Naïve Atlantic salmon (Salmo Salar L.) surviving a lethal challenge with infectious pancreatic necrosis virus (IPNV) shows upregulation of antiviral genes in head-kidney, including Vig-2

The differential gene expression profile of survivors of unvaccinated Atlantic salmon challenged by cohabitation (81% mortality) with a highly virulent strain of IPNV was studied using suppressive subtractive hybridisation (SSH). RNA was extracted from head-kidney from fish prior to IPNV challenge and 4 weeks post challenge (survivors). Five hundred and seventy six cDNA clones were randomly selected for sequencing, BLAST N and BLAST X analyses were performed. 180 unique genes were found, out of these 167 were singletons and 13 were contigs. These genes were grouped according to their putative functions using Blast2Go and TrEMBL. Ten out of 14 genes identified by SSH were confirmed by quantitative real time PCR. Representatives of almost all the biological functional groups were found, including immune and stress response, transcription, translation, metabolism and protein transport and all were upregulated in the survivor fish. Viral Haemorrhagic Septicaemia Virus induced gene 2 (Vig-2) was among the genes found to be upregulated in the survivors and this prompted us to assess the expression level of IFN-α and Mx, which were both found to be significantly upregulated, alongside inflammatory markers (P-selectin) and proteolysis genes (proteasome subunit alpha type 2). In summary the results obtained point towards innate responses being induced in surviving fish combined with factors involved in protein degradation and yet un-classified genes with regard to antiviral functions (Vig-2).