- Volume 69, Issue 5, 1988

A collection of monoclonal antibodies (MAbs) against the haemagglutinin—neuraminidase (HN) and fusion (F) glycoproteins of parainfluenza virus type 3 (PIV3) was used for passive immunization of intracerebrally infected newborn hamsters. A significant degree of protection was obtained with MAbs against both the HN and F viral proteins, but no individual antibody conferred complete protection against disease. MAbs against different epitopes provided different degrees of protection. A MAb to the Sendai virus HN protein was found to confer protection against PIV3 brain infection.

The nucleotide sequence of an 11·2 kilobase fragment of the fowlpox virus genome is presented. The fragment comes from near one end of the genome and contains part of the terminal inverted repeat. Twenty open reading frames (ORFs) are predicted from the sequence and are classified into 13 major and seven minor ORFs. The 100 base pairs immediately upstream of each ORF are up to 83% AT-rich, with some motifs similar to those seen in vaccinia virus early gene promoters. The TTTTTNT element which has been identified as a termination signal for vaccinia virus early genes is also found downstream of several ORFs. Three ORFs are predicted to specify polypeptides with significant homology to proteins coded by genes near termini of orthopoxvirus genomes: the vaccinia virus 42K early gene and 32·5K host range gene, and the cowpox virus 38K red pock gene. In addition, there are two families of ORFs within the fragment which potentially encode related polypeptides. One of these, family B, contains three ORFs which are related to those of chicken and rat hepatic lectins.

A bacterial expression vector was constructed to encode a fusion protein which had, at its carboxy terminus, a polypeptide encoded within the 5′ proximal open reading frame of the coronavirus MHV-JHM mRNA 4. This polypeptide was isolated and used to produce an antiserum. The antiserum reacted specifically with a 15000 M r polypeptide synthesized in MHV-JHM-infected cells, or in vitro translations of infected cell poly(A) RNA enriched for mRNA 4. These results demonstrate the translational activity of mRNA 4 during infection, identify conclusively the translation product and provide a means to investigate the synthesis and function of this protein.

Epstein—Barr virus (EBV), an agent with growth transforming potential for human B cells, is associated with certain B cell lymphomas in man and also with an epithelial tumour, undifferentiated nasopharyngeal carcinoma (NPC). Since B cell growth transformation is associated with the constitutive expression of a small number of EBV-coded latent proteins, the nuclear antigens EBNA 1, EBNA 2, EBNA 3 and EBNA-LP and the latent membrane protein (LMP), the present work sought to determine whether this same pattern of virus gene expression occurred in NPC. Tumour biopsies were taken from NPC patients from three areas of differing tumour incidence (Kenya, Algeria, Britain) and immediately snap-frozen, as were biopsies of non-EBV-related carcinomas for controls. Immunoblotting of PAGE-separated proteins with selected human sera identified 24 NPC biopsies clearly expressing EBNA 1. When the analysis was extended using selected human sera with antibodies against the other EBNAs, there was no detectable expression of EBNA 2, EBNA 3 or EBNA-LP in any of these 24 biopsies; their EBNA 2-negative status was confirmed using a monoclonal antibody (MAb) PE2 which was reactive in immunoblotting and in immunoprecipitation with EBNA 2A and EBNA 2B proteins. Similar experiments with two different LMP-specific MAbs, CS1 to 4 and S12, revealed heterogeneity between NPC biopsies; 9/24 biopsies were demonstrably LMP-positive, the degree of expression varying considerably between individual tumours in a manner which was not related to the level of EBNA 1 expression. None of the 24 NPC biopsies expressed detectable amounts of EBV lytic cycle antigens. A nude mouse-passaged NPC cell line, C15, likewise expressed EBNA 1 and LMP but none of the other EBV latent proteins nor lytic cycle antigens. This work identifies a novel type of EBV-cell interaction in NPC cells which is distinct from that seen in in vitro transformed B cell lines and from that seen to date in EBV-positive B cell lymphomas.

Marek’s disease virus (MDV) infections normally have an early cytolytic phase in lymphoid organs at 3 to 6 days post-infection followed by a period of latent infection. Little is known about the mechanisms that govern latency with herpesvirus infections, including Marek’s disease (MD). To investigate the importance of immunocompetence for either the establishment or the maintenance of latency in MD, immunosuppressive treatments were applied prior to infection with MDV or after latency was established. These included cyclosporin (Cs) or betamethasone (BM) treatments, neonatal thymectomy plus cyclophosphamide treatment (Tx/Cy), and infection at a young age before full competence. The effect of all the treatments was determined by examining tissues and spleen cells for evidence of virus replication before and after cultivation in vitro. Induced (Cs or Tx/Cy treatments) or natural (infection at a young age) incompetence resulted in prolonged and more widespread early cytolytic infection. Immunosuppression by Cs after latency had developed resulted in a reappearance of cytolytic infection in the spleen and it enhanced the cytolytic infection in the thymus and the bursa of Fabricius. After immunosuppression with Cs, cytolytic infection was found mostly in T cells, although many of the virus-positive cells did not have markers for either T cells or B cells. Immunosuppression by BM after latency had developed also resulted in the reappearance of cytolytic infection in the spleen but only at a very low level. These results suggest that immunocompetence is required for the establishment and maintenance of latency.

