Germinal center formation reduction in SWAP-70^−/− mice. Wt and SWAP-70^−/− mice were immunized with SRBCs, or injected with PBS as control. (A) Spleen sections were stained for GCs using PNA (green), B220 (red), and CD3 (blue) 6 days after immunization. (B) Percentage of B follicles containing GCs in spleen sections of immunized animals at the indicated time. (C) Flow cytometry of GC B cells, defined as B220⁺ B cells that are positive for PNA. Numbers indicate percentage of cells. Data are representative of 5 independent experiments. (D) Flow cytometry of nonswitched (IgM) and switched (IgG1) isotypes among the GC B cells gated as in panel C. Numbers in outlined areas indicate percentage of cells in each. Data are representative of 2 independent experiments. (E) Spleens stained for BrdU (green) and PNA (red) after a 5-hour pulse of BrdU 6 days after SRBC immunization. (F) B220 expression and BrdU incorporation 6 days after immunization. (G) BrdU staining in B220⁺PNA⁺ GC B cells. Numbers indicate percentage of cells. Data are representative of 2 independent experiments. (H) Spleen sections stained for PNA (green) and CD35 (red, left) or FDCM-1 (red, right) at day 6 after immunization. Data are representative of 3 independent experiments. Scale bars represent 200 μm.