FIGURE 4.

Erk2 is critical for activated CD8 T cell survival. A and B, Purified WT or Erk2^T−/− CD8 T cells were activated with plate-bound anti-CD3 and soluble anti-CD28, and analyzed by FACS following staining with (A) annexin V or (B) PI. The annexin V histograms were gated on all events, and numbers indicated are percentage of all events. The PI data were analyzed using ModFit LT software, and the proportion of subdiploid cells is expressed as a percentage of total events, while the proportion of cells at the different stages of cell cycle (G₀/G₁ or S/G₂/M) are expressed as a percentage of live events. The data presented are representative of three (for annexin V) and four (for PI) independent experiments. C, Purified WT or Erk2^T−/− CD8 T cells were activated as in A, and the levels of IL-2 in culture supernatants were estimated at indicated time points using an ELISA. (n.d. indicates not detected). The data presented are the means ± SD and are representative of two independent experiments. D, CFSE-labeled CD45.1⁺ WT and CD45.2⁺ Erk2^T−/− CD8 T cells were activated for indicated time points in the presence of rhIL-2 (left panel) or were cocultured in the same wells (right panel). CFSE profiles are gated on WT or Erk2^T−/− CD8⁺ cells and the actual number of cells run on the FACS in a fixed period is plotted. Also shown in the coculture experiments is the ratio of WT to Erk2^T−/− cells. This ratio in unstimulated cultures was ~45:55. The data presented are representative of two independent experiments.