Antigenicity analysis of the recombinant fusion proteins NlpI of Mannheimia haemolytica and DsbA of Pasteurella multocida

To analyze the antigenic characteristics of the recombinant fusion proteins rNlpI-DsbA (rND) of bovine Mannheimia haemolytica and Pasteurella multocida, respectively, and lay a foundation for the development of bivalent subunit vaccine development. The recombinant rND protein was successfully expressed and used to immunize mice with white oil, propolis, or astragalus polysaccharide adjuvants, respectively. Protective efficacy was evaluated by challenging mice with 5×LD₅₀ of WT M. haemolytica (Mh95) or WT P. multocida (PmA1). The rND–white oil group showed nearly 90% protection against Mh95 and 60% against PmA1, while all PBS controls died within 7 days. No significantly pathological damage was observed in the white oil group after challenge, whereas the other adjuvant groups exhibited tissue lesions following PmA1 infection. Both white oil and propolis adjuvants significantly enhanced antigen-specific IFN-γ responses and IgG titers compared to PBS controls. These results indicate that rND with white oil adjuvant induces strong immune protection and represents a promising cross-protective vaccine candidate. The rND exhibited favorable reactogenicity and immunogenicity and effectively prevented the invasion of homotypic strains. The study’s results laid a foundation for developing subunit vaccines against M. haemolytica and P. multocida.