We performed RNA sequencing, identified components of the immune system and mapped early immune responses of lumpfish (Cyclopterus lumpus) leukocytes following in vitro exposure to the pathogenic bacterium Vibrio anguillarum O1. This is the first characterization of immune molecules in lumpfish at the gene level. In silico analyses revealed that genes encoding proteins involved in pathogen recognition, cell signaling and cytokines in mammals and teleosts are conserved in lumpfish. Unique molecules were also identified. Pathogen recognition components include 13 TLRs, several NLRs and complement factors. Transcriptome-wide analyses of immune responses 6 and 24 hours post bacterial exposure revealed differential expression of 9033 and 15225 genes, respectively. These included TLR5S, IL-1β, IL-8, IL-6, TNFα, IL-17A/F3, IL-17C and several components of the complement system. The data generated will be valuable for comparative studies and make an important basis for further functional analyses of immune and pathogenicity mechanisms. Such knowledge is also important for design of immunoprophylactic measures in lumpfish, a species of fish now farmed intensively for use as cleaner-fish in Atlantic salmon (Salmo salar) aquaculture.

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The interleukin (IL)-1 family play a fundamental role as immune system modulators. Our previous transcriptome-analyses of leukocytes from lumpfish (Cyclopterus lumpus L.) showed that IL-1β was among the most highly upregulated genes following bacterial exposure. In the present study, we characterized IL-1 signaling pathways, identified and characterized four ligands of the IL-1 family in lumpfish; IL-1β type I and type II, IL-18, and the novel IL-1 family members (nIL-1F), both at mRNA and gene levels. The two IL-1β in lumpfish is termed IL-1β1 (type II) and IL-1β2 (type I). Furthermore, a comprehensive phylogenetic analysis of 277 IL-1 ligands showed that nIL-1F, in common with IL-1β, likely represents an ancestral gene, as representatives for nIL-1F were found in cartilaginous and lobe-finned fish, in addition to teleosts. This shows that nIL-1F is not exclusively present in teleosts as previously suggested. Our analyses of exon-intron structures, intron phases, phylogeny and synteny clearly show the separation of IL-1β into groups; type I and type II, which likely is a result of the third whole genome duplication (3R WGD). The phylogenetic analysis shows that most teleosts have both type I and type II. Furthermore, we have determined transcription levels of the IL-1 ligands in leukocytes and 16 different tissues, and their responses upon in vitro stimulation with seven different ligands. In addition, we have identified the IL-1 receptors IL-1R1, IL-1R2, IL-1R4 (ST2/IL-33 receptor/IL-1RL), IL-1R5 (IL-18R1), and partial sequences of DIGIRR and IL-1R3 (IL-RAcP). Identification of immune molecules and description of innate responses in lumpfish is interesting for comparative and evolutionary studies and our study constitutes a solid basis for further functional analyses of IL-1 ligands and receptors in lumpfish. Furthermore, since lumpfish are now farmed in large numbers to be used as cleaner fish for removal of sea lice on farmed salmon, in-depth knowledge of key immune molecules, signaling pathways and innate immune responses is needed, as the basis for design of efficient immune prophylactic measures such as vaccination.

Lumpfish (Cyclopterus lumpus L.) has shown to be an efficient biological tool in the fight against salmon lice (Lepeophtheirus salmonis) and are chosen by many fish farmers in Norway as an alternative to medicinal treatment. However, to improve the fish health and increase the overall efficiency of the cleaner fish strategy, more knowledge about its immune system and protective vaccines are required. We will present the current knowledge of its immune cells and its innate and adaptive immune responses upon bacteria challenge.

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