[Pathogenesis of autoimmunity in thymoma].

The analysis of thymic epithelial tumors (TET) with and without myasthenia gravis (MG) has identified both a residual organotypic differentiation of TETs and the aberrant expression of acetylcholine receptor (AChR)-epitopes in TET epithelial cells to be associated with MG. These findings have suggested an abnormal selection of helper T cells as a mechanism of paraneoplastic MG. Here we show by electronmicroscopy that epithelial cells of TETs and normal thymus exhibit the morphological features (autophagic vacuoles) thought to be necessary to process endogenous proteins for presentation by MHC class II molecules to immature T cells.