Late entering B cells continue to encounter FDC bound antigen. (A) Immunofluorescence analysis of LN sections taken at the indicate time points after HEL-PE immunization, visualizing PE (red) and stained to detect CD35 (green) and B220 (blue). Bar, 200 µm. Data are representative of follicles from at least four inguinal LNs at each time point in two experiments. (B) Summary of flow cytometric data showing the frequency of transferred MD4 B cells that were PE⁺, PE⁺CD86⁺, or CD83⁺ when the cells were harvested 12 h after transfer to mice immunized with HEL-PE or SA-PE the indicated number of days before the cell transfer. Error bars indicate means + SD of at least six LNs from four mice in two experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001.