T reg cells are dynamically regulated during LCMV infection. (a) Proportion of Ki-67⁺ cells among CD4⁺Foxp3⁺ T reg cells (left) and absolute number of CD4⁺Foxp3⁺ T reg cells (right) in spleens of mice left uninfected (U) or at various dpi with LCMV-Armstrong. (b) Proportion of Ki-67⁺ cells (left) and absolute number (right) of CD4⁺Foxp3⁻ T cells (bottom) and CD8⁺ T cells (top) in spleens of mice infected with LCMV-Armstrong. (c) Fold induction of Ifnb mRNA from whole spleens of mice infected with LCMV-Armstrong relative to uninfected controls. Ifnb mRNA expression was normalized to Gapdh expression. (d) Median fluorescence intensity (MFI; top) and representative staining (bottom) of phospho-STAT1 in gated CD4⁺Foxp3⁺ T reg cells directly ex vivo from spleens of mice infected with LCMV-Armstrong. For all panels, n = 3–4 mice per group. Statistical significance was determined using one-way ANOVA with Tukey’s post-test (a–d). *, P < 0.05; **, P < 0.005; ***, P < 0.0001. Data are representative of two independent experiments with 3–4 mice per time point. All data are presented as the mean values ± SEM.