Fig 3. Humoral immune response induced by vaccination.

(A) The antibody production induced by VTnF1 vaccination (10⁸ CFU) was quantified at various days post vaccination using an ELISA measuring IgG directed against purified F1 antigen. Shown are the means ± sem of titers observed in two experiments performed during the first month post-vaccination (Exp.1, 7 mice) and during the six-months post-vaccination period (Exp.2, 14 mice). Mean IgG titers at each time point were compared statistically to that on day zero using the Mann-Whitney test, and all were significantly higher (p<0.001), except those on day 1. (B) The different Ig mouse isotypes present in sera were analyzed at sequential times. (C) The IgG response against antigens other than F1 was analyzed by ELISA against a Y. pestis CO92Δcaf sonicate, and (D) by western blotting. The Y. pestis CO92 wild type or CO92Δcaf (noted F1-) were used as source of blotted antigens and sera pooled either from naive mice or mice vaccinated 30 days earlier (noted VTnF1). The Caf1 band is indicated by an asterisk and the Caf1M band by a triangle. (E) The response against purified Yops was also analyzed by ELISA. Shown are results from 14 individual animals (dots), and group medians (horizontal line). The Mann-Whitney test was used for statistical analysis: ***: p<0.001.