Acetylcholine receptor in rabbit thymus: antigenic similarity between acetylcholine receptors of muscle and thymus.

This study was performed to examine the presence and immunological properties of acetylcholine receptor (AChR) in rabbit thymus. Binding of 125I-alpha Bungarotoxin (alpha BGT) to Triton extract from rabbit thymus was saturable (half saturation value: 10 X 10(-9) M) and occurred with at least two affinities, a high one with a dissociation constant of 1.1 X 10(-10)M and a low affinity one with a dissociation constant of 2 X 10(-9)M. The complex formation of 125I-alpha BGT-thymus extract was inhibited by both carbamylcholine and D-tubocurarine. These results indicate the existence of AChR in rabbit thymus. Antibody to AChR which was purified from experimental myasthenic rabbits with Narke AChR-affinity gel and labelled with 125I was used to identify the receptor antigenicity in rabbit thymus. Specific binding of 125I-antibody to thymic extract was demonstrated by the DEAE-paper disc assay. It is concluded from these results that AChRs with a similar antigenicity to that of skeletal muscle AChR exist in rabbit thymus. Our findings obtained in this study will support a hypothesis that the primary immunogen in myasthenia gravis may be AChR in thymus and an autoimmune reaction against AChR might be initiated within the thymus gland itself.