Fig 1.

Serum IgM specific for ST 3 in immunized and infected mice and IgM-binding activity in mouse serum at day 2 p.i. (A) Mice (n = 8 per group) were immunized with vehicle (PBS), PPS3, or PPS3 and LPS and 5 days later challenged with 1 × 10⁵ CFU of S. pneumoniae ST 3. Serum IgM is depicted as fold change in the optical density value relative to the noninfected control 5 days after immunization (vehicle, day 0) and to the infected control (vehicle, day 2). (B) IgM-binding activity was assessed by flow cytometry with serum from noninfected or immunized, infected mice at day 2 p.i. (n = 10/group; LPS-immunized, n = 4). The percentage of IgM binding is depicted as fold change normalized to noninfected control values. Asterisks denote P values of <0.05 (*) and <0.0001 (**) as detected by one-way ANOVA with Tukey's posthoc test (day 0) (A), (B) or two-way repeated-measures ANOVA with Bonferroni's multiple comparison post hoc test (A) (day 0 versus day 2). Data are shown combined from two independent experiments.