Loss of TGF-β signaling in the GC compartment induces GC B-cell hyperproliferation. (A-E) Tgfbr2^fl/fl mice were crossed with AID-Cre mice; Tgfbr2^wt/wt, Tgfbr2^fl/wt, and Tgfbr2^fl/fl x AID-Cre mice were immunized IV with 200 μL 10% SRBCs, euthanized 10 days after immunization, and GC cells were analyzed by flow cytometry as described in Figure 2. (A-C) GC B-cell frequencies in % of all CD19⁺ B cells as well as absolute numbers per spleen are shown alongside representative FACS plots. Nonimmunized littermates are shown as control. (D-E) The GC area (arbitrary units) of immunized mice was determined by quantifying 3 Ki-67-stained spleen sections per mouse (D) using ImageJ. (E) Representative pictures of spleens of immunized mice of the indicated genotypes. Size bar represents 1000 μm; arrows point to GCs. (A-B,D) Every dot represents 1 mouse, and data from 3 pooled experiments are shown. Graphs show medians. *P < .05; **P < .01.