A higher percentage of apoptotic neutrophils is present in the BALF of G-CSFR^−/− mice following P aeruginosa infection. (A) Neutrophils isolated from the bone marrow of wild-type mice were cultured for 48 hours under conditions that induced apoptosis (“Materials and methods”). Cells were harvested at the indicated times and stained for Gr-1, annexin V, and 7AAD. Whereas the majority of neutrophils is viable (annexin V⁻, 7AAD⁻) at time 0 (left panel), an increasing percentage of early apoptotic (annexin V⁺, 7AAD⁻) and then late apoptotic (annexin V⁺, 7AAD⁺) cells was seen with prolonged culture (middle panel, right panel). Histograms are gated for Gr-1⁺ (granulocytic) cells. (B) Representative dot plots of neutrophils recovered from the BALF of wild-type (left panel) and G-CSFR^−/− (right panel) mice. Data are gated for Gr-1⁺ (granulocytic) cells.