IL-7–induced STAT5 phosphorylation is not a marker of T-cell proliferation. CD4⁺ RTEs were cultured in the presence of 0.01 to 10 ng/mL rIL-7 for 120 hours and STAT5 phosphorylation was then assessed. Cells were permeabilized and stained with the Alexa Fluor 647–conjugated polyclonal antibody recognizing the Tyr694-phosphorylated form of STAT5 (P-STAT5). Representative histogram plots depicting staining (open histograms) relative to control IgG fluorescence (shaded histograms) are shown. Data are representative of results obtained in 3 independent experiments.