A novel inactivated vaccine for cross-protection against Actinobacillus pleuropneumoniae in pigs.

Actinobacillus pleuropneumoniae (APP) causes porcine contagious pleuropneumonia (PCP), a highly contagious respiratory disease that inflicts substantial economic losses to the global swine industry. Given the high serotypic diversity of APP and limited cross-protective efficacy of current vaccines, novel candidates are urgently needed. In contrast to commercial APP vaccines relying on formalin-inactivated native Apx toxoids, and to experimental antigens that frequently use truncated Apx fragments or proteins refolded from insoluble inclusion bodies, this study successfully expressed full-length, soluble recombinant ApxIA and ApxIIA. These novel recombinant antigens were combined with inactivated APP serotype 1 to construct an inactivated whole-cell subunit combination vaccine, designated BAA. Its protective efficacy against multiple APP serotypes was evaluated in a porcine challenge model. The BAA vaccine showed a favorable safety profile. Compared with control and toxin-free inactivated bacterial vaccine (Bac) groups, BAA-immunized pigs exhibited significantly higher levels of specific antibodies against ApxIA, ApxIIA, and bacterial antigens. After challenge with APP serotypes 1, 3, 5, and 7, BAA-vaccinated pigs achieved survival rates of 100%, 80%, 80%, and 100%, respectively, with milder clinical signs, reduced lung lesions, and significantly lower pulmonary bacterial loads than other groups. Histopathology confirmed markedly alleviated pulmonary pathology in BAA-vaccinated pigs. These results indicate that the BAA vaccine confers robust cross-protection against heterologous APP serotypes and is a promising candidate for PCP prevention.