PRMT5 is required for GC formation and affinity maturation. (A) Immunohistochemistry of paraffin-embedded splenic tissue from Cγ1-Cre^−/−Prmt5^fl/fl and Cγ1-Cre^+/−Prmt5^fl/fl mice (n = 7 per group) immunized with SRBCs for 10 days. (B) Quantification of PNA⁺ clusters from panel A. (C) Representative flow cytometry plot showing percentage of GC B cells (GL7⁺ FAS⁺ or CD38^dim FAS⁺) gated on live B220⁺ splenocytes in Cγ1-Cre^−/−Prmt5^fl/fl and Cγ1-Cre^+/−Prmt5^fl/fl mice (n = 7 per group) immunized with SRBC as described in panel A. (D) Titers of low-affinity NP-specific immunoglobulin were measured using NP26-BSA in the serum of Cγ1-Cre^−/−Prmt5^fl/fl and Cγ1-Cre^+/−Prmt5^fl/fl mice (n = 6 per group) immunized with NP-CGG for 8 days. (E) Ratio of high- to low-affinity NP-specific immunoglobulin detected with NP4-BSA and NP26-BSA, respectively, in NP-CGG immunized Cγ1-Cre^−/−Prmt5^fl/fl and Cγ1-Cre^+/−Prmt5^fl/fl mice described in panel D.