Cytokine and chemokine concentrations in lung lavage fluid of wild-type (WT) and S100A9 knockout (KO) mice. Animals were spontaneously breathing (C), high tidal mechanically ventilated (HVT MV), exposed to LPS followed by spontaneously breathing (LPS), or exposed to LPS followed by HVT mechanical ventilation (HVT MV+LPS). Levels of interleukin (IL)–6 (A), macrophage inflammatory protein (MIP)-2 (B), tumor necrosis factor-α (TNF-α) (C), IL-1β (D), and keratinocyte–derived chemokine (KC) (E) were determined. Data represent means (SEM) of 6–8 mice per group. *p<0.05, **p<0.01, ***p<0.001 KO versus WT mice, ###p<0.001, ##p<0.01, and #p<0.05 versus WT C, §§§p<0.001 and §§p<0.01 versus LPS-only, +++p<0.001, and ++p<0.01 versus HVT MV-only.