Figure 4. IL-18 does not alter bacterial clearance during superinfection.

C57BL/6 and ASC^–/– mice were infected with influenza A/PR/8/34 or vehicle for 6 days, and then challenged with 10⁸ CFU of methicillin-sensitive Staphylococcus aureus (MSSA) or vehicle for 24 hours. (A) Gene expression of caspase-1 (n = 7–8). (B and C) Protein measurement of caspase-1 p20 and caspase-1 p45 products measured by Western blot (n = 8). (D) Gene expression of IL-18 (n = 7–8). (E) IL-18 concentrations measured by ELISA (n = 6). C57BL/6 mice were infected with influenza A/PR/8/34 for 6 days, received 200 μg of IL-18 inhibitor or IgG control, and then challenged with 10⁸ CFU of MSSA 4 hours later and harvested at 24 hours. (F) CFU in lung homogenate (n = 6). *P < 0.05 versus Flu/SA by 1-way ANOVA or unpaired t test. Data points reflect individual values ± SEM. Each experiment was independently performed at least twice and data are shown from combined experiments with the exception of the IL-18 inhibition experiment that was performed once. NS, not significant.