Intermediate Replicative Form Research Articles

Replication of Hepatitis E Virus (HEV) in Primary Human-Derived Monocytes and Macrophages In Vitro.

HEV is the most causative agent of acute viral hepatitis globally. HEV causes acute, chronic, and extrahepatic manifestations. Chronic HEV infection develops in immunocompromised patients such as organ transplant patients, HIV-infected patients, and leukemic patients. The source of chronic HEV infection is not known. Also, the source of extrahepatic manifestations associated with HEV infection is still unclear. Hepatotropic viruses such as HCV and HBV replicate in peripheral blood mononuclear cells (PBMCs) and these cells become a source of chronic reactivation of the infections in allograft organ transplant patients. Herein, we reported that PBMCs and bone marrow-derived macrophages (BMDMs), isolated from healthy donors (n = 3), are susceptible to HEV in vitro. Human monocytes (HMOs), human macrophages (HMACs), and human BMDMs were challenged with HEV-1 and HEV-3 viruses. HEV RNA was measured by qPCR, the marker of the intermediate replicative form (ds-RNA) was assessed by immunofluorescence, and HEV capsid protein was assessed by flow cytometry and ELISA. HEV infection was successfully established in primary HMOs, HMACs, and human BMDMs, but not in the corresponding cells of murine origin. Intermediate replicative form (ds RNA) was detected in HMOs and HMACs challenged with HEV. The HEV load was increased over time, and the HEV capsid protein was detected intracellularly in the HEV-infected cells and accumulated extracellularly over time, confirming that HEV completes the life cycle inside these cells. The HEV particles produced from the infected BMDMs were infectious to naive HMOs in vitro. The HEV viral load was comparable in HEV-1- and HEV-3-infected cells, but HEV-1 induced more inflammatory responses. In conclusion, HMOs, HMACs, and human BMDMs are permissive to HEV infection and these cells could be the source of chronic and recurrent infection, especially in immunocompromised patients. Replication of HEV in human BMDMs could be related to hematological disorders associated with extrahepatic manifestations.

Development of a strand-specific RT-PCR to detect the positive sense replicative strand of Soybean blotchy mosaic virus

Soybean blotchy mosaic virus (SbBMV), a plant virus of the genus Cytorhabdovirus is an economically important virus of soybean reported only from the warmer, lower-lying soybean production areas in South Africa. The virus consistently appears in soybean crops annually in spite of the absence of soybean plants in winter. One possible reason for this may be that the virus replicates and hence persists in the SbBMV vector, a leafhopper, Peragallia caboverdensis. RNA viruses with antisense genomes as inferred for SbBMV produce positive sense RNAs as intermediate replicative forms during replication in their hosts, and detection of the positive strand in the plant host or vector is evidence of virus replication. In this study, a positive-strand specific RT-PCR (pss-RT-PCR) was developed to detect the positive RNA strand of SbBMV and validated on nine SbBMV isolates from soybean. The effect of tagged reverse transcription (RT) primers for cDNA synthesis, coupled with PCR using a tag-specific primer, as well as removal of unincorporated RT primers following cDNA synthesis was assessed. The positive RNA strand of SbBMV in infected plants was successfully detected following this protocol. Reverse transcription with forward and unmodified reverse primers confirmed that the assay was not able to detect the genomic sense RNA or self-primed cDNAs, lacking the non-viral tag, respectively. However, Exonuclease I (ExoI) treatment of cDNA was required to eliminate false-positive results during PCR amplification.

Measles Epidemics Among Children in Vietnam: Genomic Characterization of Virus Responsible for Measles Outbreak in Ho Chi Minh City, 2014

