Loss of bone marrow neutrophils during sepsis. CD1 mice challenged with burn and inoculation of the PA14 (PA14) or 33C7 (33C7) strain, burn only (B), and normal controls (N) were killed at the indicated time points. Bone marrow (BM) cells were harvested and stained with antibodies directed to Gr1 and Mac1 markers and analyzed by flow cytometry. (A) Dot blots in the left panel show FSC (indicative of size) and SSC (indicative of granularity) of total BM samples. The FCS^low/SSC^high population was gated (R1) and analyzed for Gr1/Mac1 expression (middle panel), and sorted for morphologic analysis (right panel). (B) Dot blots show Gr1 and Mac1 expression in a representative experiment. Numbers indicate percentage of cells within the gate. (C) Line graph summarizes 3 independent experiments. Values are the average of 6 to 10 mice and indicate percentages of BM Gr1⁺/Mac1⁺ cells. The value at time 0 is the average of 15 normal controls. Error bars indicate SD. (D) Bar graph shows percentages of annexin V expression on Gr1⁺/Mac1⁺ population in N, B, and PA14 mice. Values are averages of 3 to 4 mice. Error bars indicate SD. *P = .04. (E) Bar graph shows the average percentage of total BM Gr1⁺/Mac1⁺ cells in PA14-challenged mice; percentages are normalized to Gr1⁺/Mac1⁺ cells in normal controls to equal 100%. The light portion of the column represents the average percentage of living cells; the dark portion of the column represents average percentage of annexin V⁺ apoptotic cells (n = 4). Error bars indicate SD.