Comparative Longitudinal Serological Study of Anti-SARS-CoV-2 Antibody Profiles in People with COVID-19

Serological diagnostic assays are essential tools for determining an individual's protection against viruses like SARS-CoV-2, tracking the spread of the virus in the community, and evaluating population immunity. To assess the diversity and quality of the anti-SARS-CoV-2 antibody response, we have compared the antibody profiles of people with mild, moderate, and severe COVID-19 using a dot blot assay. The test targeted the four major structural proteins of SARS-CoV-2, namely the nucleocapsid (N), spike (S) protein domains S1 and S2, and receptor-binding domain (RBD). Serum samples were collected from 63 participants at various time points for up to 300 days after disease onset. The dot blot assay revealed patient-specific differences in the anti-SARS-CoV-2 antibody profiles. Out of the 63 participants with confirmed SARS-CoV-2 infections and clinical COVID-19, 35/63 participants exhibited diverse and robust responses against the tested antigens, while 14/63 participants displayed either limited responses to a subset of antigens or no detectable antibody response to any of the antigens. Anti-N-specific antibody levels decreased within 300 days after disease onset, whereas anti-S-specific antibodies persisted. The dynamics of the antibody response did not change during the test period, indicating stable antibody profiles. Among the participants, 28/63 patients with restricted anti-S antibody profiles or undetectable anti-S antibody levels in the dot blot assay also exhibited weak neutralization activity, as measured by a surrogate virus neutralization test (sVNT) and a microneutralization test. These results indicate that in some cases, natural infections do not lead to the production of neutralizing antibodies. Furthermore, the study revealed significant serological variability among patients, regardless of the severity of their COVID-19 illness. These differences need to be carefully considered when evaluating the protective antibody status of individuals who have experienced primary SARS-CoV-2 infections.

Clinical stage drugs targeting inhibitor of apoptosis proteins purge episomal Hepatitis B viral genome in preclinical models

A major unmet clinical need is a therapeutic capable of removing hepatitis B virus (HBV) genome from the liver of infected individuals to reduce their risk of developing liver cancer. A strategy to deliver such a therapy could utilize the ability to target and promote apoptosis of infected hepatocytes. Presently there is no clinically relevant strategy that has been shown to effectively remove persistent episomal covalently closed circular HBV DNA (cccDNA) from the nucleus of hepatocytes. We used linearized single genome length HBV DNA of various genotypes to establish a cccDNA-like reservoir in immunocompetent mice and showed that clinical-stage orally administered drugs that antagonize the function of cellular inhibitor of apoptosis proteins can eliminate HBV replication and episomal HBV genome in the liver. Primary human liver organoid models were used to confirm the clinical relevance of these results. This study underscores a clinically tenable strategy for the potential elimination of chronic HBV reservoirs in patients.

Hepatitis Delta Virus (HDV) and Delta-Like Agents: Insights Into Their Origin

Hepatitis delta virus (HDV) is a human pathogen, and the only known species in the genus Deltavirus. HDV is a satellite virus and depends on the hepatitis B virus (HBV) for packaging, release, and transmission. Extracellular HDV virions contain the genomic HDV RNA, a single-stranded negative-sense and covalently closed circular RNA molecule, which is associated with the HDV-encoded delta antigen forming a ribonucleoprotein complex, and enveloped by the HBV surface antigens. Replication occurs in the nucleus and is mediated by host enzymes and assisted by cis-acting ribozymes allowing the formation of monomer length molecules which are ligated by host ligases to form unbranched rod-like circles. Recently, meta-transcriptomic studies investigating various vertebrate and invertebrate samples identified RNA species with similarities to HDV RNA. The delta-like agents may be representatives of novel subviral agents or satellite viruses which share with HDV, the self-complementarity of the circular RNA genome, the ability to encode a protein, and the presence of ribozyme sequences. The widespread distribution of delta-like agents across different taxa with considerable phylogenetic distances may be instrumental in comprehending their evolutionary history by elucidating the transition from transcriptome to cellular circular RNAs to infectious subviral agents.

Glycoengineered hepatitis B virus-like particles with enhanced immunogenicity

Virus-like particles (VLP) represent biological platforms for the development of novel products such as vaccines and delivery platforms for foreign antigenic sequences. VLPs composed of the small surface antigen (HBsAgS) derived from the hepatitis B virus (HBV) are the immunogenic components of a licensed, preventative vaccine, which contains aluminum hydroxide as adjuvant. Herein, we report that glycoengineering of N-glycosylated HBsAgS to generate hyper-glycosylated VLPs display an enhanced immunogenicity relative to the wild type (WT) HBsAgS VLPs when expressed in FreeStyle HEK 293F cells. Comparative mass spectrometry-based N-glycan profiling, gel electrophoresis, and immunoassays demonstrated that WT and hyper-glycosylated HBsAgS VLPs contain the same type and distribution of N-glycan structures, but the latter shows a higher glycan abundance per protein mass. The antigenic integrity of the modified VLPs was also shown to be retained. To assess whether hyper-glycosylated VLPs induce an enhanced immune response in the presence of the adjuvant aluminum hydroxide, the anti-HBV surface antigen (anti-HBsAgS) antibody response was monitored in BALB/c mice, subcutaneously injected with different VLP derivatives. In the absence and presence of adjuvant, hyper-glycosylated VLPs showed an enhanced immunogenicity compared to WT VLPs. The ability of hyper-glycosylated VLPs to promote potent anti-HBsAgS immune responses compared to VLPs with a native N-glycan level as well as non-glycosylated, yeast-derived HBsAgS VLPs opens exciting avenues for generating more efficacious VLP-based vaccines against hepatitis B and improved HBsAgS VLP carrier platforms using glycoengineering.

