Effect of Thymectomy on the Termination of Immunological Tolerance in Rabbits

Abstract

IT is well established that the thymus plays an important part in the neonatal development of the immune mechanisms. Thymectomy during early life inhibits the rejection of homografts made later^1,2. Similarly, animals thymectomized during early life show a decreased ability to produce circulating antibodies, while thymectomy during adult life has no apparent effect on the production of circulating antibodies^3–6. Rabbits thymectomized within five days after birth showed either the absence of or greatly reduced response to injections of bovine serum albumin (BSA)⁷. Although the thymus appears to exert its influence primarily during the neonatal period, it also can function during adult life in that thymectomy pro longs the recovery of immunological capacity following X-radiation^8–11. Furthermore, Claman and Talmage¹² have shown that adult mice made tolerant by neonatal injection of bovine γ-globulin do not spontaneously lose their tolerant state so rapidly if the thymus is removed. They interpreted their data as supporting the hypothesis that immunological tolerance occurs through irreversible inhibition or death of competent cells and that the loss of tolerance occurs through the development of newly arisen (uninhibited) cells which may originate in the thymus.