Evidence that the major hemolymph protein of the Pacific oyster, Crassostrea gigas, has antiviral activity against herpesviruses.

Viruses belonging to the family Malacoherpesviridae currently pose a serious threat to global production of the Pacific oyster, Crassostrea gigas. Hemolymph extracts from C. gigas are known to have potent antiviral activity. The compound(s) responsible for this broad-spectrum antiviral activity in oyster hemolymph have not been identified. The objective of this study was to identify these antiviral compound(s) and establish whether hemolymph antiviral activity is under genetic control in the Australian C. gigas population. Hemolymph antiviral activity of 18 family lines of C. gigas were assayed using a herpes simplex virus type 1 (HSV-1) and Vero cell plaque reduction assay. Differences in anti-HSV-1 activity between the family lines were observed (p<0.001) with heritability estimated to be low (h(2)=0.21). A glycoprotein that inhibits HSV-1 replication was identified by resolving oyster hemolymph by native-polyacrylamide gel electrophoresis (PAGE) and assaying extracted protein fractions using the HSV-1 and Vero cell plaque assay. Highest anti-HSV-1 activity corresponded with an N-linked glycoprotein with an estimated molecular mass of 21kDa under non-reducing SDS-PAGE conditions. Amino acid sequencing by tandem mass spectrometry revealed this protein matched the major hemolymph protein, termed cavortin. Our results provide further evidence that cavortin is a multifunctional protein involved in immunity and that assays associated with its activity might be useful for marker-assisted selection of disease resistant oysters.