Actinobacillus pleuropneumoniae serotype 2 exoproteome LF-LC-MS/MS

Porcine pleuropneumonia caused by Actinobacillus pleuropneumoniae affects pig health status and the swine industry worldwide. Despite of the extensive number of studies focused on A. pleuropneumoniae infection and vaccine development, its exoproteome is still rather unexplored. By combining high-throughput mass spectrometry and immunoproteomic approaches, with our current work we provide an in-depth characterisation of A. pleuropneumoniae serotype 2 exoproteome. Label-free liquid chromatography - tandem mass spectrometry (LC-MS/MS) combined with a comprehensive bioinformatics analysis revealed 484 secreted proteins, of which 84 were predicted to be virulence factors and 142 to be exported via different export mechanisms. The RTX toxins ApxIIA, ApxIIIA and ApxIVA were found to be the most abundant proteins in the A. pleuropneumoniae serotype 2 exoproteome, although ApxIVA is commonly assumed to be expressed exclusively in vivo. Immunoproteomic approaches coupled to LC-MS/MS analysis allowed to portray the immunogenic proteins within the bacterial exoproteome to identify potential vaccine candidates. Using serum pools from uninfected, acutely infected and chronically infected animals, we were able to monitor the seroconversion during disease progression. Overall, our work is expected to contribute to the understanding of the complex pathogenic mechanisms and to facilitate the discovery of potential antimicrobial agents for controlling porcine pleuropneumonia.