Effects of BAFF on B-cell responses with coligation of BCR and CD19. Human peripheral blood B cells (1 × 10⁵) pretreated with anti-BCR mAbs (anti-Igκ and anti-Igλ; 1 μg/mL), anti-CD19 mAb (0.5 μg/mL), and/or control mAb (1 μg/mL) were cultured with or without sBAFF (0.1 μg/mL) in triplicate in 96-well plates precoated with mitomycin-treated DT70 cells (2 × 10⁴ per well) in the presence or absence of IL-15 (50 ng/mL) together with or without mitomycin-treated CD154 transfectant (1 × 10⁴ per well). (A) After treatment for 48 hours, the expression level of CD40 was analyzed by FACS analysis. (B) [³H]thymidine (0.5 μCi [18.5 kBq] per well) incorporation of B cells was measured during the last 18 hours of a total of 72 hours. (C) After 10 days, IgG concentration in the supernatant was measured by ELISA. For the blocking assay, TACI-Ig fusion protein was used at 0.4 μg/mL. The values are reported as the mean ± SD of triplicate wells, and data shown are representative of 3 different experiments; ^*P < .05; ^**P < .01.