BackgroundMeasles remains poorly controlled in Southeast Asia, including Vietnam. ObjectivesThe aim of this study was to characterize genes of virus responsible for a measles outbreak among children in Vietnam in 2014. Study designThroat swab samples were collected from 122 pediatric patients with suspected measles. Furthermore, peripheral blood mononuclear cells (PBMCs) from 31 of these cases were also collected. Measles virus (MV) RNA was obtained directly from the clinical specimens, amplified by PCR, and then the N and H genes were sequenced. ResultsMV RNA was detectable in throat swabs from all 122 patients tested. Positive-strand viral RNA, which indicates the intermediate replicative form of MV, was also detected in PBMCs from all 31 cases from whom these cells were collected. One hundred and eighteen strains with the N gene were obtained by RT-PCR and sequenced. Using phylogenetic analysis with measles reference sequences, all of the Vietnamese strains were found to be genotype D8. However, all strains formed a distinct cluster within the genotype D8 group (D8-VNM) suggesting their own lineage. This distinct cluster was supported by a branch with a 99% bootstrap value and 3.3% nucleotide divergence in the N-450 region of the N gene from the D8 reference strain. Notably, all of the D8-VNM variant strains represented unique amino acid sequences consisting of R442, S451 and G452 in the N-450 region of the N gene. ConclusionsMeasles viruses responsible for outbreaks in Southern Vietnam belonged to a genotype D8 variant group which had unique amino acid sequences in the N gene. Our report provides important genomic information about the virus for measles elimination in Southeast Asia.

Occult viral hepatitis: What is the significance?

Occult viral hepatitis: What is the significance?

Evidences of Hepatitis C Virus Replication in Hepatocytes and Peripheral Blood Monocuclear Cells from Patients Negative for Viral RNA in Serum

In this study, we examined the expression of hepatitis C virus (HCV) components in hepatocytes and peripheral blood mononuclear cells (PBMC) from patients positive for anti-HCV antibodies and negative for serum HCV-RNA. The samples obtained from 25 randomly selected patients (13 of 25 patients showed no histological evidences of chronic hepatitis and had normal serum ALAT and GGTP levels) were studied by in situ Hybridization and Immunofluorescence assays. The findings show that HCV-RNA of both positive and negative polarity was carried in the hepatocytes of more than 80% of cases. The proportion of cells expressing the negative strand (mean ± SD, 10.25% ± 5.56%) was lower than those expressing positive strand (mean ± SD, 19.88% ± 9.19%) (p=0.0076; Student’s t test). In addition, reaction products suggestive of HCV core, E1 and E2 antigens within hepatocytes were also observed. Both hybridization and immunofluorescence signals were localized in the cytoplasm suggesting that this is the place of active HCV replication. On the other hand, the HCV-RNA of positive polarity was detected in PBMC from 16 out of 17 samples analyzed (94%) while the HCV-RNA of negative polarity was detected in 82% of samples investigated. Positive hybridization signals were localized in the cytoplasm of PBMC. Interestingly, 12 out of 13 patients with clinical and histological resolution of hepatitis, contain HCV-RNA in either liver or PBMC. These results provide further evidences that the intermediate replicative form of the HCV genome can persist in hepatocytes and PBMC after apparently complete resolution of chronic hepatitis C.

Hepatitis C Virus Persistence after Spontaneous or Treatment-Induced Resolution of Hepatitis C

It is presumed that resolution of hepatitis C, as evidenced by normalization of liver function tests and disappearance of hepatitis C virus (HCV) RNA from serum, as determined by conventional laboratory assays, reflects virus eradication. In this study, we examined the expression of the HCV genome in the sera, peripheral blood mononuclear cells (PBMC), and, on some occasions, monocyte-derived dendritic cells (DC) long after resolution of hepatitis C by using a highly sensitive reverse transcription (RT)-PCR-nucleic acid hybridization (RT-PCR-NAH) assay. The samples obtained from 16 randomly selected patients (5 with spontaneous and 11 with treatment-induced resolution), monitored for up to 5 years, were studied by qualitative and semiquantitative RT-PCR-NAH and by real-time RT-PCR to detect the HCV RNA positive strand. The replicative HCV RNA negative strand was examined in PBMC after culture with a T-cell proliferation stimulating mitogen. The findings show that HCV RNA was carried in the convalescent-phase sera and/or PBMC in all 16 individuals investigated. Also, DC from six of seven patients were reactive for the HCV genome. Importantly, traces of the HCV RNA negative strand, suggesting progressing virus replication, were detected in the majority of mitogen-stimulated PBMC, including four samples collected 5 years after recovery. Sequencing of the HCV 5' untranslated region fragment revealed genotype 1b in four of nine individuals examined and genotypes 1a and 2a in three and two patients, respectively. These results imply that HCV RNA can persist at very low levels in the serum and peripheral lymphoid cells and that an intermediate replicative form of the HCV genome can persist in PBMC for many years after apparently complete spontaneous or antiviral therapy-induced resolution of chronic hepatitis C.

