Mouse IgG2a Antibodies Specific for the Commensal Streptococcus mitis Show Stronger Cross-Reactivity with Streptococcus pneumoniae than IgG1 Antibodies

Figure 1

IgG2a and IgG1 antibodies from the S. mitis-immunized mice cross-react with S. pneumoniae. CD1 mice were intranasally immunized with live S. mitis, and sera were collected to analyze antibody responses to S. pneumoniae strains D39 (serotype 2) and TIGR4 (serotype 4). (a) Cross-reactivity of S. mitis-specific IgG isotypes with S. pneumoniae serotypes by Western blotting. Each lane was loaded with 50 μg of protein from the indicated bacterial species. The sera were diluted to 1 : 1000. (b) Levels of antibodies reactive to S. mitis and S. pneumoniae serotypes by the whole-cell ELISA. The sera were diluted to 1 : 100. Data are shown as and pooled from two independent experiments with 4 mice in each group. Unpaired Student’s -test was used to compare the levels of antibodies between sham-treated and immunized mice. ; . ns: not significant; D39: S. pneumoniae D39; TIGR4: S. pneumoniae TIGR4.

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