Thymocyte/stromal cell chimaerism in allothymus-grafted Xenopus: developmental studies using the X. borealis fluorescence marker.

These experiments employ the X. borealis (quinacrine-fluorescence) cell marker to illustrate that froglet (normal or in vivo-irradiated) thymuses, alloimplanted to 4- to 6-week-old, 7-day-thymectomized hosts, become filled with host lymphoid cells, while a range of thymic stromal cell types (e.g. epithelial derivatives and reticuloendothelial cells) remain donor derived. A time-course study of 4 micron historesin-embedded sections reveals that for normal thymus implants, host cells begin to immigrate in good number only after metamorphosis. In contrast, 3000 rad-irradiated thymus implants begin to be repopulated with host lymphocytes within 2 weeks postimplantation, when hosts are still at a late larval stage of development. Despite rapid colonization by host lymphoid cells, irradiated thymuses remain small and often disappear in early adult life. Donor-derived lymphocytes frequent the blood and both the red pulp and perifollicular regions of the spleen following normal thymus implantation, whereas such thymic emigrants were not seen in the periphery of thymectomized hosts grafted with irradiated thymus glands.