Hepatitis E genotype 4 virus from feces of monkeys infected experimentally can be cultured in PLC/PRF/5 cells and upregulate host interferon-inducible genes

Research Progress on Hepatitis E Virus Culture

Hepatitis E virus (HEV) is a zoonotic pathogen and the main cause of acute viral hepatitis in China, resulting in a significant burden on public health. Developing a highly efficient in vitro culture system for HEV is crucial for understanding the determinants of HEV infection in humans and other animals, the pathogenic mechanisms, as well as the screening and evaluation of antiviral drugs. In this paper, the research progress on HEV in vitro culture systems is reviewed to provide a convenient reference for further research on HEV, aiding comprehensive efforts toward the widespread prevention and control of related diseases.

Hepatitis E virus: from innate sensing to adaptive immune responses

Hepatitis E virus (HEV) infections are a major cause of acute viral hepatitis in humans worldwide. In immunocompetent individuals, the majority of HEV infections remain asymptomatic and lead to spontaneous clearance of the virus, and only a minority of individuals with infection (5-16%) experience symptoms of acute viral hepatitis. However, HEV infections can cause up to 30% mortality in pregnant women, become chronic in immunocompromised patients and cause extrahepatic manifestations. A growing body of evidence suggests that the host immune response to infection with different HEV genotypes is a critical determinant of distinct HEV infection outcomes. In this Review, we summarize key components of the innate and adaptive immune responses to HEV, including the underlying immunological mechanisms of HEV associated with acute and chronic liver failure and interactions between T cell and B cell responses. In addition, we discuss the current status of vaccines against HEV and raise outstanding questions regarding the immune responses induced by HEV and treatment of the disease, highlighting areas for future investigation.

Identification of interferon-stimulated genes with modulated expression during hepatitis E virus infection in pig liver tissues and human HepaRG cells

Introduction

Hepatitis E virus (HEV) is a common cause of enterically transmitted acute hepatitis worldwide. The virus is transmitted by the fecal-oral route via the consumption of contaminated water supplies and is also a zoonotic foodborne pathogen. Swine are the main reservoir of zoonotic HEV. In humans, HEV infection is usually asymptomatic or causes acute hepatitis that is self-limited. However, fulminant hepatic failure and chronic cases of HEV infection can occur in some patients. In contrast, HEV infection in pigs remains asymptomatic, although the virus replicates efficiently, suggesting that swine are able to control the virus pathogenesis. Upon viral infection, IFN is secreted and activates cellular pathways leading to the expression of many IFN-stimulated genes (ISGs). ISGs can restrict the replication of specific viruses and establish an antiviral state within infected and neighboring cells.

Methods

In this study, we used PCR arrays to determine the expression level of up to 168 ISGs and other IFN-related genes in the liver tissues of pigs infected with zoonotic HEV-3c and HEV-3f and in human bipotent liver HepaRG cells persistently infected with HEV-3f.

Results and discussion

The expression of 12 and 25 ISGs was found to be up-regulated in infected swine livers and HepaRG cells, respectively. The expression of CXCL10, IFIT2, MX2, OASL and OAS2 was up-regulated in both species. Increased expression of IFI16 mRNA was also found in swine liver tissues. This study contributes to the identification of potential ISGs that could play a role in the control or persistence of HEV infection.

Combined inhibitory effect of interferon and antiserum on avian hepatitis E virus

Epidemiologic investigations in recent years have shown that the detection rate of avian hepatitis E virus (HEV) in chicken flocks is increasing in China. Nevertheless, effective prevention and control measures are still lacking. In this study, specific pathogen-free (SPF) chicken serum against HEV was prepared using recombinant HEV open reading frames (ORF2 and ORF3) proteins as immunogens. An SPF chicken infection model was established by intravenous inoculation of chick embryos. Swab samples were collected at 7, 14, 21, and 28 d of age and used to detect avian HEV load, along with other indicators, by fluorescence quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) assay. The therapeutic effects on blocking vertical HEV transmission were observed, by using the methods of antibody application alone, mixed, or combined application of each of the 2 antibodies with type I interferon. The results showed that type I interferon alone or in combination with antiserum reduced the positive rate of HEV from 100 to 62.5% and 25%, respectively. However, the avian HEV-positivity rate was reduced to 75, 50, and 37.5% after type I interferon was used alone or in combination with antisera against ORF2 and ORF3, respectively. The inhibitory effect of type I interferon alone or in combination with an antiserum, on HEV replication was more significant in cells than in vivo. In this study, the inhibitory effect of type I interferon alone or in combination with an antiserum on avian HEV replication was observed in vitro and in vivo, providing the necessary technical reserve for disease prevention and control.

