Yoshikazu Honda

Monoclonal Antibody #5-2-26 Recognizes the Phosphatase-Sensitive Epitope of Rabies Virus Nucleoprotein

We prepared monoclonal antibodies (MAbs) against the rabies virus N protein, among which one antibody (MAb 5‐2‐26) was shown to lack reactivity with the phosphatase‐treated N protein. The MAb was able to recognize the sodium dodecyl sulfate (SDS)‐denatured N protein. The MAb did not recognize the N‐protein analogues produced in Escherichia coli (E. coli), indicating that the N‐gene products were not normally processed in E. coli after translation. On the other hand, the MAb reacted normally with N‐gene products produced in COS‐7 cells, but not with those produced in the presence of K‐252a (a protein kinase inhibitor of a broad spectrum). The MAb displayed weak cross‐reactivity with the Triton‐insoluble network structures composed of several components, while another phosphoprotein (M1) of the virus was not recognized at all. These results suggest that MAb 5‐2‐26 preferentially recognizes a phosphatase‐sensitive linear epitope of N protein, which may enable further investigations to be conducted on the mechanism of N‐protein phosphorylation and its role(s) in virus replication.

Structural relationship between nucleocapsid-binding activity of the rabies virus phosphoprotein (P) and exposure of epitope 402-13 located at the C terminus.

The structural changes of the nominal phosphoprotein (P) of rabies virus using a monoclonal antibody, mAb #402-13, was investigated. This mAb recognized a linear epitope that was mapped roughly to a C-terminal region of the P protein, ranging from aa 256 to 297. The P gene products were detected by the mAb in immunoblot assays, the products of which were produced either in BHK-21 cells or in Escherichia coli cells. The mAb, however, detected very low levels of P gene products in immunoprecipitation assays. The mAb recognized the nucleocapsid (NC)-associated P proteins but recognized free P protein and free N-P complex produced in the infected cells much less efficiently. When the P proteins were released from the NC, however, they were no longer recognized by the mAb. Similar results were obtained from BHK-21 cells co-transfected with P and N cDNAs. Furthermore, studies with C-terminally truncated P protein mutants revealed that the NC-binding ability of the P protein was dependent on the presence of the C-terminal epitope region. From these results, it is thought that the 402-13 epitope region is concealed when the P protein is present in a free form or free N-P complex but is exposed when it is associated with the NC. The C-terminal epitope region seemed to be essential for the P protein to be associated with the NC but not for the formation of free N-P complexes with newly synthesized N protein.

Hepatitis C virus core region: helper T cell epitopes recognized by BALB/c and C57BL/6 mice

In this study, we characterized the B cell and T cell responses to the hydrophilic portion of hepatitis C virus (HCV) core protein in two strains of mice and identified the respective antigen determinants. BALB/c (H-2d) and C57BL/6 (B6:H-2b) mice were immunized by a subcutaneous injection of recombinant HCV core protein together with Freunds complete adjuvant. The level of antibody production, as determined by ELISA, was consistently higher in BALB/c than in B6 mice. However, antibodies in sera from each strain bound to the N-terminal region of the core protein within amino acids 1 to 28 (MSTNPKPQRKIKRNTNRRPQDVKFPGGG), according to an experiment using non-overlapping peptides that covered the hydrophilic portion of HCV core protein. The T cell responses were also higher in BALB/c than in B6 mice with respect to the proliferative responses of the draining lymph node cells in vitro. By limiting dilution cultures of the draining lymph node cells in vitro repetitively stimulated with recombinant core protein, T cell clones were established from both strains of mice and characterized. The surface markers of these clones were Thy-1.2+, CD3+, TCR alpha beta+, CD4+ and CD8+. The proliferative responses were inhibited in the presence of anti-CD4 or anti-MHC class II monoclonal antibodies. The T cell lines in BALB/c mice recognized an epitope in HCV core at amino acids 72 to 91 (EGRAWAQPGYPWPLYGNEGL). The T cell lines in B6 mice recognized an epitope at amino acids 55 to 74 (RPQPRGRRQPIPKARQPEGR). Thus, mice with different MHC haplotypes recognized different non-overlapping T cell antigenic determinants of HCV core proteins.

