Multigene Expression Assay for Assessment of the Immune Status of Atlantic Salmon.

Aleksei Krasnov,Sergey Afanasyev,Alexander Rebl,Stian Nylund

doi:10.3390/genes11111236

Abstract

We report the development of a multigene gene expression assay on the BioMark HD platform for the evaluation of immune competence (ImCom) in farmed Atlantic salmon. The first version of the assay included 92 genes selected on the basis of transcriptome analyses in 54 trials that challenged the immune system; annotations were taken into account to represent the key pathways of innate and adaptive immunity. ImCom was tested on samples collected from seven independent projects. Fish were reared from the start feeding to eight months in the sea at eight units in different parts of Norway. Several tissues were analyzed. Linear discriminant analysis (LDA) showed that no more than 10 genes were required to separate groups, and a set of 46 immune genes was sufficient for any task. The second version of the assay was tested in the gills of two groups of high-performing healthy smolts and in groups with intermediate and high mortality rates (IM and HM, respectively). A set of 645 gill samples from clinically healthy Atlantic salmon was used as a reference. The IM group showed general suppression of immunity. All HM group salmon were above the threshold by the squared deviation from the reference. This group showed marked upregulation of genes involved in acute stress and inflammation: mmp-9, mmp-13, hsp70, il-1b, lect2, and cathelicidin. Further work will clarify the boundaries of the norm and explore various cases of impaired immunity.

Highlights

Linear discriminant analysis (LDA) showed that no more than 10 genes were required to separate groups, and a set of 46 immune genes was sufficient for any task
We present the development of a tool for assessment of the immune status of farmed Atlantic salmon
High risks from transportation stress, rearrangement of osmoregulation, and adaptation to the marine environment with increased pathogen pressure are aggravated by immune suppression during smoltification [3], which is most likely associated with dramatic endocrine changes during this period [4,5], and continues for several months after seawater transfer (SWT) [6]

Summary

Introduction

We present the development of a tool for assessment of the immune status of farmed Atlantic salmon. The ability of fish to combat pathogens is one of the key factors determining the success of salmon production. Assessment of immune status in fish is especially important before seawater transfer (SWT) and during the first several months in the sea when most disease outbreaks occur. High risks from transportation stress, rearrangement of osmoregulation, and adaptation to the marine environment with increased pathogen pressure are aggravated by immune suppression during smoltification [3], which is most likely associated with dramatic endocrine changes during this period [4,5], and continues for several months after SWT [6]. This study is a step toward the assessment of immune status based on a multigene expression assay

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