Figure 3. IL-13-dependent inhibition of IFN-γ is responsible for reduced susceptibility to secondary MRSA infection.

IL-13^−/− and WT C57BL/6 mice were infected with influenza and challenged with MRSA 3 days later. One day prior to and at the time of MRSA challenge IL-13^−/− mice were intraperitronealy (i.p.) injected with 250 µg anti-IFN-γ antibody or PBS (A, B) and WT mice were intratracheally (i.t.) treated with 1.5 µg of mrIFN-γ or PBS (C–F). (A,C) Survival of mice was evaluated daily. (B,D) In a separate experiment, lung bacterial burdens were evaluated 24 h after MRSA challenge. Levels of IL-13 in BALF samples (E) and IL-13Rα2 in serum samples (F) were evaluated 4 h after MRSA challenge of WT mice treated with mrIFN-γ. Each data point represents mean ± SEM of 5 mice per group from one representative experiment. Experiments of similar design were independently performed at least twice with similar results. Statistical significances: “*” corresponds to PBS + MRSA infected mice (white symbols in each figure panel), whereas “#” corresponds to mice infected with influenza on day 0 and MRSA on day 3 (one-way ANOVA with a Bonferroni’s post test, or Logrank test for differences in survival).