Low frequency of NK cells with rearranged TCRγ genes. (A) Purity of IL-2–activated NK-cell samples from adult and neonatal mice after 2 rounds of cell sorting. The numbers show the percentages of NK cells (NK1.1⁺CD3^–). (B) Genomic PCR (Vγ2-Jγ1) performed with γδT-cell DNA and fibroblast DNA mixed at various ratios and with fresh and IL-2–activated adult and neonatal NK cells. The PCR products were analyzed by agarose gel electrophoresis and stained with ethidium bromide. (C) Southern hybridization to Jγ1 probe of the genomic PCR products generated from IL-2–activated NK cells from adult and neonatal mice in panel B. The top panel shows a short exposure of the Southern blot, whereas the bottom panel shows a long exposure to visualize rearranged Vγ2-Jγ1 in adult NK cells. (D) Southern blot of genomic PCR, as in panel C, but with freshly isolated adult and neonatal cell DNA. (E) The frequency of IL-2–activated NK cells from TCRβ^–/–δ^–/– mice with Vγ2-Jγ1 rearrangement was estimated by genomic PCR and ethidium bromide staining of agarose gel as in panel B. Gels divided by lines are groupings of images from different parts of the same gel.