Development of Transplantation Immunity and Restoration Experiments in the Thymectomized Amphibian

This paper examines the thymic dependence of alloimmunity inamphibians. In Xenopus, the presence of a thymus during thefirst 2 weeks of life is essential for the development of normalfirst-set skin allograft immunity. Thymectomy during this earlyperiod always impairs the alloimmune response of young adulttoads. However, most of these thymectomized animals are ableto completely destroy skin allografts, albeit with prolongedrejection times. Chronic graft rejection, rather than tolerance,still occurs following thymectomy as early as 5 days, when thethymus contains no small lymphocytes. In contrast to the considerabledifferences in first-set allograft survival times in controland early-thymectomized Xenopus, second-set grafts, appliedsubsequent to first-set destruction, are rejected in acute fashion(<3 weeks) in both groups. That the defect in first-set alloimmunityis specifically related to absence of thymus has been confirmedby implanting allogeneic thymus 2 weeks post-thymectomy. Thedonor thymus remains healthy and restores the allograft responseto normal. In contrast, allogeneic spleen does not reconstituteand itself often undergoes destruction. Preliminary autoradiographicexperiments on lymphoid tissue involvement in first-set allograftrejection are also described.