Unpulsed DCs activate NK cells to induce IL-12 in endogenous DCs and to prime CTL responses. (A) Mice were treated with CD40-/- DCs without (▪) or with () anti–IFN-γ mAb. Draining lymph nodes were taken at different time points, the cells counted, and the different cell populations analyzed by flow cytometry. The total number of cytokine-positive cells was calculated and expressed as a ratio compared with the number calculated for naive mice at each time point (value = 1 for naive mice, indicated as dotted line). Typical result from 2 independent experiments with identical outcome. (B) Role of IFN-γ and IL-12 in vivo. Mice treated with anti–IFN-γ (□), anti–IL-12 mAb (▴), or irrelevant isotype-matched mAb () received 2 immunizations with CD40-/- DCs and were challenged with A20 lymphoma 1 week after the second vaccination. × indicates tumor control.