THYMIC ABNORMALITY IN SYSTEMIC LUPUS ERYTHEMATOSUS

Summary A young female patient with fulminant systemic lupus erythematosus, mainly affecting the brain and kidneys, required treatment with very high doses of prednisolone, up to 400 mg. per day. This led to moderate improvement in renal function, but without corresponding histological improvement. A fatal cerebral hæmorrhage occurred after ten weeks of treatment. Necropsy revealed diffuse and focal epithelial hyperplasia and “atypical germinal centres” in the medulla of the thymus, resembling thymic abnormalities observed in lupus erythematosus by McGehee Harvey. These abnormalities were interpreted on the basis of Clark's concept of localized thymic units or “packets of cells” delimited by epithelium ; special importance was given to processes concerned with lymphocyte proliferation within these units and the passage of lymphocytes through the epithelial and endothelial barrier into the blood‐stream. We suggest that cells entering, or arising in, these thymic units undergo primary immunological differentiation : any cells reactive with self‐components are suppressed by a substance which inhibits the development of immunological competence. The emergence of cell‐lines intrinsically resistant to control results in immunological reactions being initiated within the thymus, so causing proliferative activity of labile epithelial and endothelial cells. This, with the modifying effects of corticosteroid therapy, could produce the appearances seen in the present case.