Monocytes are recruited from the circulation into the lung during resolution. Bacterial pneumonia was induced by i.t. instillation of viable K. pneumoniae in eGFP⁻ WT mice. Mice were injected with isolated monocytes from eGFP⁺ or eGFP⁻ donor mice. 5 d after induction of pneumonia, mice were sacrificed and BAL fluid was harvested for flow cytometry analysis. (A and B) Monocytes/macrophages in BAL fluid were identified by (A) native side scatter (SSC)/forward scatter (FSC) gating and (B) expression of F4/80. (C) Expression of GFP in the F4/80⁺ cell population in WT mice that were injected with monocytes from eGFP⁻ (control, red) or eGFP⁺ (green) donor mice (exemplary flow cytometry plots from two independent experiments with five mice per group). Macrophage depletion was performed by injection of chlodronate liposomes. Bacterial pneumonia was induced in control mice and macrophage-depleted mice by i.t. instillation of viable K. pneumoniae (1.5 × 10⁷ CFUs/mouse). (D–G) The number of neutrophils in the BAL fluid (D) and interstitial compartment (IS; E), and the percentage of apoptotic neutrophils in the BAL (F) and interstitial compartment (G) was analyzed by flow cytometry (data pooled from two independent experiments with four to six mice in each group; Mann-Whitney test was used for statistical analysis, *, P < 0.05). BAL supernatant was obtained on day 5 from control mice and mice in which intravascular platelets were depleted by i.v. injection of a platelet-depleting antibody (clone R300, 2 µg/g bodyweight) 2 d after induction of pneumonia. (H and I) Concentrations of TNF⍺ (H) and IFNγ (I) in the supernatant were analyzed by ELISA assays (data pooled from two independent experiments with four to five mice in each group; Mann-Whitney test was used for statistical analysis, *, P < 0.05). Arrows indicate time point of platelet depletion.