A Linear Surface Epitope in a Proline-Rich Region of ORF3 Product of Genotype 1 Hepatitis E Virus

Multifunctional ORF3 protein of hepatitis E virus

Hepatitis E virus (HEV) is an emerging zoonotic pathogen that is transmitted primarily through the fecal-oral route and can cause acute hepatitis in humans. Since HEV was identified as a zoonotic pathogen, different species of HEV strains have been globally identified from various hosts, leading to an expanding range of hosts. The HEV genome consists of a 5' noncoding region, three open reading frames (ORFs), and a 3' noncoding region. The ORF3 protein is the smallest but has many functions in HEV release and pathogenesis. In this review, we systematically summarize recent progress in understanding the functions of the HEV ORF3 protein in virion release, biogenesis of quasi-enveloped viruses, antigenicity, and host environmental regulation. This review will help us to understand HEV replication and pathogenesis mechanisms better.

Hepatitis E Virus

Since the sequence of hepatitis E virus (HEV) was determined from a patient with enterically transmitted non-A, non-B hepatitis in 1989, similar sequences have been isolated from many different animals, including pigs, wild boars, deer, rabbits, bats, rats, chicken, and trout. All of these sequences have the same genomic organization, which contains open reading frames (ORFs) 1, 2, and 3, although their genomic sequences are variable. Some have proposed that they be classified as new family, Hepeviridae, which would be further divided into different genera and species according to their sequence variability. The size of these virus particles generally ranged from 27 to 34 nm. However, HEV virions produced in cell culture differ in structure from the viruses found in feces. Those from cell culture have a lipid envelope and either lack or have a little ORF3, whereas the viruses isolated from feces lack a lipid envelope but have ORF3 on their surfaces. Surprisingly, most of the secreted ORF2 proteins from both these sources are not associated with HEV RNA.

Development of a competitive ELISA for detecting antibodies against genotype 1 hepatitis E virus

Hepatitis E, a significant global public health issue in China, is caused by sporadic infections with regional hepatitis E virus (HEV) genotypes 1, 3, and 4. To date, most immunoassays currently used to test human sera for the presence of anti-HEV antibodies cannot identify HEV at the genotype level. However, such information would be useful for identifying the source of infecting virus. Therefore, here we describe the development of a competitive enzyme-linked immunosorbent assay (ELISA) for detecting anti-genotype 1 HEV antibodies in human sera. Using recombinant genotype 1 HEV ORF3 protein as immunogen, traditional hybridoma technology was employed to generate seven monoclonal antibodies (mAbs), of which two mAbs specifically reacted with the immunogen. One of these two mAbs, 1D2, was labeled with horseradish peroxidase (HRP) for use in competitive ELISA (cELISA). After cELISA optimization using a checkerboard assay design, the amount of ORF3^SAR-55 as coating antigen (100 ng/well), HRP-1D2 mAb concentration (1 μg/mL), and test serum dilution (1:10) were selected and a result ≥ 19.5 was used as the cutoff for a positive result. Importantly, cross-genotype cELISA results indicated that the cELISA could not detect anti-genotype 3 rabbit and 4 swine HEV antibodies. Moreover, human sera confirmed as negative for anti-HEV antibodies using the commercial ELISA kit were all negative via cELISA. However, because the commercial ELISA kit detects anti-all genotypes HEV antibodies and the cELISA only detects anti-genotype 1 HEV antibodies, the consistence rate of two assays detecting positive sera is low. In summary, here a cELISA for detecting anti-genotype 1 HEV antibodies was developed for use in epidemiological investigations of genotype 1 HEV infections in humans. KEY POINTS: • Seven mAbs were produced using genotype 1 HEV ORF3 protein as immunogen. • One mAb that specifically bound to genotype 1 HEV ORF3 protein was selected and labeled for use in a cELISA to detect anti-genotype 1 HEV antibodies. • The competitive ELISA developed here will aid clinical diagnosis of HEV infections and will be useful for large-scale serological testing of genotype 1 HEV infections in humans.