HEV Cell Culture

Cell culture is an important research method in virology. Although many attempts have been conducted to culture HEV in cells, only a few cell culture systems were considered to be efficient enough for usage. Concentration of virus stocks, host cells, and medium components affects the culture efficiency and the genetic mutations during HEV passage were found to be associated with the increased virulence in cell culture. As an alternative method for traditional cell culture, the infectious cDNA clones were constructed. The viral thermal stability, factors that impact the host range, post-translation of viral proteins, and function of different viral proteins were studied using the infectious cDNA clones. HEV cell culture studies on progeny virus showed that the viruses secreted from host cells have an envelope and its formation was associated with pORF3. This result explained the phenomenon that virus could infect host cells in the presence of anti-HEV antibodies.

Immunobiology and Host Response to HEV

Hepatitis E virus (HEV) usually causes acute self-limiting hepatitis but sometimes leads to chronic infection in immunocompromised persons. HEV is not directly cytopathic. Immunologically mediated events after HEV infection are believed to play important roles in the pathogenesis and clearance of infection. The anti-HEV antibody responses have been largely clarified since the determination of major antigenic determinant of HEV, which is located in the C-terminal portion of ORF2. This major antigenic determinant also forms the conformational neutralization epitopes. Robust anti-HEV immunoglobulin M (IgM) and IgG responses usually develop 3-4 weeks after infection in experimentally infected nonhuman primates. In humans, potent specific IgM and IgG responses occur in the very early phase of the disease and are critical in eliminating the virus, in concert with the innate and adaptive T-cell immune responses. Testing anti-HEV IgM is valuable in the diagnosis of acute hepatitis E. The long-term persistence and protection of anti-HEV IgG provide the basis for estimating the prevalence of HEV infection and for the development of a hepatitis E vaccine. Although human HEV has four genotypes, all the viral strains are considered to belong to a single serotype. It is becoming increasingly clear that the innate and adaptive T-cell immune responses play critical roles in the clearance of the virus. Potent and multispecific CD4+ and CD8+ T cell responses to the ORF2 protein occur in patients with acute hepatitis E, and weaker HEV-specific CD4+ and CD8+ T cell responses appear to be associated with chronic hepatitis E in immunocompromised individuals.

The mitochondrial gene-CMPK2 functions as a rheostat for macrophage homeostasis

In addition to their role in cellular energy production, mitochondria are increasingly recognized as regulators of the innate immune response of phagocytes. Here, we demonstrate that altering expression levels of the mitochondria-associated enzyme, cytidine monophosphate kinase 2 (CMPK2), disrupts mitochondrial physiology and significantly deregulates the resting immune homeostasis of macrophages. Both CMPK2 silenced and constitutively overexpressing macrophage lines portray mitochondrial stress with marked depolarization of their membrane potential, enhanced reactive oxygen species (ROS), and disturbed architecture culminating in the enhanced expression of the pro-inflammatory genes IL1β, TNFα, and IL8. Interestingly, the long-term modulation of CMPK2 expression resulted in an increased glycolytic flux of macrophages akin to the altered physiological state of activated M1 macrophages. While infection-induced inflammation for restricting pathogens is regulated, our observation of a total dysregulation of basal inflammation by bidirectional alteration of CMPK2 expression only highlights the critical role of this gene in mitochondria-mediated control of inflammation.

Characterization of highly expressed novel hub genes in hepatitis E virus chronicity in rabbits: a bioinformatics and experimental analysis

BACKGROUND

Hepatitis E virus (HEV), which is the leading cause of acute viral hepatitis worldwide, usually causes self-limited infections in common individuals. However, it can lead to chronic infection in immunocompromised individuals and its mechanisms remain unclear. Rabbits are the natural host of HEV, and chronic HEV infections have been observed in rabbits. Therefore, we aimed to investigate potential key genes in HEV chronicity process in rabbits. In this study, both bioinformatics and experimental analysis were performed to deepen the understanding of hub genes in HEV chronic infection in rabbits.

RESULTS

Ninety-four candidate differentially expressed genes (DEGs) and the pathways they enriched were identified to be related with HEV chronicity. A total of 10 hub genes were found by protein-protein interaction (PPI) network construction. Rabbits of group P (n = 4) which showed symptoms of chronic HEV infection were selected to be compared with HEV negative rabbits (group N, n = 6). By detecting the identified hub genes in groups P and N by real-time PCR, we found that the expressions of MX1, OAS2 and IFI44 were significantly higher in group P (P < 0.05).

