Role of the IFN I system against the VHSV infection in juvenile Senegalese sole (Solea senegalensis).

Daniel Alvarez-Torres,Julia Bejar,M Carmen Alonso,Isabel Bandin,Esther Garcia-Rosado,Ana M Podadera

doi:10.1186/s13567-015-0299-4

Daniel Alvarez-Torres, Julia Bejar + Show 4 more

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https://doi.org/10.1186/s13567-015-0299-4

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Abstract

Senegalese sole is susceptible to marine VHSV isolates but is not affected by freshwater isolates, which may indicate differences regarding virus-host immune system interaction. IFN I induces an antiviral state in fish, stimulating the expression of genes encoding antiviral proteins (ISG). In this study, the stimulation of the Senegalese sole IFN I by VHSV infections has been evaluated by the relative quantification of the transcription of several ISG (Mx, Isg15 and Pkr) after inoculation with marine (pathogenic) and freshwater (non-pathogenic) VHSV isolates. Compared to marine VHSV, lower levels of RNA of the freshwater VHSV induced transcription of ISG to similar levels, with the Isg15 showing the highest fold induction. The protective role of the IFN I system was evaluated in poly I:C-inoculated animals subsequently challenged with VHSV isolates. The cumulative mortality caused by the marine isolate in the control group was 68%, whereas in the poly I:C-stimulated group was 5%. The freshwater VHSV isolate did not cause any mortality. Furthermore, viral RNA fold change and viral titers were lower in animals from the poly I:C + VHSV groups than in the controls. The implication of the IFN I system in the protection observed was confirmed by the transcription of the ISG in animals from the poly I:C + VHSV groups. However, the marine VHSV isolate exerts a negative effect on the ISG transcription at 3 and 6 h post-inoculation (hpi), which is not observed for the freshwater isolate. This difference might be partly responsible for the virulence shown by the marine isolate.

Highlights

The type I interferon (IFN I) promotes an antiviral state by inducing the transcription of numerous interferon stimulated genes (ISG), such as Mx, interferon-stimulated gene 15 (Isg15), and the protein kinase R (Pkr) genes [1], which will be considered as markers of the Senegalese sole (Solea senegalensis) IFN I activity in this study
The transcription of different ISG (Mx, Isg15 and Pkr) has been quantified in Senegalese sole after the inoculation with polycytidylic acid (poly I):C or Viral Haemorrhagic Septicaemia Virus (VHSV) isolates with different levels of virulence, a marine isolate, pathogenic to sole under experimental conditions [26], and a freshwater isolate, which replicates in sole, it does not cause mortality in this fish species. This is the first report of Isg15 and Pkr transcriptional induction in Senegalese sole, whereas high levels of Mx mRNA had been previously reported after poly I:C inoculation in this species [27]
I:C inoculation resulted in the transcription of the three ISG under study, with the Isg15 gene showing the earliest and highest transcriptional levels, which is in concordance with previous studies

Summary

Introduction

The type I interferon (IFN I) promotes an antiviral state by inducing the transcription of numerous interferon stimulated genes (ISG), such as Mx, interferon-stimulated gene 15 (Isg15), and the protein kinase R (Pkr) genes [1], which will be considered as markers of the Senegalese sole (Solea senegalensis) IFN I activity in this study.Mx proteins are large GTPases involved in intracellular membrane remodelling and intracellular trafficking [2]. ISG15 are ubiquitin-like proteins containing two tandem repeats of ubiquitin-like domains In mammals, these proteins can conjugate to either, cellular or viral target proteins, via the C-terminal LRLRGG sequence (ISGylation), which is controlled by a series of IFNinducible enzymes [6, 7]. Unlike ubiquitin, ISGylated proteins are not degraded in the proteasome [8] In addition to their antiviral activity, ISG15 proteins seem to be involved in regulating the IFN I signalling [9, 10]. Isg gene transcription has been studied in different species [11,12,13,14,15], determining that fish ISG15 proteins contain the critical C-terminal glycine residues, which suggests that they could conjugate to target proteins and have antiviral activity similar to their

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