The production of IFN-gamma by IL-12/IL-18-activated macrophages requires STAT4 signaling and is inhibited by IL-4

Macrophages release IFN-gamma on combined stimulation with IL-12 and IL-18, but the signaling requirements of this process and its regulation by other cytokines are unknown. Here, we demonstrate that STAT4 is indispensable fo r IL-12/LL-18-induced producHon of IFN-gamma by mouse peritoneal macrophage s. Type 2 NO synthase (NOS2), which we previously found to be a prerequisit e for IL-12-induced IFN- gamma production in NK cells, was not required for IFN-gamma production by these macrophages, IL-12 alone already induced the expression of IFN-gamma mRNA, but nuclear translocation of STAT4, the rele ase of IFN-gamma protein, and the subsequent production of NO was strictly dependent on the simultaneous presence of IL-18, NF-kappaB, which mediates IL-18 effects in T cells, was only weakly activated by IL-12 and/or IL-18 i n macrophages. Known inhibitors of macrophage functions (e.g,, IL-4 and TGF -beta) also suppressed macrophage IFN-gamma production and the subsequent p roduction of NOS2-derived NO. The inhibitory effect of IL-4 was paralleled by nuclear translocation of STAT6, which in EMSAs was able to bind to the s ame DNA oligonucleotide as STAT4, These results further define the producti on of IFN-gamma by macrophages and point to a diversity in the signals requ ired for IFN-gamma production by various cell types.