CONCLUSIONS

In this work, we presented that MX1, OAS2 and IFI44 were significantly upregulated in HEV chronic infected rabbits, indicating that they may be involved in the pathogenesis of HEV chronicity.

A Role for the Chicken Interferon-Stimulated Gene CMPK2 in the Host Response Against Virus Infection

Virus infection can lead to the production of interferon, which activates the JAK/STAT pathway and induces the expression of multiple downstream interferon-stimulated genes (ISGs) to achieve their antiviral function. Cytidine/uridine monophosphate kinase 2 (CMPK2) gene has been identified as an ISG in human and fish, and is also known as a rate-limiting enzyme in mitochondria to maintain intracellular UTP/CTP levels, which is necessary for de novo mitochondrial DNA synthesis. By mining previous microarray data, it was found that both Avian Influenza Virus (AIV) and Newcastle Disease Virus (NDV) infection can lead to the significant upregulation of chicken CMPK2 gene. However, little is known about the function of CMPK2 gene in chickens. In the present study, the open reading frame (ORF) of chicken CMPK2 (chCMPK2) was cloned from DF-1, a chicken embryo fibroblasts cell line, and subjected to further analysis. Sequence analysis showed that chCMPK2 shared high similarity in amino acid with CMPK2 sequences from all the other species, especially reptiles. A thymidylate kinase (TMK) domain was identified in the C-terminus of chCMPK2, which is highly conserved among all species. In vitro, AIV infection induced significant increases in chCMPK2 expression in DF-1, HD11, and the chicken embryonic fibroblasts (CEF), while obvious increase only detected in DF-1 cells and CEF cells after NDV infection. In vivo, the expression levels of chCMPK2 were up-regulated in several tissues from AIV infected chickens, especially the brain, spleen, bursa, kidney, intestine, heart and thymus, and notable increase of chCMPK2 was detected in the bursa, kidney, duodenum, lung, heart, and thymus during NDV infection. Here, using MDA5 and IFN-β knockdown cells, we demonstrated that as a novel ISG, chCMPK2 could be regulated by the MDA5/IFN-β pathway. The high expression level of exogenous chCMPK2 displayed inhibitory effects on AIV and NDV as well as reduced viral RNA in infected cells. We further demonstrated that Asp135, a key site on the TMK catalytic domain, was identified as critical for the antiviral activities of chCMPK2. Taken together, these data demonstrated that chCMPK2 is involved in the chicken immune system and may play important roles in host anti-viral responses.

Cell Culture Isolation and Whole Genome Characterization of Hepatitis E Virus Strains from Wild Boars in Germany

Infection with hepatitis E virus (HEV) can cause acute and chronic hepatitis in humans. The HEV genotype 3 can be zoonotically transmitted from animals to humans, with wild boars representing an important reservoir species. Cell culture isolation of HEV is generally difficult and mainly described for human isolates so far. Here, five sera and five liver samples from HEV-RNA-positive wild boar samples were inoculated onto PLC/PRF/5 cells, incubated for 3 months and thereafter passaged for additional 6 weeks. As demonstrated by RT-qPCR, immunofluorescence and immune electron microscopy, virus was successfully isolated from two liver samples, which originally contained high HEV genome copy numbers. Both isolates showed slower growth than the culture-adapted HEV strain 47832c. In contrast to this strain, the isolated strains had no insertions in their hypervariable genome region. Next generation sequencing using an HEV sequence-enriched library enabled full genome sequencing. Strain Wb108/17 belongs to subtype 3f and strain Wb257/17 to a tentative novel subtype recently described in Italian wild boars. The results indicate that HEV can be successfully isolated in cell culture from wild boar samples containing high HEV genome copy numbers. The isolates may be used further to study the zoonotic potential of wild boar-derived HEV subtypes.

UMP-CMP kinase 2 gene expression in macrophages is dependent on the IRF3-IFNAR signaling axis

