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Context: Alum is thought to induce inflammation resulting in the release of danger signals such as uric acid (UA) which in turn enhances the immune response to an antigen. Hydrogen peroxide (H2O2) is produced as a byproduct in the purine catabolic pathway that leads to the production of UA. In addition, serum nitric oxide (NO) levels are increased in inflammation. Objective: To further explore the mechanism of action of alum, this study was designed to determine the effects of catalase and 1400W on the number of interleukin-4 (IL-4) and interferon-γ (IFN-γ) secreting spleen cells in mice given ovalbumin (OVA) with alum. Materials and methods: Groups of BALB/c mice were injected intraperitoneally with alum + OVA, alum, OVA, catalase, or 1400W. Other groups were treated with catalase or 1400W and given alum + OVA. The number of IL-4 and IFN-γ secreting spleen cells were determined at days 4 and 7 postinjection by enzyme-linked immunosorbent spot (ELISPOT). Results: Catalase and 1400W caused a decrease in the number of IL-4 secreting spleen cells induced by alum + OVA. 1400W caused a decline in the IFN-γ secreting spleen cells induced by alum + OVA. Catalase caused an increase in IFN-γ secreting spleen cells. Discussion and conclusion: It appears that H2O2 and NO are needed for alum-induced production of a T-helper 2 cytokine. NO also appears to be needed, whereas H2O2 appeared to inhibit an alum-induced production of a T-helper 1 cytokine. These results might explain why alum is mainly a promoter of a T-helper 2 response. [ABSTRACT FROM AUTHOR]