P aeruginosa's LPS causes reduction of BM common myeloid progenitors and granulocyte-monocyte progenitors. Cohorts of CD1 or C57BL/6J mice were injected intraperitoneally with P aeruginosa's LPS (0.8 mg/kg) or PBS. (A) BM was harvested 24 hours after injection, stained with specific antibodies, and analyzed by multicolor flow cytometry. The dot blot on the left insight shows expression of c-Kit and Sca-1 in Lin⁻/IL-7R⁻ cells. Dot blot on the right insight shows FcγRII/III expression on gated Lin⁻/IL7-R⁻/Sca⁻/Kit⁺ cells to determine CMP, GMP, and MEP subsets. Bar graphs indicate percentages of CMPs and GMPs on the Lin⁻ population. Values are average of 10 to 12 mice and summarize 3 independent experiments. Error bars indicate SE. CMP: LPS versus PBS *P < .001; GMP: LPS versus PBS *P < .001. (B) Lys-GFP reporter mice were challenged with P aeruginosa's LPS or PBS, and the BM was harvested at 24 hours from injection. Dot plots show GFP expression on CMPs, GMPs, and granulocytes in a representative experiment. Values in the bar graph indicate percentage of cells that express no or low levels of Lys-GFP (gate A) within each specific subset and are average of 4 mice. CMP: LPS versus PBS *P = .05; GMP: LPS versus PBS *P < .001; granulocytes: LPS versus PBS *P = .035. (C) BM of C57/B6 mice challenged with LPS or PBS was analyzed for the presence of MEPs (left panel), CLPs (middle panel), and MPPs (right panel) at 24 hours from challenge. Bar graphs indicate percentages of MEPs and CLPs on the Lin⁻ population. Values are average of 10 to 12 mice and summarize 3 independent experiments. Error bars indicate SE. MEP: LPS versus PBS *P < .001; CLP: LPS versus PBS *P < .001. Short-term hematopoietic stem cells (ST-HSCs; or MPPs) were defined as Lin⁻/IL-7R⁻/Sca⁺/Kit⁺/CD34⁺/Flt3⁺ cells. Bar graph shows percentage of ST-HSCs () and long-term HSCs (LT-HSCs; ■) on total Lin⁻ population. Values are average of 12 mice and summarize 3 independent experiments. Error bars indicate SE. *P < .001. (D) In each experiment, a sample of sorted LSK was derived from a pool of BM of 4 to 6 mice. RNA was extracted from LSK (IL-7R⁻) cells from PBS- and LPS-challenged mice. Samples were analyzed for expression of C/EBPα and PU.1 by qRT-PCR. Bar graphs represent averages of fold changes in expression in 3 independent samples. Error bars indicate SD. LPS versus PBS: C/EBPα, *P = .033; PU.1 *P = .029. (E) Sepsis causes alterations in HSC differentiation (working model). During severe sepsis, bacterial LPS induces TLR4-dependent expansion of dysfunctional LSK cells displaying a defective ability to progress into the pool of myeloid progenitors: CMPs and GMPs. Reduction in CMPs and GMPs results in neutropenia.