Expression of T cell antigen receptor genes in the thymus of irradiated mice after bone marrow transplantation

Sequential appearance of the expression of T cell antigen receptor genes was investigated in the thymus of irradiated mice at the early stage after transplantation of Thy-1 congeneic H-2 compatible allogeneic bone marrow cells. The first cells to repopulate the thymus on day 7 after bone marrow transplantation were intrathymic radioresistant T cell precursors, which expanded mainly to CD4⁺CD8⁺ host-type thymocytes by day 14. A high level of γ gene expression but a much reduced level of α and β gene expression were detected in the host-type thymocytes on day 7. During regeneration of these cells, γ-chain messages fell to low level and α and β mRNA levels increased. The thymus of the recipients began to be repopulated by donor-derived T cells about 2 wk after bone marrow transplantation and was almost completely replaced by the third week. An ordered expression of γ then β and α-chain gene transcript was also observed in the donor-type thymocytes at the early stage after bone marrow transplantation. The use of thymocytes at an early stage in whole-body irradiated bone marrow chimera provides a pertinent source for investigating the molecular mechanism of T cell differentiation in adult thymus.