Antigenicity of a recombinant capsid protein from an Italian swine HEV strain

Hepatitis E virus (HEV) is a single-stranded, positive-sense RNA virus. The genome contains three ORFs, of which ORF2 encodes the major structural capsid protein PORF2. HEV is responsible for sporadic infections as well as large epidemics of acute viral hepatitis in developing countries, and is emerging in industrialized areas where it accounts for an increasing number of sporadic cases. Recent observations of indigenous cases in developed regions suggest that pigs may act as a zoonotic source and reservoir of infection. This hypothesis is also supported by the high genetic similarity between human and swine HEV strains circulating in the same geographical areas. In 2006, we investigated the presence of HEV in swine farms in Northern Italy. The results of molecular diagnosis indicated a wide presence of genotype 3 HEV strains, the genotype predominating in pigs in industrialized areas. We expressed a 111-aa deletion fragment of the capsid protein PORF2 of an Italian swine HEV strain in a recombinant baculovirus system using Sf9 insect cells. The 55 kDa recombinant PORF2 did not self-assemble as virus-like particles in insect cells, but was produced at high levels in the cytoplasm and supernatant of cells, as demonstrated by immunocytochemical (ICC) staining and by Western blotting (WB) with immune animal sera. The PORF2 protein was used to produce hyperimmune sera and a panel of monoclonal antibodies (MAbs), which were selected by ELISA. The results showed that the expressed HEV protein is immunogenic and is specifically recognized by MAbs using different assay, including WB and ICC. Further study are being conducted to characterize the MAbs and PORF2.