TLR-9 dependence of PDC response to EBV. PDC response to EBV is dependent on TLR-9 signaling. The presence of chloroquine 0.05 mM (4.7 ± 0.6 spots/3 × 10⁵ T cells) and an inhibitory CpG oligonucleotide 1 μg/mL (84.7 ± 7.6 spots/3 × 10⁵ T cells) in culture significantly inhibited the ability of EBV-stimulated PDCs to induce the generation of IFN-γ–producing CD3⁺ T cells (249.3 ± 18.5 spots/3 × 10⁵ T cells, *Student t test P < .001). HSV-1–stimulated PDCs with CD3⁺ T cells alone or in the presence of chloroquine and inhibitory CpG oligonucleotide are shown for comparison. Results are expressed as mean ± SEM.