CD11c⁺ populations were isolated from the spleens of B6 mice (sDCs) and from 10- to 14-day cultures of bone marrow cells from B6 mice (BM-DCs). One million DCs were plated in each well of a 96-well culture plate in a volume of 200 μL, in the presence or absence of 1000 neutralizing units of antimouse IFN-α/β sheep immunoglobulin. Cultures were incubated at 37°C in 5% CO₂ for 18 hours, after which supernatant was harvested. An aliquot of 100 μL or 50 μL of each sample was assayed for IFN-α/β activity. Data represent the IFN-α/β titer in each individual experiment, expressed in experimental units of IFN-α/β per 10⁶ cells. One of these units is the equivalent of 4 international IFN units. IFN indicates interferon; BM-DC, bone marrow–derived dendritic cell; sDC, splenic DC.