Antiserum generated by DNA vaccine binds to hepatitis E virus (HEV) as determined by PCR and immune electron microscopy (IEM): application for HEV detection by affinity-capture RT-PCR

Previously, we have described that injection of an expression vector containing hepatitis E virus (HEV) open reading frame 2 (HEV-ORF-2) generated a strong antibody response in mice. To characterize the reaction of this antiserum with native HEV and to evaluate its potential diagnostic application, we tested the antiserum's ability to bind HEV using immune electron microscope (IEM) and affinity-capture reverse transcription polymerase chain reaction (RT-PCR) amplification. Antiserum to ORF-2 aggregated HEV virions as seen by electron microscopy, providing direct evidence that ORF-2 encodes a structural protein. Antiserum also captured HEV for RT-PCR amplification. This antiserum bound HEV from diverse origins (Asia, Africa, Mexico) at virus concentrations found in patient fecal specimens and bile from inoculated non-human primates. The specificity of the affinity binding was demonstrated when pre-immune sera or sera collected from mice injected with control DNA vector (lacking the HEV ORF-2 gene) failed to bind HEV for RT-PCR amplification and IEM. Specific RT-PCR amplification was confirmed by restriction enzyme digestion of PCR products. The sensitivity of the binding was evaluated by RT-PCR amplification of serially diluted bile containing a genetically divergent HEV, Mexico'86. HEV was detected in a 10(-8) dilution of this bile. This is the first report that antibodies elicited by a DNA vaccine recognize native HEV. Our results indicate that ORF-2 encodes a structural protein and that antiserum to this protein enables simple, sensitive, and specific HEV detection by affinity-capture RT-PCR. (C) 1999 Elsevier Science B.V. All rights reserved.