CD8+ T cells rapidly acquire NK1.1 and NK cell-associated molecules upon stimulation in vitro and in vivo

• NKT cells express both NK cell-associated markers and TCR. Classically, these NK1.1+TCRαβ+ cells have been described as being either CD4+CD8− or CD4−CD8−. Most NKT cells interact with the nonclassical MHC class I molecule CD1 through a largely invariant Vα14-Jα281 TCR chain in conjunction with either a Vβ2, -7, or -8 TCR chain. In the present study, we describe the presence of significant numbers of NK1.1+TCRαβ+ cells within lymphokine-activated killer cell cultures from wild-type C57BL/6, CD1d1−/−, and Jα281−/− mice that lack classical NKT cells. Unlike classical NKT cells, 50–60% of these NK1.1+TCRαβ+ cells express CD8 and have a diverse TCR Vβ repertoire. Purified NK1.1−CD8α+ T cells from the spleens of B6 mice, upon stimulation with IL-2, IL-4, or IL-15 in vitro, rapidly acquire surface expression of NK1.1. Many NK1.1+CD8+ T cells had also acquired expression of Ly-49 receptors and other NK cell-associated molecules. The acquisition of NK1.1 expression on CD8+ T cells was a particular property of the IL-2Rβ+ subpopulation of the CD8+ T cells. Efficient NK1.1 expression on CD8+ T cells required Lck but not Fyn. The induction of NK1.1 on CD8+ T cells was not just an in vitro phenomenon as we observed a 5-fold increase of NK1.1+CD8+ T cells in the lungs of influenza virus-infected mice. These data suggest that CD8+ T cells can acquire NK1.1 and other NK cell-associated molecules upon appropriate stimulation in vitro and in vivo.

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