Immune responses against chimeric DNA and protein vaccines composed of plpEN-OmpH and PlpEC-OmpH from Pasteurella multocida A:3 in mice

Pasteurella multocida is a pathogenic bacterium causing many diseases that are of significant economic importance to livestock industries. Outer membrane protein H (ompH) gene and two fragments of Pasteurella lipoprotein E (plpE) gene, namely plpEN and plpEC, were cloned from P. multocida A:3. Three DNA vaccine formulations, namely pCMV-ompH, pCMV-plpEN-ompH and pCMV-plpEC-ompH and two protein-based prototype vaccines, alum adjuvanted PlpEN-OmpH and PlpEC-OmpH, were generated. Antibody levels were induced in mice vaccinated with chimeric DNA or protein vaccines. A significant (p < 0.05) increase in serum IFN-g titer was obtained by vaccination with 100 μg of pCMV-ompH, pCMV-plpEC-ompH and PlpEC-OmpH. DNA vaccines did not provide protection upon intraperitoneal challenge with 10 LD₅₀ of live P. multocida A:3. However, 40% protection was conferred by 100 μg of PlpEC-OmpH which was not statistically significant. These results showed that plpEN-ompH and plpEC-ompH chimeric DNA vaccines and alum adjuvanted PlpEN-OmpH or PlpEC-OmpH protein vaccines were immunogenic but not protective against P. multocida A:3 in mice. Prime-boost strategies, i.e. priming with DNA vaccines and boost with protein formulations or different adjuvants can be utilized to obtain significant protection.