A Single Cell Analysis of TCR AV24AJ18⁺ DN T Cells

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The T-cell receptor (TCR) BV gene of human TCR AV24⁺ double-negative (DN) T cells, a novel subset of natural killer (NK) T cells, was investigated by single-cell sorting and single-cell polymerase chain reaction (PCR) methods. Seven of eleven TCR AV24⁺ DN T-cell clones utilized TCR BV8, three BV9, and one BV6. Six of seven TCR AV24/BV8⁺ DN T-cell clones had identical TCR β and α chains, indicating that they were the same clone. All three TCR AV24/BV9⁺ DN T-cell clones also demonstrated the same amino acids in the CDR3 region. These findings strongly suggest that the usage of TCR β and α chains on TCR AV24⁺ DN T cells is extremely restricted, supporting the notion that these cells recognize highly limited T-cell epitopes on antigens. All TCR AV24⁺ clones expressed the NKR-P1A mRNA, and so were true NK T cells. IL-2 and IL-4 mRNAs were detected in all clones, suggesting that the majority of these cells were Th0-type T cells. Six clones overexpressed Fas-ligand (Fas-L) mRNA and Fas antigen was detected on all clones at the mRNA level. In conclusion, TCR AV24⁺ DN T cells might recognize restricted T-cell epitopes on antigens and function as Th0-type T cells, inducer cells to Th1-or Th2-type T cells (regulatory T cells), and as Fas-L-positive cytolytic T cells.