2.6 Interferon-γ induction assay
NK-92MI cell were maintained in completed α-MEM medium supplemented with 12.5% FBS and 12.5% horse serum at 37°C in CO2incubator and was used to evaluate the activity of each type of IL-18. The experiment was performed as previously described. Briefly, cells were suspended in 0.2 ml complete media at 0.5 × 106cell/ml. The induction was performed by using each type of recombinant IL-18 at the concentration of 75, 150 and 300 ng/ml with 0.5 ng/ml of human IL-12. After 16–18 h of incubation at 37°C in CO2incubator, the supernatants were collected and IFN-γ ELISA assay was then performed by using Human IFN-γ Quantikine ELISA Kit (R&D system, USA).