True epithelial hyperplasia in the thymus of early-onset myasthenia gravispatients: implications for immunopathogenesis

The early-onset myasthenia gravis (EOMG) thymus shows characteristic medull ary epithelial bands (MEB), greatly expanded perivascular infiltrates and f enestrations of the intervening basement membranes. We now compare epitheli al expression of epidermal growth factor receptor (EGFR) and many integrins in EOMG and control samples. The main differences are striking/consistent thickening (in MEB) of what is normally a monolayer of perivascular epithel ium. with focal protrusion into the infiltrates. This evidently hyperplasti c epithelial subpopulation also strongly expresses EGFR and certain integri ns. We suggest that its enhanced interactions with the locally increased ex tracellular matrix protein deposits may play an important role in autosensi tization. (C) 2001 Elsevier Science B.V. All rights reserved.