Figure 3.

Mouse serum antibodies against CT toxin in vitro antibody neutralization assays with T-84 cells and EIA cAMP kit. Pooled serum samples (30 μl) from each immunization group or the control group were used to incubate CT (10 ng). The serum/toxin mixture samples were added to T-84 cells. After 3 h incubation, intracellular cAMP levels (pmole ml⁻¹) in T-84 cells were measured. (A)Intracellular cAMP levels in T-84 cells incubated with CT toxin and pooled serum from the SC immunized groups using 2 μg dmLT or ISA51 adjuvant or the control group. (B)Intracellular cAMP levels in T-84 cells incubated with CT toxin and pooled serum from the IP immunized groups using 2 μg dmLT, 0.2 μg dmLT or FIA as the adjuvant or the control group. Baseline cAMP levels (T-84 cells incubated with cell culture medium) and cAMP levels in T-84 cells incubated with 10 ng CT (as positive reference) were included as controls. P values were calculated with Student's t-test. Boxes and bars represented means and standard deviations of cAMP levels, respectively.