Haemophilus parasuis, the causative agent of Glӓsser’s disease in pigs, is widespread and results in significant financial losses to the swine industry annually. The majority of vaccines are based on a killed, whole cell platform, in which the immune response tends to be serotype or strain specific and unable to provide broad cross protection against H. parasuis. This has stimulated interest in the development of subunit vaccines, where the immune response can be directed to highly conserved, surface exposed antigens.
Outer membrane proteins (OMPs) with potential protective capability from H. parasuis were identified via 2D gel electrophoresis and Western blotting. Blots were probed with antisera from pigs vaccinated with H. parasuis serovar 5 strain 265 or Nagasaki, which did and did not afford heterologous protection to serovar 1 strain 12939, respectively. OMPs recognized by 265 antisera and not recognized by Nagasaki antisera were identified using LC-MS/MS. After verifying sequence conservation, three OMPs were selected for use in a vaccine trial: ApbE, LpoA, and YaeT.
These three recombinant OMPs were immunogenic, generating a significant antibody titer; however, OMP vaccinated animals were not protected from homologous (265) or heterologous (12939) challenge. Further investigation into differences between immunity generated by 265 bacterin vaccination and Nagasaki bacterin vaccination is warranted to better understand the immunogens conferring protection.