The enterically transmitted hepatitis E virus (HEV) adopts a unique strategy to exit cells by cloaking its capsid (encoded by the viral ORF2 gene) and circulating in the blood as "quasi-enveloped" particles. However, recent evidence suggests that the majority of the ORF2 protein present in the patient serum and supernatants of HEV-infected cell culture exists in a free form and is not associated with virus particles. The origin and biological functions of this secreted form of ORF2 (ORF2) are unknown. Here we show that production of ORF2 results from translation initiated at the previously presumed AUG start codon for the capsid protein, whereas translation of the actual capsid protein (ORF2) is initiated at a previously unrecognized internal AUG codon (15 codons downstream of the first AUG). The addition of 15 amino acids to the N terminus of the capsid protein creates a signal sequence that drives ORF2 secretion via the secretory pathway. Unlike ORF2, ORF2 is glycosylated and exists as a dimer. Nonetheless, ORF2 exhibits substantial antigenic overlap with the capsid, but the epitopes predicted to bind the putative cell receptor are lost. Consistent with this, ORF2 does not block HEV cell entry but inhibits antibody-mediated neutralization. These results reveal a previously unrecognized aspect in HEV biology and shed new light on the immune evasion mechanisms and pathogenesis of this virus.

Background: The E2s domain of hepatitis E virus (HEV) capsid protein is the major target for antibody response. Results: Six antigenic sites of the E2s domain were identified by constructing, clustering, and characterizing a tool box containing representative anti-HEV monoclonal antibodies. Conclusion:The comprehensive functional epitopes of E2s domain were identified. Significance: This study provided a novel method for the comprehensive characterization of conformational antigenic domains.

Hepatitis E virus (HEV) is a serious public health problem. The commonly used tests that are specific for current HEV infection diagnosis include the detection of anti-HEV IgM and HEV RNA. Here, we report an improved enzyme-linked immunosorbent assay (ELISA) method for HEV antigen detection with a linear range equivalent to 6.3 ؋ 10 3 to 9.2 ؋ 10 5 RNA copies per ml. The monoclonal antibody (MAb) 12F12, a high-ability MAb that binds HEV virus, was selected as the capture antibody from a panel of 95 MAbs. The positive period of HEV antigenemia in infected monkeys using this test was, on average, 3 weeks longer than previously reported and covered the majority of the acute phase. The positive detection rates of IgM, RNA, and new antigen from the first serum samples collected from 16 confirmed acute hepatitis E patients were 81% (13/16), 81% (13/16), and 100% (16/16), respectively. In three patients, the initial serum specimens that tested negative for IgM, despite the presence of symptoms of acute hepatitis and elevated alanine aminotransferase (ALT) levels, were positive for HEV antigen and HEV RNA. In contrast, the serum samples of the three RNA-negative patients were antigen positive (and IgM positive), possibly due to the degradation of HEV nucleic acids. Our results suggest that this new antigen detection method has acceptable concordance with RNA detection and could serve as an important tool for diagnosing acute hepatitis E. H epatitis E is an enterically transmitted viral hepatitis caused by hepatitis E virus (HEV) infection (1). Hepatitis E is a serious public health problem in many countries (especially developing countries), with a mortality rate of approximately 20 to 25% among pregnant women (2). HEV is a 34-nm, nonenveloped, and icosahedral virus (3) with a 7.2-kb positive-sense single-stranded RNA genome containing three open reading frames. Open reading frame 2 (ORF2) (660 amino acids) encodes the major viral capsid (4). Mammalian HEV is divided into four genotypes with distinct geographic distributions and prevalences (5, 6).Most patients with acute hepatitis E infection present with typical acute hepatitis symptoms, such as jaundice and dark urine. Typical biochemical changes in acute HEV patients include increased serum levels of alanine aminotransferase and aspartate aminotransferase (ALT and AST, respectively) and bilirubin; however, these factors are not specific for hepatitis E, as increases also occur due to other viral and nonviral forms of liver injury. The most commonly used tests specific for diagnosing HEV infection detect anti-HEV IgM and HEV RNA. In acute hepatitis E patients, anti-HEV IgM can typically be detected within 3 to 4 days after the onset of jaundice and can persist for an average of 5 months (7). The presence of anti-HEV IgM provides evidence of recent HEV infection; however, its short detection period indicates that anti-HEV IgM is unsuitable as a single marker for current infection in acute hepatitis E patients. In contrast, the detection of HEV RNA provides a specific ...

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