Survival of S. suis cps7 strains in the blood of 6.5 week old piglets of a herd infected with different S. suis serotypes, including cps7, is partially IgM restricted. A IgM titers against inactivated S. suis cps7 (strain 13-00283-02) rose significantly in these piglets from 4.5 to 6.5 and 8.5 weeks of age. Horizontal lines and error bars indicate means and standard deviations, respectively. B Survival of the indicated S. suis cps7 strains in porcine blood ex vivo is higher in weaning (4.5 weeks) than in growing piglets (8.5 and 10.5 weeks). Survival of the S. suis cps7 strains was determined in blood drawn from the same piglets every 2 weeks. The survival factor represented the ratio of CFU at 120 min to CFU at time zero. To investigate the impact of intact IgM on bacterial survival, blood was incubated with the highly specific IgM protease rIde
(10 µg). Bars and error bars represent mean values and standard deviations, respectively. C Anti-IgM Western blot for detection of IgM and its cleavage products in plasma samples of a piglet aged 4.5 weeks after bactericidal assays conducted as shown in B. Bactericidal assays included 10 μg rIde
as indicated. Sizes of the marker bands (kDa) are indicated on the left. Significant differences were determined using one-way (A) or two-way ANOVA (B) and subsequently Tukey’s multiple comparisons test. Significances are indicated (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).