FIG. 2.

Influence of amounts of LT or LTK63 synthesized by S. typhimurium on anti-Salmonella immune response. Serum IgG activity to S. typhimurium in mice immunized with two doses of strain χ3987 containing the low-copy-number plasmids pYA3074-LT and pYA3074-LTK63, the high-copy-number plasmid pYA3137-LTK63, or the control plasmid pYA3074 without the enterotoxin gene insert was determined. The two doses were given to groups of five mice on days 0 and 10. IgG responses were detected by ELISA 24, 36, and 66 days after primary immunization. The standard error of the mean was calculated for all data, and mean values were compared by Student’s t test. P values of ≤0.0001 were considered statistically significant.