Altered venules in the stimulated human thymus as evidence of lymphocyte recirculation.

Human thymic tissue was examined by light microscopy to determine the presence or absence of germinal centres and plump venule endothelium. Five out of fifteen thymuses from control patients showed occasional germinal centres. A suggestion of plump venule endothelium was seen in only three of these. Among forty-one thymuses removed from patients with myasthenia gravis, thymoma, thymic enlargement or chronic renal failure nineteen contained definite germinal centres and of these fifteen showed plump venule endothelium. The evidence that this indicates a large scale recirculation of lymphocytes through the thymus has been reviewed.