Protective Immunity of the Pore-Forming Domains of Actinobacillus pleuropneumoniae Apx Toxins in a Mouse Model

The hemolytic/leukolytic toxins ApxI, II, and III play a central role in the pathogenicity of Actinobacillus pleuropneumoniae and may serve as effective vaccine antigens. However, since these toxins are large in size, we aimed to determine whether only the pore-forming domain of the toxins may be sufficient for protective immunity. Mice were vaccinated with the pore-forming domains for immune response analysis and challenge test. Significant antibody response was observed for the ApxI and II vaccine groups. For cellular immune response, CD4+ and CD8+ T cell expansion was observed for ApxI. Pro-inflammatory cytokine (IL-1b, IL-6) and TH2-type cytokine (IL-4, IL-10) gene expression was detected for the ApxI and II groups. Finally, in a challenge test with a A. pleuropneumoniae serotype 1 strain, the pore-forming domains of ApxI, II, III and three of pore-forming domains conferred 100%, 40%, 0% and 100% protection, respectively. The pore-forming domain of the Apx toxins shows promise as vaccine antigen against A. pleuropneumoniae.