FIG. 1.

Serum caspase-3 neutralizing activity and survival after challenge of mice vaccinated twice with F1-V. Mφs were exposed to Y. pseudotuberculosis pTrcV that had been pretreated with serum from vaccinated mice as described in Materials and Methods. The infected cells were lysed, and the caspase-3 apoptosis-specific enzyme was measured by immunoassay. The association between the percent change in caspase levels in Mφs incubated with organisms and sera and the probability of survival is shown; the sera were collected over the course of the vaccination period. The caspase levels in Mφs were determined for the day 0, 14, and 35 sera and for the prechallenge day 56 sera, and the percent changes in caspase from day 0 to days 14, 35, and 56 were calculated. The decline in Mφ caspase-3 levels in assays determined using sera from days 1 to 56, together with the vaccine dose, was significantly associated with survival (P = 0.0014 by regression analysis). The F1-V vaccine doses were as follows: 10 μg (▾, 9 of 9 survived), 5 μg (5 of 10 survived), 1 μg (▪, 12 of 15 survived), 0.1 μg (•, 6 of 14 survived), and 0 μg (Alhydrogel-only control, 0 of 9 survived).