Innate immune response of lumpfish (Cyclopterus lumpus) to oil-based and water-soluble adjuvants

Adjuvants play a key role in boosting vaccine effectiveness. Adjuvant type and composition influence immune response, which can vary across fish species and populations. This study investigates the innate immune response of lumpfish (Cyclopterus lumpus) individuals collected from Newfoundland (NL), Canada, and Iceland (IC) to oil-based and water-soluble adjuvants, respectively. Fish were intraperitoneally injected with Carbigen (a carbomer-based adjuvant), Freund's Incomplete Adjuvant (FIA), or Phosphate-Buffered Saline (PBS). Head kidney samples were collected at 24 h post-injection (hpi) for RNA sequencing and qPCR analysis. At 24 hpi, Carbigen triggered a significantly higher number of differentially expressed genes (DEGs 594) compared to FIA-treated fish (DEGs 14). Gene Ontology enrichment analysis indicated dysregulation of cytokine signaling and pathogen recognition. The genes ccl25a, il34, il10, vwal1, and serpinf2b for Carbigen treatments, and ccl20b, cd22, il6r, atp2a1l, and il8b for FIA treatments were validated by quantitative polymerase chain reaction (qPCR). These genes were either up- or downregulated in both Carbigen and FIA treatments at 24 hpi, compared to the PBS control. The gene expression pattern was different between NL and IC lumpfish. NL lumpfish showed a stronger transcript level response to adjuvants than IC. This suggests underlying immunogenetic variation, possibly shaped by distinct environmental pressures in their native habitats. Overall, the study highlights the potential of a water-soluble vs oil-based adjuvant to effectively stimulate innate immune responses in teleost fish for aquaculture applications.