Fish vaccines promote blood cell transcriptional remodeling in Atlantic salmon against pathogens

Chilean salmon farming confronts persistent challenges, including climate change risks and pathogens, where the most prevalent diseases impacting Atlantic salmon are Caligidosis and Rickettsial Salmonid Septicemia (SRS). As a sustainable strategy, fish vaccines hold promise for preventing diseases and reducing the use of antibiotics. While most studies on Atlantic salmon responses to vaccines emphasize transcriptome profiling from tissues such as the liver, head kidney, and skin, blood cell transcriptomics to monitor immune response dynamics is emerging as a promising tool in salmon aquaculture. This study evaluated the Atlantic salmon blood cell transcriptome in response to vaccination and subsequent infection with the sea louse Caligus rogercresseyi and the intracellular bacterium Piscirickettsia salmonis. The vaccination trial included four groups: fish immunized with the recombinant IPath® vaccine and two commercial vaccines currently used in Chile for salmon production. (BlueGuard® and Alpha Ject LiVac® SRS), and the unvaccinated control group. The group vaccinated with IPath® showed a higher transcriptomic response than commercial vaccines. Additionally, all three groups significantly modulated genes associated with iron homeostasis and metabolism. Furthermore, the HIF-1 signaling pathway and ferroptosis were notably activated in the IPath® group, suggesting a potential role of IPath® in the hypoxia response and cell death. This research highlights the effectiveness of using Atlantic salmon blood cells to assess immune responses, offering valuable insights into the fish immune system without resorting to lethal sampling.