Hepatitis B virus-like particles expressing Plasmodium falciparum epitopes induce complement-fixing antibodies against the circumsporozoite protein

The repetitive structure of compact virus-like particles (VLPs) provides high density displays of antigenic sequences, which trigger key parts of the immune system. The hepatitis B virus (HBV) and human papilloma virus (HPV) vaccines exploit the assembly competence of structural proteins, which are the effective immunogenic components of the prophylactic HBV and HPV vaccines, respectively. To optimize vaccine designs and to promote immune responses against protective epitopes, the "Asp-Ala-Asp-Pro" (NANP)-repeat from the Plasmodium falciparum circumsporozoite protein (CSP) was expressed within the exposed, main antigenic site of the small HBV envelope protein (HBsAgS); this differs from the RTS,S vaccine, in which CSP epitopes are fused to the N-terminus of HBsAgS. The chimeric HBsAgS proteins are assembly competent, produce VLPs, and provide a high antigenic density of the NANP repeat sequence. Chimeric VLPs with four or nine NANP-repeats (NANP4 and NANP9, respectively) were expressed in mammalian cells, the HBsAgS- and CSP-specific antigenicity of the VLPs was determined, and the immunogenicity of the VLPs assessed in relation to the induction of anti-HBsAgS and anti-CSP antibody responses. The chimeric VLPs induced high anti-CSP titres in BALB/c mice independent of the number of the NANP repeats. However, the number of NANP repeats influenced the activity of vaccine-induced antibodies measured by complement fixation to CSP, one of the proposed effector mechanisms for Plasmodium neutralization in vivo. Sera from mice immunized with VLPs containing nine NANP repeats performed better in the complement fixation assay than the group with four NANP repeats. The effect of the epitope-specific density on the antibody quality may instruct VLP platform designs to optimize immunological outcomes and vaccine efficacy.

A Divergent Hepatitis D-Like Agent in Birds

Hepatitis delta virus (HDV) is currently only found in humans and is a satellite virus that depends on hepatitis B virus (HBV) envelope proteins for assembly, release, and entry. Using meta-transcriptomics, we identified the genome of a novel HDV-like agent in ducks. Sequence analysis revealed secondary structures that were shared with HDV, including self-complementarity and ribozyme features. The predicted viral protein shares 32% amino acid similarity to the small delta antigen of HDV and comprises a divergent phylogenetic lineage. The discovery of an avian HDV-like agent has important implications for the understanding of the origins of HDV and sub-viral agents.

Viral regulation of host cell biology by hijacking of the nucleolar DNA-damage response

Recent studies indicate that nucleoli play critical roles in the DNA-damage response (DDR) via interaction of DDR machinery including NBS1 with nucleolar Treacle protein, a key mediator of ribosomal RNA (rRNA) transcription and processing. Here, using proteomics, confocal and single molecule super-resolution imaging, and infection under biosafety level-4 containment, we show that this nucleolar DDR pathway is targeted by infectious pathogens. We find that the matrix proteins of Hendra virus and Nipah virus, highly pathogenic viruses of the Henipavirus genus in the order Mononegavirales, interact with Treacle and inhibit its function, thereby silencing rRNA biogenesis, consistent with mimicking NBS1–Treacle interaction during a DDR. Furthermore, inhibition of Treacle expression/function enhances henipavirus production. These data identify a mechanism for viral modulation of host cells by appropriating the nucleolar DDR and represent, to our knowledge, the first direct intranucleolar function for proteins of any mononegavirus.

Many RNA viruses that replicate in the cytoplasm express proteins that localize to nucleoli, but the nucleolar functions remain largely unknown. Here, the authors show that the Henipavirus matrix protein mimics an endogenous Treacle partner of the DNA-damage response, resulting in suppression of rRNA biogenesis.

Signalome-wide assessment of host cell response to hepatitis C virus

Host cell signalling during infection with intracellular pathogens remains poorly understood. Here we report on the use of antibody microarray technology to detect variations in the expression levels and phosphorylation status of host cell signalling proteins during hepatitis C virus (HCV) replication. Following transfection with HCV RNA, the JNK and NF-κB pathways are suppressed, while the JAK/STAT5 pathway is activated; furthermore, components of the apoptosis and cell cycle control machineries are affected in the expression and/or phosphorylation status. RNAi-based hit validation identifies components of the JAK/STAT, NF-κB, MAPK and calcium-induced pathways as modulators of HCV replication. Selective chemical inhibition of one of the identified targets, the JNK activator kinase MAP4K2, does impair HCV replication. Thus this study provides a comprehensive picture of host cell pathway mobilization by HCV and uncovers potential therapeutic targets. The strategy of identifying targets for anti-infective intervention within the host cell signalome can be applied to any intracellular pathogen.

Development of antiviral strategies depends on an understanding of virus–host interactions. Here, using HCV, Haqshenas et al. show that antibody microarray combined with a targeted siRNA screen can be a powerful tool to identify cellular signalling pathways that are important for virus replication.

Subverting Host Cell P21-Activated Kinase: A Case of Convergent Evolution across Pathogens

Intracellular pathogens have evolved a wide range of strategies to not only escape from the immune systems of their hosts, but also to directly exploit a variety of host factors to facilitate the infection process. One such strategy is to subvert host cell signalling pathways to the advantage of the pathogen. Recent research has highlighted that the human serine/threonine kinase PAK, or p21-activated kinase, is a central component of host-pathogen interactions in many infection systems involving viruses, bacteria, and eukaryotic pathogens. PAK paralogues are found in most mammalian tissues, where they play vital roles in a wide range of functions. The role of PAKs in cell proliferation and survival, and their involvement in a number of cancers, is of great interest in the context of drug discovery. In this review we discuss the latest insights into the surprisingly central role human PAK1 plays for the infection by such different infectious disease agents as viruses, bacteria, and parasitic protists. It is our intention to open serious discussion on the applicability of PAK inhibitors for the treatment, not only of neoplastic diseases, which is currently the primary objective of drug discovery research targeting these enzymes, but also of a wide range of infectious diseases.

Nuclear localization and secretion competence are conserved among henipavirus matrix proteins

Viruses of the genus Henipavirus of the family Paramyxoviridae are zoonotic pathogens, which have emerged in Southeast Asia, Australia and Africa. Nipah virus (NiV) and Hendra virus are highly virulent pathogens transmitted from bats to animals and humans, while the henipavirus Cedar virus seems to be non-pathogenic in infection studies. The full replication cycle of the Paramyxoviridae occurs in the host cell's cytoplasm, where viral assembly is orchestrated by the matrix (M) protein. Unexpectedly, the NiV-M protein traffics through the nucleus as an essential step to engage the plasma membrane in preparation for viral budding/release. Comparative studies were performed to assess whether M protein nuclear localization is a common feature of the henipaviruses, including the recently sequenced (although not yet isolated) Ghanaian bat henipavirus (Kumasi virus, GH-M74a virus) and Mojiang virus. Live-cell confocal microscopy revealed that nuclear translocation of GFP-fused M protein is conserved between henipaviruses in both human- and bat-derived cell lines. However, the efficiency of M protein nuclear localization and virus-like particle budding competency varied. Additionally, Cedar virus-, Kumasi virus- and Mojiang virus-M proteins were mutated in a bipartite nuclear localization signal, indicating that a key lysine residue is essential for nuclear import, export and induction of budding events, as previously reported for NiV-M. The results of this study suggest that the M proteins of henipaviruses may utilize a similar nucleocytoplasmic trafficking pathway as an essential step during viral replication in both humans and bats.

