Role of the complementarity-determining region 3 (CDR3) of the TCR-β chains associated with the Vα14 semi-invariant TCR α-chain in the selection of CD4+ NK T cells

The NK1.1(+)TCR alpha beta (int) CD4(+), or double negative T cells (NK T cells) consist of a mixture of CD1d-restricted and CD1d-unrestricted cells. The relationships between CD4(+)NK1.1(+) T cells and conventional T cells are not understood. To compare their respective TCR repertoires, NK1.1(+)TCR alpha beta (int), CD4(+) T cells have been sorted out of the thymus, liver, spleen, and bone marrow of C57BL/6 mice. Molecular analysis showed that thymus and liver used predominantly the V alpha 14-J alpha 281 and V beta 2, 7, and 8 segments. These cells are CD1d restricted and obey the original definition of NK T cells. The complementarity-determining region 3 (CDR3) sequences of the TCR V beta8.2-J beta2.5 chain of liver and thymus CD4(+) NK T cells were determined and compared with those of the same rearrangements of conventional CD4+ T cells. No amino acid sequence or usage characteristic of NK T cells could be evidenced: the V beta8.2-J beta2.5 diversity regions being primarily the same in NK T and in T cells. No clonal expansion of the beta -chains was observed in thymus and liver CD1d-restricted CD4(+) NK T cells, suggesting the absence of acute or chronic Ag-driven stimulation. Molecular analysis of the TCR used by V alpha 14-J alpha 281 transgenic mice on a C alpha (-/-) background showed that the alpha -chain can associate with beta -chains using any V beta segment, except in NK T cells in which it paired predominately with V beta 2, 7, and 8(+) beta -chains, The structure of the TCR of NK T cells thus reflects the aanity for the CD1d molecule rather than a structural constraint leading to the association of the invariant cu-chain with a distinctive subset of V beta segment.