Fig. 4
Humoral immune responses induced by the plasmids. Mice were immunized with plasmid pPCFN-CpG, pVAX1-PCFN, pVAX1-PCF, pVAX1-PC, or pPCFN-CpG-CS-NPs respectively, and boosted once with a 3-week interval. PBS was used as a control. Serum samples were collected from the tail vein of mice at the indicated time points. The titers of the PLO-specific antibody were detected by indirect ELISA assay. a Serum total IgG titers against PLO in immunized mice; b serum IgG1 titers against PLO in immunized mice; c serum IgG2a titers against PLO in immunized mice; d the dynamic changes of serum IgG2a/IgG1 against PLO in immunized mice. Data represented mean ± SD of OD at 490 nm. *p < 0.05 and **p < 0.01 (determined by one-way ANOVA followed by a Tukey–Kramer post hoc test)