Effects of coligation of TACI and HSPG on PKA phosphorylation and IgA production. (A) IgA-negative B cells were cultured with anti-TACI mAb (11H3), anti–heparan sulfate side chain mAb (10E4), mouse IgG2a, or mouse IgM (5 μg/mL each) for 45 minutes. Then anti–mouse Igκ (1 μg/mL) antibody was added to establish the cross-linking of cell-bound mAbs. APRIL (8 μg/mL) was used as a positive control. After 45-minute incubation, cell lysates were prepared and subjected to immunoblot analysis (B) IgA concentrations in culture supernatant were measured by ELISA after 10 days. Data are mean ± SD. *P < .05. Data are representative of 3 independent experiments with similar results.