B-cell proliferation and immunoglobulin synthesis in vitro. Naive B cells were examined for (A) proliferation, (B) IgG1, and (C) IgA synthesis in response to APRIL, 5 and 25 nM. For controls, B cells were stimulated with anti-CD40+IL-4 for proliferation and IgG1 production and with TGF-β+LPS for IgA production (n = 5-9 mice per group). Mann-Whitney test was used to calculate significance. P values as in Figure 4.