Formation of infectious pancreatic necrosis virus-like particles followingexpression of segment A by recombinant Semliki Forest virus

Segment A of the Sp strain (a Norwegian field isolate) of infectious pancre atic necrosis virus (IPNV) was amplified by reverse transcriptase polymeras e chain reaction in two stages from RNA isolated from infected cells, and c loned into the Semliki Forest virus (SFV) expression vector pSFV1. Expressi on and correct processing of IPNV proteins was confirmed by transfection of RNA transcribed from this plasmid into BHK cells. This clone was then used to produce recombinant replication-defective SFV particles (rSFV) expressi ng the IPNV segment A. Immunofluorescence studies with conformation-depende nt monoclonal antibodies to IPNV confirmed that the recombinant proteins pr oduced after infection of the salmonid cell line CHSE-214 with such rSFV re tain their antigenicity. Infection of the CHSE cells with the rSFV resulted in the formation of IPNV-like particles, which were similar in size and mo rphology to IPNV.