Xenopus toadlets thymectomized as larvae at 8 days post-fertilization developed relatively normal lymphoid tissues but the spleen was reduced in weight. The increase in numbers of pyroninophilic cells and in the size of the white pulp regions which occurs in the spleen of intact, control Xenopus in response to administration of human γ-globulin (HGG) in adjuvant was less marked in thymectomized animals.
HGG localization in an outer zone of the white pulp was demonstrated by immunofluorescence in the spleens of intact Xenopus. Following early thymectomy this reaction was abrogated or severely diminished, as was also the production of circulating antibody to HGG.