The immunological evaluation of plague vaccine in cynomolgus monkeys

Abstract

Objective To evaluate the immune effect of a new plague vaccine composed of Yersinia pestis F1 antigen and recombinant V (rV) antigen in cynomolgus monkeys. Methods Twenty cynomolgus monkeys were simply randomized into 3 groups and intramuscularly injected with low-dose plague vaccine, high-dose plague vaccine and saline at 0 and 2 weeks, respectively. The serum samples were collected 2 weeks after first and second immunization, examined for total IgG antibodies by ELISA. In addition, enzyme-linked immunospot assay was used to detect IFN-γ-secreting lymphocytes in isolated peripheral blood lymphocytes. The results were compared by Student’s t-test. Results No IgG antibody was detected in the control group, but the plague vaccine induced strong antibody response. In cynomolgus monkeys immunized with low-dose or high-dose vaccine, 2 weeks after the second immunization, the geometric mean titers of anti-F1 IgG were (4.71±0.32)lg and (5.09±0.21)lg (t=-2.76, P﹤0.05), and anti-V IgG titers were (4.75±0.52)lg and (5.12±0.58)lg (t=-1.37, P﹥0.05), respectively. No significant increase of IFN-γ-secreting lymphocytes was found after in vitro stimulation with F1 and rV antigens. In cynomolgus monkeys immunized with low-dose or high-dose vaccine, when stimulated with F1, the number of IFN-γ-secreting cells was (1±1)/106 and (1±2)/106 (t=-0.16, P﹥0.05), respectively, and (7±15)/106 and (6±7)/106 (t=0.88, P﹥0.05) when stimulated with rV. Conclusion Plague vaccine can elicit strong specific humoral response but weak cellular response in cynomolgus monkeys. Key words: Plague vaccine; Models, animal; Immunity, humoral; Immunity, cellular