Towards a Mechanism for Poly(I·C) Antiviral Priming in Oysters

Abstract

Viral diseases cause significant losses in aquaculture. Prophylactic measures, such as immune priming, are promising control strategies. Treatment of the Pacific oyster (Crassostrea gigas) with the double-stranded RNA analog poly(I·C) confers long-term protection against infection with ostreid herpesvirus 1, the causative agent of Pacific oyster mortality syndrome. In a recent article in mBio, Lafont and coauthors (M. Lafont, A. Vergnes, J. Vidal-Dupiol, J. de Lorgeril, et al., mBio 11:e02777-19, 2020, https://doi.org/10.1128/mBio.02777-19) characterized the transcriptome of oysters treated with poly(I·C). This immune stimulator induced genes related to the interferon and apoptosis pathways. This response overlaps the response to viral infection, and high expression levels of potential effector genes are maintained for up to 4 months. This work opens the door to characterization of the phenomena of immune priming in a poorly studied invertebrate model. It also highlights the importance of interferon-like responses for invertebrate antiviral immunity.

Keywords: interferons; invertebrate-microbe interactions; mollusks; ostreid herpesvirus.

FIG 1

Simplified metazoan taxonomy of the major animal clades discussed in the text. Invertebrates are not monophyletic, comprising both deuterostomes (e.g., sea urchins) and protostomes. Innate antiviral defenses are defined mainly for mammalian vertebrates (Chordata), insects (Arthropoda), and roundworms (Nematoda). The production of interferons (IFN), controlled by interferon regulatory factors (IRFs), among other transcription factors, is the hallmark of the vertebrate innate antiviral immunity. Constitutive RNA interference (RNAi) is described as the major antiviral defense in invertebrates but has mainly been characterized in ecdysozoa. Inducible responses are poorly described outside vertebrates. Multiple invertebrate clades (Ambulacraria, Lophotrochozoa, and some arthropods) have homologs for IRFs which may play a role in their antiviral response. IRFs were lost in insects (*) and nematodes. The work by Lafont et al. (5) identified an IFN-like response in the mollusk Crassostrea gigas. The scale bar is in million years (MY).