The non-pathogenic Henipavirus Cedar paramyxovirus phosphoprotein has a compromised ability to target STAT1 and STAT2

Immune evasion by the lethal henipaviruses, Hendra (HeV) and Nipah virus, is mediated by its interferon (IFN) antagonist P gene products, phosphoprotein (P), and the related V and W proteins, which can target the signal transducer and activator of transcription 1 (STAT1) and STAT2 proteins to inhibit IFN/STAT signaling. However, it is not clear if the recently identified non-pathogenic Henipavirus, Cedar paramyxovirus (CedPV), is also able to antagonize the STAT proteins. We performed comparative studies between the HeV P gene products (P/V/W) and CedPV-P (CedPV does not encode V or W) and demonstrate that differences exist in their ability to engage the STAT proteins using immunoprecipitation and quantitative confocal microscopic analysis. In contrast to HeV-P gene encoded proteins, the ability of CedPV-P to interact with and relocalize STAT1 or STAT2 is compromised, correlating with a reduced capacity to inhibit the mRNA synthesis of IFN-inducible gene MxA. Furthermore, infection studies with HeV and CedPV demonstrate that HeV is more potent than CedPV in inhibiting the IFN-α-mediated nuclear accumulation of STAT1. These results strongly suggest that the ability of CedPV to counteract the IFN/STAT response is compromised compared to HeV.

Anti-hepatitis B activity of isoquinoline alkaloids of plant origin

Hepatitis B virus (HBV) is the causative agent of B-type hepatitis in humans, a vaccine-preventable disease. Despite the availability of effective vaccines, globally, 2 billion people show evidence of past or current HBV infection, of which 350 million people are persistently infected, with an estimated annual increase of 1 million. There is no cure for chronic HBV infections, which are associated with cirrhotic liver failure and with an increased risk of developing hepatocellular carcinoma. Hepatitis antiviral research has focused primarily on the development of inhibitors of viral polymerase through the use of nucleoside analogues. Therefore, there is an urgent need for the development of non-nucleoside compounds to be used as an alternative or to complement the current therapy. To address this need, 18 isoquinoline alkaloids were evaluated for their potential antiviral activity against HBV in vitro.

Production, characterization, and immunogenicity of a secreted form of Plasmodium falciparum merozoite surface protein 4 produced in Bacillus subtilis

Plasmodium falciparum is the causative agent of the most serious form of malaria. Although a combination of control measures has significantly limited malaria morbidity and mortality in the last few years, it is generally agreed that sustained control or even eradication will require additional tools including an effective malaria vaccine. Merozoite surface protein 4, MSP4, which is present during the asexual stage of P. falciparum, is a recognized target that would be useful in a subunit vaccine against blood stages of malaria. Falciparum malaria is most prevalent in developing countries, and this in turn leads to a requirement for safe, low-cost vaccines. We have attempted to utilize the nonpathogenic, gram-positive organism Bacillus subtilis to produce PfMSP4. PfMSP4 was secreted into the culture medium at a yield of 4.5 mg/L. Characterization studies including SDS-PAGE, mass spectrometry, and N-terminal sequencing indicated that the B. subtilis expression system secreted a full length PfMSP4 protein compared to a truncated version in Escherichia coli. Equivalent amounts of purified B. subtilis and E. coli-derived PfMSP4 were used for immunization studies, resulting in statistically significant higher mean titer values for the B. subtilis-derived immunogen. The mouse antibodies raised against B. subtilis produced PfMSP4 that were reactive to parasite proteins as evidenced by immunoblotting on parasite lysate and indirect immunofluorescence assays of fixed parasites. The B. subtilis expression system, in contrast to E. coli, expresses higher amounts of full length PfMSP4 products, decreased levels of aggregates, and allows the development of simplified downstream processing procedures.

Identification of specific regions in hepatitis C virus core, NS2 and NS5A that genetically interact with p7 and co-ordinate infectious virus production

The p7 protein of hepatitis C virus (HCV) is a small, integral membrane protein that plays a critical role in virus replication. Recently, we reported two intergenotypic JFH1 chimeric viruses encoding the partial or full-length p7 protein of the HCV-A strain of genotype 1b (GT1b; Virology; 2007; 360:134). In this study, we determined the consensus sequences of the entire polyprotein coding regions of the wild-type JFH1 and the revertant chimeric viruses and identified predominant amino acid substitutions in core (K74M), NS2 (T23N, H99P) and NS5A (D251G). Forward genetic analysis demonstrated that all single mutations restored the infectivity of the defective chimeric genomes suggesting that the infectious virus production involves the association of p7 with specific regions in core, NS2 and NS5A. In addition, it was demonstrated that the NS2 T23N facilitated the generation of infectious intergenotypic chimeric virus encoding p7 from GT6 of HCV.

Hepatitis B virus-like particles access major histocompatibility class I and II antigen presentation pathways in primary dendritic cells

Virus-like particles (VLPs) represent high density displays of viral proteins that efficiently trigger immunity. VLPs composed of the small hepatitis B virus envelope protein (HBsAgS) are useful vaccine platforms that induce humoral and cellular immune responses. Notably, however, some studies suggest HBsAgS VLPs impair dendritic cell (DC) function. Here we investigated HBsAgS VLP interaction with DC subsets and antigen access to major histocompatibility complex (MHC) class I and II antigen presentation pathways in primary DCs. HBsAgS VLPs impaired plasmacytoid DC (pDC) interferon alpha (IFNα) production in response to CpG in vitro, but did not alter conventional DC (cDC) or pDC phenotype when administered in vivo. To assess cellular immune responses, HBsAgS VLPs were generated containing the ovalbumin (OVA) model epitopes OVA(257-264) and OVA(323-339) to access MHCI and MHCII antigen presentation pathways, respectively; both in vitro and following immunisation in vivo. HBsAgS VLP-OVA(257-264) elicited CTL responses in vivo that were not enhanced by inclusion of an additional MHCII helper epitope. HBsAgS VLP-OVA(257-264) administered in vivo was cross-presented by CD8(+) DCs, but not CD8(-) DCs. Therefore, HBsAgS VLPs can deliver antigen to both MHCI and MHCII antigen presentation pathways in primary DCs and promote cytotoxic and helper T cell priming despite their suppressive effect on pDCs.

