Identification of candidate vaccine antigens using 2-D gel electrophoresis and immunoproteomics for cross protection against Glaesserella parasuis

Glaesserella parasuis infection in swine causes polyserositis, arthritis, and meningitis. A range of virulent to nonvirulent strains exists between and within the 15 serovars. This has created difficulty in generating broadly protective vaccines against G. parasuis. Subunit vaccines are of interest in protection against bacterial pathogens, where the individual proteins within the vaccine are highly conserved and widely present. To identify novel subunit vaccine candidates for heterologous protection against G. parasuis, previously generated serum from bacterin vaccinated pigs that were protected (HS069 bacterin) or non-protected (Nagasaki bacterin) against heterologous challenge with 12939 was used to differentiate the antibody response using 2-D gel electrophoresis and immunoblotting. Proteins with differential representation between blots probed with serum from HS069 or Nagasaki bacterin vaccinated animals were identified by mass spectrometry. Thirteen unique proteins were associated with the protective immune response and four of these proteins were tested in two combinations against G. parasuis in a swine challenge model (ApbE, LpoA, YaeT, and LppA). All four proteins were immunogenic and stimulated high antibody titers in pigs. While the protein combination of ApbE, LpoA, and YaeT did not provide improved survival, the combination of LpoA, YaeT, and LppA did, suggesting LppA is important for protection. This work identified a group of proteins capable of improving survival in pigs challenged with G. parasuis. Additionally, this work highlights a novel and effective method to identify candidate vaccine antigens utilizing the protective immune response.