Hepatitis E virus (HEV) is a pathogenic agent that causes fecally-oral
ly transmitted acute hepatitis. The genome, a single-stranded positive
-sense RNA encodes three forward open reading frames (ORFs), in which
an approximately 2-kb structural protein is located in the 3' end, To
produce HEV-like particles the structural protein, with its N terminus
truncated (amino acid residues 112 to 660 of ORF2), was expressed in
insect Tn5 cells by a recombinant baculovirus, In addition to the prim
ary translation product with a molecular mass of 58 kDa, a large amoun
t of a further-processed molecule with a molecular mass of 50 kDa was
generated and efficiently released into the culture medium, Electron m
icroscopic observation of the culture medium revealed that the 50-kDa
protein self-assembled to form empty virus-like particles (VLPs), The
buoyant density of the VLPs in CsCl was 1.285 g/cm(3) and their diamet
er was 23.7 nm, a little smaller than the 27 nm of native HEV particle
s secreted into the bile or stools of experimentally infected monkeys,
The yield of the VLPs was 1 mg per 10(7) cells as a purified form, Th
e particles possess antigenicity similar to that of authentic HEV part
icles and, consequently, they appear to be a good antigen for the sens
itive detection of HEV-specific immunoglobulin G (IgG) and IgM antibod
ies, Furthermore, the VLP may be the most promising candidate get for
an HEV vaccine, owing to its potent immunogenicity.