Increased numbers of DCs in prf^−/− mice contain viral antigen and present it to T cells after LCMV infection. (A) Example dot plots are shown of live gated spleen cells, analyzed 6 days after LCMV infection, stained for CD11c and LCMV antigens. (B) The total number of LCMV antigen⁺ DCs (staining above isotype) per spleen in WT and prf^−/− mice, 6 days after LCMV infection, is displayed. *P < .01. (C) Splenic DCs were sorted from WT and prf^−/− mice 6 days after LCMV infection and cultured in limiting numbers in a high-sensitivity antigen presentation assay with LCMV (GP33)–specific effector CD8⁺ T cells (see “Methods”). To define the sensitivity of this assay and provide a positive control, a portion of sorted DCs from prf^−/− mice were loaded with GP33 peptide and plated in parallel wells. The percentage of individual wells producing measurable IFN-γ at each concentration of DCs is plotted against the number of DCs per well. *P < .01, comparing WT and prf^−/− response curves at DC concentrations of 30 to 1000 cells per well.