Type I IFN, but not IL-12, is required for cross-presentation. WT, IFN-αβR−/− (A), or IL-12– blocked mice (B,C) were immunized in the footpad with 50 μg OVA-TLR7a conjugate as outlined in panel A. Twenty-four hours after immunization, popliteal LN were harvested as before, the cell suspensions from each mouse group pooled, and the DC purified by flow sort based on CD11c expression. Sorted DCs were incubated at (C) 1 × 106 cells per well or at (B) the indicated titration of cell numbers (DCs from WT and IL-12–blocked mice) with 0.5 × 106 effector OTI T cells differentiated in 5 days of peptide-pulsed culture. The cells were coincubated for 4-6 hours in the presence of brefeldin A and then stained for intracellular IFNγ. Production of IFNγ by OTI T cells was assessed by gating on expression of the congenic marker CD45.1. The level of IFNγ response by the OTI T cells was expressed as a percent of the maximal production of IFNγ induced by DCs pulsed with the SIINFEKL peptide. The data shown are representative of 2 independent experiments.
