PIR-B represses the development of Flt3-L–induced PDCs. (A) Splenocytes isolated from 8-week-old mice are stained with anti–PDCA-1 and CD11c. The percentages of PDCA-1⁺CD11c⁺ PDCs (circled). Data are mean ± SEM (n = 4 mice per group). (B) Flow cytometric analysis of PIR-A/B expression on B6 and Pirb^−/− splenic PDCs. Black line indicates B6 PDCs; and gray line, Pirb^−/− PDCs. Occupied gray area represents isotype control. Mean fluorescent intensities of PIR-A/B expression. (C) BM cells from B6 and Pirb^−/− mice are incubated with Flt3-L (150 ng/mL) for 8 days. The total cell numbers of BM cells. ● represents B6 BM cells; and ○, Pirb^−/− BM cells. Data are mean ± SEM (n = 6 mice per group). (D) The percentages of Flt3-L–induced PDCs (circled). Data are mean ± SEM (n = 3 mice per group). (E) Flow cytometric analysis of PIR-A/B, Flt3, and I-A/E expression on B6 and Pirb^−/− Flt3-L–induced PDCs. Mean fluorescent intensities. (F) The progenitor fraction of PDCs (Flt3⁺lineage⁻) in B6 and Pirb^−/− BM cells. Data are mean ± SEM (n = 3 mice per group). (G) The percentages of B220⁺CD11c⁺ BM cells at 4 and 6 days after Flt3-L administration (circled). Data are mean ± SEM (n = 3 mice per group). (H) Flow cytometric analysis of Flt3 expression on day 4 and 6 B220⁺CD11c⁺ BM cells. Mean fluorescent intensities. (I) B220⁺CD11c⁺ BM cells at 6 days after Flt3-L administration were cultured in Flt3-L–free conditions for 3 hours to reduce endogenous signaling activity and were then stimulated with Flt3-L (300 ng/mL). Immunoblot analysis of phospho-STAT3 (pSTAT3), STAT3, pErk1/2, Erk1/2, pShc, and Shc. All results are representative of 3 separate experiments. All statistical analyses were performed using Student t test: *P < .05, **P < .01.