Ligation of Siglec-H does not modulate pDC activation. (A) Bone marrow cells were expanded for 14 days with Flt-3 ligand and labeled with anti-B220 and anti-Ly6c mAbs to identify pDC precursor (left panel). Double-positive cells (top right quadrant, left panel) were sorted and an aliquot stained with either sheep anti–Siglec-H⁺ (open histogram, right panel) or preimmune immunoglobulin (gray histogram, right panel). (B) FACS-sorted B220⁺ Ly6c⁺ cells were cultured with no Ab, MB15 mAb (10 μg/mL), or sheep anti–Siglec-H pAb (10 μg/mL) in the presence or absence of 10 μM CpG 1668 for 18 hours. The concentrations of the indicated cytokines in the cell culture supernatants were determined by flow cytometry.