A Single Cell Analysis of TCR AV24AJ18+ DN T Cells

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Abstract
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 BY9, 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.