Flow cytometric analysis of IL-21R expression in MCL cell lines. (A) The indicated MCL cell lines were stained for IL-21R and analyzed by flow cytometry. Gray histograms represent IL-21R–stained population and white histograms represent background fluorescence observed with matched isotype control. HeLa cells were used as a negative control. Data are representative of 3 independent experiments. (B) MCL cell lines (Mino, HBL-2, SP-53, IRM-2, Z-138, L-128, G-519, and Jeko-1), DLBCL cell line (RCK8; positive control), and 293T cell line (negative control), (C) neoplastic B cells isolated from de novo primary MCL tumors, and (D) normal B cells isolated from peripheral blood or lymph node (tonsil) were treated with IL-21 (100 ng/mL) for 72 hours. The cell death was measured by YO-PRO and PI staining followed by flow cytometry analysis. IL-21–responsive and non-responsive cell lines, and primary tumors are indicated as sensitive (S) and resistant (R), respectively. In panels A-B, data are representative of 3 independent experiments and error bars correspond to standard deviation (SD) between triplicate samples from a single experiment.