Allograft rejection in larval and adult Xenopus following early thymectomy.

The effect of thymectomy (performed on 7- to 8-day old larvae) on the development of alloimmunity in the clawed toad is examined. Rejection of first-set skin grafts applied in larval life (30 days of age) and at intervals following metamorphosis (70 to 370 days of age) was always impaired following thymectomy. However, most of the thymectomized animals, even those grafted as larvae and blocked in the larval state by thiourea treatment, were able to destroy the transplants, albeit with prolonged rejection times. The pattern of graft rejection in thymectomized larvae was similar to that seen in adults. After thymectomy, these seemed to be no improvement or impairment of the alloimmune response with the passage of time. Experiments with second-set grafts applied subsequent to first-set destruction demonstrated the existence of an alloimmune memory component throughout ontogeny in both control and thymectomized animals. The results indicate that a population of cells involved in graft rejection develops early in ontogeny, independent of the thymus and the emergency of bone marrow at metamorphosis.