Figure 3. Liver STAT3 and RelA are required for blood-borne host defense during pneumonia.

(A) Living bacteria were enumerated in blood collected 48 hours after intratracheal S. pneumoniae serotype 3 (10⁴ CFU). Data points represent individual mice, and lines indicate medians (n = 16–18). (B) Survival through 48 hours was documented after intratracheal instillation of S. pneumoniae serotype 19F (10⁶ CFU) (n = 15). (C and D) Effects of serum on opsonophagocytosis were measured by quantifying fluorescence/cell using flow cytometry after J774A.1 mouse macrophage-like cells were incubated with fluorescent S. pneumoniae and mouse serum. Representative histograms and the percentage of cells fluorescent illustrate effects of (C) pneumonia (in control CRE- mice) or (D) genotype (during pneumonia). Results represent 3 experiments, each containing pooled sera from distinct mice. (E) C3 deposition was measured on serum-opsonized S. pneumoniae by flow cytometry. Data represent mean ± SEM of the percentage of C3⁺ bacteria exposed to serum from different mice (n = 4–7). Colors in C–E correspond to serum collected from uninfected mice (green), 24-hour infected CRE^– control mice (red), or 24-hour infected CRE⁺ mutant mice (blue). Shaded curves represent background (nonopsonized) bacterial fluorescence (E) or background J774A.1 fluorescence (C and D), which was similar for cells alone, cells exposed to nonopsonized bacteria, or experiments conducted at 0°C. *P < 0.05, difference between groups.