Importance of strain selection in the generation of heterologous immunity to Glaesserella (Haemophilus) parasuis

Authors: HAU, SAMANTHA - Orise Fellow; EBERLE, KRISTEN - Orise Fellow; Brockmeier, Susan

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2021
Publication Date: 2/12/2021
Citation: Hau, S.J., Eberle, K.C., Brockmeier, S. 2021. Importance of strain selection in the generation of heterologous immunity to Glaesserella (Haemophilus) parasuis. Veterinary Immunology and Immunopathology. 234. Article 110205. https://doi.org/10.1016/j.vetimm.2021.110205.
DOI: https://doi.org/10.1016/j.vetimm.2021.110205

Interpretive Summary: Glaesserella parasuis is a bacteria that causes severe disease in pigs and can lead to death. G. parasuis strains are identified by the type of capsule, a sugar matrix that surrounds the cell, they produce. This matrix protects the cell from the host immune system and the environment. Because of the capsule, using vaccines made from killed bacteria tends to produce immunity specific to the strain used in the vaccine or the capsule type (serovar) of that strain. In this study, we compared the use of two killed vaccines generated from serovar 5 strains (Nagasaki and HS069) for their ability to provide protection against the vaccine strain (homologous) and a non-serovar 5 isolate (heterologous) strain. Both vaccines generated high antibody responses and protected against homologous challenge. However, only the vaccine generated from G. parasuis HS069 was able to protect against the heterologous challenge. The HS069 vaccine was able to induce more effective antibody and the antibody targets differed from the Nagasaki vaccine. This study provides information on the importance of the strain utilized in the vaccine and provides an area for future research, where we can explore the difference in antibody targets to identify proteins for use as vaccine candidates.

Technical Abstract: Glaesserella parasuis is a part of the microbiota of healthy pigs and also causes the systemic condition called Glässer’s disease. G. parasuis is categorized by it capsular polysaccharide into 15 serovars. Because of the serovar and strain specific immunity generated by whole cell vaccines and the rapid onset of disease, G. parasuis has been difficult to control in the swine industry. This report investigated the protection afforded by the use of two serovar 5 isolates (Nagasaki and HS069) as whole cell, killed bacterins against homologous and heterologous challenge with the serovar 1 strain 12939 to better understand bacterin generated immunity. Both bacterins induced high antibody titers to the vaccine strain and the heterologous challenge strain. Protection was seen with both bacterins against homologous challenge; however, after heterologous challenge, the HS069 bacterin provided complete protection and all Nagasaki bacterin vaccinated animals succumbed to disease. The differences in protection appear to be due to differences in antibody specificity and the capacity of induced antibody to fix complement and opsonize G. parasuis, as shown by Western blotting and functional assays. This report shows the importance of strain selection when developing bacterin vaccines, as some strains are better able to generate heterologous protection. The difference in protection seen here can also be utilized to detect proteins of interest for subunit vaccine development.