Increased number of Hassall's corpuscles in myasthenia gravis patients with thymic hyperplasia

• We examined Hassall’s corpuscles (HCs) in thymuses from MG (+) and MG (−) patients.
• The number of HCs was elevated in the thymuses of MG patients with hyperplasia.
• CCL21 mRNA expression also increased in the hyperplastic MG thymuses.
• CCL21 immunoreactivities were much more prominent in the hyperplastic MG thymuses.

The thymus is implicated as an organ that contributes to autoimmunity in myasthenia gravis (MG) patients. Hassall's corpuscles (HCs) are assumed to represent the terminally differentiated stage of medullary thymic epithelial cells (mTECs). By using multicolor immunohistofluorescence analysis, we examined HCs in thymuses that were therapeutically excised from MG (+) and MG (−) patients. We found that the number of HCs per unit area of the thymic medulla was significantly elevated in the thymuses of MG (+) patients with thymic hyperplasia. CCL21 expression increased in the hyperplastic MG thymuses. We speculate that the altered differentiation of mTECs is associated with the thymic hyperplasia and the onset of MG.