FDC ablation abrogates the GC response. CD21-DTR chimeras were immunized with SRBCs, control (Ctrl) or DTx treated at day 6, and analyzed at day 8. (A) Dot plots and histograms show flow cytometric analysis of GC B cells (IgD^lowFas⁺GL7⁺) in pLNs. Numbers show frequency of cells in indicated gate. Bar graphs show a summary of the data for IgD^lowFas⁺GL7⁺ GC B cell numbers in pLNs, spleen, and mLNs, in which bars represent means and dots represent individual mice. (B and C) Sections of pLNs, spleen, and mLNs stained to detect follicular B cells (IgD; brown) and GC B cells (GL7; blue; B) or GC FDCs (FDC-M1, left; and FcγRIIb, right; blue; C). Data are representative of at least three experiments (three mice per experiment). Bars: (B) 400 µm; (C) 200 µm. (D) Flow cytometric analysis of CD4⁺CXCR5^hiPD1^hiGL7^hi follicular helper T cells in pLNs. Bar graphs show cell numbers (bars represent means, and dots represent individual mice). (E) Frequency and number of CD4 and CD8 DP thymocytes in control- and DTx-treated mice at day 2 after treatment. In A, D, and E, statistical analysis was performed with the two-tailed unpaired Student’s t test. Numbers below p-values in A and D indicate fold change. n.s., not significant.