Identification of structural proteins of koi herpesvirus.

As a prerequisite for development of improved vaccines and diagnostic tools for control of the fish pathogen koi herpesvirus, or cyprinid herpesvirus 3 (CyHV-3), we have started to identify putative viral envelope and capsid proteins. The complete or partial CyHV-3 open reading frames ORF25, ORF65, ORF92, ORF99, ORF136, ORF138, ORF146, ORF148, and ORF149 were expressed as bacterial fusion proteins, which were then used for preparation of monospecific rabbit antisera. All of the sera that were obtained detected their target proteins in cells transfected with the corresponding eukaryotic expression plasmids. However, only the type I membrane proteins pORF25, pORF65, pORF99, pORF136 and pORF149 and the major capsid protein pORF92 were sufficiently abundant and immunogenic to permit unambiguous detection in CyHV-3-infected cells. In indirect immunofluorescence tests (IIFT), sera from naturally or experimentally CyHV-3-infected carp and koi predominantly reacted with cells transfected with expression plasmids encoding pORF25, pORF65, pORF148, and pORF149, which represent a family of related CyHV-3 membrane proteins. Moreover, several neutralizing monoclonal antibodies raised against CyHV-3 virions proved to be specific for pORF149 in IIFT of transfected cells and in immunoelectron microscopic analysis of CyHV-3 particles. Since pORF149 appears to be an immunorelevant envelope protein of CyHV-3, a recombinant baculovirus was generated for its expression in insect cells, and pORF149 was shown to be incorporated into pseudotyped baculovirus particles, which might be suitable as diagnostic tools or subunit vaccines.