sIL-2Rα enhances IL-2–induced phosphorylation of Stat5 in dose-limited manner in FL. (A) Dot plots from a representative of normal individuals and FL biopsy specimens showing constitutive expression of phosphorylated Stat5 in intratumoral CD4⁺ T cells. (B) Summary of the numbers of CD4⁺ T cells expressing phosphorylated Stat5 in normal individuals and FL patients (n = 5). (C) Representative dot plots (n = 3) showing induction of Stat5 phosphorylation in T cells treated with either IL-2 or aIL-2 Ab or in combination. Stat5 phosphorylation was measured by flow cytometry by using PhosFlow assay. (D) Representative dot plots (n = 4) showing induction of Stat5 phosphorylation in T cells treated with either IL-2 or sIL-2Rα alone or in combination with a series of doses. (E) Representative histogram (n = 2) showing induction of Stat5 phosphorylation in intratumoral CD4⁺ T cells from FL patient treated without (NIL) or with IL-2 or IL-2+sIL-2Rα.