'Radioresistant' CD4^-CD8^- intrathymic T cell precursors differentiate into mature CD4⁺CD8^- and CD4^-CD8⁺ T cells. Development of 'radioresistant' CD4^-CD8^- intrathymic T cell precursors

Using lectin (PNA) and monoclonal antibodies for Pgp-1, IL-2R, H-2(k), CD3 and F23.1 (T cell receptor V(β)8), we chacterized the 'radioresistant' CD4^-CD8^- double negative thymocytes at an early stage after 800 rad irradiation. Most of the CD4^-CD8^- cells on day 8 after irradiation expressed a high level of Thy-1, H-2(k), and PNA, while a small proportion of these cells were CD3⁺ and/or F23.1⁺. The appearance of Pgp-1 and IL-2R on the 'radioresistant' double negative precursors was also sequentially examined from day 5 to day 9 after irradiation. The double negative thymocytes at day 5 expressed the highest level of Pgp-1 antigens and these cells gradually decreased in number from day 7 to day 9. By contrast, IL-2R was transiently expressed on the double negative cells on the day 7 and 8 after irradiation. These results indicate that progression of thymocyte development occurred within the CD4^-CD8^- thymocytes after irradiation. We further examined the homing ability of the double negative 'radioresistant' intrathymic T cell precursors to the periphery by intrathymic cell transplantation method. The double negative thymocytes proliferate and differentiate into CD4⁺CD8⁺ cells and CD4⁺CD8^- cells but few CD4^-CD8⁺ cells in the thymus, while only CD4^-CD8⁺ cells were detected in the peripheral lymphoid organs 14 days after intrathymic transplantation of the double negative cells in the H-2 compatible Thy-1 congenic mice. These results suggest that the 'radioresistant' intrathymic precursors differentiate and mature in the thymus and migrate to the periphery.