Persistence of hepatitis C virus after successful treatment of chronic hepatitis C: Is hepatitis C infection for life?

It is presumed that resolution of hepatitis C, as evidenced by normalization of liver function tests and disappearance of hepatitis C virus (HCV) RNA from serum, as determined by conventional laboratory assays, reflects virus eradication. In this study, we examined the expression of the HCV genome in the sera, peripheral blood mononuclear cells (PBMC), and, on some occasions, monocyte-derived dendritic cells (DC) long after resolution of hepatitis C by using a highly sensitive reverse transcription (RT)-polymerase chain reaction-nucleic acid hybridization (RT-PCR-NAH) assay. The samples obtained from 16 randomly selected patients (5 with spontaneous resolution and 11 with treatment-induced resolution), monitored for up to 5 years, were studied by qualitative and semiquantitative RT-PCR-NAH and by real-time RT-PCR to detect the HCV RNA positive strand. The replicative HCV RNA negative strand was examined in PBMC after culture with a T cell proliferation stimulating mitogen. The findings show that HCV RNA was carried in the convalescent-phase sera and/or PBMC in all 16 individuals investigated. Also, DC from six of seven patients were reactive for the HCV genome. Importantly, traces of the HCV RNA negative strand, suggesting progressing virus replication, were detected in the majority of mitogen-stimulated PBMC, including four samples collected 5 years after recovery. Sequencing of the HCV 5' untranslated region fragment revealed genotype 1b in four of nine individuals examined and genotypes 1a and 2a in three and two patients, respectively. In conclusion, these results imply that HCV RNA can persist at very low levels in the serum and peripheral lymphoid cells and that an intermediate replicative form of the HCV genome can persist in PBMC for many years after apparently complete spontaneous or antiviral therapy-induced resolution of chronic hepatitis C. (J Virol 2004;78:5867–5874.)

The small envelope protein is required for secretion of a naturally occurring hepatitis B virus mutant with pre-S1 deleted.

Naturally occurring deletions in the hepatitis B virus pre-S1 domain have been frequently found during persistent viral infection. In this study we have investigated the functional properties of a mutant viral genome that carries an in-frame deletion of 183 nucleotides in the pre-S1 region. This deletion removes the promoter of the small envelope gene. Transfection into human hepatocellular carcinoma cells of a replication-competent construct containing this deletion resulted in an increase of intermediate DNA replicative forms compared to those produced by wild-type hepatitis B virus. Northern blot analysis revealed that such cells lack the 2.1-kb transcripts encoding the small envelope protein and that hepatitis B surface antigen was absent as well. Furthermore, nucleocapsids containing the genome with pre-S1 deleted were not secreted, and the deleted large envelope protein was retained with the cytoplasm and exhibited a perinuclear pattern of distribution. However, coexpression with the small envelope protein was sufficient to restore virion secretion and to change the cellular distribution of the deleted large envelope protein. In addition, the creation of point mutations that prevent the synthesis of large or small envelope proteins also inhibited viral secretion and led to increased levels of hepatitis B virus intermediate replicative forms within the cell. These studies suggest that naturally occurring viral mutants with pre-S1 deletions involving the promoter region of the small envelope gene will generate a deleted large envelope protein that is retained in the endoplasmic reticulum, resulting in the accumulation of nucleocapsids containing viral DNA; transcomplementation with the wild-type small envelope protein will allow mutant virion secretion to occur.

In vitro neutralization of hepatitis B virus by monoclonal antibodies against the viral surface antigen.

