ALLOGRAFT REJECTION IN LARVAL AND ADULT XENOPUS FOLLOWING EARLY THYMECTOMY

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Abstract
The effect of thymectomy (performed on 7-8 day old larvae) on the development of alloimmunity in the clawed toad [X. laevis] is examined. Rejection of 1st-set skin grafts applied in larval life (30 days of age) and at intervals following metamorphosis (70-370 days of age) was always impaired following thymectomy. 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, there seemed to be no improvement or impairment of the alloimmune response with the passage of time. Experiments with 2nd-set grafts applied subsequent to 1st-set destruction demonstrated the existence of an alloimmune memory component throughout ontogeny in control and thymectomized animals. A population of cells involved in graft rejection apparently develops early in ontogeny, independent of the thymus and the emergence of bone marrow at metamorphosis.