CXCR3^−/− effector CD8⁺ T cells exhibit shortened activation phenotype. (A–C) 1 d after transfer of mixed CXCR3^−/− and WT OT-I cells (total ∼1–3 × 10⁶ cells), recipient mice were infected with VV-OVA as in Fig.1 B. (A) Surface expression of CD25 and CD69 and forward scatter (FSC) at the indicated times after infection. (B) Cell division (CFSE) and CXCR3 expression at indicated times after infection. (C) MFI of CD25 staining on OT-I cells at indicated times after infection. Data are shown as mean ± SEM. *, P < 0.0001; **, P < 0.005. (D) Relative Prdm1 mRNA expression in OT-I cells was measured by quantitative RT-PCR at day 7 after infection. All data represent two independent experiments (n = 4 independent samples per time point) and are shown as mean ± SEM. *, P < 0.0001. (E) Mixed OT-I cells were stimulated by anti-CD3 and anti-CD28 antibodies, cultured in the presence and absence of CXCL9, CXCL10, and CXCL11 for 3 d, and stained for CD25. Representative histograms at 100 ng/ml CXCR3 ligand stimulation from two independent experiments are shown.