Splenic protection againstS. pneumoniae infection. (a) S. pneumoniae bacterial counts in blood, spleen, lung, and liver 1 h after i.v. infection. Black lines show the median. n = 6 pooled from two independent experiments. (b) Mean (± SD) bacterial counts in the blood (red circles) and spleen (blue squares) over 120 h. n = 5–7 pooled from two independent experiments. (c) Survival curve for S. pneumoniae i.v. infection at 10⁴-CFU dose in sham-operated (black line) or splenectomized (SPX; solid blue line) mice and at 2 × 10³–CFU dose in splenectomized mice (dotted red line). n = 5 from one experiment. (d) Representative flow cytometry plots of MZ B cell (MZB) depletion (dep), immunohistochemistry of MZ macrophage (MZM) depletion (green, RP macrophage [RPM]; red, MZ macrophage) and survival curves to S. pneumonia infection at 10⁴-CFU dose in MZ macrophage–depleted (continuous green line), MZ B cell–depleted (continuous blue line), or MZ macrophage– and MZ B cell–depleted (dotted red line) animals. n = 6–10 from two independent experiments. Bar, 300 µm. Fo B, follicular B cell. Histograms and images are representative of two to three independent experiments. (e) Representative flow cytometry histograms and quantification of S. pneumoniae IgM (left) and IgG (right) serum antibodies after S. pneumoniae infection in WT (orange histogram; black lines) or MZ B cell–depleted S. pneumoniae (blue histogram; blue lines) mice. n = 3 for WT and n = 8 for MZ B cell depletion pooled from three independent experiments. Inf, infected. Data are represented as mean ± SEM, except in b. *, P < 0.01; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Kruskal-Wallis test (a), one-way ANOVA (b), log-rank Mantel-Cox test (c and d), and two-way ANOVA (e) statistical analyses were performed.