Interleukin-12 treatment restores normal resistance to bacterial challenge after burn injury

Background. Preliminary studies in this laboratory have shown that treatment with interleukin-12 (IL-12), a cytokine that induces expression of the T-helper-1 lymphocyte phenotype, in an animal model of burn injury increased survival after a septic challenge. The purpose of this study was to define the efficacy of IL-12 therapy and to explore its mechanism of action. Methods. Adult male A/J mice were subjected to 25% full-thickness scald or sham burn. Starting on day 3 after burn, groups of mice received five daily injections of IL-12, interferon-gamma (IFN-gamma), or saline solution. Some animals received anti-IFN-gamma monoclonal antibody. At day 10 most animals underwent cecal ligation and puncture (CLP) and were observed for survival. Some animals were killed at day 10, and CD4-enriched splenocytes were stimulated with anti-CD3 antibody or concanavalin A and were studied for cytokine production and mRNA expression. Results, IL-12 treatment, 25 ng dairy for 5 days, increased survival of the burn group after CLP to that of the sham burn control group. Anti-IFN-gamma antibody, 500 mu g, administered I day before IL-12 treatment, reduced reduced the efficacy of IL-12 IFN-gamma treatment, 7000 units, moderately increased survival. IL-12 had no effect on survival of the sham burn group. At the time of CLP IL-12 therapy had induced a marked decrease in CD4(+) lymphocyte IL-4 and a moderate increase in IFN-gamma production and mRNA expression without affecting IL-2. Conclusions, IL-12 is the most effective therapy so far tested in this burn plus CLP model. It acts at least in part through IFN-gamma. However, IFN-gamma therapy was not as effective as IL-12.