Inhibition of interleukin-12 production in mouse macrophages by hydroquinone, a reactive metabolite of benzene, via suppression of nuclear factor-kappaB binding activity.

Exposure to cigarette smoke is known to increase the risk of the development of allergic disease associated with T helper type 2 (Th2)-mediated immune responses. IL-12 is known to suppress Th2 responses. In this study we investigated the effects of hydroquinone (HQ), a major metabolite of benzene present in large quantities in cigarette tar, on the production of IL-12 from mouse macrophages stimulated with lipopolysaccharide (LPS). HQ potently inhibited the LPS-induced IL-12 production in both primary mouse macrophages and RAW164.7 monocytic cells in a dose-dependent manner. The effect of HQ on IL-12 p40 promoter activation was analyzed by transfecting RAW264.7 monocytic cells with p40 promoter/luciferase constructs. The repressive effect mapped to a region in the p40 promoter containing a binding site for nuclear factor-kappaB (p40-kappaB). Furthermore, activation of macrophages by LPS resulted in markedly enhanced binding activity to the kappaB site, which significantly decreased upon addition of HQ. Pre-incubation with HQ significantly prevented degradation of IkappaB protein in LPS-stimulated macrophage cells, indicating that HQ suppressed NF-kappaB binding activity by inhibiting the degradation of IkappaB protein. These findings suggest that HQ may, at least in part, enhance allergic immune responses by inhibiting the production of IL-12 in macrophages.