Figure 9. The F1mut-V and F1mut-V10 mutants show comparable immunogenicity and protection against pneumonic plague.

The immunogenicity and protective efficacy of F1mut-V and F1mut-V10 were compared both as adjuvanted soluble antigens or adjuvant-free T4 nanoparticle decorated antigens. (A) The vaccine formulations used in the study, eight mice per group. (B) Total F1-V specific antibody titers as determined by ELISA. Note that the sera of the control T4 phage-immunized mice showed higher background than the pre-immune sera, probably because T4 phage induces a strong antibody response to its components which raises the levels of the IgGs in the sera and gives more non-specific background at low dilutions. (C) Survival of vaccinated mice against intranasal challenge with 5,350 LD₅₀ of Y. pestis CO92. The survived mice were re-challenged with 20,000 LD₅₀ at day-88 post-first challenge. The animal mortality data was analyzed by Kaplan Meier's survival estimates and a p value of ≤0.05 was considered significant.