Toll-like receptors (TLRs) are highly-conserved pattern recognition receptors that mediate innate immune responses to invading pathogens and endogenous danger signals released from damaged and dying cells. Activation of TLRs trigger downstream signaling cascades, that culminate in the activation of interferon regulatory factors (IRFs), which subsequently leads to type I interferon (IFN) response. In the current study, we sought to expand the scope of gene expression changes in THP1-derived macrophages upon TLR4 activation and to identify interferon-stimulated genes. RNA-seq analysis led to the identification of several known and novel differentially expressed genes, including CMPK2, particularly in association with type I IFN signaling. We performed an in-depth characterization of CMPK2 expression, a nucleoside monophosphate kinase that supplies intracellular UTP/CTP for nucleic acid synthesis in response to type I IFN signaling in macrophages. CMPK2 was significantly induced at both RNA and protein levels upon stimulation with TLR4 ligand-LPS and TLR3 ligand-Poly (I:C). Confocal microscopy and subcellular fractionation indicated CMPK2 localization in both cytoplasm and mitochondria of THP-1 macrophages. Furthermore, neutralizing antibody-based inhibition of IFNAR receptor in THP-1 cells and BMDMs derived from IFNAR KO and IRF3 KO knockout mice further revealed that CMPK2 expression is dependent on LPS/Poly (I:C) mediated IRF3- type I interferon signaling. In summary, our findings suggest that CMPK2 is a potential interferon-stimulated gene in THP-1 macrophages and that CMPK2 may facilitate IRF3- type I IFN-dependent anti-bacterial and anti-viral roles.

CMPK2 accelerates liver ischemia/reperfusion injury via the NLRP3 signaling pathway

Cytidine monophosphate kinase 2 (CMPK2) is a mitochondrial nucleotide monophosphate kinase which is important for the substrates of mitochondrial DNA synthesis and has been reported to participate in macrophage activation and the inflammatory response. The purpose of the present research was to determine the potential role of CMPK2 in hepatic ischemia/reperfusion (I/R) injury and to elucidate the underlying molecular mechanisms. The present study investigated the role of CMPK2 in regulating the NLRP3 pathway and liver dysfunction induced by hepatic I/R both in vivo and in vitro. It was revealed that hypoxia/reoxygenation (H/R) treatment enhanced the mRNA expression levels of CMPK2, NLRP3, IL-18, IL-1β and TNF-α in RAW 264.7 cells. The protein expression levels of IL-18, IL-1β and cleaved-caspase-1 were decreased following CMPK2 knockdown. Furthermore, the inhibition of AIM2 downregulated the expression level of IL-1β, IL-18 and cleaved-caspase-1 in the CMPK2 knockdown group followed by H/R treatment, while the inhibition of NLRP3 did not. CMPK2 deficiency also decreased alanine aminotransferase and aspartate aminotransferase expression in mice serum, as well as the pathological changes in the liver. Similarly, the release of IL-18 and IL-1β in mouse serum was also restrained with the decline of CMPK2. In conclusion, the results of the present study demonstrate that CMPK2 is indispensable for NLRP3 inflammasome activation, making CMPK2 an effective target to relieve the liver from I/R injury. In addition, the function of CMPK2 is closely associated with NLRP3 inflammasome activation, instead of AIM2.

A Bioinformatic Analysis of Correlations between Polymeric Immunoglobulin Receptor (PIGR) and Liver Fibrosis Progression

OBJECTIVE

This study is aimed at investigating the enriched functions of polymeric immunoglobulin receptor (PIGR) and its correlations with liver fibrosis stage.

METHODS

PIGR mRNA expression in normal liver, liver fibrosis, hepatic stellate cells (HSCs), and hepatitis virus infection samples was calculated in Gene Expression Omnibus (GEO) and Oncomine databases. Enrichment analysis of PIGR-related genes was conducted in Metascape and Gene Set Enrichment Analysis (GSEA). Logistic model and ROC curve were performed to evaluate the correlations between pIgR and liver fibrosis.

RESULTS

PIGR mRNA was upregulated in advanced liver fibrosis, cirrhosis compared to normal liver (all p < 0.05). PIGR mRNA was also overexpressed in activated HSCs compared to senescent HSCs, liver stem/progenitor cells, and reverted HSCs (all p < 0.05). Enrichment analysis revealed that PIGR-related genes involved in the defense response to virus and interferon (IFN) signaling. In GEO series, PIGR mRNA was also upregulated by hepatitis virus B, C, D, and E infection (all p < 0.05). After adjusting age and gender, multivariate logistic regression models revealed that high PIGR in the liver was a risk factor for liver fibrosis (OR = 82.2, p < 0.001). The area under curve (AUC), positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity of PIGR for liver fibrosis stage >2 were 0.84, 0.86, 0.7, 0.61, and 0.90.

CONCLUSION

PIGR was correlated with liver fibrosis and might involve in hepatitis virus infection and HSC transdifferentiation.

