TABLE 1.

Antibody responses and survival after challenge of mice in vivoa

GroupMouseChallenge (no. of survivors/ total no.)Mean ± SEM
MTTD (days)Antibody titer
cpCaf1BALB/c1/69.6 ± 0.601:83 ± 30
C57BL/66/6>141:1,967 ± 463
rCaf1BALB/c6/6>141:15,333 ± 3,291
C57BL/66/6>141:13,333 ± 3,955
ΔC-Caf1BALB/c0/64.5 ± 1.3ND
C57BL/61/65.3 ± 0.611:75 ± 25
Adjuvant onlyBALB/c0/63.8 ± 0.54ND
C57BL/60/65.3 ± 0.33ND
  • a Groups of six BALB/c or C57BL/6 mice were immunized intramuscularly with 10 μg of rCaf1, cpCaf1, or ΔC-Caf1 antigen adsorbed to Alhydrogel adjuvant on days 1 and 21 and bled on day 28. Anti-Caf11 antibody was measured by ELISA, and the results are expressed as the mean IgG endpoint titers. The same mice were challenged with 58 CFU per mouse of Y. pestis strain GB (one median lethal dose is ∼1 CFU/mouse for BALB/c mice and <5 CFU/mouse in C57BL/6 mice) on day 37 after primary immunization. Mice were observed for 14 days postchallenge to determine their protected status. The number of animals surviving at 14 days is reported. MTTD, mean time to death. ND, not detectable.