TABLE 4.

Antibody production and survival from anthrax spore challenge after booster immunization with 1 μg of PAa

Day postboosting% survivalb (no. of live animals/total)Time to death for each animal (MTD for group)Anti-PA Ab titerc (GMT ± SD)Neutralizing Ab titerc (GMT ± SD)
00 (0/12)2, 2, 3, 3, 2, 3, 3, 3, 2, 2, 3, 2 (2.5)25 ± 1<50 ± 1
229 (2/7)4, 4, 4, 3, 4 (3.75)54 ± 1<50 ± 1
433 (3/9)3, 3, 4, 3, 5, 4 (3.75)50 ± 1<50 ± 1
665 (11/17)4, 5, 6, 7, 3, 4 (4.8)171 ± 5.293 ± 6.6
890 (9/10)5617 ± 3.3259 ± 5.0
12100 (10/10)1,467 ± 3.0951 ± 3.4
  • a Three months after the primary immunization with 1 μg of PA, guinea pigs were boosted with 1 μg of PA vaccine on days 12, 8, 6, 4, 2, and 0 (see text).

  • b At day zero, animals from all groups were challenged with 40 LD50 of B. anthracis Vollum spores. A control group of 10 unimmunized animals which received the same challenge died, with a MTD of 2.5 days.

  • c Parallel groups (each with 10 immunized guinea pigs) were used for Ab titer determination.