CMPK2 of triploid crucian carp is involved in immune defense against bacterial infection

Cytidine/uridine monophosphate kinase 2 (CMPK2) is a thymidylate kinase and in mammals is known to be involved in mitochondrial DNA (mtDNA) synthesis and antiviral immunity. However, very little is known about the function of CMPK2 in fish. With an aim to elucidate the antimicrobial mechanism of CMPK2 in fish, we in this study examined the function of CMPK2 from triploid crucian carp (3nCmpk2). 3nCmpk2 is 426 residues in length and possesses the conserved thymidylate kinase domain. The deduced amino acid sequence of 3nCmpk2 shares 53.2%-99.1% overall identities with the CMPK2 of several fish species. Quantitative real time RT-PCR (qRT-PCR) analysis showed that 3nCmpk2 expression occurred in multiple tissues and was upregulated by bacterial infection in a time-dependent manner. Recombinant 3nCmpk2 (r3nCmpk2) induced mtDNA synthesis and NLRP3 activation. Overexpression of 3nCmpk2 protects the intestinal barrier and hampers the bacterial colonization in fish tissues. These results provide the first evidence that 3nCmpk2 is involved in host innate immunity and plays a protective role in antimicrobial responses during bacterial infection.

Transcriptomic Analysis and Functional Characterization Reveal the Duck Interferon Regulatory Factor 1 as an Important Restriction Factor in the Replication of Tembusu Virus

Duck Tembusu virus (DTMUV) infection has caused great economic losses to the poultry industry in China, since its first discovery in 2010. Understanding of host anti-DTMUV responses, especially the innate immunity against DTMUV infection, would be essential for the prevention and control of this viral disease. In this study, transcriptomic analysis of duck embryonic fibroblasts (DEFs) infected with DTMUV reveals that several innate immunity-related pathways, including Toll-like, NOD-like, and retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathways, are activated. Further verification by RT-qPCR confirmed that RIG-I, MAD5, TLR3, TLR7, IFN-α, IFN-β, MX, PKR, MHCI, MHCII, IL-1β, IL-6, (IFN-regulatory factor 1) IRF1, VIPERIN, IFIT5, and CMPK2 were up-regulated in cells infected with DTMUV. Through overexpression and knockdown/out of gene expression, we demonstrated that both VIPERIN and IRF1 played an important role in the regulation of DTMUV replication. Overexpression of either one significantly reduced viral replication as characterized by reduced viral RNA copy numbers and the envelope protein expression. Consistently, down-regulation of either one resulted in the enhanced replication of DTMUV in the knockdown/out cells. We further proved that IRF1 can up-regulate VIPERIN gene expression during DTMUV infection, through induction of type 1 IFNs as well as directly binding to and activation of the VIPERIN promoter. This study provides a genome-wide differential gene expression profile in cells infected with DTMUV and reveals an important function for IRF1 as well as several other interferon-stimulated genes in restricting DTMUV replication.

Identification of fish CMPK2 as an interferon stimulated gene against SVCV infection

Cytidine/uridine monophosphate kinase 2 (CMPK2) is known as a nucleoside monophosphate kinase in mitochondria to maintains intracellular UTP/CTP, and could be induced by immunostimulants LPS and Poly (I:C) in mammals, suggesting its potential antiviral and antibacterial role. In this study, CMPK2 was cloned and characterized in Fathead minnow (FHM) cells. In vivo analysis of tissue distribution revealed that CMPK2 transcript was detected in all the tissues of zebrafish (Danio rerio) examined in this study, particularly abundant in liver, spleen and kidney. In addition, indirect immunofluorescence showed that CMPK2 was localized in the cytoplasm of FHM cells. Expression of CMPK2 mRNA was significantly up-regulated following challenge with Spring viraemia of carp virus (SVCV), poly(I:C), or zebrafish IFN1 and IFN3 both in vitro and in vivo. Furthermore, overexpression and RNA interference of CMPK2 in SVCV-infected FHM cells showed significantly antiviral effect. In summary, this study for the first time shows the presence and distribution of CMPK2 in different tissues of zebrafish, but also demonstrates its antiviral potential against SVCV infection in vivo. These new findings could contribute to explain the molecular mechanism of the CMPK2 mediated antiviral function.

Innate Immunity to Enteric Hepatitis Viruses

Although hepatitis A virus (HAV) and hepatitis E virus (HEV) are both positive-strand RNA viruses that replicate in the cytoplasm of hepatocytes, there are important differences in the ways they induce and counteract host innate immune responses. HAV is remarkably stealthy because of its ability to evade and disrupt innate signaling pathways that lead to interferon production. In contrast, HEV does not block interferon production. Instead, it persists in the presence of an interferon response. These differences may provide insight into HEV persistence in immunocompromised patients, an emerging health problem in developed countries.

