Primary cultures of human myasthenia gravis thymus and normal thymus. Studies of cell morphology, cell proliferative pattern and localization of alpha-bungarotoxin binding sites on cultured thymic cells.

We have established primary cultures of human myasthenia gravis (MG) thymuses and normal thymuses. In cultures of 19 thymuses with hyperplasia among 23 MG thymuses and 12 thymuses among 13 normal thymuses, epithelial cells migrated in a mosaic-like arrangement and were maintained for more than 5-10 weeks. There were, among mononuclear epithelial cells, some multinucleated cells, some of which were considered to be derived from epithelial cells because they had a desmosome-like structure and contained tonofilaments in their cytoplasm. There was no significant difference in the morphology of epithelial cells between MG thymuses and normal thymuses. The growth rate of thymic epithelial cells was identified by [3H]thymidine autoradiography(ARG), labeling indices rising to a peak around a week and falling to low levels gradually. There was no significant difference in the growth rate of epithelial cells between MG thymuses and normal thymuses. An autoradiographic method with 125I-labeled alpha-bungarotoxin was used to detect the presence of acetylcholine receptor (AChR) on the cultured cells. ARG of human MG thymuses and normal thymuses, which were cultured for 4 weeks, revealed diffusely distributed silver grains on the epithelial cells. Toxin binding sites (AChRs) were considered to be present on the epithelial cells. There was no significant difference in the distribution of AChR on the epithelial cells between MG thymuses and normal thymuses.