Functional analysis of PDCs in response to EBV stimulation. (A) Cell-surface expression of costimulatory molecules on immunomagnetic bead-isolated PDCs before and after stimulation with EBV. Flow cytometric analysis revealed up-regulation of cell surface expressions of CD86 and to a lesser extent MHC class II and other costimulatory molecules (CD40, CD80) following EBV stimulation in vitro for 48 hours. An HSV-1–stimulated PDC is shown as the positive control. Open black profiles denote isotype controls, dotted line profiles denote freshly isolated unstimulated PDCs, and solid filled in histograms represent EBV-matured PDCs. Isotype controls of EBV-stimulated PDCs and freshly isolated PDCs were similar and hence only the former histogram was shown. Representative histograms of 3 separate experiments. (B) Cytokine production by PDCs and MDCs in response to EBV stimulation measured by ELISA. Both PDCs (1203.1 ± 100.5 pg/mL) and MDCs (1116.4 ± 90.5 pg/mL) produced significantly greater amounts of IL-10 following EBV stimulation (10% vol/vol) for 20 hours compared to the amount present in the EBV supernatant (449.5 ± 71.4 pg/mL, Student t test P < .01). For comparison, HSV-1–stimulated BDCA-4⁺ PDCs and BDCA-1⁺ MDCs did not produce measurable IL-10 (data not shown). PDCs cultured in complete medium did not produce any detectable IL-10. Results are expressed as mean ± SEM. (C) PDCs produced IFN-α following EBV stimulation that is enhanced in the presence of anti–IL-10 mAb. PDCs cultured in complete medium did not produce any detectable IFN-α. Results are expressed as mean ± SEM.