Does RNA interference provide new hope for control of chronic hepatitis B infection?

Hepatitis B virus (HBV) infection is a global human health problem, with an estimated 350 million people having chronic hepatitis B (CHB) infection worldwide. The majority of infections acquired during adulthood are resolved without intervention; however, infections acquired at birth or during early childhood have a 90% chance of progressing to CHB, leading to a host of adverse effects on the liver, including cirrhosis and cancer. CHB is currently treated with a combination of cytokines and/or nucleoside/nucleotide analogues; however, adverse side effects to cytokine therapy and the selection of resistance mutations to nucleoside analogues often abrogate the efficacy of treatment. The recent discovery that small interfering RNA and microRNA are active in mammalian cells suggests it might be possible to supplement existing HBV therapies with small RNA-based therapeutic(s).

Failure of the lamivudine-resistant rtM204I hepatitis B virus mutants to efficiently support hepatitis delta virus secretion

Hepatitis delta virus (HDV) is encapsidated by the envelope proteins of hepatitis B virus (HBV). The major HBV lamivudine (LMV)-resistant mutations in the polymerase gene within the reverse transcriptase (rt) region at rtM204V or rtM204I are associated with changes in the overlapping envelope gene products, in particular, the gene encoding small envelope protein (s) at sI195M or sW196L/S/Stop. We have demonstrated that the LMV resistance mutations corresponding to sW196L/S inhibited secretion of HDV particles, while changes corresponding to sI195M did not affect secretion. Differential efficiencies of HBsAg proteins expressed by LMV-resistant HBV to support HDV secretion may have consequences for clinical prognosis as coinfected patients are treated with antiviral agents.

Immunogenicity of recombinant HBsAg/HCV particles in mice pre-immunised with hepatitis B virus-specific vaccine

Due to their spatial structure virus-like particles (VLPs) generally induce effective immune responses. VLPs derived from the small envelope protein (HBsAg-S) of hepatitis B virus (HBV) comprise the HBV vaccine. Modified HBsAs-S VLPs, carrying the immunodominant hypervariable region (HVR1) of the hepatitis C virus (HCV) envelope protein E2 within the exposed 'a'-determinant region (HBsAg/HVR1-VLPs), elicited HVR1-specific antibodies in mice. A high percentage of the human population is positive for anti-HBsAg antibodies (anti-HBs), either through vaccination or natural infection. We, therefore, determined if pre-existing anti-HBs could influence immunisation with modified VLPs. Mice were immunised with a commercial HBV vaccine, monitored to ensure an anti-HBs response, then immunised with HBsAg/HVR1-VLPs. The resulting anti-HVR1 antibody titre was similar in mice with or without pre-existing anti-HBs. This suggests that HBsAg/HVR1-VLPs induce a primary immune response to HVR1 in anti-HBs positive mice and, hence, they may be used successfully in individuals already immunised with the HBV vaccine.

Identification and analysis of a new hepadnavirus in white storks

We identified, cloned, and functionally characterized a new avian hepadnavirus infecting storks (STHBV). STHBV has the largest DNA genome of all avian hepadnaviruses and, based on sequence and phylogenetic analysis, is most closely related to, but distinct from, heron hepatitis B virus (HHBV). Unique for STHBV among the other avian hepadnaviruses is a potential HNF1 binding site in the preS promoter. In common only with HHBV, STHBV has a myristylation signal on the S and not the preS protein, two C terminally located glycosylation sites on the precore/core proteins and lacks the phosphorylation site essential for the transcriptional transactivation activity of duck-HBV preS protein. The cloned STHBV genomes were competent in gene expression, replication, and viral particle secretion. STHBV infected primary duck hepatocytes very inefficiently suggesting a restricted host range, similar to other hepadnaviruses. This discovery of stork infections unravels novel evolutionary aspects of hepadnaviruses and provides new opportunities for hepadnavirus research.

Antigenicity and immunogenicity of novel chimeric hepatitis B surface antigen particles with exposed hepatitis C virus epitopes

The small envelope protein of hepatitis B virus (HBsAg-S) can self-assemble into highly organized virus like particles (VLPs) and induce an effective immune response. In this study, a restriction enzyme site was engineered into the cDNA of HBsAg-S at a position corresponding to the exposed site within the hydrophilic a determinant region (amino acid [aa] 127-128) to create a novel HBsAg vaccine vector allowing surface orientation of the inserted sequence. We inserted sequences of various lengths from hypervariable region 1 (HVR1) of the hepatitis C virus (HCV) E2 protein containing immunodominant epitopes and demonstrated secretion of the recombinant HBsAg VLPs from transfected mammalian cells. A number of different recombinant proteins were synthesized, and HBsAg VLPs containing inserts up to 36 aa were secreted with an efficiency similar to that of wild-type HBsAg. The HVR1 region exposed on the particles retained an antigenic structure similar to that recognized immunologically during natural infection. VLPs containing epitopes from either HCV-1a or -1b strains were produced that induced strain-specific antibody responses in immunized mice. Injection of a combination of these VLPs induced antibodies against both HVR1 epitopes that resulted in higher titers than were achieved by vaccination with the individual VLPs, suggesting a synergistic effect. This may lead to the development of recombinant particles which are able to induce a broad anti-HCV immune response against the HCV quasispecies or other quasispecies-like infectious agents.

