Figure 5

Protection against intracerebral challenge with B. pertussis. Three weeks after immunization, all mice (sixteen mice per group) were challenged intracerebrally with a lethal dose of B. pertussis 18323, and survival of challenge mice was monitored. For recombinant proteins immunized groups, A, B, and C indicated 100 μg, 20 μg, and 4 μg dose of immunization. The reference vaccine is used as national reference standard in the intracerebral challenge assay in China and this standard have an assigned activity of 14 IU/ampoule. A, B and C indicated 0.5 IU, 0.1 IU and 0.02 IU dose of immunization. All mice of control group were immunized adjuvant alone. An asterisk symbol (*) indicates a significant difference (P < 0.05) between immunized and control group.