IL18 and infection: Since IL-18 is induced in small amounts only, even after infection by Salmonella, we determined whether IL-18 was a limiting factor in the induction of IFN-γ in CD56+ cells by supernatants of Mφ1 infected with Salmonella. The addition of recombinant IL-18 to the supernatants increased the IFN-γ production by these CD56+ cells (Fig. 5A).