IL-10 pretreatment suppresses secretion of proinflammatory cytokines and APC function of DCs. Bone marrow–derived DCs were pretreated with varying doses of IL-10 for 24 hours, stimulated with (A) 10 μg/mL anti-CD40 antibody or (B) 500 ng/mL LPS for 48 hours. IL-12p70 (○) and TNF-α (•) levels were measured in culture supernatants using ELISA. Levels of pIL-12p40 and TNF-α were lower than 25 pg/mL in the absence of (A) anti-CD40 antibody or (B) LPS stimulation. (C) DCs were stimulated with varying concentrations of LPS alone (• and ▴) or cotreated with 50 ng/mL IL-10 for 48 hours (○ and ▵), and the amounts of IL-12p70 (• and ○) and TNF-α (▴ and ▵) were measured in culture supernatants. (D) DCs were pretreated with varying concentrations of IL-10 for 24 hours, pulsed with 5 μg/mL HA peptide, and cultured with 3.5 × 105 NOD.CL4 T cells for 48 hours. Levels of IL-2 secretion in culture supernatants were measured using ELISA. Less than 20 pg/mL IL-2 was detected in cultures lacking HA peptide. Data represent mean ± SD of 4 individual cultures and are representative of 3 independent experiments. *P < 10^–4 compared with no IL-10 pretreatment. ^#P < 10^–3 compared with no IL-10 pretreatment (Student t test).