FIG. 5.

Challenge of F1 antigen- or Psa-immunized mice. Groups of 7 to 10 mice were immunized s.c. with Alhydrogel (A, B, and C) or Freund's adjuvant (D, E, and F) either alone (filled circles) or together with the F1 antigen (filled squares) or Psa (open triangles). Mice received either one boost immunization at a 3-week interval (A, B, and C) or two boost immunizations at 3- and 2-week intervals (D, E, and F). Two weeks following the last boost immunization, mice were administered 4 mg iron dextran i.p. 2 to 3 h before challenge with 210 LD₅₀s (A, B, and C) or 17 LD₅₀s (D, E, and F) of Y. pestis KIM5 by i.n. instillation. The second group of mice received additional administrations of 4 mg iron dextran i.p. at days 2 and 3. Survival (A and D) and weight (B and E) were monitored for 10 days. F1-specific and Psa-specific antibodies were measured by ELISAs in sera from F1-immunized mice (C and F, left panels), and from Psa-immunized mice (C and F, right panels).