Comparative immunity of Salmo salar and Oncorhynchus kisutch during infestation with the sea louse Caligus rogercresseyi: An enrichment transcriptome analysis

Caligus rogercresseyi, an ectoparasite affecting the Chilean salmon industry, can cause immunosuppression and physiological stress in farmed fish. Interestingly, coho salmon (Oncorhynchus kisutch) are notably resistant to infestation, whereas Atlantic salmon (Salmo salar) are phenotypically more susceptible to sea lice. However, comparative studies on immune responses to C. rogercresseyi have not been conducted. In this study, Illumina sequencing was conducted to evaluate head kidney and skin samples taken 7 and 14 days post-infestation, yielding a total of 1492 and 1522 contigs annotated to immune related, genes for Atlantic and coho salmon, respectively. Both species evidenced an upregulation of inflammatory genes. Atlantic salmon had highly upregulated TLR22 and MHC11 at 14 days post infestation, while coho salmon had highly upregulated stat5 and il1r transcripts. Fourteen transcripts related to T(H)1, T(H)2, TLR, and macrophage responses were corroborated via RT-qPCR. Statistical analyses indicated an upregulation of mmp13, cox2, i110, ccr3, tIr22a2, and t1r21 in Atlantic salmon and of ifn gamma, cd83, T-bet, t1r13, and t1r19 in coho salmon. These results suggest strong differences between the Atlantic and coho salmon immune responses, where coho salmon, the more resistant species, presented a primary T(H)1 response. Additionally, putative roles of TLRs in salmonids against sea lice were evidenced. This study is the first comparative transcriptome analysis that reveals species-specific immune responses in salmons infected with C. rogercresseyi. (C) 2016 Elsevier Ltd. All rights reserved.