AbstractIt is controversial whether acetylcholine receptors (AChR) or AChR‐like proteins exist in human thymus. To evaluate this question we isolated RNA from paraffin‐embedded thymic tissue of 5 myasthenics and 5 nonmyasthenics. RNA was subjected to reverse transcription followed by polymerase chain reaction (RT‐PCR) using primers specific for β‐actin, subunits of the fetal‐ and adult‐type AChR, andMyf‐4, a gene product which regulates AChR expression in muscle. β‐Actin transcripts were identified in specimens from 8 of 10 patients. In these 8 patients α‐and ε‐subunit transcripts were identified. Presence of these transcripts did not correlate with thymic pathology or clinical presentation. No γ‐subunit (specific for the fetal‐type AChR) orMyf‐4 transcripts were found. Our results indicate that mRNA for subunits of the adult‐type AChR are expressed in thymic tissue by mechanisms not involvingMyf‐4. AChR subunits in pathological thymus may provide a target for immune attack in MG. However, as AChR subunits were found in thymus tissue from myasthenics and nonmyasthenics, the presence of AChR subunits in the thymus alone is not sufficient to produce myasthenia g
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