Preliminary approach to find synthetic peptides from nodavirus capsid potentially protective against sea bass viral encephalopathy and retinopathy

Four synthetic peptides of 15 amino acids (aa), corresponding to sequences of the nodavirus DIEV RNA(2) protein, were chosen to test their potential immunogenicity in sea bass. Two of these included the N or C terminal regions (N-ter or C-ter) and the sequences of the others contained a potential external site (aa 127-140: Lp1 and as 266-279: Lp2). Two heat inactivated strains of nodavirus (HI Sb1 and HI Sb2), were used as positive controls and the carrier (KLH) as a negative control. ELISAs were performed to quantify serum antibodies specific to nodavirus, to peptides, and to the carrier in order to monitor their immunogenicity. All the fish reacted to the peptides C-Ter, Lp1 and Lp2 but only 55% of animals injected with N-ter produced specific antibodies. The proportion of fish that produced antibodies that cross reacted with nodavirus was very different with regard to the antigen injected: HI Sb1=88%; HI Sb2=85%; N-ter=38%; C-ter=27%. Protection against nodavirus was investigated by challenging the fish with a virulent viral suspension. The results showed that heat-inactivated Nodavirus protect fish and the N-ter peptide is a potential protective peptide. This initial approach showed that although vaccinating fish with peptides is possible, the tools and strategies of the research used in this field still need to be adapted to fish.