miR-217 expression in B cells enhances the GC response. (A) Representative FACS analysis of B220⁺ lymphocytes in lymph nodes after primary (upper) or secondary (lower) NP-CGG immunization of miR-217^TG mice or littermate controls. (B) miR-217^TG mice (closed circles) or littermate controls (open circles) were immunized by subcutaneous injection of NP-CGG in complete Freund’s adjuvant, and 14 days after immunization, lymph nodes were analyzed for the presence of GC B cells (Fas⁺GL7⁺) and switched B cells (IgG1⁺). Mice injected with PBS (open triangles) were used as nonimmunized controls. Each symbol represents an individual mouse. Data were normalized to the mean value of control mice in each experiment; results are shown for a total of 4 experiments performed with 4 independent miR-217^TG mouse lines (P = .01 for GC B cells and P = .08 for switched B cells). (C) Fourteen days after a primary immunization as in B, mice were reimmunized by subcutaneous injection of NP-CGG and analyzed 7 days later. Symbol code as in B. Data from 2 independent experiments was normalized to the mean response of control mice in each experiment (P = .019 for GC and P = .018 for switched B cells). (D) Spleen memory IgG1⁺ B cells analyzed by flow cytometry 1 year after NP-CGG immunization of miR-217^KI mice. The FACS plots show the frequency of cells in the gate referred to proportion within B220⁺ cells. Symbol code as in B (P = .003).