Neoplastic epithelial cells express alpha-subunit of muscle nicotinic acetylcholine receptor in thymomas from patients with myasthenia gravis.

We studied the expression of mRNAs coding for the alpha-subunit of the muscle nicotinic acetylcholine receptor (AChR) in thymomas from patients with myasthenia gravis (MG). Northern blot analysis failed to detect the expression, but amplification of mRNAs derived from thymomas by reverse transcription and polymerase chain reaction produced the DNA fragments containing the nucleotide sequence coding for part of the alpha-subunit. We further revealed that the alpha-subunit mRNA was derived from neoplastic epithelial cells of thymoma. Our results support the hypothesis that AChR expressed in thymoma is a candidate for the primary antigen which induces autoimmune responses to muscle AChR. The close relationship between MG and thymoma may be at least in part explained by this hypothesis.