Phenotypic changes of the subseptal thymic epithelium in myasthenia gravis.

We studied the phenotype of thymic epithelial cells of hyperplastic thymuses from myasthenia gravis, (MG) patients, in respect to the expression of a 64 Kd protein defined by the monoclonal antibody T2/30 and normally present in the whole cortical epithelium. In hyperplastic thymuses, epithelial cells bordering the basement membrane (subseptal epithelial layer) were consistently T2/30-negative whereas other cortical epithelial cells did bind the monoclonal antibody. These results clearly demonstrate a phenotypic change in hyperplastic thymus of MG patients. Such change might be correlated with the damage of basement membrane previously reported in myasthenia gravis hyperplastic thymuses, and eventually with an invasion of B cells into the parenchyma of the organ.