Maturational arrest from CD4+8+ to CD4+8- thymocytes is caused by the bone marrow-derived cells in LEC mutant rats.

LEC rats exhibit a congenital maturational arrest from CD4+8+ to CD4+8- but not to CD4-8+ cells in the thymus. To elucidate a cause of this mutation, bone marrow (BM) chimera rats were made between LEC and normal (WKAH) rats. In (WKAH-->LEC) BM chimera rats, donor-derived T cells matured normally, suggesting that LEC rat thymic stroma has a normal ability in supporting thymocyte differentiation. On the other hand in (LEC-->WKAH) BM chimera rats, LEC rat BM-derived T cells showed the arrest of maturation from CD4+8+ to CD4+8- cells in spite of having normal functions of WKAH rat-derived thymic stroma. In these chimeric rats, even though the maturational arrest from CD4+8+ to CD4+8- cells occurred in the thymus, CD4+ cells were found in peripheral lymph nodes (LNs), suggesting that these CD4+ cells differentiated extrathymically. These results suggest that the maturational arrest from CD4+8+ to CD+8- thymocytes is caused by BM-derived cells but not by thymic stroma.