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In the past decade, important discoveries have shown that resistance to reinfection can be achieved without a functional adaptive immunity system, introducing the concept of innate immune memory in invertebrates. However, this field has been constrained by the limited number of molecular mechanisms identified to support these phenomena. Taking advantage of an invertebrate species, the Pacific oyster (Crassostrea gigas), in which we evidenced one of the longest and most effective periods of protection against viral infection observed in an invertebrate, researchers from the IHPE unit, a unit that joined TULIP in 2019, provides the first comprehensive transcriptomic analysis of innate antiviral immune priming in an invertebrate species.

The initiation of an innate immune priming has been evidenced in many invertebrate phyla. While mechanistic models have been proposed, evidence to substantiate these models has remained scarce. In this article, researchers from the IHPE laboratory reveal the transcriptional signature associated with immune priming the oyster Crassostrea gigas, the Pacific oyster, a species of economic interest because it is the most cultivated in the world.

After priming with poly (I: C), a synthetic double-stranded RNA structurally similar to the double-stranded RNA of certain viruses, the oysters were fully protected against the herpes virus Ostreid 1 (OsHV-1), a major pathogen of oysters. Global analysis through RNA sequencing of oyster and viral genes after immune priming and viral infection revealed that poly(I:C) induces a strong antiviral response that impairs OsHV-1 replication.

Protection is based on a sustained upregulation of the immune genes that control subsequent viral infection. This persistent antiviral alert state remains active over 4 months and supports long-term antiviral protection. This acquired resistance mechanism reinforces the molecular foundations of the sustained response model of immune priming. It further opens the way to applications (pseudovaccination) to cope with a recurrent disease that causes dramatic economic losses in the shellfish farming industry worldwide.