Passive immunization facilitates neutrophil-mediated capture and clearance of S. pneumoniae in the spleen. (a) Schematic of serum transfer protocol. (b) Representative spinning disk confocal images and quantification of neutrophils (Neu; red) and RP macrophages (RPM; purple) containing S. pneumoniae (green) at 30–60 min after infection in animals given control serum (blue bars), immunized serum (solid red bars), and immunized serum from MZ B cell–depleted (MZB dep) animals (checkered red bars). Bars, 30 µm. White arrows indicate neutrophil containing bacteria, and blue arrows indicate RP macrophage containing bacteria. Eight fields of view (FOV) were averaged per animal. n = 3–4 pooled from two independent experiments. Data are represented as mean ± SEM. (c) S. pneumoniae bacterial counts in the blood and spleen at 1 h after i.v. infection in wild-type mice receiving either control serum (blue circles) or immunized serum (red squares). n = 5–6 pooled from two independent experiments. (d) Survival curve to S. pneumoniae infection at 104-CFU dose in sham-operated and splenectomized (Spx) animals receiving control (CT) serum or immunized serum. n = 4–5 from one experiment. *, P < 0.05; **, P < 0.01; ***, P < 0.001. One-way ANOVA (b), Mann-Whitney test (c), and Log-rank Mantel-Cox test (d) statistical analyses were performed.
