Similar to e.g. enhanced IFN-γ production by NK cells sensing IL-18 and IL-12 during infection with the protozoan Toxoplasma gondii (Cai et al., 2000), Th2/1 cells co-induced with conventional Th2 cells during helminth infections and co-infiltrating the infected organs may contribute to early IFN-γ production in response to cytokine triggers produced upon protozoan, bacterial and viral infections. Here, IL18 is linked to viral infectious disease.