Replication steps in the HEV life cycle are not easily elucidated due to lack of a suitable cell culture system. However, proposed replication cycle commences with the viral attachment to the surface of target cells (hepatocyte) and binding to the unknown receptor(s). Next, the virus penetrates, uncoats, and releases the genomic RNA. Translation of the nonstructural proteins occurs in the cytoplasm. RdRp synthesizes the negative-sense intermediate RNA from the positive-sense genome, which subsequently acts as a template for the synthesis of subgenomic RNA and the full-length positive-sense transcripts. The subgenomic RNA is then translated into ORF2 and ORF3 proteins, which facilitates viral assembly and optimizes the host cell environment for viral replication[11,12]. The mechanism of viral egress from the host cells remains unclear[15,16].
Go to:
IMMUNE RESPONSES IN HEV INFECTION
Investigation of host immune responses against virus infection are essential to understand host immunity and for vaccine development. Several studies have examined the host immune responses following HEV infection and the roles of immune components responsible for causing liver damage as a consequence of HEV infection. Although the mechanisms of hepatic injury enhanced by the host immune responses to HEV infection are still unclear[17-19], we review here the available literatures on HEV infection and how it affects host immunity and induction of liver injury.
Once HEV enters the body, viral clearance involves recruitment of immune cells against infection. These cells recognize HEV in the early stages through pattern recognition receptors. HEV components are then detected by toll-like receptors and retinoic acid-inducible gene-I like receptors. Subsequent recruitment of adapter proteins MyD88 and TRIF mediate interferon regulatory transcription factor 3 (IRF3) and nuclear factor κB (NF-κB) to produce type I interferons and pro-inflammatory cytokines vital to antiviral response[20].