Duck hepatitis B virus expresses a regulatory HBx-like protein from a hidden open reading frame

Duck hepatitis B viruses (DHBV), unlike mammalian hepadnaviruses, are thought to lack X genes, which encode transcription-regulatory proteins believed to contribute to the development of hepatocellular carcinoma. A lack of association of chronic DHBV infection with hepatocellular carcinoma development supports this belief. Here, we demonstrate that DHBV genomes have a hidden open reading frame from which a transcription-regulatory protein, designated DHBx, is expressed both in vitro and in vivo. We show that DHBx enhances neither viral protein expression, intracellular DNA synthesis, nor virion production when assayed in the full-length genome context in LMH cells. However, similar to mammalian hepadnavirus X proteins, DHBx activates cellular and viral promoters via the Raf-mitogen-activated protein kinase signaling pathway and localizes primarily in the cytoplasm. The functional similarities as well as the weak sequence homologies of DHBx and the X proteins of mammalian hepadnaviruses strongly suggest a common ancestry of ortho- and avihepadnavirus X genes. In addition, our data disclose similar intracellular localization and transcription regulatory functions of the corresponding proteins, raise new questions as to their presumed role in hepatocarcinogenesis, and imply unique opportunities for deciphering of their still-enigmatic in vivo functions.

A new avian hepadnavirus infecting snow geese (Anser caerulescens) produces a significant fraction of virions containing single-stranded DNA

We describe the identification and functional analysis of an evolutionary distinct new avian hepadnavirus. Infection of snow geese (Anser caerulescens) with a duck hepatitis B virus (DHBV)-related virus, designated SGHBV, was demonstrated by detection of envelope proteins in sera with anti-DHBV preS and S antibodies. Comparative sequence analysis of the PCR-amplified SGHBV genomes revealed unique SGHBV sequence features compared with other avian hepadnaviruses. Unlike DHBV, SGHBV shows an open reading frame in an analogous position to orthohepadnavirus X genes. Four of five cloned genomes were competent in replication, gene expression, and virus particle secretion in chicken hepatoma cells. Primary duck hepatocytes were permissive for infection with SGHBV, suggesting a similar or identical host range. SGHBV was found to secrete a significant fraction of virion-like particles containing single-stranded viral DNA. This was observed both in cell culture medium of SGHBV DNA-transfected LMH cells and in viremic sera of several birds, suggesting that it is a stable trait of SGHBV. Taken together, SGHBV has several unique features that expand the knowledge of the functional and evolutionary diversity of hepadnaviruses and offers new experimental opportunities for studies on the life cycle of hepadnaviruses.

Sequence heterogeneity of heron hepatitis B virus genomes determined by full-length DNA amplification and direct sequencing reveals novel and unique features

So far, only a single heron hepatitis B virus genome (HHBV-4) has been cloned and sequenced. Therefore, neither the significance of its sequence divergence from other avian hepadnaviruses nor the sequence variability of HHBV genomes in general are known. Here we have analysed the sequence heterogeneity of HHBV genome populations in several sera from naturally infected herons. A highly sensitive PCR method for full-length HHBV genome amplification was established which allowed direct sequencing of entire HHBV populations without prior cloning. Sequences of HHBV genomes from four sera were thus obtained which differed from those of HHBV-4 by up to 7%. Some of the divergent nucleotides and the corresponding amino acids of the predicted viral proteins were conserved in all four new HHBV isolates and varied only in HHBV-4. This indicates that the HHBV-4 genome is not in all aspects representative of this class of viruses. Interestingly, a highly conserved ORF upstream of the C-gene present in a position analogous to that of the mammalian hepadnavirus X-gene became apparent in all HHBV genomes. In contrast to the duck hepadnaviruses, the small (sAg-S) instead of the largest (sAg-L) envelope protein of all HHBVs has a myristylation site. These data confirm the significant sequence divergence of HHBV from other avian hepadnaviruses. Moreover, they show that HHBV has low sequence variability and indicate two new and unique features not evident in other avihepadnaviruses: an additional, highly conserved gene and potential myristylation of the sAg-S instead of the sAg-L envelope protein.

Effects of nucleotide changes on the ability of hepatitis delta virus to transcribe, process, and accumulate unit-length, circular RNA

The circular RNA genome of hepatitis delta virus (HDV) can fold into an unbranched rodlike structure. We mutagenized the two ends of this structure and assayed the effects on the ability of the genomes to replicate and accumulate processed RNA transcripts in transfected cells. The top end, defined as that nearest to the 5' end of the putative mRNA for delta antigen, was much more sensitive than the other end, defined as the bottom. Most of the 22 mutants made at the bottom were able to accumulate RNA as well as the wild type. For deletions extending as close as 2 nucleotides (nt) from the predicted domains needed for the two ribozymes, the accumulation levels dropped to <0.1%. In one mutant, 13 nt of HDV was replaced with 57 nt of non-HDV sequences, and accumulation was at 20% of the wild-type level, consistent with the potential of HDV to act as a vector. However, after replacement with a second sequence, accumulation dropped to 1%. For most of the 14 mutants made at the top of the rod, we observed dramatic inhibitory effects. For example, after removal of 3 bp from the stem adjacent to the terminal loop, accumulation dropped to <0.06% of the wild-type genome level. The top region that we considered was adjacent to both the 5' end of the putative mRNA and the domain that has been proposed to contain a promoter for RNA-directed RNA synthesis. The RNA accumulation abilities of certain mutants were tested under additional different experimental conditions. It was found that after longer times, some mutants began to catch up with the wild type. Also, it was found that certain top mutants gave much greater levels of accumulation when transfected into cells containing the small delta antigen. One interpretation of these data is that certain features at the top of the rod are needed for the accumulation of essential delta antigen mRNA species.

Nucleotide sequence stability of the genome of hepatitis delta virus

Cultured cells were cotransfected with a fully sequenced 1,679-base cDNA clone of human hepatitis delta virus (HDV) RNA genome and a cDNA for the genome of woodchuck hepatitis virus (WHV). The HDV particles released were able to infect a woodchuck that was chronically infected with WHV. The HDV so produced was passaged a total of six times in woodchucks in order to determine the stability of the HDV nucleotide sequence. During a final chronic infection with such virus, liver RNA was extracted, and the HDV nucleotide sequence for the 352-base region, positions 905 to 1256, was obtained. By means of PCR, we obtained double-stranded cDNA both for direct sequencing and also for molecular cloning followed by sequencing. By direct sequencing, we found that a consensus sequence existed and was identical to the original sequence. From the sequences of 31 clones, we found 32% (10 of 31) to be identical to the original single nucleotide sequence. For the remainder, there were neither insertions nor deletions but there was a small number of single-nucleotide changes. These changes were predominantly transitions rather than transversions. Furthermore, the transitions were largely of just two types, uridine to cytidine and adenosine to guanosine. Of the 40 changes detected on HDV, 35% (14 of 40) occurred within an eight-nucleotide region that included position 1012, previously shown to be a site of RNA editing. These findings may have significant implications regarding both the stability of the HDV RNA genome and the mechanism of RNA editing.

