CD8⁺ T-cell populations from prf^−/− mice display cell-signaling patterns indicating heightened antigenic stimulation after LCMV infection. (A) Phospho-c-Jun and IFN-γ staining of CD8⁺ T cells from prf^−/− mice 8 days after LCMV infection. (B) Spleen cells from uninfected or LCMV-infected mice were fixed immediately ex vivo and analyzed for intracellular NFAT localization. CD8⁺/MHC II⁻ cells are displayed, plotting CD8 area (a measure of cell size) against an index of nuclear localization (NLI) of NFATc1. Examples of cells with an NLI of 1 or 3 are shown. (C) NLI of CD8⁺/MHC II⁻ cells from the indicated animals is plotted. (D) Percentage of CD8⁺ cells with nuclear-localized NFATc1 (NLI > 2) from uninfected and infected mice are displayed. P < .001 when comparing the NLI of CD8⁺ cells from LCMV-infected WT and prf^−/− mice. Data are representative of 3 experiments.