Increase in the surface expression of the integrin chains α4 and β1 on splenic ASCs in Zfp36l1^fl/fl CD79a^Cre/+ mice becomes more pronounced on ASCs generated late in the immune response and is associated with a partial retention of ASCs in the liver. (A and B) Conservation of the sequence surrounding cross-linked nucleotides in the 3′ UTRs of the Itga4 (A) and Itgb1 (B) transcripts among a selection of primates and rodents. Cross-linked nucleotides were visualized using the UCSC Genome Browser (http://genome.ucsc.edu). In the gene diagram, the blue boxes denote exons, the thinner lines denote 3′ UTRs, and the thin lines show introns. Arrows identify nucleotides cross-linked to ZFP36L1. (C) Representative flow cytometry plot gated as in Fig. 1 D on CD138⁺NIP⁺IgG1⁺ cells from the spleen of Zfp36l1^fl/fl CD79a^+/+ mice at day 4 after reimmunization. The number close to the enclosed area shows the percentage of α4β7-high NP-specific ASCs and the number in the bottom right corner shows the number of cells in the plot. (D) Percentages of cells with a high α4β7 surface abundance in the splenic populations of CD138⁺NIP⁺IgG1⁺ cells in Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice at day 4 following reimmunization (n ≥ 3; two-way ANOVA; the P value shown is for the main genotype effect). (E–H) Plots showing geometric mean fluorescent intensities (gMFIs) for the surface integrin α4 (E and G) and β1 (F and H) signals on the population of CD138⁺NIP⁺IgG1⁺ cells from the spleens of Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice at day 14 (E and F) and day 42 (G and H) after primary immunization (n ≥ 3 per experiment; the P values are for a Student’s t test [E and F] or for the main genotype effect in a two-way ANOVA on logarithmically transformed data [G and H]). Where it is not indicated otherwise data are representative of at least two independent experiments. Exp, experiment. (I) Enumeration of CD138⁺NIP⁺IgG1⁺ cells (gated as eFluor780⁻TCRβ⁻CD138⁺CD267⁺NIP⁺IgG1⁺ cells) in the livers of Zfp36l1^fl/fl CD79a^+/+ (closed circles) and Zfp36l1^fl/fl CD79a^Cre/+ (open squares) mice at day 14 after primary immunization; the numbers of CD138⁺NIP⁺IgG1⁺ cells are calculated for whole livers. For all plots in all panels, each symbol represents data from an individual mouse, and lines represent means (the P value is for a Student’s t test; n = 5; data pooled from two independent experiments).