The GC reaction is not affected in the absence of ZFP36L1 in B cells. (A) Representative flow cytometry plots used for detection of NP-specific GC B cells; surface NIP⁺, IgG1⁺ cells (middle plot) were identified in the population of CD95⁺CD38^low GC cells (left plot, pregated on eFluor780⁻IgM⁻IgD⁻CD90.2⁻ cells), and the absence of such NIP⁺, IgG1⁺ cells was confirmed in a nonimmunized mouse (right plot). (B) Frequency of surface NIP⁺IgG1⁺ GC cells in the spleens of Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice at days 14 and 21 after immunization; the number of surface NIP⁺IgG1⁺ GC cells in the spleen is normalized to the number of all live CD19⁺ cells (n ≥ 4; two-way ANOVA on logarithmically transformed data; the P value shown is for the main genotype effect). For all plots in all panels, each symbol represents data from an individual mouse, and lines represent means. Data are representative of two independent experiments. (C) Ratio of anti-NP₂ IgG1 to anti-NP₂₀ IgG1 (NP₂/NP₂₀) antibody in the serum of Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice measured by ELISA at various time points after immunization with NP-KLH in alum. (D) ELISPOT analysis of NP-specific ASCs in Zfp36l1^fl/fl CD79a^+/+ and Zfp36l1^fl/fl CD79a^Cre/+ mice. Enumeration of ASCs secreting anti-NP₂₃ (high and low affinity) IgG1 antibody in the spleen (n ≥ 4; two-way ANOVA on logarithmically transformed data; the P value shown is for the main genotype effect). (E and F) Titers of anti-NP₂ IgG1 (E) and anti-NP₂₀ IgG1 (F) antibody in the serum of Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice (each data point is a mean ± SD of dilution for a 50% inhibitory concentration for n = 5 mice for each genotype; two-way ANOVA on logarithmically transformed data with Sidak’s correction for multiple testing; the P value shown is for the genotype effect for day 56). For all flow cytometry plots, the numbers next to the enclosed areas (gates) represent percentages of the cells falling into the gate, and the number in the bottom right corner shows the number of cells in the plot. SA, streptavidin; PE, R-phycoerythrin.