pDCs promote IL-12 production by mDCs through type 1 IFNs. Purified CD11c⁺ mDCs were cocultured with or without different doses of autologous purified pDCs for 24 hours in the presence of the indicated stimuli. Numbers of mDCs and pDCs indicate 10³ × the cell number per well. Concentrations of IL-12 p70 in the supernatant cultures were measured by ELISA. Mean ± SEM obtained from 3 independent experiments are shown. Statistical significance was determined using paired Student t test. ^*P < .05; ^**P < .01. rIFN-α; recombinant human IFN-α 2a, anti-IFNs Abs; mixture of neutralizing Abs to IFN-α, IFN-β Ab, and IFN-α/β receptor, cont. Ig; mixture of rabbit IgG and mouse IgG.