Dendritic cell progenitors are significantly reduced in the absence of GM-CSF and FL. Quantification of total cell numbers of lineage-negative (lin⁻) cells (A) and for each progenitor population (B) (n = 5-7 mice/group). *P < .05; **P < .01; ***P < .001. (C) Representative fluorescence-activated cell sorting (FACS) plots of stained BM cells from WT, GM-CSF^−/−, FL^−/−, and DKO mice. Gating of lin⁻ cells (dead cells excluded by PI staining; first row). Second and third rows were first gated on lin⁻ cells. MDP^Δ gate: M-CSFR^hi (second row). CDP and Flt3⁺ CLP gates were as follows: CDP, c-kit^intFlt3⁺M-CSFR⁺IL7Rα⁻; Flt3⁺ CLP, c-kit^intFlt3⁺M-CSFR^lo/−IL7Rα⁺ (third and fourth rows). Numbers in or beside boxes indicate percentage of cells shown.