Homology between Fas and nicotinic acetylcholine receptor protein in a thymoma with myasthenia gravis--immunohistochemical and biochemical study.

Nicotinic acetylcholine receptor (nAChR) protein and Fas were detected in a cortical type thymoma from a patient with myasthenia gravis (MG). Immunohistochemical study showed the presence of these two antigens in the neoplastic thymic epithelial cells. This was confirmed by immunoblot analysis of the thymoma extract using polyclonal anti-nAChR (FCT) antibody and two monoclonal anti-Fas antibodies. A homology search between each of five subunits of nAChR and Fas in sequences of nucleotides and amino acids were performed. In nucleotides the percent identity revealed 44.1 and 44.4 in the alpha and gamma subunits, respectively. The places of homology in amino acids sequences between nAChR and Fas were found in alpha 316-355 and Fas 232-271, gamma 321-352 and Fas 3-34. These portions with homology include previously reported T-cell epitopes, alpha 320-337 and gamma 321-340. These two antigens may play a role in triggerring autoimmunity in MG.