Fig. 3.

Survival of CD8⁺ memory T cells in the absence of IRF4. Rag1^−/− mice were reconstituted, infected, and tamoxifen treated as described in Fig. 2. GFP⁺ and GFP⁻ CD8⁺ T cells from Irf4^fl/+×CreER^T2 and Irf4^fl/−×CreER^T2 donors were analyzed at the indicated time points. (A) Frequencies of ovalbumin-specific CD8⁺ T cells in peripheral blood were determined with OVA_257–264 dextramers at 13, 19, and 23 wk after tamoxifen treatment. (B and C) Dextramer⁺ CD8⁺ T cells in spleens 6 mo after tamoxifen treatment. (B) Representative dot plot and (C) %-values of dextramer⁺ CD8⁺ T cells. (A–C) Representative result of two independent experiments with five or six mice in infected groups and two or four mice in not infected groups. Mean ± SEM, paired t test. (D and E) Following 3 wk after tamoxifen treatment, spleen cells were stimulated with OVA_257–264 peptide for 4 h, and the production of IFN-γ and TNF-α in CD8⁺ T cells was determined by FACS. (D) Representative dot plots for CD8-gated cells and (E) %-values of cytokine-positive CD8⁺ T cells. (D and E) Representative results of three independent experiments with five to eight mice in infected groups and four or five mice in not infected groups. Mean ± SEM, paired t test. *P ≤ 0.05.