Objective: To investigate the immunogenicity of vaccine strategies about human interleukin 12 associated with combined DNA (Ag85A and ESAT-6) prime-BCG boost.
Methods: BALB/c mice were divided into PBS negative control and 4 immunity groups: BCG group, DNA/BCG group, DNA + IL-12/BCG group and DNA/BCG + IL-12 group. All mice received three immunizations at 2-week interval. Specific IgG antibody in serum of mice was determined with indirect ELISA in 4, 6, 8 weeks respectively after final vaccination. The splenic lymphocytes of mice were separated and stimulated with PPD to measure their proliferation by flow cytometry, and to evaluate the production of interferon-gamma (IFN-gamma) in cell suspensions of spleen cells by ELISA. The levels of CD4+ and CD8+ T-cell on surface of spleens lymphocyte were determined by flow cytometry.
Results: PPD could stimulate specific IgG responses in 4 immunity groups, and the average valences of 4 groups are 1:80, 1:120,1:160,1:160; the splenic lymphocyte proliferation reactions and IFN-gamma production were detectable in 4 immunity groups, and the most significant response occurred in 12 weeks. DNA + IL-12/BCG group and DNA/ BCG+IL-12 group induced higher production than BCG group and DNA/BCG group (P < 0.05), and the effects between DNA + IL-12/BCG group and DNA/BCG + IL-12 group had little difference. The numbers of CD4+ and CD8+ T-cell in 4 immunity groups were much higher than PBS group (P < 0.05), and DNA+IL-12/BCG group and DNA/BCG+IL-12 group were detected much more CD4+ and CD8+ T-cell than BCG group and DNA/BCG group (P < 0.05). The level of T-cell between DNA + IL-12/BCG group and DNA/BCG + IL-12 group had little difference.
Conclusion: Interleukin 12 associated with the strategy of priming with the combined DNA vaccines and boosting with attenuated M. bovis vaccine (BCG) could induce much stronger specific cellular immunity compared with simple DNA/BCG or attenuated M. bovis vaccine alone.