hAPRIL.01A and hAPRIL.03A block APRIL driven IgA production and proliferation of mouse B cells. Mouse B220⁺ B cells were stimulated with conditioned medium containing soluble FLAG-hAPRIL (A) or soluble FLAG-hBAFF (B) for 6 days and the supernatants assayed by ELISA for IgA production. The same cells were treated with anti-IgM (5μg/mL), costimulated with medium containing FLAG-hAPRIL (C) or soluble FLAG-hBAFF (D) for 2 days and pulsed with tritiated thymidine for 18 hours before harvesting. Cross-linking condition (via the addition of anti-FLAG antibody) was used to optimize the APRIL and BAFF signal. Aprily-5 (A-5) was used as a nonantagonistic control, mouse IgG1 (msIgG1) was used as an isotype control for hA.01A/hA.03A and human IgG (HmIg) as control for TACI-Fc. Each sample was analyzed in triplicate. ***P < .001, 1-way ANOVA; error bars = SD.