Up-regulation of MHC class I and class II in the skeletal muscles of myasthenia gravis.

The up-regulation of MHC in muscles is thought to be associated with inflammatory myopathies. The expression of MHC class I and class II was examined in muscles of myasthenia gravis (MG). MG muscle specimens from all 5 patients with thymoma and 2 of 5 without thymoma showed MHC class I up-regulation and 3 of 5 with thymoma showed MHC class II. The up-regulation of MHC in MG muscles is thus considered to be a common phenomenon. MG muscles expressed not only MHC class I but also class II, and these muscles could thus act as immunoregulating cells in MG.