Figure 5.

N-ras is intrinsically required in CD8⁺ T lymphocytes for an efficient secondary response but not for a primary response. (A and B) Around 200 purified CD8⁺ T cells from CD45.1⁺ CD45.2⁺ N-ras^+/+ OT-I and CD45.1⁺ CD45.2⁻ N-ras^−/− OT-I TCR transgenic mice were cotransferred into the same CD45.1⁻ CD45.2⁺ N-ras^+/+ C57BL/6 recipients, which were then infected with rVACV-OVA. At 7 d p.i., the frequency and numbers of both N-ras^+/+ and N-ras^−/− OT-I cells (A) and ex vivo IFN-γ production by OVA-specific CD8⁺ T lymphocytes were determined (n = 4, two experiments) (B). Results are expressed as mean ± SEM. **, P < 0.005. (C) Around 200 purified CD8⁺ N-ras^+/+ or N-ras^−/− transgenic OT-I cells were separately transferred into N-ras^+/+ recipients that were then immunized with mDCs pulsed with OVA peptide. From each recipient, CD45.1⁺ cells were purified 8 d after priming and 200 cells cotransferred into the same congenic recipients that were then infected with rVACV-OVA. The frequency and numbers of both splenic N-ras^+/+ and N-ras^−/− transgenic OT-I cells were determined 5 d after challenge (n = 3, 2 experiments, results are expressed as mean ± SEM). For comparison, naive OT-I cells were adoptively transferred into recipient mice that were subsequently infected as in A and euthanatized 5 d later (primary response; not depicted). ***, P < 0.0005.