5-Azacytidine (5-AZC) reduces cytosine methylation in DNA and has been reported to activate quiescent virus genes. Treatment of explant cultures of latently herpes simplex virus type 2 (HSV-2)-infected guinea-pig dorsal root ganglia and spinal cords in vitro with 5-AZC significantly enhanced the rate of HSV recovery. Both the number of isolates from ganglia (P < 0.001) and the rate of recovery (P < 0.001) were significantly increased with the addition of 50 µM-5-AZC to explant cultures. Increased virus recovery appeared to be due to the induction of reactivation of latent virus, rather than an increase in replication, since 5-AZC inhibited HSV replication. These data support a role for methylation in HSV latency and reactivation.

The M variant of encephalomyocarditis (EMC) virus consists of two biologically distinct variants: one, diabetogenic D variant (EMC-D) and the other, non-diabetogenic B variant (EMC-B). These two variants cannot be distinguished by hyperimmune sera. Monoclonal antibodies were generated against EMC-D or EMC-B to identify antigenic differences between these two variants. Fourteen independent hybrid cell lines, selected from seven separate fusions of mouse myeloma cells to spleen cells isolated from mice immunized with EMC-D, consisted of 12 hybrids which produced monoclonal antibodies that neutralized both EMC-D and EMC-B, and two hybrids (ED-HJ-23 and ED-HJ-31) which produced monoclonal antibodies that neutralized EMC-D but not EMC-B. Similarly, 16 independent hybrid cell lines, selected from eight separate fusions using spleen cells prepared from mice immunized with EMC-B, consisted of 15 hybrids which produced monoclonal antibodies neutralizing both EMC-D and EMC-B, and one hybrid (EB-48A-F1) which produced antibody that neutralized EMC-B, but not EMC-D. The specificities of these monoclonal antibodies (ED-HJ-23, ED-HJ-31, EB-48A-F1) were further confirmed using an immunofluorescent technique. The D variant-specific monoclonal antibodies reacted with cells infected with EMC-D but not EMC-B. In contrast, the B variant-specific monoclonal antibody reacted with the cells infected with EMC-B but not EMC-D. It is concluded that the EMC-D- and EMC-B-specific monoclonal antibodies are able to identify antigenic differences between diabetogenic and non-diabetogenic variants of EMC virus which cannot be distinguished by hyperimmune sera.

The genomic sequences of a portion of the 5′ non-coding region of polioviruses excreted by recipients of the Sabin vaccine strains of poliovirus were examined. It was found that in all three types a residue changed in the course of excretion to give a sequence representing the consensus of poliovirus sequences. For type 1 this residue was at position 481, which altered in half the vaccinees, for type 2 it was at position 480, which altered in all vaccinees and for type 3 it was at position 472 in all vaccinees, as previously reported. Other vaccine strains unrelated to the Sabin strains but used in limited vaccination programmes did not have such changing residues. It was concluded that these regions indicated sequences that were strongly selected during replication in the human gut. Such sequences were further defined by examination of strains of poliovirus unrelated to the vaccine strains, the sequences of which may be expected to vary at less stringently defined regions.

The proteins of an isolate of caprine arthritis-encephalitis virus (CAEV) were analysed by SDS-PAGE and Western blotting. Monoclonal antibodies (MAbs) produced to the main core protein p24 and the small structural protein p14 also recognized two major polypeptides of M r 41K and 55K in infected cell material, consistent with a precursor role for these gag polypeptides. In addition, the p24 MAbs detected a 33K polypeptide in extracellular virus preparations, while the p14 MAbs reacted strongly with a polypeptide of 18K (corresponding to structural protein p18) and weakly with another of 21K. The use of these MAbs in an indirect fluorescent antibody method revealed an intracytoplasmic location of these viral antigens in both mononucleated and multinucleated (syncytial) infected cells. Cross-reactivity with several other isolates indicated that these MAbs may be useful for diagnosis of CAEV infection.

