The Acetylcholine Receptor and its Role in Induction of Experimental Autoimmune Myasthenia Gravis

I. Rabbit antibodies were produced against purified acetylcholine receptor (AcChR) and each of the four acetylcholine receptor subunits from Torpedo californica. Using the technique of double immunodiffusion in agar, specific- and cross-reactivities were observed between these antibodies and purified acetylcholine receptor and receptor subunits from Torpedo californica, Torpedo marmorata, Torpedo nobiliana, and Narcine brasiliensis. The specificity of each of the four anti-subunit antibodies was shown, suggesting the lower molecular weight polypeptide chains of the AcChR were not degradation products of the higher molecular weight polypeptide chains. The study also demonstrated conservation of AcChR and AcChR subunit antigenic determinants in the four electric rays investigated. II. Experimental autoimmune myasthenia gravis (EAMG) has been induced in a wide variety of animals using AcChR purified from a variety of electric organ and muscle sources. Electrophoresis of sodium dodecyl sulfate (SDS) polyacrylamide gels heavily loaded with purified AcChR often reveals the presence of minor contaminants. To test if these contaminants or any other components present in Torpedo californica AcChR preparations could induce EAMG, solubilized T. californica membrane fragments were depleted of AcChR by passage over an a-bungarotoxin resin and then injected into Lewis rats in an attempt to induce EAMG. The results demonstrated that some of the minor contaminants present in purified AcChR preparations were antigenic but EAMG could not be induced with preparations enriched in these contaminants or containing other T. californica non-AcChR components. III. Antisera prepared in rabbits and Lewis rats against Torpedo californica AcChR (purified and denatured to various degrees) were tested for the ability to inhibit 125I α-bungarotoxin (α-BuTx) binding to native and detergent solubilized T. californica AcChR. Similar inhibition studies were performed using antisera and antigen-binding fragments (Fabs) directed against each of the four isolated AcChR subunits. None of these antisera or Fabs could inhibit α-BuTx binding to native AcChR. Antisera and Fabs directed against AcChR could inhibit a maximum of 50% α-BuTx binding to solubilized AcChR. The results using Fabs indicated the inhibition was not due to antibody-mediated aggregation of AcChR molecules. A strong correlation was seen between animals with EAMG and the ability of their antisera to inhibit 5096 of α-BuTx binding to AcChRs. The results indicated that particular antigenic determinants on AcChRs could induce EAMG and that these determinants were lost with SDS denaturation of AcChR.