Figure 3. Increased GC B Cell Diversity in the Absence of FcγRIIB on FDCs.

(A) Experimental setup to assess the role of FcγRIIB on FDCs during B cell selection. B6 or FcγRIIB^−/− mice received mixed BM cells from 564Igi and Aicda^CreERT2Confetti mice (1:2 ratio) after lethal irradiation. Six to seven weeks after BM transfer, mice were treated with a single gavage of tamoxifen to induce the confetti cassettes in GC B cells. Splenic GC in ~2-mm-thick splenic sections were imaged ex vivo at the indicated time points post-tamoxifen treatment.

(B) Representative images cropped from multiphoton optical sectioning of spleens from B6 or FcγRIIB^−/− recipients 3, 14, or 31 days post-tamoxifen treatment. Scale bar, 100 μm. All of the images are scaled equally.

(C–E) Quantification of color dominance in splenic GCs from B6 (red circles) or FcγRIIB^−/− (blue squares) mixed BM recipients. Images were blinded for recipient genotype before counting. The graphs depict the frequency of the most dominant color (C), the sum of frequencies of 1^st and 2^nd most dominant clone (D), and the divergence index (E). The color distribution for B6 recipients at day 3 was used to calculate the divergence index for all of the points. Each point represents one GC; the line indicates the median. Pooled data from 4 independent experiments, n = 3–6 mice for each genotype at each time point. Kruskal-Wallis with Dunn’s post hoc testing for statistical analysis. Asterisks above the graphs indicate significance relative to day 3 post-tamoxifen within genotypes; asterisks below the graphs indicate the significance between genotypes within time points. The tests comparing between time points and between genotypes were included in adjusted p value calculations, but they are not indicated.