Recombinant human IL-18 induced IFN-γ expression of purified NK cells in the presence of TLR agonists at nanogram concentrations. Freshly isolated human liver sinusoidal NK cells from adult live donors were stimulated by TLR agonists for 16 h in the presence of different concentrations of IL-18. Intracellular IFN-γ expression was assessed in CD3⁻, CD56⁺ NK cells by flow cytometry. Only poly I:C synergistically induced an NK cell IFN-γ response together with IL-18. However, note that the effective concentration of IL-18 was in the range of 100 ng/ml.