Fine mapping of a salmonid E2 alphavirus neutralizing epitope

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Salmonid alphavirus (SAV) poses a significant threat to aquaculture.
• The 17H23 monoclonal antibody (mAb) is crucial for SAV diagnosis, targeting the E2 glycoprotein.
• Previous studies suggested neutralizing epitopes are often located in Domain B of the E2 glycoprotein.

Purpose of the Study:

• To precisely characterize the epitope recognized by the neutralizing 17H23 mAb against the SAV E2 glycoprotein.
• To confirm the location of the 17H23 epitope within Domain B of the SAV E2 protein.
• To investigate the in vivo effects of mutations within the identified epitope.

Main Methods:

• Alanine scanning mutagenesis was employed to create ten mutant recombinant SAV (rSAV) strains.
• Mutant rSAVs were characterized in vitro using indirect immunofluorescence assays with specific mAbs.
• In vivo studies involved bath immersion of juvenile trout with mutant rSAVs to assess attenuation.

Main Results:

• Two mutant rSAVs (G and H) demonstrated resistance to neutralization by the 17H23 mAb.
• Mutant rSAVs D, E, and G showed complete attenuation, while mutant H was partially attenuated in juvenile trout.
• The data pinpointed the amino acid sequence (227)FTSDS(231) as the core epitope for the 17H23 mAb.

Conclusions:

• The study successfully mapped the 17H23 epitope to a specific amino acid sequence on the SAV E2 glycoprotein.
• This precise epitope characterization is vital for improving SAV diagnostic tools and developing targeted antiviral strategies.
• The identified epitope and its role in viral attenuation provide insights for future vaccine design against SAV.