Development of Transplantation Immunity and Restoration Experiments in the Thymectomized Amphibian

Abstract

This paper examines the thymic dependence of alloimmunity in amphibians. In Xenopus , the presence of a thymus during the first 2 weeks of life is essential for the development of normal first-set skin allograft immunity. Thymectomy during this early period always impairs the alloimmune response of young adult toads. However, most of these thymectomized animals are able to completely destroy skin allografts, albeit with prolonged rejection times. Chronic graft rejection, rather than tolerance, still occurs following thymectomy as early as 5 days, when the thymus contains no small lymphocytes. In contrast to the considerable differences in first-set allograft survival times in control and early-thymectomized Xenopus , second-set grafts, applied subsequent to first-set destruction, are rejected in acute fashion (<3 weeks) in both groups. That the defect in first-set alloimmunity is specifically related to absence of thymus has been confirmed by implanting allogeneic thymus 2 weeks post-thymectomy. The donor thymus remains healthy and restores the allograft response to normal. In contrast, allogeneic spleen does not reconstitute and itself often undergoes destruction. Preliminary autoradiographic experiments on lymphoid tissue involvement in first-set allograft rejection are also described.