Generation of NK1.1(+) T cell antigen receptor α/β(+) thymocytes associated with intact thymic structure

The development of T cells within the thymus is largely dependent on intact cortical and medullary epithelial cells. However, it has been reported that positive selection of natural killer antigen 1.1(+) (NK1.1(+)) T cell antigen receptor (TCR)-α/β(+) thymocytes recently identified among CD4(+)8(−) and CD4(−)8(−) subpopulations is attributable to major histocompatibility complex class Ib ligands expressed on bone marrow (BM)-derived components in the thymus. In the present study, we investigated generation of NK1.1(+) TCR-α/β(+) cells in the thymus of the aly/aly mouse which lacks lymph nodes and Peyer’s patches and shows abnormalities of thymic and splenic structure. We found that the proportion of the NK1.1(+) TCR-α/β(+) thymocytes was extremely low in these mice as compared with aly/+ and normal C57BL/6 mice. Thymic reconstitution by BM cells from aly/+ mice that possess a normal population of NK1.1(+) TCR-α/β(+) cell population did not restore the NK1.1(+) TCR-α/β(+) cell population in the thymus of lethally irradiated aly/aly mouse. When deoxyguanosine-treated fetal thymi from (B6 × B10.G)F(1) mice were transplanted to aly/aly mice that had been thymectomized and reconstituted with BM cells of aly/aly mice, normal proportions of the NK1.1(+) TCR-α/β(+) thymocytes were present in the thymus grafts. These findings demonstrate that the development of NK1.1(+) TCR-α/β(+) thymocytes is accomplished under the influence not only of BM-derived components, but also of irradiation-resistant or deoxyguanosine-resistant components and an intact microenvironment of the thymus.