ITRAQ-Based Quantitative Proteomics Reveals the Proteome Profiles of Primary Duck Embryo Fibroblast Cells Infected with Duck Tembusu Virus

Outbreaks of duck Tembusu virus (DTMUV) have caused substantial economic losses in the major duck-producing regions of China since 2010. To improve our understanding of the host cellular responses to virus infection and the pathogenesis of DTMUV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with multidimensional liquid chromatography-tandem mass spectrometry to detect the protein changes in duck embryo fibroblast cells (DEFs) infected and mock-infected with DTMUV. In total, 434 cellular proteins were differentially expressed, among which 116, 76, and 339 proteins were differentially expressed in the DTMUV-infected DEFs at 12, 24, and 42 hours postinfection, respectively. The Gene Ontology analysis indicated that the biological processes of the differentially expressed proteins were primarily related to cellular processes, metabolic processes, biological regulation, response to stimulus, and cellular organismal processes and that the molecular functions in which the differentially expressed proteins were mainly involved were binding and catalytic activity. Some selected proteins that were found to be differentially expressed in DTMUV-infected DEFs were further confirmed by real-time PCR. The results of this study provide valuable insight into DTMUV-host interactions. This could lead to a better understanding of DTMUV infection mechanisms.

The Amino-Terminal Region of Hepatitis E Virus ORF1 Containing a Methyltransferase (Met) and a Papain-Like Cysteine Protease (PCP) Domain Counteracts Type I Interferon Response

Hepatitis E virus (HEV) is responsible for large waterborne epidemics of hepatitis in endemic countries and is an emerging zoonotic pathogen worldwide. In endemic regions, HEV-1 or HEV-2 genotypes are frequently associated with fulminant hepatitis in pregnant women, while with zoonotic HEV (HEV-3 and HEV-4), chronic cases of hepatitis and severe neurological disorders are reported. Hence, it is important to characterize the interactions between HEV and its host. Here, we investigated the ability of the nonstructural polyprotein encoded by the first open reading frame (ORF1) of HEV to modulate the host early antiviral response and, in particular, the type I interferon (IFN-I) system. We found that the amino-terminal region of HEV-3 ORF1 (MetYPCP), containing a putative methyltransferase (Met) and a papain-like cysteine protease (PCP) functional domain, inhibited IFN-stimulated response element (ISRE) promoter activation and the expression of several IFN-stimulated genes (ISGs) in response to IFN-I. We showed that the MetYPCP domain interfered with the Janus kinase (JAK)/signal transducer and activator of the transcription protein (STAT) signalling pathway by inhibiting STAT1 nuclear translocation and phosphorylation after IFN-I treatment. In contrast, MetYPCP had no effect on STAT2 phosphorylation and a limited impact on the activation of the JAK/STAT pathway after IFN-II stimulation. This inhibitory function seemed to be genotype-dependent, as MetYPCP from HEV-1 had no significant effect on the JAK/STAT pathway. Overall, this study provides evidence that the predicted MetYPCP domain of HEV ORF1 antagonises STAT1 activation to modulate the IFN response.

Immunity against hepatitis E virus infection: Implications for therapy and vaccine development

Hepatitis E virus (HEV) is the leading cause of acute viral hepatitis worldwide and an emerging cause of chronic infection in immunocompromised patients. As with viral infections in general, immune responses are critical to determine the outcome of HEV infection. Accumulating studies in cell culture, animal models and patients have improved our understanding of HEV immunopathogenesis and informed the development of new antiviral therapies and effective vaccines. In this review, we discuss the recent progress on innate and adaptive immunity in HEV infection, and the implications for the devolopment of effective vaccines and immune-based therapies.

Immunobiology and Host Response to HEV

Hepatitis E virus (HEV) causes acute self-limiting hepatitis in most cases and chronic infection in rare circumstances. It is believed to be noncytopathic, so immunologically mediated events should play important roles in its pathogenesis and infection outcomes. The anti-HEV antibody response was clarified when the major antigenic determinants on the ORF2 polypeptide were determined, which are located in its C-terminal portion. This subregion also forms the conformational neutralization epitopes. Robust anti-HEV immunoglobulin M (IgM) and IgG responses usually develop 3-4 weeks after infection in experimentally infected nonhuman primates. In humans, potent specific IgM and IgG responses occur in the very early phase of the disease and are critical in eliminating the virus, in concert with the innate and adaptive T-cell immune responses. They are also very valuable in the diagnosis of acute hepatitis E, when patients are tested for both anti-HEV IgM and IgG. The long-term persistence and protection of anti-HEV IgG provide the basis for estimating the prevalence of HEV infection and for the development of a hepatitis E vaccine. Although HEV has four genotypes, all the viral strains are considered to belong to a single serotype. It is becoming increasingly clear that the innate and adaptive T-cell immune responses play critical roles in the clearance of the virus. Potent and multispecific CD4⁺ and CD8⁺ T-cell responses to the ORF2 protein occur in patients with acute hepatitis E, and weaker HEV-specific CD4⁺ and CD8⁺ T-cell responses appear to be associated with chronic hepatitis E in immunocompromised individuals.

