then detected by incubation with AChR crude extract. Bound AChR was revealed by incubation with B alpha BGT followed by horseradish peroxidase-conjugated avidin. This assay is specific, more sensitive than the commonly used double antibody radioimmunoassay, avoids the use of radioactive material, is practical for large numbers of samples and is particularly suitable for detecting anti-AChR antibodies in tissue culture supernatants.

Complement-dependent toxicity of serum from myasthenic patients to muscle cells in culture

The toxicity of myasthenic sera to rat myotubes in monolayer culture was examined by measuring the release of [Me-3H]carnitine from pre-loaded cells. In the presence of guinea pig complement, heat-inactivated serum samples from 9 out of 13 myasthenic patients showed clear myotoxicity, in contrast to 0 out of 11 normal controls and 0 out of 6 polymyositis patients. Neither heat-inactivated sera alone nor guinea pig complement sera alone showed myotoxicity. Removal of anti-acetylcholine receptor (anti-AChR) antibodies from a myasthenic serum sample by affinity absorption led to loss of myotoxicity. Myotoxicity of myasthenic sera could, in most cases, be confirmed by light microscopy. These results support the idea that complement-mediated cell damage, initiated by anti-AChR antibodies, contributes to post-synaptic membrane degeneration in myasthenia gravis.

Immunological cross-reactivity between the alpha-bungarotoxin-binding component from rat brain and nicotinic acetylcholine receptor

An alpha-bungarotoxin-binding protein was partially purified from rat brain and, when complexed with [125I] alpha-bungarotoxin, was shown to behave as a single radiolabelled protein that is distinct from the similarly complexed nAChR from Torpedo marmorata. The alpha-bungarotoxin-binding protein was used as antigen in radioimmunoassays for rabbit anti-(rat muscle nAChR) and rabbit anti-(Torpedo nAChR) antibodies, giving titres approximately 5% and 0.5%, respectively, of those obtained by using homologous antigen in the same assay.