Expression and antigenic characterization of the major core protein VP7 of Chuzan virus, a member of the Palyam serogroup orbiviruses

The Palyam serogroup-specific antigen, VP7, of Chuzan virus strain K-47 was expressed in insect cells by a recombinant baculovirus. The expressed protein appeared as a single band of 38kDa corresponding to the predicted molecular mass of Chuzan virus VP7 by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). In immunoprecipitation analysis, the recombinant VP7 was not only recognized by all polyclonal antibodies against the Palyam serogroup viruses (PALV) tested in this study, but also by antisera to bluetongue virus (BTV) serotype 1, epizootic haemorrhagic disease virus (EHDV) serotypes 1 and 2. However, in Western immunoblot assay, no positive signals were observed between this protein and these antisera, even in the homologous reaction using antiserum to Chuzan virus. These findings demonstrate that the common antigenic determinants on the VP7 proteins of Chuzan virus and the other PALV serotypes are mainly conformational and that the proteins share some epitopes with those of BTV and EHDV beyond the serogroup. No cross-reactivities were detected between Chuzan virus VP7 and antisera to BTV and EHDV in agar gel immunodiffusion (AGID) and indirect ELISA tests, indicating that the recombinant VP7 is useful as a diagnostic reagent for serological tests of congenital abnormalities of cattle caused by PALV.