ACETYLCHOLINE-RECEPTOR SUBUNIT GENE-EXPRESSION IN THYMIC TISSUE

It is controversial whether acetylcholine receptors (AChR) or AChR-lik e proteins exist in human thymus. To evaluate this question we isolate d RNA from paraffin-embedded thymic tissue of 5 myasthenics and 5 nonm yasthenics. RNA was subjected to reverse transcription followed by pol ymerase chain reaction (RT-PCR) using primers specific for beta-actin, subunits of the fetal- and adult-type AChR, and Myf-4, a gene product which regulates AChR expression in muscle. Beta-Actin transcripts wer e identified in specimens from 8 of 10 patients. In these 8 patients a lpha-and epsilon-Subunit transcripts were identified. Presence of thes e transcripts did not correlate with thymic pathology or clinical pres entation. No gamma-subunit (specific for the fetal-type AChR) or Myf-4 transcripts were found. Our results indicate that mRNA for subunits o f the adult-type AChR are expressed in thymic tissue by mechanisms not involving Myf-4 AChR subunits in pathological thymus may provide a ta rget for immune attack in MG. However, as AChR subunits were found in thymus tissue from myasthenics and nonmyasthenics, the presence of ACh R subunits in the thymus alone is not sufficient to produce myasthenia gravis. (C) 1993 John Wile & Sons Inc.