Measurement of splenic natural killer (NK) cells and hapten-specific hypersensitivity. (A) Splenic NK cell activity of C57BL/6J (B6J) versus C57BL/6N (B6NTac) mice: (upper panel) male and (lower panel) female. Splenic NK cells from C57BL/6J or C57BL/6N mice were stimulated under the indicated conditions (six mice per group). Mean ± SD of interferon (IFN)γ-positive cells among a population of CD3- NK1.1+ NK cells was measured by flow cytometry. (B) Hapten-specific hypersensitivity. Male or female C57BL/6J or C57BL/6N mice were sensitized by the application of 25 μl of 0.5% dinitrofluorobenzene (DNFB) solution on the ventral skin. They were then challenged by the application of 5 μl of 0.15% DNFB solution on the left ear 5 days later (DNFB group). The right ears were painted with vehicle (-) and used as controls. Ear thickness was measured 48 hours after challenge. Results are representative of three independent experiments with six mice per group. *P < 0.05; **P < 0.005 (Mann-Whitney U -test).