EVIDENCE THE PACIFIC OYSTER, Crassostrea gigas HAS A TYPE I INTERFERON RESPONSE: IMPLICATIONS FOR DISEASE MANAGEMENT  

Massive mortality events of the Pacific oyster (Crassostrea gigas) have been recently reported worldwide and these disease events are often associated with infection with Ostreid herpesvirus type 1 (OsHV-1). Little is known about the immune responses of non-model invertebrates, such as oysters, to viral infection. This lack of knowledge is hampering novel management solutions for OsHV-1. The vertebrate innate immune system detects virus-derived nucleic acids to trigger the type I interferon (IFN)-pathway, leading to the transcription of hundreds of IFN-stimulated genes (ISGs) that exert antiviral functions.  Human medicine has exploited the IFN-pathway to routinely treat several common viral diseases. Invertebrates were thought to lack the IFN-pathway based on the absence of IFN or ISGs encoded in model-invertebrate genomes.  However, the oyster genome encodes many ISGs, including the well-described antiviral protein, viperin. Viperin is one of the first genes up-regulated in oysters inoculated with OsHV-1 or poly(I:C) (Fig. A). Poly(I:C) is a synthetic dsRNA molecule that mimics viral infection. We characterised oyster viperin and showed it localises to caveolin-1 and inhibits Dengue virus replication in a heterologous model (Fig. C). In a second set of experiments, we provide evidence that the hemolymph from poly(I:C)-injected oysters contains a heat-stable peptide that induces hemocyte transcription of viperin mRNA in conjunction with upregulation of IFN-regulatory factor (Fig. B). Collectively, these results support the concept that oysters have antiviral systems that are homologous to the vertebrate IFN-pathway. The presence of an IFN-pathway in oysters is of considerable interest in progressing novel therapeutics for the aquaculture industry.