H₂O₂ down-regulates IL-12 p40 and IL-12 p70 induction in RAW 264.7 macrophages. The RAW 264.7 macrophages were either left untreated or treated with varying doses of H₂O₂ for 1 hour and further stimulated with LPS plus IFN-γ for 48 hours. The IL-12 p40 (A) and IL-12 p70 (B) levels secreted in the culture supernatants were measured by EIA. The cell viability was measured by the MTT assay (C). In another experiment, H₂O₂ from a different source (Sigma-Aldrich) is either left untreated or pretreated with 100 U/mL catalase for 30 minutes and then added into the macrophage cultures. After 48 hours, both IL-12 p40 and IL-12 p70 levels were measured by EIA (D). This experiment is representative of 3 experiments performed with similar results. Results are expressed as mean ± SD.