N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride: An immune-enhancing adjuvant for hepatitis E virus recombinant polypeptide vaccine in mice

Adjuvants are essential for enhancing vaccine potency by improving the humoral and/or cell-mediated immune response to vaccine antigens. This study was performed to evaluate the immuno-enhancing characteristic of N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (HTCC), the cationically modified chitosan, as an adjuvant for hepatitis E virus (HEV) recombinant polypeptide vaccine. Animal experiments showed that HTCC provides adjuvant activity when co-administered with HEV recombinant polypeptide vaccine by intramuscularly route. Vaccination using HTCC as an adjuvant was associated with increases of the serum HEV-specific IgG antibodies, splenocytes proliferation and the growths of CD4⁺CD8^- T lymphocytes and IFN-γ-secreting T lymphocytes in peripheral blood. These findings suggested that HTCC had strong immuno-enhancing effect. Our findings are the first to demonstrate that HTCC is safe and effective in inducing a good antibody response and stimulating Th1-biased immune responses for HEV recombinant polypeptide vaccine.

Hepatitis E virus persists in the presence of a type III interferon response

The RIG-I-like RNA helicase (RLR)-mediated interferon (IFN) response plays a pivotal role in the hepatic antiviral immunity. The hepatitis A virus (HAV) and the hepatitis C virus (HCV) counter this response by encoding a viral protease that cleaves the mitochondria antiviral signaling protein (MAVS), a common signaling adaptor for RLRs. However, a third hepatotropic RNA virus, the hepatitis E virus (HEV), does not appear to encode a functional protease yet persists in infected cells. We investigated HEV-induced IFN responses in human hepatoma cells and primary human hepatocytes. HEV infection resulted in persistent virus replication despite poor spread. This was companied by a type III IFN response that upregulated multiple IFN-stimulated genes (ISGs), but type I IFNs were barely detected. Blocking type III IFN production or signaling resulted in reduced ISG expression and enhanced HEV replication. Unlike HAV and HCV, HEV did not cleave MAVS; MAVS protein size, mitochondrial localization, and function remained unaltered in HEV-replicating cells. Depletion of MAVS or MDA5, and to a less extent RIG-I, also diminished IFN production and increased HEV replication. Furthermore, persistent activation of the JAK/STAT signaling rendered infected cells refractory to exogenous IFN treatment, and depletion of MAVS or the receptor for type III IFNs restored the IFN responsiveness. Collectively, these results indicate that unlike other hepatotropic RNA viruses, HEV does not target MAVS and its persistence is associated with continuous production of type III IFNs.

Asialoglycoprotein receptor facilitates infection of PLC/PRF/5 cells by HEV through interaction with ORF2

Although the biological and epidemiological features of hepatitis E virus (HEV) have been studied extensively in recent years, the mechanism by which HEV infects cells is still poorly understood. In this study, coimmunoprecipitation, pull‐down, and ELISA were used to show that the HEV ORF2 protein interacts directly with the ectodomain of both ASGR1 and ASGR2. Susceptibility to HEV correlated positively with the expression level of surface asialoglycoprotein receptor (ASGPR) in cell lines. ASGPR‐directed small interfering RNA (siRNA) in HEV‐infected PLC/PRF/5 cells had no significant effect on HEV release, suggesting that ASGPR mainly regulates the viral binding and entry steps. Both the purified ASGPR ectodomain and anti‐ASGPR antibodies disturbed the binding of HEV to PLC/PRF/5 cells. The classic ASGPR ligands asialofetuin, asialoganglioside, and fibronectin competitively inhibited the binding of HEV to hepatocytes in the presence of calcium. HeLa cell lines stably expressing ASGPR displayed increased HEV‐binding capacity, whereas ASGPR‐knockout PLC/PRF/5 cell lines had lower HEV‐binding capacity. Thus, our study demonstrates that ASGPR is involved in and facilitates HEV infection by binding to ORF2. J. Med. Virol. 88:2186–2195, 2016. © 2016 Wiley Periodicals, Inc.

