Abstract
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.
Highlights
Teleost fish, the earliest evolutionary group with an immune system exerting both innate and adaptive immunity, is highly diverse, consisting of more than 32 000 species
Sequencing of RNA isolated from nontreated head kidney leukocytes (HKL) and HKL exposed to Vibrio resulted in 516 million reads
Conserved structures on potential pathogenic organisms such as flagellin are recognized by the host’s pattern recognition receptor (PRR) and trigger intracellular signaling pathways which results in production of inflammatory cytokines and initiation of adaptive immune responses tailored to the infecting agent
Summary
The earliest evolutionary group with an immune system exerting both innate and adaptive immunity, is highly diverse, consisting of more than 32 000 species. The TLRs is the most studied family of the PRRs and an enormous diversity has been identified in teleosts (reviewed in[1,3,4]) This diversity is suggested to be driven by adaptation to specific environments and host-intrinsic factors[3]. There is currently little information regarding the downstream cell signaling pathways following activation of the fish-specific TLRs. As for the TLR family, some NLRs play a role in antimicrobial immune responses. The transcriptome of lumpfish, as a representative for Cyclopteridae is highly valuable as this group is poorly characterized genetically and no reference genome or immune gene sequences are available in public databases. In Norway alone, the number of lumpfish farmed increased from 0.4 million in 2012 to approximately 15 million in 201621
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