Human thymuses express incomplete sets of muscle acetylcholine receptor subunit transcripts that seldom include the delta subunit

In myasthenia gravis (MG) the muscle acetylcholine receptor (AChR) is the t arget of an immune response that might begin in the thymus. The thymus expr esses binding sites for specific ligands of muscle AChR, a complex protein composed of alpha, beta, gamma (or epsilon) and delta subunits. The thymus expresses the AChR cr subunit, but there is controversy regarding the expre ssion in the thymus of the gamma, epsilon and delta subunits. We investigat ed the presence of messenger RNA (mRNA) for the different muscle AChR subun its in thymus tissue from 20 healthy subjects and 13 myasthenic patients, W e detected mRNA for the alpha and epsilon subunits in all samples, for the beta subunit in all but one sample and for the gamma subunit in most sample s although at lower levels than the epsilon subunit. Myasthenic thymuses ex pressed levels of gamma subunit mRNA similar to control thymuses but more a bundant epsilon subunit mRNA. None of the myasthenic thymuses and only two control thymuses expressed detectable delta subunit mRNA. This supports the hypothesis that human thymus may express AChR proteins that do not include the delta subunit. Such receptors, which would have different antigenic st ructure than the muscle AChRs, might have a role in triggering the autoimmu ne response that causes MG. (C) 2001 John Wiley & Sons, Inc.