ISG12a Restricts Hepatitis C Virus Infection through the Ubiquitination-Dependent Degradation Pathway

Interferons (IFNs) restrict various kinds of viral infection via induction of hundreds of IFN-stimulated genes (ISGs), while the functions of the majority of ISGs are broadly unclear. Here, we show that a high-IFN-inducible gene, ISG12a (also known as IFI27), exhibits a nonapoptotic antiviral effect on hepatitis C virus (HCV) infection. Viral NS5A protein is targeted specifically by ISG12a, which mediates NS5A degradation via a ubiquitination-dependent proteasomal pathway. K374R mutation in NS5A domain III abrogates ISG12a-induced ubiquitination and degradation of NS5A. S-phase kinase-associated protein 2 (SKP2) is identified as an ubiquitin E3 ligase for NS5A. ISG12a functions as a crucial adaptor that promotes SKP2 to interact with and degrade viral protein. Moreover, the antiviral effect of ISG12a is dependent on the E3 ligase activity of SKP2. These findings uncover an intriguing mechanism by which ISG12a restricts viral infection and provide clues for understanding the actions of innate immunity.

IMPORTANCE

Upon virus invasion, IFNs induce numerous ISGs to control viral spread, while the functions of the majority of ISGs are broadly unclear. The present study shows a novel antiviral mechanism of ISGs and elucidated that ISG12a recruits an E3 ligase, SKP2, for ubiquitination and degradation of viral protein and restricts viral infection. These findings provide important insights into exploring the working principles of innate immunity.

Hepatitis E virus infection: Epidemiology and treatment implications

Hepatitis E virus (HEV) infection is now established as an emerging enteric viral hepatitis. Standard treatments in acute and chronic hepatitis E remain to be established. This study undertakes a review of the epidemiology, treatment implication and vaccine prevention from published literature. HEV infection is a worldwide public health problem and can cause acute and chronic hepatitis E. HEV genotypes 1 and 2 are primarily found in developing countries due to waterborne transmission, while the zoonotic potential of genotypes 3 and 4 affects mostly industrialized countries. An awareness of HEV transmission through blood donation, especially in the immunocompromised and solid organ transplant patients, merits an effective anti-viral therapy. There are currently no clear indications for the treatment of acute hepatitis E. Despite concerns for side effects, ribavirin monotherapy or in combination with pegylated interferon alpha for at least 3 mo appeared to show significant efficacy in the treatment of chronic hepatitis E. However, there are no available treatment options for specific patient population groups, such as women who are pregnant. Vaccination and screening of HEV in blood donors are currently a global priority in managing infection. New strategies for the treatment and control of hepatitis E are required for both acute and chronic infections, such as prophylactic use of medications, controlling large outbreaks, and finding acceptable antiviral therapy for pregnant women and other patient groups for whom the current options of treatment are not viable.

Evaluation of an antigen-capture EIA for the diagnosis of hepatitis E virus infection

An enzyme immunoassay (EIA) has been developed for hepatitis E virus (HEV) antigen (HEV-Ag) detection and marketed in China. This study aimed to evaluate the sensitivity of the assay and assess the value of HEV-Ag detection in the diagnosis of HEV infection in comparison with HEV RNA detection. Using serial dilutions of a genotype 4 HEV strain, significant correlation was found between the EIA (S/CO) and HEV RNA (IU/mL) concentration in the range 10(3.5) to 10(0.5) IU/mL HEV RNA, the Pearson correlation coefficient r approached 0.97. The EIA detection limit was 54.6 IU/mL, compared to 24 IU/mL for HEV RNA using real-time RT-PCR. In clinical samples from hepatitis E patients, the HEV-Ag and HEV RNA positivity rates were 55.6% (65/117) and 60.7% (71/117) in sera and 76.7% (56/73) and 84.9% (62/73) in stools, and the concordance of these two markers was 77.8% in sera and 80.8% in stools. In serum samples, the HEV-Ag positivity rate and the concordance between HEV-Ag and HEV RNA were inversely proportional to the presence of anti-HEV antibody. The presence of anti-HEV IgG could reduce the S/CO of the HEV-Ag EIA. These results reveal a significant correlation between the detection of HEV-Ag and HEV RNA. The sensitivity of the HEV-Ag EIA was lower than real-time RT-PCR but could be higher than conventional nested RT-PCR. Therefore, the detection of HEV-Ag in serum and faeces is valuable for the diagnosis and prognosis of HEV infection in developing regions where real-time RT-PCR is not available.