(a) The flow cytometry gating strategy to characterize CD19+ B cells as either naïve (N), memory (M) or germinal centre (G) B cells in wild and laboratory mice, and (b) the proportions of these three subpopulations, (c) their expression of MHC class II and (d) binding of PNA, with the latter shown on a log10 scale. Mice are wild (shaded) and laboratory (unshaded). The box centres are medians, and box limits the 25th and 75th percentiles, the whiskers 1.5 times the interquartile range and outliers are represented by dots. Asterisks denote significant differences as **P<0.01, ***P<0.001 (Mann–Whitney U test; Supplementary Table 2), and § denotes that there are additional sex effects detailed in Supplementary Table 2. Sample sizes are shown in Supplementary Table 2 and Supplementary Data 1. The gating strategy for CD19+ lymphocytes is shown in Supplementary Fig. 1.