Figure 2. FcγRIIB Contributes to IC Binding in 564Igi Mixed BM Chimeras.

(A) Confocal micrographs of FDC networks in splenic cryosections from passively immunized 564Igi mixed BM chimeras. The recipients of 564Igi mixed BM chimeras were passively immunized with pooled serum from WT mice immunized with PE in complete Freund’s adjuvant (CFA), followed by i.v. PE injection. The left panels show representative FDC networks from a WT and FcγRIIB^−/− recipient with indicated staining. The right panels show the same networks with the mask outline (based on CD35 staining) used for quantification and the PE signal only. Only FDC networks associated with clusters of Ki67⁺ GC were included in the analysis. The arrowhead in the left panel indicates non-FDC-associated PE, likely derived from a dendritic cell (DC) or macrophage. Scale bar, 100 μm. All of the panels are scaled equally.

(B) Quantification of PE on FDCs in passively immunized 564Igi chimeras. B6, C57BL/6 recipients of 564Igi mixed BM and FcγRIIB^−/− (KO, knockout) recipients of 564Igi mixed BM, n = 3 mice per group; each point represents 1 FDC network. No IgG and no PE are negative controls, with B6 564Igi mixed BM chimeras receiving PE only or no IgG and PE, respectively.

(C) Area of each FDC network mask in number of pixels. NS, not significant, ****p < 0.0001, ANOVA with Tukey post hoc test, B6 versus all other groups.