Apparent helper-independent infection of woodchucks by hepatitis delta virus and subsequent rescue with woodchuck hepatitis virus

Hepatitis delta virus (HDV) is a subviral agent of humans which is dependent upon hepatitis B virus as a helper for transmission. HDV can be experimentally transmitted to woodchucks by using woodchuck hepatitis virus (WHV) as the helper. We used this model system to study two types of HDV infections: those of animals already chronically infected with WHV and those of animals without any evidence of prior exposure to WHV. At 5 to 10 days after infection with HDV, liver biopsies of these two groups of animals indicated that around 1% of the hepatocytes were infected (HDV antigen positive). Moreover, similar amounts of replicative forms of HDV RNA were detected. In contrast, by 20 days postinfection, the two groups of animals were quite different in the extent of the HDV infection. The animals chronically infected with WHV showed spread of the infection within the liver and the release of high titers of HDV into the serum. In contrast, the animals not previously exposed to WHV showed a progressive reduction in liver involvement, and at no time up to 165 days postinfection could we detect HDV particles in the serum. However, if these animals were inoculated with a relatively high titer of WHV at either 7 or even 33 days after the HDV infection, HDV viremia was observed. Our data support the interpretation that in these animals, hepatocytes were initially infected in the absence of helper virus, HDV genome replication took place, and ultimately these replicating genomes were rescued by the secondary WHV infection. The observation that HDV can survive in the liver for at least 33 days in the absence of coinfecting helper virus may be relevant to the reemergence of HDV infection following liver transplantation.

Introduction of hepatitis delta virus into animal cell lines via cationic liposomes

Cationic liposomes are known to facilitate efficient transfection of animal cells with DNA and even some viruses. As reported here, we have been able to use such a commercially available formulation (Lipofectamine) and introduce human hepatitis delta virus (HDV) into lines of cultured cells and demonstrate replication of the HDV genome both by immunofluorescence and by Northern (RNA) analysis. As much as 10% of the human hepatoma cell line Huh7 was transfected with HDV. Also transfected were the baby hamster kidney cell line BHK-21 and the Morris rat hepatoma line 7777. Two initial applications of HDV transfection have been made. (i) The ribonucleoprotein structure of HDV was isolated from disrupted virions and demonstrated as being sufficient to transfect Huh7 cells. In contrast, naked HDV RNA was not sufficient. (ii) From a study of cells transfected with HDV particles, it was found that, even after as long as 7 weeks and the associated replication of the transfected cells, the HDV RNA genome was still replicating. Apparently, HDV, in the absence of helper virus and in the absence of virus assembly, can maintain persistent replication and expression of the HDV genome. Transfection was also achieved with woodchuck hepatitis virus introduced into Huh7 cells. In summary, this transfection procedure should be of use for the study of these and maybe other recalcitrant animal viruses.

Pathogenesis associated with replication of hepatitis delta virus

Hepatitis delta virus (HDV) is a subviral satellite of human hepatitis B virus (HBV). HDV was discovered in patients chronically infected with HBV who had a more severe form of disease. Subsequent studies have attempted to understand the cytopathic effects due to HDV, and this article reviews the progress along with newer studies that suggest that HDV genome replication per se causes no more than a moderate inhibition of cellular growth rate. This inhibition nevertheless provides a selective pressure for reduced levels of HDV genome replication. Such a reduction is apparently achieved by a host cell activity that edits the HDV RNA genome.

RNA editing in the replication cycle of human hepatitis delta virus

For some time it has been known that the RNA genome of human hepatitis delta virus (HDV) undergoes a specific RNA editing event. This review describes the editing phenomenon and its potential biological significance, and evaluates the data regarding the mechanism involved, including the possible relationship to other RNA editing phenomena.

Ribonucleoprotein complexes of hepatitis delta virus

Human hepatitis delta virus (HDV) is a subviral satellite agent of hepatitis B virus (HBV). The envelope proteins of HDV are provided by the helper virus, HBV, but very little is known about the internal structure of HDV. The particles contain multiple copies of the delta antigen and an unusual RNA genome that is small, about 1,700 nucleotides in length, single stranded, and circular. By using UV cross-linking, equilibrium density centrifugation, and immunoprecipitation, we obtained evidence consistent with the interpretation that delta antigen and genomic RNA form a stable ribonucleoprotein (RNP) complex within the virion. Furthermore, electron-microscopic examination of the purified viral RNP revealed a roughly spherical core-like structure with a diameter of 18.7 +/- 2.5 nm. We also isolated HDV-specific RNP structures from the nuclei of cells undergoing HDV genome replication; both the genome and antigenome (a complement of the genome) of HDV were found to be in such complexes. From the equilibrium density analyses of the viral and nuclear RNPs, we were able to deduce the number of molecules of delta antigen per molecule of HDV RNA. For virions, this number was predominantly ca. 70, which was larger than for the nuclear RNPs, which were more heterogeneous, with an average value of ca. 30.

Experimental transmission of human hepatitis delta virus to the laboratory mouse

Human hepatitis delta virus (HDV), obtained from the serum of an experimentally infected woodchuck, was injected into either the peritoneal cavity or the tail vein of both adult CB17 mice and mice with a severe combined immunodeficiency (CB17-scid mice). Three lines of evidence indicated that the virus was able to reach the liver and infect hepatocytes: (i) the amount of HDV genomic RNA detected in the liver by Northern (RNA) analysis increased during the first 5 to 10 days postinoculation, reaching a peak that was about threefold the amount in the original inoculum; (ii) also detected in the liver was the viral antigenomic RNA, which is complementary to the genomic RNA found in virions, and is diagnostic for virus replication; and (iii) by immunoperoxidase staining of liver sections, the delta antigen was detected in the nuclei of scattered cells identifiable as hepatocytes. In all of the mice, clearance of the infection occurred between 10 and 20 days after inoculation. The half-life for clearance was about 3 days in CB17-scid mice, indicating that clearance of infection did not involve a T- and B-cell-dependent immune response. Cell-to-cell spread of the initial infection was not detected. One possible interpretation of our results is that HDV infection of hepatocytes is directly cytopathic. Also, the results imply that chronic infection of the liver in humans may require continuous spread of virus within the liver. Alternatively, HDV in the absence of helper virus may be unable to cause a chronic infection of hepatocytes in vivo.

