NK cytotoxic activity controls T-cell activation. (A) Rag2^−/−Il2rg^−/− and Rag2^−/− mice were reconstituted with BM from Prf1^−/− and control B6 donors. After 8 weeks, reconstituted mice were adoptively transferred with 1 × 10⁶ CFSE labeled perforin-sufficient or perforin-deficient P14 cells. The day after, mice were infected with 200 PFU of LCMV-WE. The figure shows representative histograms of CFSE staining in P14 cells 3 days after infection transferred into T^Prf1+NK^Prf1+ (left panel/black bars), T^Prf1−NK^Prf1− (middle panel/open bars) and T^Prf1−NK^Prf1+ (right panel/gray bars). Graph represents the mean ± SEM values from 2 independent experiments with 3 mice in each group. (B) Absolute numbers of P14 cells per spleen 3 days after infection. Data (mean ± SEM) are representative of 2 independent experiments with 3 mice in each group. (C) T^Prf1−NK^Prf1− (open bars/middle panel), T^Prf1−NK^Prf1+ (gray bars/right panel), and T^Prf1+NK^Prf1+ mice (black bars/left panel) were infected with 200 PFU of LCMV-WE. The figure shows representative FACS analysis of blood MNC gated on CD8⁺. Graph represents the quantification of KLRG1⁺ Ly6C⁺ CD8⁺ cells from blood on day 8 postinfection. Data (mean ± SEM) are representative of 3 to 4 independent experiments. (D) Control (left panel/black bars), Stx11^−/− (middle panel/open bars), and T⁺NK^Stx11− (right panel/gray bars) mice were adoptively transferred with 1 × 10⁶ CFSE-labeled perforin-sufficient or perforin-deficient P14 cells. The day after, mice were infected with 200 PFU of LCMV-WE. The figure shows representative histograms of CFSE staining in P14 cells 3 days after infection and the percentages of cells dividing between 0 and 4 times and more than 4 times. Graph represents the mean ± SEM values from 2 independent experiments with 3 mice in each group. (E) Absolute numbers of P14 cells per spleen 3 days after infection in control (black bars) and T⁺NK^Stx11− (gray bars) mice. Data (mean ± SEM) are representative of 2 independent experiments with 3 mice in each group. Statistical analysis was performed using 1-way ANOVA or Student t-test. *P < .05; **P < .01; ***P < .001.