A monoclonal antibody specific to the non-epitope region of hepatitis B virus preS1 contributes to more effective HBV detection

Construction of an anti-hepatitis B virus preS1 antibody and usefulness of preS1 measurement for chronic hepatitis B patients: Anti-HBV PreS1 antibody

OBJECTIVES

The preS1 region plays an essential role in hepatitis B virus (HBV) infection. We construct an antibody that binds to preS1 and a measurement system for serum preS1 in chronic HBV-infected patients.

METHODS

Hybridoma clones that produce anti-preS1 antibodies were obtained by the iliac lymph node method. Epitope mapping was conducted, and an enzyme-linked immunosorbent assay (ELISA)-based method was developed. Using this ELISA system, serum preS1 levels were measured in 200 chronic HBV-infected patients.

RESULTS

Eight types of hybridomas were obtained, of which antibody 3-55 using amino acids 38-47 as the epitope showed high binding affinity to preS1. Serum preS1 levels measured by ELISA using 3-55 antibody were correlated with HBsAg, HBcrAg and HBV DNA levels. Among HBeAg-negative patients without antiviral therapeutic objective (HBV DNA <3.3 log IU/mL or alanine aminotransferase ≤30 U/L), preS1 was significantly higher in subjects who had progressed to the point of requiring antiviral therapy compared to subjects who had maintained their status for the preceding three years (p<0.01).

CONCLUSIONS

We constructed an antibody against preS1 and an ELISA system capable of measuring serum preS1 levels. PreS1 may serve as a novel tool to predict the need for antiviral therapy in HBeAg-negative HBV-infected patients.

A Highly Sensitive Detection System based on Proximity-dependent Hybridization with Computer-aided Affinity Maturation of a scFv Antibody

The hepatitis B virus (HBV) infection is a critical health problem worldwide, and HBV preS1 is an important biomarker for monitoring HBV infection. Previously, we found that a murine monoclonal antibody, mAb-D8, targets the preS1 (aa91-107) fragment of HBV. To improve its performance, we prepared the single-chain variable region of mAb-D8 (scFvD8) and constructed the three-dimensional structure of the scFvD8-preS1 (aa91-107) complex by computer modelling. The affinity of scFvD8 was markedly increased by the introduction of mutations L96Tyr to Ser and H98Asp to Ser. Furthermore, a highly sensitive immunosensor was designed based on a proximity-dependent hybridization strategy in which the preS1 antigen competitively reacts with an antibody labelled with DNA, resulting in decreased proximity-dependent hybridization and increased electrochemical signal from the Fc fragment, which can be used for the quantisation of preS1. The results showed a wide detection range from 1 pM to 50 pM with a detection limit of 0.1 pM. The sensitivity and specificity of this immunosensor in clinical serum samples were 100% and 96%, respectively. This study provides a novel system based on proximity-dependent hybridization and the scFv antibody fragment for the rapid quantisation of antigens of interest with a high sensitivity.

Detection methods of Cyprinid herpesvirus 2 infection in silver crucian carp (Carassius auratus gibelio) via a pORF72 monoclonal antibody

Cyprinid herpesvirus 2 (CyHV-2) is the main pathogen responsible for causing haematopoietic necrosis disease in Carassius auratus gibelio. Although many nucleic acid-based diagnostic methods have been applied, no stable and sensitive immunological diagnostic approaches have been reported. In this study, to detect CyHV-2 in clinical samples using immunological methods, recombinant ORF72 protein (pORF72), encoded by the CyHV-2 ORF72 gene, was used as a capture antigen to identify blood and tissues infected with CyHV-2. First, ORF72 gene was amplified from the CyHV-2 genome and cloned into a PGEX-4t-3 expression vector to produce pORF72 in Escherichia coli. The purified pORF72 was used as an immunogen to prepare monoclonal antibodies. The Western blotting assays revealed that the monoclonal antibody could specifically identify the pORF72. Furthermore, an immunohistochemical protocol and a blood smear method were established to detect CyHV-2 in carps. The results indicate that the monoclonal antibody against pORF72 could be utilized as an effective detection tool for haematopoietic necrosis disease in Carassius auratus gibelio.

