Figure 1. T_r cells compete for a limiting supply of Il-2.

(A) Rat IgG or Il-2 blocking antibody (S4B6-1) was administered to mice I.V. at the indicated time-points prior to sacrifice to assess Il-2 activation kinetics in splenic T_r cells by phosphorylation of STAT5 (pSTAT5). (B and D) Representative flow cytometry plots assessing T_r cell frequencies and pSTAT5 (B), and activation of FoxP3⁻ T cells (D), in WT (Il-2^+/+) Il-2 heterozygous (Il-2 ^+/−) and Il-2 knockout (Il-2^−/−) mice. (C) T_r cell frequencies amongst TCRβ⁺ CD4⁺ T cells in the spleen (left) and blood (middle) of Il-2^{+/+, +/−,} and ^−/− mice (N = 5). (Right) Compiled data for T_r cell pSTAT5 in mice of the indicated genotype (N = replicate mice per group). (E) Spleen weight (left) and frequency of activated (CD44^hi CD62L^lo) CD4⁺ and CD8⁺ T cells as gated in D (N=5). Data representative of at least 2 independent experiments. Error bars in all panels represent mean ±SEM. **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001, as calculated by one-way ANOVA with Tukey’s post hoc test.