Deletion of self-reactive T cells in the donor-derived T cells but not in the host-derived T cells in fully allogeneic radiation chimeras. Mls-reactive T cells in allogeneic radiation chimeras

Kinetics of T cells bearing V beta 6 capable of recognizing Mls-1a were examined in the thymus and peripheral lymphoid organs of two allogeneic bone marrow chimeras; AKR/J(H-2k, Thy1.1,Mls-1a)----C3H/He(H-2k, Thy1.2,Mls-1b) and AKR/J----C57BL/6(H-2b,Thy1.2, Mls-1b). Sequential appearance of host- and donor-derived T cells occurred in the thymus and the peripheral lymphoid organs of both AKR----C3H and AKR----B6 chimeras. The first cells to repopulate the thymus were Thy1.2+ host-derived radioresistant cells, which were synchronized in their development. The host-derived cells in thymus of AKR----B6 chimeras differentiate more rapidly than those in AKR----C3H chimeras. An almost complete replacement from host-derived cells to donor-derived cells occurred by day 21 after reconstitution in AKR----C3H and AKR----B6 chimeras. In the donor-derived thymocytes, none of CD4- or CD8-single positive thymocytes expressed high density of V beta 6 in either AKR----C3H or AKR----B6 chimeras, whereas the host-derived thymocytes in AKR----B6 chimeras contained an appreciable number of CD4-single positive thymocytes bearing V beta 6. In the peripheral lymphoid organs, T cells bearing V beta 6 were virtually abolished in Thy1.1+ cell pool of both AKR----C3H and AKR----B6 chimeras. While V beta 6+ T cells of host-origin were detected in the peripheral lymphoid organs in AKR----B6 chimeras. These result indicated that the donor-derived mature T cells showed deletion of V beta 6 in the thymus and the peripheral lymphoid organs in both AKR----C3H and AKR----B6 chimeras, whereas lack of V beta 6 deletion was observed in the host-derived mature T cells in the AKR----B6 chimeras. These results suggested that the host-derived thymocytes may likely to escape undergoing a negative selection against donor-phenotype in the radiation bone marrow chimeras.