Expression of T cell receptor Vγ5 in the adult thymus of irradiated mice after transplantation with fetal liver cells

T cell receptor (TcR) γ/δ displays limited diversity and its diversity is distinct in different stages of ontogeny and in different anatomical sites. The V_γ5 and V_δ1 gene products are preferentially expressed on the early fetal thymocytes and on Thy‐1⁺ dendritic epidermal cells, whereas the V_γ4 and V_δ5 gene products are abundantly expressed on the adult thymocytes. To elucidate whether the developmentally ordered appearance of thymocytes expressing TcR γ/δ is dependent on the source of T cell precursors or is controlled by the thymic environment where T cells develop, we compared the expression of V_γ5 on the early‐appearing thymocytes between irradiated mice after transplantation with fetal liver (FL) cells and those after transplantation with bone marrow (BM) cells. Sequential appearance of thymocyte subpopulations was observed in the thymus of radiation FL chimeras similar to that seen in radiation BM chimeras. A substantial number of thymocytes bearing V_γ5 appeared in the thymus at the early stage of radiation FL chimeras, whereas few, if any, of such V_γ5‐bearing thymocytes were detected in the thymus at any stage of radiation BM chimeras. These results suggested that the ordered expression of V_γ repertoire may depend on the origin of the T cell precursors but not on the thymic environment.