APRIL stimulation promotes the proliferation of FL B cells. (A) Karpas cells were cultured alone or with APRIL, heparin, or both for 48 hours, and proliferation was assessed. Bar graph shows mean plus or minus SDs (n = 3). (B) Karpas cells were treated with APRIL for 48 hours, and cell-cycle analysis was performed. Results are represented as fold induction (APRIL compared with the nil control) of cells in G₁, S, and G₂ phase (n = 3) mean (± SDs). (C) Control and TACI siRNA-transfected (100 nM) Karpas cells were treated with APRIL for 48 hours, and proliferation was assessed. (D) Control and TACI siRNA–transfected (100 nM) Karpas cells were stained with PE-conjugated anti-TACI. (E) Expression of TACI in control siRNA (100 nM) and TACI siRNA–transfected (50 nM and 100 nM) Karpas cells was analyzed by Western blot using a TACI-specific antibody, as described in “Methods.” For panel A, *P < .05, APRIL compared with nil control.