Autoantibodies to the nuclear Sp100 protein in primary biliary cirrhosis and associated diseases: epitope specificity and immunoglobulin class distribution

Sp100, a protein with a dot-like intranuclear localization in immunofluorescence microscopy, is a major target for patient autoantibodies in primary biliary cirrhosis (PBC) and occasionally in rheumatic disorders. The human Sp100 cDNA has recently been cloned, and the deduced amino acid sequence was found to contain sequence similarities with an MHC class I domain and several transacting regulatory proteins, including HIV-1 nef proteins. In this study, recombinant Sp100 fusion proteins were used to differentiate the immunoglobulin isotypes and to map the epitopes involved in the anti-Sp100 autoimmune response. PBC patients developed IgG as well as IgM and/or IgA class anti-Sp100 autoantibodies whereas most patients with rheumatic diseases developed IgG class autoantibodies only. For epitope mapping, truncated versions of the Sp100 protein were probed for immunoreactivity in ELISA and immunoblotting. With 55 sera, 17 different reaction patterns were obtained, and at least three non-overlapping major autoantigenic domains were recognized by the majority of sera. One domain, which contains the sequence similarity with HIV nef proteins, was recognized by all anti-Sp100 sera and harbours multiple, in part discontinuous, epitopes. These data demonstrate a heterogeneous and patient-specific anti-Sp100 autoimmune response which is antigen-driven and, at least in terms of isotype composition, different in PBC and non-PBC patients.

Characterization of cDNA encoding the mouse hepatic triglyceride lipase and expression by in vitro translation

A cDNA coding for the mouse hepatic triglyceride lipase has been isolated from a mouse liver cDNA library. The nucleotide sequence of the cDNA shows an open reading frame encoding a polypeptide of 510 amino acids that is 91.5% and 86% homologous to rat and human hepatic lipase, respectively. The most drastic protein sequence divergence is found at the carboxyterminal end which was speculated to harbour one heparin-binding site. By in vitro translation of cRNA in the presence of pancreatic membranes the hepatic lipase was shown to be glycosylated and to have an electrophoretic mobility of 53 kDa.

Cloning and expression of antigenic epitopes of the human 68-kDa (U1) ribonucleoprotein antigen in Escherichia coli

Autoantibodies directed against the 68-kDa (U1) ribonucleoprotein antigen are mainly found in sera of patients with mixed connective tissue disease. The corresponding cDNA was fragmented into four regions coding for the major antigenic epitopes A', B', C' and D'. All the epitopes were subcloned and expressed as fusion proteins with the glutathione S-transferase in Escherichia coli using the novel expression system pGEX that allows very high yields of recombinant proteins after a single-step purification. The sera of patients with the autoimmune disease were analyzed for the expressed recombinant proteins by an immunoblotting technique. All positive sera showed a patient-specific behavior and could be divided into four groups regarding recognition of the four antigenic epitopes of the 68-kDa (U1) ribonucleoprotein antigen. The epitope B' was reactive to all patient sera positively tested and classified as the marker antigenic epitope for the mixed connective tissue disease.

Repetitive P68-autoantigen specific epitopes recognized by human anti-(U1) small nuclear ribonucleoprotein autoantibodies

The major target of anti-(U1)snRNP autoantibodies, a serological marker of patients with mixed connective tissue disease and related rheumatic disorders, is a 68 kDa protein (p68) associated with (U1)RNA-containing small nuclear ribonucleoprotein particles. With recombinant p68 fusion proteins, multiple autoepitopes have been identified, and one of these has been mapped to the pentamer sequence ERKRR, which is located within antigenic domain A in the amino-terminal half of p68. The lysine residue (K) of this epitope can be replaced by isoleucine without loss of autoantibody binding. Here we have investigated whether other variants of this epitope are present on the p68 autoantigen and if these are recognized by anti-p68 autoantibodies. We identified four related motifs in the carboxy-terminal half of the p68-protein, and three of these (all containing glutamic acid instead of lysine (ERERR] mapped to the previously characterized autoantigenic domains C and D. Immunoreaction of anti-ERKRR autoantibodies, affinity-purified from domain A with recombinant fusion proteins containing either domain C or domain D of p68, revealed that anti-ERKRR autoantibodies cross-react with the ERERR-motifs. This finding, which was confirmed by competitive inhibition-ELISA with solid-phase coupled domain A-, C- and D-fusion proteins and ERKRR-containing synthetic peptides as competitors, suggests that a subset of patient autoantibodies is directed against repetitive structures on a single snRNP component.

Isolation and characterization of cDNA encoding a human nuclear antigen predominantly recognized by autoantibodies from patients with primary biliary cirrhosis

Autoantibodies to a novel nuclear Ag, Sp100, have recently been described that recognize a nuclear protein with an apparent molecular mass of 95 to 100 kDa and a dot-like distribution within cell nuclei. By immunoscreening of a lambda gt11 cDNA expression library derived from HeLa cells with an anti-Sp100 autoimmune serum a 0.7-kb cDNA (Sp26) coding for a fragment of Sp100 was isolated. Expression of this cDNA and use of the recombinant protein in ELISA revealed that the fragment carries major Sp100 autoepitopes and that anti-Sp100 autoantibodies predominantly occur in patients suffering from primary biliary cirrhosis (50/184). The Sp26 cDNA was used as hybridization probe for isolation of longer cDNA from human liver- and placenta-derived lambda gt10 cDNA libraries. Overlapping fragments were assembled to generate a full length cDNA coding for a protein with a molecular mass of 53 kDa and an isoelectric point of 4.7. The Sp100 autoantigen expressed in vitro from this cDNA and authenticated by a capture immunoblot assay, comigrated in SDS-PAGE with the authentic HeLa autoantigen of 95 to 100 kDa and thus showed an aberrant electrophoretic mobility. Computer based protein sequence analysis of the Sp100 autoantigen revealed regions of striking sequence similarities to the alpha 1 and alpha 2 domains of various human and non-human MHC class I Ag and to several transacting transcriptional regulatory proteins.

