(A) Thirty-five days after infection with influenza virus PR8, BLIMP-1–YFP mice were treated with 100 μg TACI-Fc (n = 7 mice) or human control IgG Ab (co-Ig) (n = 4 mice) every 2–3 days until analysis at day 48 p.i. (B) YFP+ ASCs were enumerated in spleen, medLN, lungs, and BM. (C) PR8-specific ASCs were determined by ELISPOT. (D) PR8-specific IgG in serum and (E) PR8-specific IgG and IgA Ab titers in BAL from mice treated with TACI-Fc and co-Ig were determined by ELISA. All data with mean ± SEM represent 2 independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001.