The fate of CD4-8- T cell receptor-alpha beta+ thymocytes

CD4-8- TCR-alpha beta+ thymocytes represent a distinct population whose fate and function have remained a mystery. We show here that this thymocyte subset bears NK1, a surface Ag previously thought to be expressed exclusively by TCR- NK cells. Analysis of peripheral lymphocytes for the coexpression of TCR-alpha beta and NK1 revealed a subset with similar characteristics to the NK1+ thymocytes: a large fraction that are CD4-8- and a skewed TCR repertoire in which V beta 8 is overrepresented. Thymus transplant experiments into congenically marked athymic (nude) mice revealed that the NK1+TCR alpha beta+ subset was exclusively thymus derived and represented a distinct subset from the thymus-independent NK1+TCR- population. Finally, the NK1+TCR alpha beta+ population preferentially localizes to the bone marrow. These results demonstrate that this T cell subset is exported to the periphery after developing in the thymus. Their unique surface Ag expression and tissue localization suggest an immune function distinct from classical T cells.