IL-15 but not IL-21 increases Shc and ERK1/2 phosphorylation. (A) CD40-activated CLL cells from 2 representative cases were stimulated with IL-15 or IL-21 (80 ng/mL) or medium (CTR) for 10 minutes, lysed in appropriate buffers, and analyzed by Western blotting using antibodies specific for phosphorylated forms of Shc or of ERK1/2 or for β-actin. (B) Densitometric analysis of Western blots performed on different cases to quantify p-Shc (5 cases) and p-ERK1/2 (9 cases) levels following treatment with IL-21 or IL-15. The data are expressed as normalized average fold of increase relative to the untreated control, as for Figure 4B. Error bars represent SD. (C) The MEK inhibitor UO126 blocks IL-15–mediated phosphorylation of ERK1/2 in CD40-activated CLL cells. Cells were pretreated with UO126 (10 μM) or DMSO (CTR) for 2 hours before the addition of IL-15 (80 ng/mL). After an additional 10 minutes of culture, cells were processed for Western blot analysis. Vertical lines have been inserted to indicate a repositioned gel lane. (D) Freshly isolated CLL cells from a representative case were stimulated for 10 or 20 minutes with IL-15 and/or IL-21, lysed, and analyzed by Western blotting using antibodies specific for phosphorylated ERK1/2 or for β-actin. Vertical lines have been inserted to indicate repositioned gel lanes.