Immunogenic potential of a membrane protein encoded by the viral gene located at ORF 81 of Cyprinid Herpesvirus-3

Cyprinid herpesvirus 3 (CyHV-3) is the causative agent of koi herpesvirus diseases (KHVD), a notifiable condition associated with mass mortalities in koi and common carp (Cyprinus carpio L.). Open reading frame 81 (ORF 81) encodes a well characterized nonglycosylated membrane protein of CyHV-3 that is thought to be highly immunogenic due to its C-terminal hydrophilic domain. To test its immunogenic potential, ORF 81 was cloned into a DNA vaccine vector and administered to common carp by intramuscular injection. To assess the protective immunity of the vaccinated carps, antibody titres against CyHV-3 following immunization were measured by ELISA and fish were submitted to a viral challenge. Additionally, a Western Blot was carried out using purified recombinant pORF81 and sera from vaccinated, infected and uninfected fish. Although the gene was found to be reliably transcribed in vitro and in vivo, no antibody response could be detected in vivo following vaccination using the existing method. These results call into question the immunogenicity of the protein derived from ORF 81 of CyHV-3 or suggest that this protein only induces antibody titres that remain below the limit of detection.