Figure 3. Non-toxin adjuvants differentially influence the induction of serum LeTx-neutralizing activity after nasal immunization with rPA.

Mice were immunized as described in Figure 1. A lethal toxin (LeTx) neutralization assay with J774A.1 macrophages was used to measure functional anti-rPA antibody responses in serum collected on days 42 of the nasal immunization regimen. The percent neutralization was plotted versus serum log₂ dilutions and the linear range was used to calculate the serum log₂ endpoint titer required for a 50% inhibition of LeTx-induced J774A.1 cell death (LeTx NT₅₀). Data is expressed as mean ± standard deviation LeTx NT₅₀. Statistical analysis was performed using one-way ANOVA and Tukey’s multiple comparison test. The numbers above the error bars indicate which groups (1-9) are significantly different from the indicated group. Samples that had no detectable LeTx-neutralizing activity were assigned a value of one less than the starting serum log₂ dilution for statistical analysis.