Induction of T-cell activation proportional to titrated Treg depletion. Injection of limiting concentrations of DT resulted in a titration of Treg ablation in the lymph nodes of Foxp3^DTR mice. (A) Representative flow cytometric profiles of a titration series of Foxp3^DTR mice injected with limiting DT, displaying the percentage of CD4⁺ T cells positive for both Foxp3 and the DTR-GFP fusion protein. (B) Proportion of Foxp3⁺GFP⁺ Tregs among CD4⁺ T cells, 9 days after treatment with 0, 2.5, 5.0, 7.5, 10, and 20 μg/kg DT (n = 4, 5, 9, 5, 8, 8). Diamonds represent individual mice, bars represent condition average. (C) The relationship between Treg numbers (within CD4⁺ T cells) and expression of CD44 on CD4⁺Foxp3⁻ T cells. Diamonds represent individual mice, and the trend line represents the optimal model for relationship fitting with the use of the least-squares approach.