miRNAs activate NK cells in vivo. (A) Mice were treated in vivo with vehicles or 20 μg RNA-Ctl, miR-122, or miR-15b for 4 days. The treated mice were then sacrificed, and total splenocytes were isolated for flow cytometric analysis to measure CD69 surface expression after gating on CD3^-NK1.1⁺ NK cells. Representative data from 1 of 6 mice with similar results (left) as well as summary data from 3 mice (right) in 1 experiment are shown. (B) The prepared splenocytes from A were cocultured with YAC-1 tumor cells for 3 hours without any exogenous IL-12 and subjected to flow cytometric analysis of CD107a expression after gating on CD3^-NK1.1⁺ NK cells. For (A) and (B), *P < .05 and **P < .01, respectively, and error bars represent standard deviation.