Antigen Penetration into the Thymus Free

Bovine serum albumin was injected intramediastinally in rats. It was found that part of the injected antigen reached the mediastinal lymph nodes as well as the adjacent thymus where it penetrated the medulla and some areas of cortex. In both thymic regions, the antigen was seen on and/or in the cytoplasm of lymphocytes. It is concluded that there exists no barrier to prevent the penetration of antigens into the thymic parenchyma, and that antigens which normally drain into the mediastinal nodes also penetrate the thymic parenchyma. This suggests that the failure of the thymus to yield antibody forming cells does not result from its nonpenetration by antigens.