FTY720 treatment inhibits GC formation in the peripheral lymphoid tissues. (A) Spleen, LNs, and PPs from immunized mice treated with water or FTY720 were analyzed for GL7⁺Fas⁺ GC B cells by flow cytometry. Cells were stained with GL-7-FITC and anti-Fas-phycoerythrin (PE) (PharMingen). The numbers shown represent percentages of GL-7⁺Fas⁺ GC B cells within the lymphocyte gate. (B) In situ GC formation was evaluated by immunohistologic staining. GL-7 and anti-B220 monoclonal antibodies were used to label all B cells (blue) and GC B cells (red), respectively. Original magnification × 50. Similar results were obtained from 3 independent experiments with 3 to 5 mice per group.