[Evaluation of immunization protection efficacy of plague subunit vaccine].

Objective: To evaluate the protective efficacy of plague subunit vaccine, BALB/c mice, guinea pigs and rabbits were used in this study.

Methods: Groups of mice (10 per group), guinea pigs (14 per group) and rabbits (6 per group) were immunized with F1 + rV270 vaccine, EV76 vaccine and alum adjuvant by intramuscular route, respectively. Serum antibody titres of mice, guinea pigs and rabbits were determined by ELISA and the immunized animals were challenged with 10(6) CFU of Y. pestis strain 141 at the 8th week after the primary immunization.

Results: The immunized mice, guinea pigs or rabbits with subunit vaccine developed anti-F1 IgG titre of 41 587.3 +/- 2.1, 11 543.7 +/- 2.1 or 522.4 +/- 22.4 and elicited statistical anti-F1 IgG titre difference among them (F = 17.58, P < 0.01). The immunized mice, guinea pigs or rabbits with subunit vaccine had anti-rV270 IgG titre of 15 748.7 +/- 1.6, 12.6 +/- 1.4 or 1648.0 +/- 5.0 and induced statistical anti-rV270 IgG titre difference among them (F value was 16.34, P < 0.01). There was significant anti-F1 IgG titre difference among mice, guinea pigs and rabbits immunized with EV76 vaccine that developed anti-F1 IgG titre of 913.4 +/- 4.5, 937.0 +/- 2.0 or 342.0 +/- 12.0 (F = 23.67, P < 0.01), whereas the immunized mice, guinea pigs and rabbits with EV76 vaccine developed anti-rV270 IgG titre of 12.0 +/- 1.0, 447.0 +/- 10.0, 40.0 +/- 11.0 and there was no anti-rV270 IgG titre difference between them (F = 2.20, P = 0.1314). The immunized mice with subunit vaccine developed significantly higher anti-F1 IgG titres than immunized guinea pigs and rabbits (q value was 30.57 and 19.04, respectively, P < 0.01), and there were no anti-F1 IgG titre differences between the immunized guinea pigs and rabbits (q = 0.04, P = 0.8485). The immunized mice with subunit vaccine developed significantly higher anti-rV270 IgG titres than immunized guinea pigs and rabbits (q value was 27.10 and 19.49, respectively, P < 0.01), and there were no anti-rV270 IgG titre differences between the immunized guinea pigs and rabbits with the subunit vaccine (q = 0.25, P = 0.6187). The immunized mice with EV76 elicited higher anti-F1 IgG titres than immunized guinea pigs and rabbits (q value was 40.67 and 29.10, respectively, P < 0.01), whereas there was no difference of F1 IgG titer between immunized guinea pigs and rabbits (q = 0.06, P = 0.8098). The immunized mice, guinea pigs and rabbits with subunit vaccine provided 100% (10/10), 86% (12/14) and 100% (5/5) protection against 10(6) CFU Y. pestis of challenge, respectively. The immunized mice, guinea pigs and rabbits with EV76 vaccine gave 100% (6/6), 93% (13/14) and 100% (6/6) protection against 10(6) CFU Y. pestis of challenge respectively.

Conclusion: BALB/c mice is the best small animal model for valuation of protective efficacy of plague subunit vaccine. The guinea pigs showed a high individual variation for this purpose. The rabbits can be used as an alternative model for evaluating plague subunit vaccine.