ACETYLCHOLINE-RECEPTOR ALPHA-SUBUNIT AND MYOGENIN MESSENGER-RNAS IN THYMUS AND THYMOMAS

Myasthenia gravis is an autoimmune disorder characterized in most case s by serological antibody against the acetylcholine receptor (AChR). E vidence for intrathymic localization of AChR suggests that the thymus has an important role in the pathogenesis of this disorder. Using reve rse transcription followed by the polymerase chain reaction, we have d emonstrated AChR alpha-subunit mRNA in thymuses and thymomas from pati ents with and without myasthenia gravis. We have also studied the expr ession of myogenin which is known to be involved in the regulation of AChR expression. By using the reverse transcription polymerase chain r eaction, we found myogenin mRNAs in all of the thymuses and thymomas. Thus, both AChR alpha-subunit and myogenin mRNA are present In all of these specimens. By immunohistochemistry, myoid cells (desmin and myog lobin positive) were present in all (four of four) thymuses studied an d in two of five thymomas. Thus, in thymomas, nonmyoid cells might exp ress both AChR and myogenin. These results indicate that cells within the thymus and thymoma express AChR and its regulatory protein myogeni n and that such cells, under certain conditions, might play a role in the triggering of myasthenia gravis.