Figure 4

In vivo immune response against recombinant Salmonella -EGFP strains. The eleven recombinant Salmonella -EGFP strains were respectively administrated to one of eleven groups of mice (5–10 mice for each group), with an additional group of non-infected mice kept as a negative control. For each group, 1 × 10¹¹ bacteria were used to prime each mouse for 3 days, and boost on day 21 and 35, by oral gavage. (A) and (B) summarize the ELISA results showing the EGFP-specific IgG responses raised by the six single-recombinant Salmonella strains (A) and the five double-recombinant Salmonella strains (B). ELISA assays were performed using mice sera collected on day 7, 28 and 42. * underneath the LP strain in (A) indicates the mean ELISA titer raised by LP strain is significantly higher than those of other strain, as determined by One-Way ANOVA ( P  < 0.05). (C) and (D) summarize the mice T cell anti-EGFP IFN-γ responses raised by the six single-recombinant Salmonella strains (C), and the five double-recombinant Salmonella strains (D), using mice splenocytes collected on day 42. The ratio of spot numbers counted for the immunized mice, to those counted for non-infected mice, were used to evaluate the anti-EGFP IFN-γ response. * underneath the CP and E strain in (C) indicates the mean ELISpot ratios raised by CP and E strain were significantly higher than those of strains with high copy plasmids HP and HO; * underneath the CP + LP, CP + E and E + LP strains in (D) indicates the mean ELISpot ratios raised by these strains were significantly lower than their relative single parental strains, as determined by One-Way ANOVA ( P  < 0.05). Each ▴ represents one mouse. In (A) and (B), red lines indicate the average titers for each strain. In (C) and (D), red lines indicate the average ratios for each strain.