A novel T cell subset characterized by cell surface NK1.1+ TCRαβ+ expression was investigated for its TCRα usage, particularly that of invariant Vα14 TCR, which was found to be preferentially used in peripheral CD4CD8T cells developed at extrathymic sites. We found that NK+ αβ T cell subsets account for 0.4% in thymocytes, 5% in the splenic T cells and 40.5% in the bone marrow T cells. Among these NK+ αβ T cells, two distinct subsets were detected; cell surface TCR Vα14+and Vα14 subpopulations. Almost all of NK+ αβ thymocytes express Vα14 mRNA; however, only<20% were positive, while >80% were negative or undetectable for Vα14 TCR expression on the cell surface in the thymus. Similarly,∼50% of NK+ αβ T cells in spleen and bone marrow are Vα14+; as revealed by FACS. TCR repertoire analysis by nucleotide sequences on inverse PCR products demonstrated that most NK+ αβ T cells express an invariant TCR encoded by the Vα14Jα281 gene with a 1 base N-region in all tissues. Thus, invariant Vα14 TCR is uniquely expressed on NK T cells, and can be a marker to distinguish NK, NK T and T cells.

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