IFN-α regulates the differentiation of CD11b⁺Gr1^HIand CD11b⁺Ly6C^HIcells from lineage negative (Lin⁻) BM progenitor cells. (A) Representative FACS plots showing preculture Lin⁻CD11b⁻ cells and their differentiation to CD11b⁺Gr1^HI or CD11b⁺Ly6C^HI cells following a 2-day culture in the presence of vehicle (PBS) or IFN-α (100 U/mL). (B) Bar graphs showing quantitation of Ly6C^HI cells (B) or Gr1^HI cells (C) following 2 days of culture. (D) Representative histogram showing CD11c expression by Ly6C^HI cells differentiated from Lin⁻ cells in the presence or absence of IFN-α. (E) Representative FACS plots showing the gating of the remaining CD11b⁻Lin⁻ cells following the 2-day culture to be examined for intracellular IRF8 expression and representative histogram showing IRF8 expression by CD11b⁻Lin⁻ cells in the presence or absence of IFN-α. Bar graph showing the MFIs of IRF8 normalized over isotype control. Data shown in panels A-E were obtained from 2 independent culture experiments performed in triplicates and presented as mean ± SD of 6 replicates. *P < .05. (F) Representative histograms depicting the expression of IRF8 in BM hematopoietic stem cells (HSCs: Lin⁻c-Kit⁺Sca-1⁺) and GMPs (Lin⁻c-Kit⁺Sca-1⁻FcγRII/III⁺) from naïve mice (solid purple line), uninfected ECDI-SP–treated mice (solid green line), or Δm157-infected ECDI-SP–treated mice (dashed blue line) 2 days post–Δm157 infection. Data shown in panel F were obtained from 2 independent experiments with a total of 4 mice in each group.