Anti-BR3 mAb reduces mouse B-cell subsets more efficiently than BR3-Fc. BALB/c mice were treated with anti-BR3 (500 μg), BR3-Fc (150 μg × 3/week) or isotype control (500 μg); 15 days later, tissues were analyzed by flow cytometry (A,C) and immunofluorescence (B). Percentages of cells in B-cell subsets are displayed near each gate as follows: Spleen: follicular (FO) B cells (CD23⁺CD21⁺), marginal zone (MZ) B cells (CD23⁻CD21^hi), and plasma cells (PC, CD138⁺B220^lo); Lymph nodes: B cells (CD23⁺CD21⁺), blood (BL) B cells (CD23⁺CD21⁺), Peyer patches (PP), follicular B cells (B220⁺CD38⁺), and germinal center (GC) B cells (B220⁺CD38^lo); peritoneal cavity (PEC): B2 cells (B220⁺CD23⁺) and B1 cells (B220⁺CD23⁻) (A,C). B cells (blue) and T cells (green) are stained in spleen sections after treatment with control, BR3-Fc or anti-BR3 mAb. Marginal zone and follicular B-cell areas are separated by the layer of metallophilic macrophages (MM [red]) (B). See “Immunofluorescence and immunohistochemistry staining” for image acquisition details. Absolute B-cell numbers or percentage of lymphocyte gate belonging to a defined subset are shown as mean plus or minus standard error. Statistical significance compared with the control treated group is indicated with asterisk (C). When 2 treatment groups are significantly different from each other, the P value is displayed. These data are representative of more than 10 independent experiments done with several maximally depleting doses of anti-BR3, using at least 5 mice/group.