A virus-like particle of the hepatitis B virus preS antigen elicits robust neutralizing antibodies and T cell responses in mice

The preS antigen of hepatitis B virus (HBV) corresponds to the N-terminal polypeptide in the large (L) antigen in addition to the small (S) antigen. The virus-like particle (VLP) of the S antigen is widely used as a vaccine to protect the population from HBV infection. The presence of the S antigen and its antibodies in patient blood has been used as markers to monitor hepatitis B. However, there is very limited knowledge about the preS antigen. We generated a preS VLP that is formed by a chimeric protein between preS and hemagglutinin (HA), and the matrix protein M1 of influenza virus. The HBV preS antigen is displayed on the surface of preS VLP. Asn112 and Ser98 of preS in VLP were found to be glycosylated and O-glycosylation of Ser98 has not been reported previously. The preS VLP shows a significantly higher immunogenicity than recombinant preS, eliciting robust anti-preS neutralizing antibodies. In addition, preS VLP is also capable of stimulating preS-specific CD8⁺ and CD4⁺ T cell responses in Balb/c mice and HBV transgenic mice. Furthermore, preS VLP immunization provided protection against hydrodynamic transfection of HBV DNA in mice. The data clearly suggest that this novel preS VLP could elicit robust immune responses to the HBV antigen, and can be potentially developed into prophylactic and therapeutic vaccines.

Production and characterization of a monoclonal antibody against a late gene encoded by grouper iridovirus 64L

Viral envelope proteins play important roles in viral infection and assembly. The grouper iridovirus ORF 64L (GIV-64L) was predicted to encode an envelope protein and was conserved in all sequenced Ranaviruses. In this study, the complete nucleotide sequence of the GIV-64L gene (1215 bp) was cloned into the isopropyl β-D-1-thiogalactopyranoside (IPTG) induction prokaryotic expression vector pET23a. The approximately 50.2 kDa recombinant GIV-64L-His protein was induced, purified and used as an immunogen to immunize BALB/c mice. Three monoclonal antibodies (mAbs), all IgG1 class antibodies against GIV-64L protein, were produced by enzyme-linked immunosorbent assay. Reverse transcription polymerase chain reaction analyses revealed GIV-64L to be a late gene when expressed in grouper kidney cells during GIV infection with cycloheximide (an inhibitor of protein synthesis) or cytosine arabinoside (an inhibitor of DNA synthesis) present. Finally, one of the established mAbs, GIV-64L-mAb-17, was used in Western blotting and an immunofluorescence assay, which showed that GIV-64L protein was expressed at 24 h post-infection and localized only in the cytoplasm in GIV-infected cells, packed into a whole virus particle. The presently characterized GIV-64L mAbs should have widespread applications in GIV immunodiagnostics and other research, and these results should offer important insights into the pathogenesis of GIV.

Identification and characterization of a late gene encoded by grouper iridovirus 2L (GIV-2L)

Grouper iridovirus (GIV) belongs to the Ranavirus genus and is one of the most important viral pathogens in grouper, particularly at the fry and fingerling stages. In this study, we identified and characterized the GIV-2L gene, which encodes a protein of unknown function. GIV-2L is 1242 bp in length, with a predicted protein mass of 46.2 kDa. It displayed significant identity only with members of the Ranavirus and Iridovirus genera. We produced mouse monoclonal antibodies against the GIV-2L protein by immunizing mice with GIV-2L-His-tag recombinant protein. By inhibiting de novo protein and DNA synthesis in GIV-infected cells, we showed that GIV-2L was a late gene during the viral replication. Finally, immunofluorescence microscopy revealed that GIV-2L protein accumulated in both the nucleus and cytoplasm of infected cells. These results offer important insights into the pathogenesis of GIV.

Development and characterization of two monoclonal antibodies against grouper iridovirus 55L and 97L proteins

Grouper iridovirus (GIV) is one of the most important viral pathogens in grouper, particularly at the fry and fingerling stages. The study of GIV pathogenicity has been hampered by the lack of proper immunological reagents to study the expression and function of viral proteins in the infected cells. In this study, two mouse monoclonal antibodies (mAbs) against GIV 55L and 97L proteins were produced. Enzyme-linked immunosorbent assay (ELISA) and Western blotting were used to screen these hybridomas, resulting in the identification of two high-affinity mAbs named GIV55L-mAb-2 and GIV97L-mAb-3, respectively. Both mAbs belong to the IgG1 isotype and were effective in detecting their respective target viral protein. Reverse-transcription polymerase chain reaction (RT-PCR) and Western blot analyses of GIV-infected GK cells revealed that GIV 97L is an immediate early gene, whereas GIV 55L a late one. The localization of 55L and 97L in GIV-infected cells was further characterized by immunofluorescence microscopy with the mAbs. The 55L protein mainly aggregated in the cytoplasm while 97L distributed in both the nucleus and cytoplasm of the infected cells. These studies demonstrate the validity of the two mAbs as immunodiagnostic and research reagents.