Monoclonal antibodies to infectious pancreatic necrosis virus: analysis of viral epitopes and comparison of different isolates.

A panel of five monoclonal antibodies (MAbs) produced against the West Buxton isolate of infectious pancreatic necrosis virus was used to investigate viral antigens and to compare different aquatic birnavirus isolates antigenically. Reciprocal blocking ELISA and neutralization assays indicated that these MAbs identified four, and possibly five, structurally and/or functionally different epitopes on the virion. Western immunoblot analysis demonstrated that one epitope was present on VP2, the large (51,000 mol. wt., 51K) capsid protein, and another epitope was located on the two smallest structural proteins, VP3 (32K) and VP4 (30K). Three MAbs did not react with any of the solubilized viral proteins; the epitopes recognized by these MAbs may have been altered when the virion was solubilized with SDS. Comparison of reactivity patterns of the five MAbs with various aquatic birnaviruses in ELISA and neutralization tests demonstrated that 14 isolates tested from four serotypes represented a minimum of nine antigenically distinct viruses; i.e., distinct patterns of reactivity were shown among several viruses within the same serotype. Two MAbs identified different epitopes that were highly conserved among, and largely restricted to, members of the West Buxton (U.S.A.) serotype, whereas two other MAbs recognized an epitope(s) present only on some members of this serotype. The other MAb defined an epitope that was more widely distributed among the aquatic birnaviruses and found on all representatives tested from two serotypes.