Formalin and ferric chloride inactivated Pasteurella multocida type a adjuvanted with bacterial DNA and alum as a new vaccine candidate in sheep pasteurellosis

The aim of the present study was to investigate humoral and cellular immune responses in sheep inoculated with inactivated P. multocida antigen with alum and bacterial DNA adjuvant by identifying IgG and cytokines from serum and cell culture. Sheep were immunized with iron and formalin-inactivated antigens at an interval of 2 weeks. These immunogens were mixed with alum adjuvant and P. multocida type A DNA (AbDNA). After injection and blood sampling, the serum antibody titer and cellular immune responses (IL-4, IFN-γ, and TNF-α) on serum samples and lymphocyte cell were tested by ELISA. The ELISA results showed a higher antibody titer in the bDNA adjuvant group compared to the alum adjuvant group and the control group. In general, the level of IgG in the serum of immunized animals was significantly increased compared to the control group. The peak antibody titer (1.794) was observed on the 28th day of injection in the IIV-AbDNA group. After immunization, inactivation with iron and bDNA adjuvant increased cytokine production compared to other experimental and control groups. High levels of lymphocyte and serum titers of IL-4, IFN-γ, and TNF-α were also obtained in the IIV-AbDNA group. The findings showed that killed P. multocida type A antigens formulated with bacterial DNA as an adjuvant are candidates for new immunogens against P. multocida infections in sheep. The inactivation of bacteria with iron also enhanced proper immune responses.