Newly generated (BrdU-high) NP-specific ASCs do not appear in the BM before day 4 after reimmunization. (A and B) An overlay of representative flow cytometry plots of BrdU-high (shaded histogram) and BrdU-low (black line) CD138⁺NIP⁺IgG1⁺ cells from the BM of Zfp36l1^fl/fl CD79a^+/+ (A) and Zfp36l1^fl/fl CD79a^Cre/+ (B) mice analyzed at day 4 after reimmunization. (C and D) Frequency of the newly generated (BrdU-high) CD138⁺NIP⁺IgG1⁺ cells in the spleen (C) and BM (D) of Zfp36l1^fl/fl CD79a^+/+ mice at days 3, 4, and 6 after reimmunization. The numbers of the BrdU-high CD138⁺NIP⁺IgG1⁺ cells are normalized to the numbers of all eFluor780⁻ cells in the sample. For all plots in all panels, each symbol represents data from an individual mouse, lines represent means, and data are representative of two independent experiments. (E and F) Immunofluorescence analysis of spleen sections from a Zfp36l1^fl/fl CD79a^+/+ mouse (E) and a Zfp36l1^fl/fl CD79a^Cre/+ mouse (F) at day 4 following secondary immunization. The sections were stained with anti-IgG1 (blue), anti-CD169 (MOMA-1, green), and anti-IgD (gray) antibody and NIP-BSA-bio Streptavidin Alexa Fluor 555 (red). The images are representative of sections taken from four mice for each of the genotypes. Original magnification, 20×; scale bars, 100 µm.