Open reading frame 3 protein of hepatitis E virus: Multi-function protein with endless potential

Hepatitis E virus (HEV), a fecal-orally transmitted foodborne viral pathogen, causes acute hepatitis in humans and is responsible for hepatitis E outbreaks worldwide. Since the identification of HEV as a zoonotic agent, this virus has been isolated from a variety of hosts with an ever-expanding host range. HEV-open reading frame (ORF) 3, the smallest ORF in HEV genomes, initially had been perceived as an unremarkable HEV accessory protein. However, as novel HEV-ORF3 function has been discovered that is related to the existence of a putative third virion structural form, referred to as “quasi-enveloped” HEV particles, HEV is challenging the conventional virion structure-based classification scheme, which assigns all viruses to two groups, “enveloped” or “non-enveloped”. In this review, we systematically describe recent progress that has identified multiple pathogenic roles of HEV-ORF3, including roles in HEV virion release, biogenesis of quasi-enveloped virus, regulation of the host innate immune response, and interference with host signaling pathways. In addition, implications of HEV-ORF3-associated quasi-enveloped virions are discussed to guide future development of improved vaccines against zoonotic HEV infection.

Advances in Hepatitis E Virus Biology and Pathogenesis

Hepatitis E virus (HEV) is one of the causative agents for liver inflammation across the world. HEV is a positive-sense single-stranded RNA virus. Human HEV strains mainly belong to four major genotypes in the genus Orthohepevirus A, family Hepeviridae. Among the four genotypes, genotype 1 and 2 are obligate human pathogens, and genotype 3 and 4 cause zoonotic infections. HEV infection with genotype 1 and 2 mainly presents as acute and self-limiting hepatitis in young adults. However, HEV infection of pregnant women with genotype 1 strains can be exacerbated to fulminant hepatitis, resulting in a high rate of case fatality. As pregnant women maintain the balance of maternal-fetal tolerance and effective immunity against invading pathogens, HEV infection with genotype 1 might dysregulate the balance and cause the adverse outcome. Furthermore, HEV infection with genotype 3 can be chronic in immunocompromised patients, with rapid progression, which has been a challenge since it was reported years ago. The virus has a complex interaction with the host cells in downregulating antiviral factors and recruiting elements to generate a conducive environment of replication. The virus-cell interactions at an early stage might determine the consequence of the infection. In this review, advances in HEV virology, viral life cycle, viral interference with the immune response, and the pathogenesis in pregnant women are discussed, and perspectives on these aspects are presented.

Vaccine Development against Zoonotic Hepatitis E Virus: Open Questions and Remaining Challenges

Hepatitis E virus (HEV) is a fecal-orally transmitted foodborne viral pathogen that causes acute hepatitis in humans and is responsible for hepatitis E outbreaks worldwide. Since the discovery of HEV as a zoonotic agent, this virus has been isolated from a variety of hosts with an ever-expanding host range. Recently, a subunit HEV vaccine developed for the prevention of human disease was approved in China, but is not yet available to the rest of the world. Meanwhile, notable progress and knowledge has been made and revealed in recent years to better understand HEV biology and infection, including discoveries of quasi-enveloped HEV virions and of a new function of the HEV-ORF3 product. However, the impact of these new findings on the development of a protective vaccine against zoonotic HEV infection requires further discussion. In this review, hallmark characteristics of HEV zoonosis, the history of HEV vaccine development, and recent discoveries in HEV virology are described. Moreover, special attention is focused on quasi-enveloped HEV virions and the potential role of the HEV-ORF3 product as antibody-neutralization target on the surface of quasi-enveloped HEV virions to provide new insights for the future development of improved vaccines against zoonotic HEV infection.

DESIGN OF HEPATITIS E VIRUS GENOTYPE 1 RECOMBINANT ORF3 PROTEIN BY CODON OPTIMIZATION METHOD

Aim. The development of the hepatitis E virus (HEV) genotype 1 full-size ORF3 recombinant polypeptide. Materials and methods. Escherichia coli strains, plasmid vectors, serological and clinical samples, ELISA reagent kits, molecular biological, bioinformatic, biotechnological, biochemical and serological methods. Results. HEV genotype 1 RNA had been isolated from clinical samples collected in Kyrgyzstan. DNA copy of subgenomic virus RNA had been cloned and used for further development of E.coli strains producing full-size recombinant protein ORF3 fused to E.coli beta-galactosidase. Codons optimization method was used in aim to increase expression level of recombinant protein. Recombinant protein ORF3 had been isolated from the inclusion bodies of the E.coli biomass and purified by size exclusion chromatography. Antigenic specificity of recombinant polypeptide had been confirmed by enzyme-linked immunosorbent assay and Western blotting with the specific sera. Conclusion. HEVgenotype 1 ORF3 recombinant antigen had been designed, and it’s applicability in diagnostic tests had been experimentally confirmed.