Fig. 4

Humoral immune response to LPS from E. coli O111 or O157 in female mice induced by the OMV for delivering E. coli O-antigen. Serums of immunized female mice were gathered at days 14, 35, and 49 post-initial vaccination. Quantitative ELISA was applied to analyze specific IgG at days 14 (A), 35 (B), and 49 (C) post-initial vaccination against LPS from E. coli O111 and/or O157, as well as the subtypes IgG1 (D) and IgG2a (E). (F) The ratio of IgG2a/IgG1. The results displayed the precise levels of antibodies, as measured by a standard curve, in female mice intraperitoneally inoculated with the OMV delivering E. coli O-antigen at the scheduled weeks. The standard differences between the mice in each group were shown by the error bars. Data are presented as the means ± SEM (n = 8). Statistical differences were assessed by a one-way ANOVA test followed by Bonferroni’s multiple comparison test; superscript letters a, b, and c indicate P < 0.05 for comparison with E. coli LPS-specific IgG antibody levels in the OMV vector group, E. coli O157 LPS-specific IgG antibody levels in the OMV2 group, and E. coli O157 LPS-specific IgG antibody levels in the OMV3 group, respectively