Infectious Pancreatic NEcrosis Virus - Immunogenicity, Virion Integrity and Virus/Cell Interaction

Abstract: Viruses are ubiquitous in all environments where life is present, also in aquatic environments. The fish-pathogenic virus, Infectious pancreatic necrosis virus (IPNV), has generally been studied because it causes high mortality amongst hatchery-reared salmonids in aqua culture facilities around the world. Today, no efficient vaccine is available to protect the fish from becoming infected. The virus is a double-stranded, unenveloped RNA virus. The icosahedral capsid is composed of multimeres of a single protein, VP2. Because of its external localization in the viral capsid, neutralizing antibodies target this protein. The position of VP2 makes it a good candidate in the research for a protective vaccine. We studied the properties of two sets of antibodies, obtained from rabbits immunized with either VP2 isolated from infectious virions, or recombinantly synthesized in Escherichia coli. Interestingly, despite that both sets of immunsera recognized and bound to VP2 with the same intensity and strength, only the sera obtained from rabbits immunized with authentic VP2 were able to neutralize the virus. We believe that the presence of O-linked sugar residues on the authentic VP2 is a part of the epitopes that are recognized by neutralizing antibodies. Neutralizing sera caused quantitative aggregation of virions. Immuno-goldlabelling studies in EM showed that a fraction of antibodies in this sera recognized the verticis of the virions. The lectin SBA also preferentially recognized this region. The virion stability might also depend on the low level of glycosylation. Virions treated with the oxidative reagent sodium periodate either lost their integrity and formed aggregates or displayed a reduction in specific infectivity as compared with control virus. The cellular receptor that IPNV utilizes for entry is not known. By using virus overlay protein binding assays (VOPBA) IPNV bound to three cellular components with a relative molecular weights of 210, 110 and 70 K.