Hydrogen peroxide increases interleukin-12 p40/p70 molecular ratio and induces Th2-predominant responses in mice

To investigate the influence of oxidative stress on the immune response, mice were injected with H(2)O(2), and peritoneal macrophages were isolated and stimulated in vitro with lipopolysaccharide (LPS). H(2)O(2) significantly augmented both interleukin (IL)-12p40 and IL-12p70 production and increased the p40/p70 molecular ratio. This was confirmed by mRNA analysis, which showed that H(2)O(2) increased LPS-induced mRNA expression of both IL-12p40 and IL-12p35 subunits with an increased p40/p35 ratio. Analysis of anti-ovalbumin (OVA) antibodies revealed that H(2)O(2) injection significantly increased the production of type 2 helper T cell (Th2)-associated antibody classes [immunoglobulin (Ig)E and IgG1] but not a Th1-associated antibody class (IgG2a). To confirm the Th2-predominant immune response, we analyzed the profile of cytokine production by spleen T cells of OVA-immunized and H(2)O(2)-injected mice. H(2)O(2) significantly increased the production of IL-4 but not that of interferon-gamma. Together, these results suggest that H(2)O(2)-induced overproduction of IL-12p40 promotes the Th2-predominant response through increased production of IL-12p40-homodimers, which could serve as an antagonist of the Th1-inducing cytokine IL-12p70.