Expression of cell-surface markers is modulated by the dose and duration of IL-7 stimulation. CD4⁺ RTEs were cultured for 120 hours in the presence of rIL-7 doses ranging from 0.01 to 100 ng/mL (A). Alternatively, the time during which cells were exposed to rIL-7 (10 ng/mL) during the 120-hour incubation was varied, ranging from 0 hours to 120 hours (B). Following the 120-hour culture, cell-surface expression of CD127 (IL-7Rα), CD25 (IL-2Rα), the CXCR4 chemokine receptor, and the VLA-4 integrin was assessed using the appropriate fluorochrome-conjugated mAbs. Histograms depicting fluorescence (open histograms) relative to control IgG (filled histograms) are shown and the delta mean fluorescence intensities (ΔMFIs) relative to control staining are indicated in the top right of each panel. Results are representative of data obtained in 2 to 5 independent experiments.