Delayed Effect of Thymectomy in Adult Life on Immunological Competence

NEONATAL thymectomy leads to the rapid development of lymphoid organ atrophy and well-characterized immunological deficiencies1–3, but thymectomy performed in adult life leads only to the slow development of a moderate degree of lymphoid atrophy4 with no loss of immunological competence when the animals are tested immediately after operation5,6. However, adult thymectomy combined with whole-body irradiation does lead to immunological deficiencies of the same general nature as those following neonatal thymectomy7. Recent investigations have shown that continuous repopulation of normal haemopoietic organs occurs in normal life8,9. This suggests that whole-body irradiation by causing cell damage and repopulation in haemopoietic organs may merely accelerate a process which occurs continually throughout life, albeit at a much slower rate. These considerations prompted a re-examination of the long-term effects of adult thymectomy on immunological competence.