FIGURE 5.

Erk2 is requisite for CD8 T cell survival, but not for effector function in vivo. Mice were infected i.p. with 2 × 10⁵ PFU LCMV. Ag-specific CD8 T cell responses within the spleen were assayed at indicated time points postinfection using H-2D^b-NP₃₉₆ tetramers (A and B) or intracellular IFN-γ staining (C). A, Representative FACS plots of WT and Erk2^T−/− mice (gated on CD8⁺ cells), percentage, and total numbers of Ag-specific cells present in spleen on days 5 and 8 postinfection. The numbers shown in the FACS plots are percentage of total lymphocytes, and the bar graphs depict the means ± SD for a cohort of mice. The data presented are representative of more than five independent experiments. B, To determine the proportion of cycling cells late in the expansion phase, mice were injected with BrdU at about day 7.5 and sacrificed 16 h later. Plots are gated on tetramer-positive CD44^highCD8⁺ T cells, and numbers indicate the percentage of gated population that are BrdU-positive. The data presented are representative of two independent experiments. C, WT, Erk1^−/−, and Erk2^T−/− mice were infected with LCMV as in A, and splenocytes were isolated at day 8 postinfection and analyzed for intracellular IFN-γ production following short-term restimulation in vitro. The data presented are the means ± SD and are representative of three independent experiments. D, CTL activity was measured using the splenocytes from day 8 LCMV-infected WT, Erk1^−/−, and Erk2^T−/− mice and an unimmunized control. Left panel, mean ± SD for one representative mouse from each group is shown; right panel, the normalized data based on the actual number of peptide-specific (tetramer-positive) CD8 T cells in each well are plotted. These data are representative of two independent experiments.