Introduction
The growing demand to adhere to sustainable practices in aquaculture has driven interest in plant-derived immunostimulants. Halophytes, such as Salicornia ramosissima, are rich in bioactive compounds that may have immunomodulatory properties and could benefit farmed fish. This study investigated the effects of several S. ramosissima extracts on head kidney primary adherent leukocytes from Atlantic salmon (Salmo salar), focusing on innate immune responses at both functional and molecular levels.
Materials and Methods
Head kidney primary cells were harvested from healthy Atlantic salmon post-smolts maintained at the Research Station of Nord University. Adherent leukocytes, isolated using established protocols, were exposed to five different types of Salicornia ramosissima extracts (CAS.EX. 1-5), derived from distinct steps of the extraction cascade. Cytotoxicity was assessed using an MTT assay, and non-toxic concentrations were identified. Adherent leukocytes were exposed to the non-toxic concentration of each extract for either 3 or 24 hours, followed by a challenge with inactivated Tenacibaculum maritimum. Phagocytosis and ROS production were measured using Imaging Flow Cytometry. Furthermore, a snapshot of the changes in the transcriptome of the leukocytes was captured to reveal the responses at the molecular level.
Results and Discussion
Exposure to CAS.EX. 4 significantly enhanced phagocytic activity and ROS production after 24 h. Transcriptomic analysis revealed distinct early and late-stage immune responses. Within 3 h, CAS.EX. 4 triggered changes in nucleocytoplasmic transport, lysosomal function and lysine degradation. Extending the incubation time to 24 h, activated immune and stress-related pathways, including proteasome function, phagosome formation and autophagy while suppressing cell cycle and DNA repair pathways. These findings suggest that CAS.EX. 4 acts as a potent immunostimulant, enhancing phagocytic activity, stress adaptation, and cellular homeostasis mechanisms in adherent leukocytes from Atlantic salmon. The observed immune modulation and functional outcomes support the potential of Salicornia ramosissima extract as a functional ingredient to promote fish health in aquaculture.
Acknowledgments
This study was co-funded by the European Union (IGNITION - GA 101084651) and the UK Research and Innovation (UKRI). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union, the Research Executive Agency (REA) or the UKRI. Neither the European Union nor the granting authorities can be held responsible for them.