IL-7–induced IL-7Rα degradation, but not internalization, is JAK3 dependent. Surface (A) and total (B) IL-7Rα expression in HPB-ALL cells was assessed by flow cytometry, as described in “Flow cytometric analysis.” Cells were pretreated with 150μM of JAK3 inhibitor (WHI-P131) or PAN-JAK inhibitor I, and then stimulated or not with IL-7 (50 ng/mL) for 30 minutes (A) or 1 hour (B). The geometric mean of fluorescence for each population was determined by flow cytometry. Data (mean ± SEM) are from 3 independent experiments. *P < .05 (Student t test, 2-tailed). Representative flow cytometric histogram overlay of surface (C) or total (D) IL-7Rα expression in HPB-ALL cells pretreated (black line) or not (gray line) with the JAK3 inhibitor WHI-P131, followed by IL-7 stimulation for 30 minutes (C) or 1 hour (D).