Cognate B cells acquire FDC surface antigens. (A) Flow cytometric analysis of wild-type (WT) noncognate or MD4 B cells, 12 h after transfer to recipients immunized as indicated, stained to detect BP-3. (B) Summary of data obtained as in A. (C) Flow cytometric analysis of Cr2^−/− noncognate or MD4 B cells, 12 h after transfer to recipients immunized as indicated, stained to detect CR1 (CD35). (D) Summary of data obtained as in C. Each point in B and D indicates a single LN, and two inguinal LNs were analyzed from each mouse (at least three mice per group). Bars indicate means. Data are from four (A and B) or two (C and D) experiments. Numbers in quadrants in A and C indicate the percentage of gated cells. (E) Fluorescence microscopy of transferred MD4 B cells isolated from LNs 12 h after transfer, visualizing bound HEL-PE (red) and stained with antibodies to detect BP-3 (green) and with DAPI to detect nuclei (blue). Bar, 3 µm. Three examples are shown that are representative of cells analyzed in two experiments. (F) Gating scheme for sorting PE^hiBP-3^hi (R1) or PE^loBP-3^lo (R2) transferred MD4 B cells and pie charts showing the number of cells that had overlapping or separate clusters of PE and BP-3 signals in these gates. The total numbers of cells analyzed are indicated in the inner circles. Data are pooled from two experiments.