Effect of miR-155 down-modulation on IFN-γ production in monokine-stimulated NK cells. (A) NK-92 cells were infected with empty vector (miR-Zip00) or a miR-155 antisense encoding vector (miR-Zip155), sorted for GFP⁺ and analyzed for miR-155 expression by real-time RT-PCR (left). GFP⁺ miR-Zip00 and miR-Zip155 NK-92 cells were stimulated with IL-12 (10 ng/mL) plus IL-18 (100 ng/mL) for 24 hours and analyzed for IFN-γ production by ELISA (middle) and real-time RT-PCR (right). (B) BIC is the precursor of miR-155. NK cells sorted from spleens of Bic^+/+ or Bic^−/− mice were analyzed for miR-155 expression by real-time RT-PCR (left), and stimulated with IL-12 (20 ng/mL) and IL-18 (10 ng/mL). Supernatants were then collected and analyzed for IFN-γ by ELISA (right). This experiment is representative of 3 performed with similar results.