Isolation and purification of a non-A, non-B hepatitis-associated microtubular aggregates protein

Blood-borne type non-A, non-B (NANB) hepatitis-associated microtubular aggregates protein was isolated and partially sequenced. The microtubular aggregates were isolated from the hepatocytes of NANB-infected chimpanzees and were found to have a buoyant density in sucrose solution of 1.21 to 1.23 g/ml. A single protein, recognized by our anti-microtubular aggregates monoclonal antibodies, was found to have an Mr of 44,000 (p44). This p44 protein was not found in uninfected chimpanzees. We determined a partial amino acid sequence for p44, and showed that it has no homology to any known proteins.

Comparative Studies of Rabies and Sindbis Virus Replication in Human Neuroblastoma (SYM-I) Cells that Can Produce Interferon

K-104 cells, a cloned cell line derived from a human neuroblastoma (SYM-I), were induced by rabies HEP-Flury virus to release large amounts of interferon, and the resulting antiviral activity significantly suppressed the rabies virus replication. The role of endogenous interferon was confirmed by treatment with anti-interferon antibody which increased the yield of progeny virus. The virus yield in the second undiluted passage through K-104 cells was much less than that in the first passage, because of the antiviral state initiated by brief contact of interferon present in the virus inoculum with cells during the short period of virus adsorption. When the m.o.i. was relatively low, as in the third undiluted passage, the effect of interferon present in the inoculum was enhanced and most of the infected cells survived but were shown to be in a state of persistent infection. Defective interfering (DI) particles did not accumulate rapidly during these three undiluted passages. When Sindbis virus was used for infection, the endogenous interferon system of K-104 cells was not activated during 12 undiluted passages. However, on the 12th passage, the yield began to decline due to the generation and accumulation of DI particles.

Studies on the escape mutants of rabies virus which are resistant to neutralization by a highly conserved conformational epitope-specific monoclonal antibody #1-46-12

We investigated a virus‐neutralizing conformational epitope of the rabies virus glycoprotein (G) that is recognized by an anti‐G monoclonal antibody (mAb; #1‐46‐12) and shared by most of the laboratory strains of the virus. To investigate the epitope structure, we isolated escape mutants from the HEP‐Flury virus (wild‐type; wt) after repeated passages in culture in the presence of the mAb. Immunofluorescence studies indicated that the mutants could be classified into two groups; the Group I lacked the epitope, while Group II preserved the epitope. The latter was dominant under the passage conditions, since Group I disappeared during the continuous passages. G proteins showed different electrophoretic mobilities; G protein of Group I migrated at the same rate as wt G protein, while that of Group II migrated at a slower rate, which was shown to be due to acquisition of an additional oligosaccharide side chain. Nucleotide sequencing of the G gene strongly suggested that amino acid substitutions at Thr‐36 by Pro and Ser‐39 by Thr of the G protein are responsible for the escape mutations of Groups I and II, respectively. The latter is a unique mutation of the rabies virus that allows the G protein to be glycosylated additionally at Asn‐37, a potential glycosylation site that is not glycosylated in the parent virus, in preserving the epitope‐positive conformation. These results suggest that to keep the 1‐46‐12 epitope structure is of greater survival advantage for the virus to escape the neutralization than to destroy it, which could be achieved by acquiring an additional oligosaccharide chain at Asn‐37.

cloning, sequencing and expression in Escherichia coli of cDNA for a non-A, non-B hepatitis-associated microtubular aggregates protein

A 1.7 kb cDNA encoding a novel antigen (p44; apparent Mr 44K) associated with non-A, non-B (NANB) hepatitis, was isolated from the hepatic cDNA library of a chimpanzee infected with NANB hepatitis. The library was screened with a monoclonal antibody against this antigen. The cDNA cloned contained an open reading frame encoding a 444 amino acid protein with an Mr calculated to be 50,468. The cDNA hybridized to a 1.9 kb mRNA obtained from chimpanzee hepatocytes infected with either the NANB or hepatitis delta viruses. It hybridized weakly to mRNA from hepatitis B virus-infected hepatocytes, and not at all to mRNA from normal chimpanzee hepatocytes. Southern blot analysis revealed that p44 is a host protein in chimpanzees, and that an identical gene exists in the human genome.

Production of antibodies directed against microtubular aggregates in hepatocytes of chimpanzees with non-A, non-B hepatitis.

