Innate Immune Response of Lumpfish to Oil-Based and Water-Soluble Adjuvants

Fish vaccinology is advancing through modern technologies that enhance long-term immunity, with adjuvants playing a key role in boosting vaccine effectiveness. The type and composition of adjuvants significantly influence immune responses, which can vary across fish species and populations. This study investigates the innate immune response of lumpfish (Cyclopterus lumpus) populations from Newfoundland and Iceland to oil-based and water-soluble adjuvants. Fish were intraperitoneally injected with either Carbigen (a carbomer-based adjuvant), Freund's Incomplete Adjuvant (FIA), or phosphate-buffered saline (PBS). Head kidney samples were collected at 3, 6, and 24 hours post-injection for RNA sequencing and qPCR analysis. At 24 hours, Carbigen-treated fish exhibited a significantly higher number of differentially expressed genes (594) compared to FIA-treated fish (14), with enrichment of immune-related pathways such as cytokine signaling and pathogen recognition. qPCR validated the transcriptomic results and revealed that immune gene upregulation in Carbigen-treated lumpfish was only significant at 24 hours post-injection, with no notable changes at 3 or 6 hours. Comparative transcriptomic analysis revealed population-specific responses, with Newfoundland fish demonstrating a stronger transcriptional response to adjuvants than their Icelandic counterparts. This suggests underlying immunogenetic variation possibly shaped by distinct environmental pressures in their native habitats. Overall, the study highlights the potential of Carbigen, a water-soluble adjuvant, to effectively stimulate innate immune responses in lumpfish for aquaculture applications.