Influence on allograft rejection of thymectomy at different stages of larval development in urodele amphibian Pleurodeles waltlii Michah. (Salamandridae).

Thymectomy was performed on the urodele amphibian Pleurodeles waltlii Michah. from the 5th to the 20th week of larval development. Thymectomized animals were allografted at 7 months of age. The results obtained are as follows: (1) Pleurodeles thymectomized before 10 weeks always tolerated allografts: (2) Pleurodeles thymectomized within 11 to 13 weeks generally rejected allografts in a chronic manner, but sometimes tolerated them; (3) normal rejections occurred in Pleurodeles thymectomized at 14 weeks, or later. Stage 52 of the developmental table (10 weeks of age) is a critical "end stage" for the efficiency of thymectomy. The results are confirmed by the fate of second set allografts performed in all these animals.