Biologic effects of IL-21 on the WM cell line, MWCL-1. (A) Viability of MWCL-1 cells cultured in the presence of IL-21 (0-200 ng/mL) for 72 hours. All values are adjusted relative to the viability of the control, which was set to 100%. Proliferation of serum-starved MWCL-1 cells cultured in the presence of IL-21 (0-200 ng/mL). (B) Proliferation was measured at 72 hours by [³H]-thymidine incorporation. (C) IgM secretion by serum-starved MWCL-1 cells cultured in the presence of IL-21 (0-200 ng/mL). After 72 hours of culture, cell-free supernatants were harvested, and IgM levels were determined by ELISA. (D) Sorted T cells (2 × 10⁵) activated with PHA were cultured with 1.5 × 10⁵ MWCL-1 cells for 72 hours in the presence of either hIL-21R:Fc (10 μg/mL) or hIgG (10 μg/mL) and IL-21 (100 ng/mL). IgM secretion was then assessed by ELISA. All experiments were performed in triplicate, and data values represent the mean ± SD of 3 separate experiments. *Statistically significant at P < .05.