Transformed GC B cells in CD27;CD137L^−/− mice expand within a FDC network. Immunohistochemical detection of FDCs with antibody to the marker MFG-E8 in representative spleen sections of a 12-month-old WT mouse (A-B), a 10-week-old mouse at day 8 after infection with influenza virus (C-D), and a representative mouse (n = 5) diagnosed with early-stage FL (E-F). Original magnifications, ×5 (A,C,E); ×40 (B,D,F). Specific staining is shown in brown and hematoxylin and eosin counterstaining in blue.