Hydrogen peroxide inhibits IL-12 p40 induction in macrophages by inhibiting c-rel translocation to the nucleus through activation of calmodulin protein.

Although the antimicrobial activity of reactive oxygen species (ROSs) is well defined, the role of ROSs in regulating the immune response of the body is not well understood. We now provide evidence that hydrogen peroxide (H 2 O 2 ), a major component of ROSs, inhibits interleukin-12 (IL-12) p40 and IL-12 p70 induction in murine macrophages and catalase pretreatment prevents H 2 O 2 -mediated down-regulation of IL-12. Endogenous accumulation of H 2 O 2 /ROSs in macrophages treated with alloxan resulted in IL-12 p40 inhibition. Although nuclear expression of both p50 and p65 NF-κB increased on H 2 O 2 exposure, nuclear c-rel level was inhibited. Overexpression of c-rel restored IL-12 p40 on stimulation with lipopolysaccharide plus IFN-γ during H 2 O 2 treatment. H 2 O 2 did not inhibit c-rel induction in cytosol; however, it prevented the transport of c-rel from cytosol to the nucleus. H 2 O 2 activated calmodulin (CaM) protein in the cytosol, which subsequently sequestered c-rel in the cytosol preventing its transport to the nucleus. The CaM inhibitor trifIuoperazine increased both nuclear c-rel and IL-12 p40 levels in H 2 O 2 -treated macrophages, emphasizing a role of CaM in these processes. H 2 O 2 /ROSs thus down-regulate IL-12 induction in macrophages by a novel pathway inhibiting c-rel translocation to the nucleus through activation of CaM protein.