[Mechanism of selection of NK-T cells in the thymus]

Thymic NK-T cells are defined as a novel T cell subset with characteristics of both T cells and NK cells, expressing TCR/CD3 complex and NK1.1. In the present study, we analyzed the mechanisms of selection of NK-T cells in the thymus by FACS and RNase protection assay. For the development of TCR alpha beta NK-T cells, class I but not class II MHC molecules are essential. However, as TCR alpha beta NK-T cell development is quite normal in TAP-1, a gene encoding peptide-transporter, deficient mice, TCR alpha beta NK-T cells may recognize vacant MHC class I molecule or MHC plus peptide presented by TAP-independent pathway. As NK-T cell express CD16 molecule, we examined whether CD16 molecule is essential for the development of NK-T cells. In FcR gamma chain mutant mice, the proportion of NK-T cells did not change as compared with normal mice, suggesting that CD16 molecule is not essential for the development of NK-T cells.