miR-155 overexpression enhances IL-12 plus IL-18–induced IFN-γ production in NK cells. (A) NK-92 cells were infected using an empty lentivirus vector (Lenti) containing GFP or a lentivirus vector containing GFP and miR-155 sense (Lenti-miR-155 vector). Cells were then sorted for high GFP expression and analyzed for miR-155 expression by RT-PCR. (B) Primary human CD56⁺ NK cells were infected using either Lenti or Lenti-miR-155, sorted by FACS for GFP (left), plated in medium and costimulated with IL-12 (10 ng/mL) plus IL-18 (100 ng/mL) or 1/5^th or 1/25^th the doses of these monokines for 24 hours. Supernatants were then collected and assayed for IFN-γ by ELISA (right). These data are representative of 3 experiments performed with moderate doses, and 2 experiments performed with high and low concentrations of monokines.