We have previously used Epstein-Barr virus transformation to established two clonal lymphoblastoid cell lines (48-1 and S-1) producing monoclonal antibodies against microtubular aggregates that appear in the hepatocytes of chimpanzees with non-A, non-B hepatitis (NANBH). To obtain additional antibodies directed against the same structure, the mouse hybridoma method was employed. Partially purified microtubular aggregates were prepared from liver homogenates of a chimpanzee with NANBH and used as the immunogen. Hybridoma cultures were first screened by radioimmunoassay against the partially purified antigen and secondly by immunofluorescence (IF) using liver sections from a chimpanzee with NANBH. Twenty-seven cultures exhibited positive IF reactions similar to those observed with the original antibodies, 48-1 and S-1, and were cloned by limiting dilution. The specificities of the monoclonal antibodies were tested by IF on liver biopsy specimens from chimpanzees with hepatitis A, B, D or NANBH and from normal chimpanzees. All the antibodies proved to be IgG. Immunoelectron microscopy revealed that all 27 antibodies bound to the same structure, the microtubular aggregates, in hepatocytes of chimpanzees with NANBH. To determine the size of the antigen polypeptide recognized by these antibodies, polyacrylamide gel electrophoresis and Western blot assays were performed. Nine of the 27 antibodies specifically reacted with a single polypeptide of Mr 44K (p44). The remaining 18 antibodies detected no antigen polypeptide on the filters. The anti-p44 antibodies were then tested using cross-competition assays with 125I-labelled antibodies, and were found to be classifiable into three groups. In addition, the results indicate that at least three distinct epitopes are located on p44: epitope A recognized by group 1, epitope B recognized by group 2 and epitope C recognized by group 3.

Monoclonal Antibody #3‐9‐16 Recognizes One of the Two Isoforms of Rabies Virus Matrix Protein That Exposes Its N‐Terminus on the Virion Surface

We investigated behaviors of the rabies virus matrix (M) protein using a monoclonal antibody (mAb), #3‐9‐16, that recognized a linear epitope located at the N‐terminus of the protein. Based on the reactivity with this mAb, M proteins could be divided into at least two isoforms; an ordinary major form (Mα) whose 3‐9‐16 epitope is hidden, and an N‐terminal‐exposed epitope‐positive form (Mβ). The Mβ protein accounted for about 25–30% of the total M proteins in the virion, while its content in the cell ranged from 10 to 15% of total M protein. Fluorescent antibody (FA) staining showed that the Mβ antigen distributed in the Golgi area where the colocalized viral glycoprotein antigen was also detected. Mβ antigen was shown to be exposed on the surface of infected cells by both immunoprecipitation and FA staining with the mAb, whereby the cells might have become sensitive to the mAb‐dependent complement‐mediated cytolysis. Similarly, the Mβ antigen was shown to be exposed on the virion surface, and the infectivity of the virus was destroyed by the mAb in the presence of a complement. Together with these results, we think that the M protein molecule takes either of two conformations, one (Mβ) of which exposes the 3‐9‐16 epitope located in the N‐terminal region of the M protein, that are also exposed on the surface of the virion and infected cells, whereby it might play a certain important role(s) in the virus replication process differently from the other form (Mα), probably through its intimate association with the Golgi area and/or the cell membrane.

Persistent Infection of Rabies Virus (HEP-Flury Strain) in Human Neuroblastoma Cells Capable of Producing Interferon

Apparent interferon-mediated persistent infection of rabies virus (HEP-Flury strain) was established in a human neuroblastoma SYM-I (clone K-104) cell line, which had the ability to produce interferon. This infection produced variable but small amounts of progeny virus and interferon (up to 100 IU/ml), and resisted superinfection with vesicular stomatitis virus (VSV) and Sindbis virus as well as homologous rabies virus. The treatment of this infection with anti-interferon antibody stimulated virus replication and extensive c.p.e. However, some cells survived and grew rapidly without any sign of c.p.e. These produced increased amounts (100 to 1000 times) of infectious and DI particles in the presence of anti-interferon antibody, becoming susceptible to superinfection with VSV but remaining resistant to the original rabies virus. Small plaque mutants appeared and replaced the original virus during the long-term cultivation of the persistent infection. Several mutants tested were all identified as Sdi (DI-resistant) mutants, suggesting that the persisting viruses were endowed by the Sdi mutation with a selective advantage over the original virus even in interferon-mediated persistent infections.