The effect of homologous and heterologous Bacterial DNA on the development of immune responses against Pasteurella multocida in BALB / c mice

Pasteurella multocida is a principal pathogen of domestic animals causing agents of pneumonia and hemorrhagic septicemia in cattle, sheep, and goats, fowl cholera in chickens, and progressive atrophic rhinitis in swine and as well as an opportunistic pathogen of humans. In this study, we investigated the humoral and cellular immune responses and protective immunity conferred by an iron-inactivated vaccine with two different bacterial DNA as an adjuvant.

P. multocida was grown in BHI broth, inactivated with FeCl3, adjuvanted with alum and P. multocida A (homologous DNA) and P. multocida B (heterologous DNA) bacterial DNAs. BALB/c mice were immunized with two whole-cell inactivated vaccine doses at 2 weeks apart. The animals were challenged 4 weeks after booster immunization. The serum antibodies titer was tested by ELISA. At 28 days post-immunization, cell mediates immunity responses were measured by assay of DTH and IL-6 and IL-12 in the serum samples.

Our results showed the levels of antibodies in bDNA adjuvant groups were higher than the alum adjuvant vaccine group. Peak antibody titers of 0.372 were obtained in the IIA+AbDNA group. The protection rate of the AbDNA adjuvant vaccine was better than of other adjuvant vaccines and they protected 100% of mice challenge groups. Peak serum IL-6 and IL-12 titers were achieved in the IIA+AbDNA groups.

These studies indicate that bDNA is effective as immune adjuvants and because of its stimulating properties it can be used as an inducer of humoral and cellular immune responses for vaccination applications. The findings also showed a better ability of homologous bDNA to induce immune responses.