IL-21 induces activation of STAT1 and STAT3 in MCL cell lines and primary tumors. For (A-B), MCL cell lines (Mino, HBL-2, SP-53, and Jeko-1) and primary tumors (specimens 1 and 4) were treated with IL-21 (100 ng/mL) for the indicated time periods. Whole cell lysates were prepared and subjected to immunoblotting to measure the levels of phosphorylated STAT1 and STAT3. Immunoblotting for nonphosphorylated STATs and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) served as loading controls. Results in panels A-B are representative of 3 independent experiments.