(A–F) Immune complex deposition of IgG (panels A, C, and E) and C3 (panels B, D, and F) was measured by immunostaining of frozen kidney sections. Positive IgG and C3 depositions are shown from 4-mo-old BCMA−/− lpr mice compared to B6 and B6 lpr mice. Images were taken at 10× magnification and are representative of >6 mice for each strain. (G) Sera from a minimum of six 4-mo-old mice were analyzed for IgG autoantibodies to dsDNA, ssDNA, histones, and rheumatoid factor (RF) by ELISA. (H) Sera in panel G were analyzed for BAFF levels by ELISA and APRIL mRNA expression in total spleen was measured by real-time PCR relative to HPRT. ND, below detection level; ns, not significant; **, p < 0.005; ***, p < 0.001 compared to wild-type and single-mutant mice.