In situ production of interleukins in hyperplastic thymus from myasthenia gravis patients

We analyzed by in situ hybridization the expression of four interleukin genes (interleukin-beta [IL-1 beta], IL-6, IL-2, and interferon-gamma) in seven thymuses displaying a follicular hyperplasia. The seven thymuses were obtained from patients with myasthenia gravis. Interleukin-1 beta- and IL-6-producing cells were detected in similar amounts and with similar distributions: mainly in perifollicular areas and in the connective structures emerging from the septae at the site of cortex disruption. The comparison of in situ hybridization and immunohistochemical results suggested that thymic epithelial cells and/or perifollicular macrophages were responsible for this production. Interleukin-2-producing cells were detected in perifollicular areas and, to a lesser extent, inside follicles. They were clearly outnumbered by CD25-positive cells which were similarly distributed. Despite the expression of these molecular and immunohistochemical markers of T-cell activation, interferon-gamma-producing cells were extremely rare in myasthenic thymuses. The pattern of interleukin production (which was virtually absent in normal control thymuses) in myasthenic thymuses was different from that in benign hyperplastic lymph nodes. This interleukin production may play a role in the development of follicular hyperplasia in myasthenic thymuses, a phenomenon which is associated with the in situ production of autoantibodies.