In vitro HBV infection and neutralization were assayed using an anti-preS1 murine monoclonal antibody (1B3) and anti-preS2 (H69K) and anti-S (CS131A) murine-human chimeric antibodies. The 1B3 (IgG1) and H69K (IgG1) was constructed previously and the CS131A was constructed for this study by expressing stably the chimeric heavy and light chains in Chinese hamster ovary cells and purifying from the culture supernatant. Previous study showed that the H69K and CS131A recognize known virus-neutralizing epitopes, while the 1B3 does not. For the assays, adult human hepatocyte primary culture was infected with the adr or ayw subtype of HBV, and the infectivity and subsequent replication was confirmed both by measuring the kinetics of HB-sAg secretion by the infected cells and detecting the intermediate replicative form of HBV DNA in the cells. Next, the hepatocytes were infected with the adr or ayw subtype of the virus that had been preincubated with various concentrations of each of the antibodies and the neutralization of HBV was analyzed. The results showed that the anti-preS2 and anti-S chimeric antibodies exhibited neutralizing activity against both the adr and ayw subtypes of the virus, with approximately 1,000 and 2,000 times higher specific activity than polyclonal hepatitis B immune globulin, respectively, but the anti-preS1 antibody scarcely neutralized the infection. The neutralizing activities of the antibodies were consistent with their epitope specificity and antigenbinding affinity, suggesting that this neutralization assay is specific. The in vitro neutralization assay will be useful for evaluating the neutralizing activity of anti-HBV antibodies before in vivo testing in chimpanzees.

Myristylation of the Hepatitis B Virus Large Surface Protein Is Essential for Viral Infectivity

The hepatitis B virus (HBV) envelope contains equimolar amounts of three viral proteins: the major (S), middle, and large (L) polypeptides. Their roles in the adsorption and penetration of the virus have not yet been elucidated. We have used a highly efficientin vitromodel that permits reproducible HBV infection to investigate whether N-myristylation, a posttranslational modification of the L protein, was essential for viral infectivity. A point mutation abolishing myristylation was introduced into the HBV genome. Mutant virions were produced by transfecting viral DNA into hepatoma cells and their infectivity was evaluated on primary human hepatocyte cultures. No difference between mutant and wild-type viral RNA production could be observed. Furthermore, intermediate DNA replicative forms were observed in transfected cells demonstrating replication competence of mutant viral genomes. In addition, complete virions were produced in the cell supernatant. However, we found that mutant viral particles contained viral DNA with a reduced mean size, probably corresponding to a larger single-stranded region in the relaxed circular DNA form. We have evidenced the presence of pre-S1, pre-S2, and S epitopes at the outer surface of these virions by using immunoprecipitation with specific monoclonal antibodies. This result confirmed that mutant viruses were normally assembled. By contrast, myristylation-defective mutants completely lost their infectivity for human hepatocytes in primary cultures as shown by the absence of HBs antigen production and viral intermediate replicative forms in hepatocytes. In conclusion, the myristylation of the L protein is not required for the production of Dane-like particles but it is absolutely necessary for HBV infectivity.

Maintenance of woodchuck hepatitis virus activity in woodchuck hepatocyte primary culture.

Primary cultures of non-proliferating hepatocytes isolated by the two-step collagenase perfusion method from woodchuck naturally infected with hepatitis virus (WHV) were used to study WHV propagation in vitro. Hepatocytes carrying WHV DNA exhibited a very high level of survival and retained their morphological characteristics for 2 to 3 months. Over this time, they were found to produce virus-specific proteins and release viral particles with DNA polymerase activity into the medium. Using Southern blot analysis and a recombinant hepatitis B virus DNA plasmid probe, intracellular and extracellular viral DNA was consistently detected. Only extrachromosomal forms of WHV DNA were observed and no integration could be demonstrated in the DNA of the cells. The WHV DNA patterns were repeatedly identical with a characteristic smear starting from 3.3 kb associated with other smaller DNA fragments which presumably represented intermediate replicative forms of viral DNA. Furthermore, dot blot hybridization of the total RNA revealed the presence of WHV-specific transcripts in cells after 3 weeks of culture. All these results are compatible with the maintenance of active WHV replication in vitro although it was somewhat reduced after the first day of culture. This provides a mammalian model for hepadnavirus replication studies in stable primary hepatocyte cultures.