Effect of Thymectomy in Adult Mice on Immunological Responsiveness

THYMECTOMY in adult animals has been associated with a lowering of the population of lymphocytes in blood, thoracic duct lymph, lymph nodes and spleen 1,2 . However, no significant defects in the capacity for rejecting allogeneic skin homografts 2 or for producing serum antibodies 2,3 have been observed in animals thymectomized in adult life and challenged within 1–2 months after thymectomy. This is in marked contrast to the severe immunological defects which occur following neonatal thymectomy 4 . These observations have suggested that, during early life, the thymus is essential for the complete and normal development of some immunological faculties. Evidence that the function of the thymus in initiating immunogenesis is not necessarily restricted to early life has, however, been produced. Adult mice thymectomized and afterwards exposed to total body irradiation have shown severe deficiencies in immunological functions 2,5 indicating that the thymus in the adult is still essential to re-establish immune mechanisms when the immunological apparatus has been damaged or destroyed. It has been shown, furthermore, that thymectomy in adult immunologically tolerant mice prevented the reappearance of reactivity with respect to that antigen 6 . The thymus in the adult would thus appear to be essential for the correction of specific immunological defects. The work described here gives further evidence for a continuing immunological function of the thymus through adult life.