Interleukin (IL)-12 plays a key role in determining the immune response pattern that results in maturation of Th0 to Th1 and Th2. To investigate the correlation between intracellular redox state and IL-12 production in macrophages, cells from the mouse cell line J774A.1 were treated with reagents modulating the glutathione-redox couple before stimulation with lipopolysaccharide (LPS). It was found that the glutathione reductase inhibitor, 1,3-bis (2-chloroethyl)-1-nitrosourea, markedly augmented LPS induced IL-12p40 production particularly when it was added for 24 h before LPS stimulation, whereas the glutathione-synthesis inhibitor, L-buthionine-(S,R)-sulfoximine, suppressed IL-12p40 production. The profile of IL-12p40 augmentation correlated well with the profile of intracellular glutathione oxidation (GSSG) and the activation profile of nuclear transcription factor kappaB (NF-kappaB), suggesting that GSSG is important in NF-kappaB activation which leads to IL-12p40 production. Our results indicate that the glutathione-redox couple plays an important role in the augmented production of IL-12p40 and thus in influencing immune response patterns.