Poly I:C induces a protective antiviral immune response in the Pacific oyster (Crassostrea gigas) against subsequent challenge with Ostreid herpesvirus (OsHV-1 μvar)

Abstract

In-vivo studies were carried out to investigate the protective effect of a synthetic viral analogue (poly I:C) against Ostreid herpes virus (OsHV-1 μvar). Pacific oysters (Crassostrea gigas) were immune-primed by intramuscular injection of 240 μg of poly I:C or sterile seawater at 1 day prior to infection with OsHV-1 μvar. Poly I:C injection induced an antiviral state in C. gigas as the percentage of viral-infected oysters at 48 h post infection was significantly lower in the poly I:C treatment (11%) compared to seawater controls (100%). In an additional experiment, we demonstrated that the protective role of poly I:C is reproducible and elicits a specific antiviral response as immune-priming with heat-killed Vibrio splendidus provided no protection against subsequent viral infection. In both experiments, genes homologous to a toll-like receptor (TLR), MyD88, interferon regulatory factor (IRF) and protein kinase R (PKR) were up-regulated in oysters immune-primed with poly I:C compared to seawater controls (p < 0.05). The MyD88, IRF and PKR genes were also significantly up-regulated in response to OsHV-1 μvar infection (p < 0.05), which is suggestive that they are implicated in the antiviral response of C. gigas. Our results demonstrate that C. gigas can recognise double-strand RNA to initiate an innate immune response that inhibits viral infection. The observed response has striking similarities to the hallmarks of the type-1 interferon response of vertebrates.

Antiviral immunity in marine molluscs

“…Studies investigating the antiviral response of molluscs have mainly focused on identifying antiviral compounds, measuring immune enzyme activity or characterizing the transcriptional response to OsHV-1 infection Dang et al, 2011Dang et al, , 2013Fleury & Huvet, 2012;Green & Montagnani, 2013;Green et al, 2014c;Jouaux et al, 2013;Moreau et al, 2015;Normand et al, 2014;Olicard et al, 2005a, b;Renault et al, 2011;Rosani et al, 2014;Segarra et al, 2014a, c). These studies suggest that the molluscan antiviral response has similarities to the vertebrate interferon pathway (Green & Montagnani, 2013). However, this interpretation may be biased by the reliance on transcriptional studies to characterize antiviral responses.…”

“…Firstly, the immune system of Crassostrea gigas can recognize nonspecific nucleic acids (i.e. poly I : C) to induce an antiviral response that inhibits subsequent infection with OsHV-1 (Green & Montagnani, 2013). This response was antiviral because inducing an anti-pathogen response by injecting Crassostrea gigas with heat-killed Vibrio bacteria provided no protection against subsequent OsHV-1 infection (Green & Montagnani, 2013).…”

“…poly I : C) to induce an antiviral response that inhibits subsequent infection with OsHV-1 (Green & Montagnani, 2013). This response was antiviral because inducing an anti-pathogen response by injecting Crassostrea gigas with heat-killed Vibrio bacteria provided no protection against subsequent OsHV-1 infection (Green & Montagnani, 2013). Several evolutionary conserved nucleic acid sensors and their downstream signalling molecules, including Toll-like receptors (TLRs), RIG-like receptors (RLRs), interferon regulatory factors (IRFs) and stimulator of interferon (STING), have been identified in the Crassostrea gigas genome (Figs 2 and 3, Table 1).…”

“…In addition, mortality events of Crassostrea gigas were reported in 2010 from New Zealand and Australia in association with a virus closely related to mVar (Jenkins et al, 2013;Keeling et al, 2014). Numerous genomic and proteomic studies investigating the host-pathogen interactions of Crassostrea gigas and OsHV-1 have been undertaken (Corporeau et al, 2014;Du et al, 2013;Fleury & Huvet, 2012;Green & Montagnani, 2013;Jouaux et al, 2013;Normand et al, 2014;Renault et al, 2011;Segarra et al, 2014a, b, c;Tamayo et al, 2014). Acute viral necrosis virus (AVNV) is the causative agent of a serious disease of Chinese scallops, Chlamys farreri (Ren et al, 2013).…”

Expression profile of pro-inflammatory cytokines in head-kidney leucocytes of rohu following stimulation with poly I:C

“…However, in addition to interferon mediated anti-viral immunity, viral infection also induces expression of TNF and other chemokines [9]. Poly I:C, the synthetic analog of double stranded RNA virus is recognized by toll-like receptor 3 (TLR3) which activates a number of signal transduction pathways and upregulates an array of immune genes [28]. In in silico analysis, rohu TLR3 has been found to possess key binding domains for poly I: C and dsRNA of fish reovirus [29].…”