Comparison of Immunoprotective Efficacy of Six Antigenic Proteins of Pasteurella multocida Serotype a in KM Mice (Mus musculus)

Pasteurella multocida serotype A (P. multocida) is frequently associated with severe respiratory disease in swine (Sus scrofa), highlighting the need for effective preventive strategies. To identify protective antigens suitable for a subunit vaccine targeting porcine P. multocida infection, six recombinant proteins (rAspA, rLolA, rOmpP6, rOppA, rRps6, rSmpA) were expressed in a prokaryotic system, and their efficacy was evaluated in a Mus musculus (Kunming) mouse model. All proteins were purified using His-tag affinity chromatography, and SDS-PAGE analysis confirmed expression with bands at the expected molecular weights (61, 26, 21, 63, 19, and 17 kDa). Each protein, formulated with ISA 201 adjuvant, was administered to mice in two immunizations. Indirect ELISA of sera collected at multiple time points demonstrated that all vaccines induced high antigen-specific IgG levels. rOppA, rLolA, rOmpP6, and rRps6 were expressed in soluble form, whereas rAspA and rSmpA formed inclusion bodies. In a lethal challenge model, rLolA and rRps6 conferred the highest protection (60% each), followed by rAspA and rOmpP6 (30%), rOppA (20%), and rSmpA (10%). Under the conditions tested, the highest protection observed was 60%, and none of the six antigens achieved complete protection against homologous A7 challenge in mice. This first head-to-head comparison under identical conditions provides a reference framework for future antigen screening studies.