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

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Abstract
The NK1.1+TCRαβint 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+TCRαβint, 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 Vα14-Jα281 and Vβ 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 Vβ8.2-Jβ2.5 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 Vβ8.2-Jβ2.5 diversity regions being primarily the same in NK T and in T cells. No clonal expansion of the β-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 Vα14-Jα281 transgenic mice on a Cα−/− background showed that the α-chain can associate with β-chains using any Vβ segment, except in NK T cells in which it paired predominately with Vβ 2, 7, and 8+ β-chains. The structure of the TCR of NK T cells thus reflects the affinity for the CD1d molecule rather than a structural constraint leading to the association of the invariant α-chain with a distinctive subset of Vβ segment.