FDC ablation leads to abnormal expression of T zone markers and less restricted positioning of T cells and DCs. Unimmunized CD21-DTR chimeras were control (Ctrl) or DTx treated for 2 d, and spleen and pLN sections were analyzed immunohistochemically as follows. (A) Serial sections were stained for T zone stromal marker ER-TR7 and collagen type IV or for naive B cells with IgD (brown). T cells and FDCs were detected with CD3 and CD35 (blue), respectively. (B) Sections were stained for CD3 to detect T cells (blue), CD11c to detect DCs (blue), and B220 to detect B cells (brown). All data are representative of at least three experiments (at least two mice per experiment). Bars: (A) 100 µm; (B) 200 µm.