Cytokines and chemokines in secondary bacterial pneumonia. Groups of 10 mice were infected with wt PR8 or PR8-PB1-F21918 followed 7 days later by bacterial challenge. Levels of (A) TNF-α, (B) IL-1α, (C) IL-6, (D), IL-10, (KC), and (F) MIP-1α from lung homogenates taken from mice 3 and 7 days after viral infection (prior to bacterial challenge) and 72 hours after bacterial challenge (10 days after viral infection) are presented. The 25th – 75th percentiles are represented by the shaded box-plots with the horizontal bar indicating the mean value. Error bars indicate the standard deviation of the measurements. An asterisk (*) indicates a significant difference by ANOVA compared to the wt PR8 group (p < 0.05).