Differential Expression of Immune Genes in Atlantic Salmon (Salmo salar L.) Challenged Intraperitoneally or by Cohabitation with IPNV

Abstract

Atlantic salmon smolts challenged intraperitoneally (ip) and by cohabitation with a highly virulent strain of infectious pancreatic necrosis virus showed strong activation of important immune genes in spleen, liver, head‐kidney and gill measured by real‐time quantitative PCR. The genes investigated were IL‐1β, IL‐10, IFN‐α, IFN‐γ, Mx, MHC‐I, MHC‐II, TCR‐α, CD8‐α and mIgM. A low final cumulative mortality of about 10% was seen in the ip‐challenged group, while more than 40% of the cohabitants died in the sampling period. Sampling was performed at day 15, 24 and 37 post ip‐challenge. Overall, the expression of the investigated genes varied highly. The expression of IL‐1β, IL‐10, MHC‐II, TCR‐α, CD8‐α and mIgM showed more or less the same patterns between the two groups of fish by being significantly upregulated at day 24 post ip‐challenge. However, the degree of regulation varied a lot among the genes. A pattern showing differences between ip‐challenged and cohabitants were seen for IFN‐γ and especially IFN‐α, where the upregulation seemed to last longer for the cohabitants. The Mx gene was the most induced gene, but also the one with highest individual variance. Mx but also MHC‐I were both still highly upregulated at the last sampling point within both groups of fish. The results seem to indicate that the differences in expression pattern(s) could reflect the different routes of entrance of the virus into the fish. This could maybe explain the different kinetics in the onset and the degree of mortality or the potential different molecular mechanisms used for combating the virus.

IPNV modulation of pro and anti-inflammatory cytokine expression in Atlantic salmon might help the establishment of infection and persistence

“…In addition, high levels of IFNa1 expression were found in head kidney of carrier fish. Results are in agreement with previous reports [19,26,36], suggesting that although an anti-viral response is produced, this is not sufficient to eliminate the virus. In fact, the interferon response is not associated with the age-dependant resistance observed in IPNV-infected fish [27,56], although induction of IFNa1 and Mx by injection of poly I:C or CpG DNA prior to bath infection with IPNV is partially protective in post-smolt Atlantic salmon [29].…”

“…Production of pro-inflammatory cytokines has been studied previously in Atlantic salmon infected with IPNV. Similarly, authors have reported that no increase of expression for IL-1b and TNFa (which was not analyzed here) was detected in any tissues with respect to controls [19,26] or at most, IL-1b was slightly up-regulated after 24 days after infection [36]. The absence of up-regulation of pro-inflammatory cytokines at early stages of IPNV immune stimulation was not due to the inability of the fish to respond because treatment with LPS or Poly I:C increased IL-1b and IL-8 cytokine levels 24 h post-injection.…”

“…Interestingly, there is only one previous work where an attempt was made to detect the IL-10 in salmonids challenged with IPNV. The results showed an induction of the expression of this anti-inflammatory cytokine in S. salar smolt, but this up-regulation was detected only after 24 days post-challenge and was not related with the establishment of viral infection [36].…”

Transcriptome profiling of immune responses to cardiomyopathy syndrome (CMS) in Atlantic salmon

“…The subsequent reduction in transcriptional activity might be due to increased paracrine effects of proteins in the induced innate responses, including both effector functions for clearance of virus and recruitment of immune cells for development of humoral and adaptive immunity. The IFN type I responses to different viral diseases have been reported in salmonids, with particular focus on IFN alpha and Mx protein [18-21]. We identified a suite of putative IFN-dependent genes with stronger upregulation which have been unknown or scarcely investigated in salmon.…”

Development of a nanoparticle-based oral vaccine for Atlantic salmon against ISAV using an alphavirus replicon as adjuvant

“…Cumulative mortality was determined daily. The table shows the RPS at the end of the experiment[35,66].…”