Figure 4.

Klebsiella pneumoniae TOP52 elicits a more robust innate immune response in the lungs at 24 hours after infection than TOP52ΔfimK. A, Representative histologic staining of murine lungs at 24 hours after infection with TOP52 (top panels) or TOP52ΔfimK (bottom panels) reveals marked differences in consolidation and acute inflammatory infiltrate. Boxes indicate areas of increased magnification in right panels (scale bars, 200 µm). B, Representative flow cytometry shows a higher proportion of neutrophils in lungs after TOP52 infection, compared with TOP52ΔfimK infection. One representative plot shown for each group, with mean neutrophil percentages indicated from 33 mice across 3 independent experiments. C, Flow cytometric quantification demonstrates significantly higher absolute numbers of neutrophils in TOP52-infected mouse lungs (solid bars) than in TOP52ΔfimK-infected lungs (open bars) at 24 hours, 1 week, and 2 weeks after infection. Data are shown as mean ± standard error of the mean (*P < .05 and **P < .01, by the Mann–Whitney U test). Abbreviation: PBS, phosphate-buffered saline.