IL-10 has cytotoxic effects on ISS-activated PDCs that is counterbalanced by IFN-α (A) Purified PDCs (3-5 × 10⁴) were stimulated with IL-3 (10 ng/mL) or ISS (5 μg/mL) for 60 hours alone or (B-E) in the presence of IL-10 (0.01-10 ng/mL) and (E) with a combination of anti-IFN-α (5000 neutralizing U/mL), anti-IFN-β (2000 neutralizing U/mL), and mouse anti-IFN-α/β receptor MAb (20 μg/mL). Viable PDCs were counted by using trypan blue exclusion criteria. Representative results of 10 donors are shown.