Characterization of self-assembled virus-like particles of rat hepatitis E virus generated by recombinant baculoviruses

Ferret hepatitis E virus (HEV), a novel hepatitis E-like virus, has been identified in ferrets in The Netherlands. Due to the lack of a cell-culture system for ferret HEV, the antigenicity, pathogenicity and epidemiology of this virus have remained unclear. In the present study, we used a recombinant baculovirus expression system to express the 112-N-terminus and 47-C-terminus-amino-acid-truncated ferret HEV ORF2 protein in insect Tn5 cells, and found that a large amount of a 53 kDa protein (F-p53) was expressed and efficiently released into the supernatant. Electron microscopic analysis revealed that F-p53 was self-assembled into virus-like particles (ferret HEV-LPs). These ferret HEV-LPs were estimated to be 24 nm in diameter, which is similar to the size of G1, G3, G4 and rat HEV-LPs derived from both the N-terminus- and C-terminus-truncated constructs. Antigenic analysis demonstrated that ferret HEV-LPs were cross-reactive with G1, G3, G4 and rat HEVs, and rat HEV and ferret HEV showed a stronger cross-reactivity to each other than either did to human HEV genotypes. However, the antibody against ferret HEV-LPs does not neutralize G3 HEV, suggesting that the serotypes of these two HEVs are different. An ELISA for detection of anti-ferret HEV IgG and IgM antibodies was established using ferret HEV-LPs as antigen, and this assay system will be useful for monitoring ferret HEV infection in ferrets as well as other animals. In addition, analysis of ferret HEV RNA detected in ferret sera collected from a breeding colony in the USA revealed the genetic diversity of ferret HEV.