Isolation and characterization of cDNA encoding a human nuclear antigen predominantly recognized by autoantibodies from patients with primary biliary cirrhosis

Autoantibodies to a novel nuclear Ag, Sp100, have recently been described that recognize a nuclear protein with an apparent molecular mass of 95 to 100 kDa and a dot-like distribution within cell nuclei. By immunoscreening of a lambda gt11 cDNA expression library derived from HeLa cells with an anti-Sp100 autoimmune serum a 0.7-kb cDNA (Sp26) coding for a fragment of Sp100 was isolated. Expression of this cDNA and use of the recombinant protein in ELISA revealed that the fragment carries major Sp100 autoepitopes and that anti-Sp100 autoantibodies predominantly occur in patients suffering from primary biliary cirrhosis (50/184). The Sp26 cDNA was used as hybridization probe for isolation of longer cDNA from human liver- and placenta-derived lambda gt10 cDNA libraries. Overlapping fragments were assembled to generate a full length cDNA coding for a protein with a molecular mass of 53 kDa and an isoelectric point of 4.7. The Sp100 autoantigen expressed in vitro from this cDNA and authenticated by a capture immunoblot assay, comigrated in SDS-PAGE with the authentic HeLa autoantigen of 95 to 100 kDa and thus showed an aberrant electrophoretic mobility. Computer based protein sequence analysis of the Sp100 autoantigen revealed regions of striking sequence similarities to the alpha 1 and alpha 2 domains of various human and non-human MHC class I Ag and to several transacting transcriptional regulatory proteins.

Major autoantigenic sites of the (U1) small nuclear ribonucleoprotein-specific 68-kDa protein

A 68-kDa protein associated with (U1)snRNP is a major target for human autoantibodies to small ribonucleoprotein particles (snRNP) prevalent in a variety of inflammatory rheumatic diseases. The epitopes recognized by these antibodies were mapped by expression of subfragments of p68 cDNA in Escherichia coli and testing of the corresponding recombinant proteins for immunoreactivity with sera of patients with autoimmune diseases. Three of four antigenic regions were analysed in detail. The immunodominant autoantigenic region was found to coincide with the RNA-binding domain of the p68 protein and was shown to contain a nested set of overlapping discontinuous epitopes. Two additional non-overlapping major antigenic domains were localized in the carboxy-terminal half of the p68 protein. Each of these two carboxy-terminal domains was shown to contain more than one conformation-dependent epitope. Taking into account previous mapping studies, the data demonstrate that p68 contains at least four antigenic regions, each of which harbours multiple epitopes which are recognized in a patient-specific manner.

Human anti-p68 autoantibodies recognize a common epitope of U1 RNA containing small nuclear ribonucleoprotein and influenza B virus

Autoantibodies from patients with systemic rheumatic diseases were used to map antigenic sites on the 68-kD autoantigen (p68) associated with (U1)RNA-containing small nuclear ribonucleoprotein (snRNP) particles. With truncated recombinant fusion proteins and synthetic peptides, a subset of anti-p68 autoantibodies was found to recognize the amino acid sequence motif Glu-Arg-Lys-Arg-Arg (ERKRR). To investigate the possible involvement of epitopes shared by microbial antigens and host self-components in initiation of autoimmunity (molecular mimicry), a sequence data bank was screened for proteins containing an amino acid motif identical or related to ERKRR. The identical motif was found on the M1 matrix protein of influenza B viruses, and affinity-purified human anti-ERKRR autoantibodies recognized this epitope also in the viral amino acid sequence context. The common epitope recognized by human autoantibodies suggests that influenza B virus infection may play a role in initiation of the anti-p68 and anti-(U1)RNP autoimmune response.

Epitope mapping with a recombinant human 68-kDa (U1) ribonucleoprotein antigen reveals heterogeneous autoantibody profiles in human autoimmune sera

Several cDNA fragments encoding parts of the (U1)RNP specific 68-kDa autoantigen were expressed in Escherichia coli and the fusion proteins were used as substrate for localization of the autoreactive epitopes. We have identified a region of approximately 30 amino acids reacting with more than 90% (16 of 17) of all human anti-p68 sera tested, regions which carry only a few and a region with no autoepitopes. Comparative analysis of epitopes recognized on partially degraded fusion proteins indicated that the anti-p68 autoimmune response is polyclonal. It involves generation of antibodies to several epitopes including one in a region with retroviral gag protein homology speculated to play a role in the initiation of the autoimmune response. Each of the 17 sera tested contained a different set of autoantibody specificities. These data are not consistent with random mutation as a sole mechanism of anti-p68 autoantibody induction and argue for an Ag-driven autoimmune response.

Epitope mapping with a recombinant human 68-kDa (U1) ribonucleoprotein antigen reveals heterogeneous autoantibody profiles in human autoimmune sera

Several cDNA fragments encoding parts of the (U1)RNP specific 68-kDa autoantigen were expressed in Escherichia coli and the fusion proteins were used as substrate for localization of the autoreactive epitopes. We have identified a region of approximately 30 amino acids reacting with more than 90% (16 of 17) of all human anti-p68 sera tested, regions which carry only a few and a region with no autoepitopes. Comparative analysis of epitopes recognized on partially degraded fusion proteins indicated that the anti-p68 autoimmune response is polyclonal. It involves generation of antibodies to several epitopes including one in a region with retroviral gag protein homology speculated to play a role in the initiation of the autoimmune response. Each of the 17 sera tested contained a different set of autoantibody specificities. These data are not consistent with random mutation as a sole mechanism of anti-p68 autoantibody induction and argue for an Ag-driven autoimmune response.

A recombinant autoantigen derived from the human (U1) small nuclear RNP-specific 68-kd protein. Expression in Escherichia coli and serodiagnostic application

A human liver complementary DNA expression library was screened using sera from patients with high titers of autoantibodies, to search for clones expressing major autoantigens that are relevant in connective tissue diseases. One of the clones isolated expressed a major epitope(s) that was immunoreactive with anti-U1 RNP sera, as shown by several techniques. Affinity-purified autoantibodies from the cloned RNP protein specifically recognized the 68-kd U1 RNP protein of HeLa cell nuclear extracts. All sera containing anti-U1 RNP antibodies detected by immunodiffusion, counterimmunoelectrophoresis, or immunoblotting also recognized the cloned RNP protein. The RNP antigen-expressing bacterial colonies and the partially purified cloned RNP fusion protein have been applied to fast and sensitive immunologic assays for the detection and quantification of anti-U1 RNP antibodies.