To complement our battery of St Louis encephalitis (SLE) virus monoclonal antibodies (MAbs), we isolated and characterized MAbs reactive with another member of the SLE virus serocomplex, Murray Valley encephalitis (MVE) virus. From 40 fusion products, we isolated 10 stable hybridomas. The combination of SLE and MVE virus MAbs defined eight epitopes on the MVE envelope (E) glycoprotein. Six of these epitopes (E-1a, E-1c, E-1d, E-3, E-4a, E-4b) were identical to those previously demonstrated on SLE virus. Two new epitopes (E-5 and E-6) were also identified. As with SLE virus, the MVE E-1c epitope elicited the most potent virus-neutralizing and protective MAb. Unlike SLE virus, however, one of the cross-reactive epitopes (E-5) elicited neutralizing antibody and protected animals from MVE virus challenge. These results indicate that, while the antigenic domains on viruses within the SLE virus serocomplex are quite similar, epitopes involved in virus neutralization or protection from virus challenge may vary and can be topologically distinct.

Canine parvovirus type 2 (CPV-2) became widespread during 1978 and was reported in many countries during 1978 and 1979. Earlier studies showed that CPV-2 was replaced in the U.S.A. around 1980 by an antigenically and genetically variant virus (CPV-2a). Here we show that CPV-2 was present in the U.S.A., Japan, Belgium and Australia prior to 1980, but that between 1979 and 1982 CPV-2 was replaced by CPV-2a in all of those countries as well as in France and Denmark. Examination of sera collected between 1979 and 1984 from wild coyotes (Canis latrans) in the U.S.A. by an agar gel precipitin assay indicated that the coyotes were originally infected by CPV-2, but that after 1980 the juvenile coyotes were being infected with CPV-2a. The natural global replacement of CPV-2 by CPV-2a over a period of 2 to 3 years indicates that CPV-2a has a strong epidemiological advantage over CPV-2, although the mechanism involved remains to be defined.

A time-resolved fluorimmunoassay (TRFIA) with europium-labelled monoclonal antibodies (MAbs) was used to detect potato virus X (PVX) at a concentration of 5 pg/ml, in potato tuber extracts diluted up to 7 × 104-fold and leaf extracts diluted up to 2 × 107-fold. When mixed with potato leaf sap, PVX was detected at 100 pg/ml. TRFIA with simultaneous incubation of antigen and labelled antibody (one incubation) was two orders of magnitude more sensitive for PVX detection than the conventional double antibody sandwich ELISA. The fluorescence signal in TRFIA with separate incubations of antigen and labelled antibody (two incubations) with MAbs was linearly related to the virus concentration between 1.6 ng/ml and 1000 ng/ml; the method can therefore be used for the quantification of PVX. PVX detection in plant specimens by one incubation ELISA with MAbs was generally 10 times more sensitive than the standard two incubation procedure. Europium TRFIA with MAbs to potato viruses was found to be a very sensitive method for the detection of PVX, potato virus M, potato virus S, potato virus Y and potato leaf roll virus.

Nicotiana edwardsonii plants were examined by electron microscopy 5 months after inoculation with Sonchus yellow net virus (SYNV). No virions were observed in leaf or root cells, but cells in sections of calyx tissue contained large numbers of virus particles. Most of these particles were only 73 to 86% as long as particles of standard SYNV. Nicotiana edwardsonii inoculated with sap extracted from chronically infected calyx became systemically infected but exhibited chlorotic mottling, instead of the normal vein-clearing symptoms. Most virus particles in these plants were short, and when purified, sedimented more slowly than standard SYNV. Purified short particles were not infective, but plants inoculated with a mixture of short and standard particles developed mottling symptoms and yielded predominantly short particles. Proteins from short particles were electrophoretically and antigenically identical to those from standard virus. RNA from short particles was 77% the size of RNA from standard SYNV and hybridized to cloned SYNV cDNA. These short particles have all the characteristics of defective interfering particles.

In vitro translation of bean yellow mosaic virus (BYMV) RNA in rabbit reticulocyte lysate without dithiothreitol (DTT) resulted in the accumulation of high M r products. These were readily processed to low M r mature proteins after the addition of DTT followed by a 2 h incubation. Immunoprecipitation analyses of the partially processed high M r products with antisera to the 49K and 54K nuclear inclusion (NI) proteins, cylindrical inclusion (CI) protein, tobacco vein mottling virus helper component (HC) protein and capsid protein (CP) resolved the following BYMV RNA genome map: 5′ end, 32K unidentified protein, 48K HC, 42K unidentified protein, 73K CI, 49K NI, 54K NI, 32K CP, 3′ end. The addition of the 49K NI protein antiserum inhibited the proteolytic processing of the high M r translation products. The inhibition of processing was diminished by diluting the 49K NI antiserum or by adding purified 49K NI protein. Preimmune serum or the antisera to the 54K NI, CI and capsid proteins were not as effective in inhibiting the proteolytic processing. These results provide evidence that the 49K NI protein or a related protein may have a protease function in the processing of the potyvirus polyproteins.