FDC ablation in CD21-DTR chimeric mice after serial DTx and anti-DTx treatment. (A) ROSA^DTR+CD21Cre⁺ mice that express the DTR in CD21⁺ cells or ROSA^DTR+CD21Cre⁻ control mice were reconstituted with wild-type BM, and the chimeric mice were saline (control [Ctrl]) or DTx treated and analyzed after the indicated number of days. In some cases, the mice were also treated with goat polyclonal antibody to DTx 3 h after DTx treatment (+Ab). Spleen (Spl) and pLN sections were stained for IgD to detect follicular B cells (brown) and CD35 to detect FDCs (blue). Bar, 400 µm. (B) Serum corticosterone concentration in control-, DTx-, or DTx- and anti-DTx antibody–treated CD21-DTR chimeric mice at day 2. Data are pooled from at least eight mice per group analyzed in two experiments (mean ± SEM). (C–E) Total cell number (C), B220⁺ B cell frequency (D), and flow cytometric analysis (E) of B cell CD69 and CD86 expression in pLNs, spleen, and mLNs at day 2 after control or DTx plus anti-DTx antibody treatment. In the bar graphs, each point indicates an individual animal, and bars indicate the mean. Data in E are representative of three mice. Statistical analysis in B–D was performed with a two-tailed unpaired Student’s t test. ***, P < 0.001; n.s., not significant.