Functional and antigenspecific serum antibodies in mice after immunization with a candidate vaccine against Shigella flexneri 1b, 2a, 3a, 6, Y

Objective.

To determine functional anti-LPS specific serum bactericidal antibody (SBA) and opsonophagocytic killing antibody (OPKA) activities in mice immunized with a pentavalent candidate vaccine against Shigella flexneri 1b, 2a, 3a, 6, Y (PF).

Materials and Methods.

(CBA x C57 B1/6) F1 mice were immunized with a PF. 14 days after the reimmunization, serum samples were collected and the level of specific IgG in them was determined by ELISA. The sera of mice immunized with individual modified lipopolysaccharides (mLPS), which are part of PF, were used for positive control. Serum from intact mice served as a negative control. The functional activity of serum antibodies was determined by the methods of SBA and OPKA assay. The result was evaluated by the percentage of bacteria killed.

Results.

In all experimental groups of mice, an increase in the titer of specific IgG is observed (p < 0.05). The endpoint titer (ET) of anti-LPS S. flexneri 1b, 2a, 3a, 6, Y antibodies in the group of mice immunized with PF does not significantly differ from ET in the groups after immunizations with individual mLPS. At the same time, the indicators in the experimental groups are about 16 times higher than in the control. We determined a functional activity of S. flexneri-specific SBA and OPRA in mice immunized with PF. The rate of SBA killing was 54%, 66%, 35%, 60%, 60% for S. flexneri 1b, 2a, 3a, 6, Y serotypes, respectively. When OPKA killing in groups of immunized mice are 37%, 55%, 27%, 56%, 53% for S. flexneri 1b, 2a, 3a, 6, Y serotypes, respectively.

Conclusions.

PF induces the production of specific anti-LPS IgG comparable to its individual components. The sera from PF immunized mice contain functional antibodies. Serum bactericidal and opsonophagocytic assay are effective for use in a mouse model.