LATE THYMECTOMY IN XENOPUS TADPOLES REVEALS A POPULATION OF T-CELLS THAT PERSISTS THROUGH METAMORPHOSIS

To investigate the persistence of larval T lymphocytes in the adult pe riod, tadpoles of the South African clawed frog, Xenopus laevis, were allowed to develop to prometamorphic stages 57-58 and thymectomized (T x). Thymectomy at this stage allows for maximal expansion of the larva l T cell population but prevents emergence of the adult T cell populat ion. Using a T cell-specific monoclonal antibody (mAb) which recognize s the XTLA-1 determinant, we examined the absolute numbers of thymic a nd splenic T cells expressing XTLA-1 in normal tadpoles, postmetamorph ic Tx frogs, and intact age-matched adult frogs. A small, but measurab le, number of larvally-derived XTLA-1(+) cells persists through metamo rphosis. By simultaneously staining with a mAb specific for class II m ajor histocompatibility (MHC) antigens, we determined the phenotype of the persisting XTLA-1(+) cells in the Tx frogs. Like XTLA-1(+) spleno cytes in intact adult controls which are predominantly class II+, most XTLA-1(+) cells in Tx adults also express class II. In contrast, most XTLA-1(+) cells in the tadpole are class II-. This suggests that a sm all population of class II+ larval T cells survives metamorphic transi tion to become a long-lived population in the adult. Alternatively, so me class II- larval T cells may express class II in the adult period. Copyright (C) 1996 Elsevier Science Ltd.