In vitro interleukin-1 (IL-1) production in thymic hyperplasia and thymoma from patients with myasthenia gravis.

Using a biological test, we measured in vitro thymic epithelial cell IL-1 activity of 14 thymomas and 8 hyperplasia from myasthenic patients. Our results demonstrate that thymic epithelial cells from hyperplastic thymuses spontaneously produce high amounts of IL-1 compared to controls, while cells from thymomas produce very low amounts of IL-1. After LPS stimulation the difference between patients and controls is no longer significant. Immunohistochemistry studies demonstrate a limited number of IL-1-positive cells on sections from normal thymuses and a variable number of IL-1-positive cells on diseased thymuses, not clearly correlated to the in vitro production. In hyperplastic thymuses an association is found between the level of hyperplasia and in vitro IL-1 production, suggesting a role for IL-1 in the expansion of thymic lymphoid follicles. In thymoma, the low IL-1 production and the loss of corticomedullary organisation raise the possibility that some autoreactive clones could emerge from the lymphocyte pool, present in the abnormal tumoral microenvironment.