Assessment of NK cell IFN-γ production in WT and Ship1^–/– mice following monokine stimulation. (A) NK cells were isolated from spleens of WT and Ship1^–/– mice and then stimulated for 24 hours in vitro with individual monokines IL-12 (10 ng/mL), IL-18 (20 ng/mL), or IL-15 (10 ng/mL) or with a combination of IL-12 plus IL-15, IL-12 plus IL-18, or IL-15 plus IL-18. Supernatants were then collected and assayed for IFN-γ by ELISA. Data summarize results from 5 mice. (B) Wild-type and Ship1^–/– mice received an intraperitoneal injection of IL-12 (1 μg) plus IL-18 (0.5 μg). After 24 hours spleens were harvested and splenocytes were cultured for 4 hours in brefeldin A and permeabilized and stained with DX5-PE and NK1.1-PE mAbs (pan-NK) and anti-muIFN-γ–FITC mAb. The histogram shows flow analysis for IFN-γ staining in DX5⁺ NK1.1⁺ NK cells from WT and Ship1^–/– mice. Results are representative of 5 experiments. Error bars indicate ± SEM.