Autoradiographic study on the distribution of thymus-derived and thymus-independent lymphocytes in the spleen of Xenopus laevis

Non-thymectomized and early-thymectomized Xenopus laevis were injected with ³H-thymidine, and labelled lymphocytes from thymus, spleen, and peripheral blood were transferred to histocompatible recipients to study their distribution by autoradiography. An extremely high proportion of labelled thymocytes was localized in the splenic red pulp of both non-thymectomized and thymectomized recipients after transfer. Labelled splenic lymphocytes were localized in a significantly higher density in the splenic white- than red pulp, particularly 24 hr after cell transfer. This preference of labelled lymphocytes in the white pulp was more evident when early-thymectomized toads were used as lymphocyte donors. These results strongly suggest that in Xenopus, thymus-independent lymphocytes preferentially localize in the splenic white pulp, and thymus-derived lymphocytes possibly in the red pulp.