CD40-mediated GC formation. (A) FACS analysis of GC formation was performed from mice 10 days after sheep erythrocyte immunization. Splenocytes were isolated and stained with B220, PNA, and GL7. Fluorescence was quantified by flow cytometry and profiles were gated on B220⁺ cells. (B) Immunohistologic analysis of GC formation was performed from the spleen treated similarly as mentioned in “The role of the C-terminus of the CD40 cytoplasmic tail in GC formation” section. In brief, spleens from sheep erythrocyte–immunized mice were cryocut and stained with B220 (green), PNA (red), and CD4 (blue). GC is indicated by white arrow. Data are representative of 8 to 12 mice from 2 independent experiments.