Male and female mice were inoculated with PR8 and monitored for changes in body mass (A), rectal temperature (B), and survival (C) for up to 21 days (n = 15/sex). Infectious virus titers (D) as well as concentrations of TNF-α (E), CCL2 (F), IFN-γ (G), and IL-6 (H) were measured in homogenates of lungs removed 0, 1, 3, 5, or 7 days p.i. (n = 10–15/sex/time-point). Fold change represents concentrations of proteins at Days 1–7 p.i. relative to concentrations at Day 0. Data represent the mean ± SEM. The dotted line in panel D represents the limit of detection for the assay. Significant differences between the sexes as determined by post hoc analyses at each time-point are represented by an asterisk (*), P<0.05.