Development and function is not altered in Cre-expressing NK cells. Neither the development nor the proliferation or cytotoxicity of NK cells was influenced by Cre recombinase. (A) Simplified scheme of NCRI expression in NK-cell development. (B-E) Flow cytometry of Ncr1-iCreTg mice and littermate controls. Dot plots indicate the percentage of (B) gated Lin⁻CD122⁺ DX5⁻NK1.1⁻ NKPs in the BM, (C) gated CD3⁻ NK cells (NK1.1⁺DX5⁺) in the periphery, and (D) expression of maturation markers of splenic NK cells gated as TCRβ⁻NK1.1⁺ stained with CD27 and CD11b antibodies (n ≥ 4 per genotype). Data are representative of at least 3 independent experiments. (E) In vivo proliferation of splenic NK cells. Mice were injected intraperitoneally with BrdU and after 12 hours, the incorporation of BrdU in splenic NK cells was analyzed. Numbers adjacent to outlined areas in the dot plot indicate the percentage of CD3⁻NK1.1⁺ cells. Histograms show the percentage of BrdU-positive cells (n ≥ 5 per genotype). Data are representative of 2 independent experiments. (F) In vitro proliferation of IL2-expanded NK cells purified from the spleens of mice of the indicated genotypes. At day 6, NK cells were seeded in triplicate in 96-well plates. After 12 hours, proliferation was measured by standard ³[H]-thymidine incorporation. Four mice per genotype were pooled. Data are representative of 2 independent experiments. (G) Cytotoxicity of IL2-expanded splenic NK cells purified from indicated genotypes. At day 10, NK cells were coincubated in triplicate with CFSE-labeled YAC-1, RMA-Rae1γ, and RMA targets at the indicated E:T ratios. Five mice per genotype were pooled. Data are representative of 2 independent experiments.