Characterization of PP pDCs and their requirement for IFN-STAT1 signaling. (A) Gating strategy of PP pDCs. Surface expression of PDCA-1, B220, CCR9, CD86, and TLR4 and intracellular TLR7 and TLR9 expression in pDCs from BM, spleen, and PP. Shaded area represents isotype control staining. (B) Gene expression of Irf7, Irf8, and Tcf4 in pDCs from BM, spleen, and PP, determined by quantitative PCR. (C-D) Proportion (C) and absolute number (D) of PP pDCs from Stat1^−/−, Ifnar^−/−, and wild-type (WT) controls. Error bars represent SEM of results from 4-8 mice. (E) PP pDC proportions in mice receiving HGT with pORF vector (NT) or pORF encoding Flt3L (10 μg), 4 days after treatment. (F) PP pDC proportions in Stat1^−/− mice at 8 days after transfer of 10⁵ congenic CD45.1⁺ DC progenitors (BM lin⁻ Flt3⁺ CD115⁺ c-kit^int cells) intravenously. Similar results were obtained after transfer into Ifnar1^−/− mice (not shown). (G) PP pDC proportions in Stat1^−/− or Ifnar1^−/− mice 8 days after transfer of 10⁵ wild-type DC progenitors (BM lin⁻ Flt3⁺ CD115⁺ c-kit^int cells) intravenously (CDP) or in animals left untreated (NT), as indicated. Some mice received Flt3L HGT 2 days before DC progenitor transfer (CDP + Flt3L) or Flt3L HGT alone (Flt3L), as shown. (B-G) Data represent 2 or 3 independent experiments. N = 4-10.