Immune responses and efficacy mediated by vaccination with a live attenuated vaccine against Piscirickettsia salmonis in Atlantic salmon (Salmo salar)
Master thesis
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https://hdl.handle.net/11250/3140069Utgivelsesdato
2024-06-03Metadata
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- Master theses [263]
Sammendrag
Salmonid Rickettsial Septicaemia (SRS), caused by Piscirickettsia salmonis, has plaguedChilean salmonid aquaculture since 1989. The bacterium evades immune responses by hidingin antigen-presenting cells, rendering inactivated vaccines ineffective. This study aimed toidentify immunological markers of successful vaccination using a live attenuated vaccine,ALPHA JECT LiVac® SRS, by evaluating vaccine efficacy, analysing antibody responses invaccinated fish and measuring immune gene regulations after in vitro exposure of leucocytes.
Fish were vaccinated with a live attenuated vaccine, a multivalent inactivated vaccine, or both.The live vaccine was also tested in suboptimal and inactivated state to highlight potential errorsin use. To assess protection under suboptimal conditions, two rearing temperatures were tested.Vaccine efficacy trial using intraperitoneal challenge model, antibody response measured withELISA and analyse in vitro exposed leucocytes for gene expression using RT-qPCR.
Fish vaccinated with the live vaccine or with a combination including the live vaccine showedgood protection, while the group at suboptimal temperature and groups with inactivatedvaccines experienced high mortalities. Levels of antibodies in plasma targeting P. salmonisincreased over time in all vaccinated groups indicating that high antibody response does notnecessarily correlate with protection against SRS.
Gene expressions were measured from isolated leucocytes 48 days post vaccination, in vitroexposed to P. salmonis and harvested after 6 hours. Despite there being a large difference inprotection between groups, no clear differences in regulation of immune genes were found aftermeasuring gene expression of RPS20 (reference gene), sIgM (secreted IgM antibody), Caspase-1 (indicating intracellular location and recognition by Nod-like receptors), GATA3 (indicatingdifferentiation of Th2 response), IL-18 (indicating differentiation of cytotoxic T-cells ), Perforin(indicating presence of activated cytotoxic T-cells), Tbet (indicating differentiation of Th1response) and IL-4/13a (indicating B-cell differentiation to plasma-and memory cells). Thestudy did not identify suitable markers for use in verification of vaccination.