- Volume 68, Issue 2, 1987

Bacteriophage Me1 is unable to grow on Escherichia coli strains harbouring the ColV,I-K94 plasmid. The nature of this inhibition was investigated, and it was found not to be due to restriction, superinfection exclusion or receptor-mediated resistance, but to be a new example of plasmid-mediated abortive infection. Investigation of events occurring during abortive Me1 infection revealed some differences from previously described cases, especially with regard to late protein synthesis, which did occur, albeit showing abnormal amounts of some proteins. No major differences were observed in membrane permeability of productively and abortively infected cells. Phage-directed DNA synthesis was reduced in abortively infected cells. Comparative studies of Me1 and T4 revealed a striking similarity despite some minor differences.

The process of DNA ejection from the head of PL-1, a Lactobacillus casei ATCC 27092 phage, was studied by electron microscopy by counting the number of ghost particles with empty heads among phages already adsorbed to the cell. The process of DNA ejection was temperature- and live cell-dependent.

Use has been made of a monoclonal antibody (designated 8F5) to map a neutralizing epitope on the viral capsid protein VP2 of human rhinovirus 2 (HRV2). This antibody which was raised against the native virus, neutralizes HRV2 and is also capable of recognizing denatured VP2 on Western blots. To examine the binding site of 8F5, VP2 of HRV2 was expressed in Escherichia coli. Deletions starting at the 3′ end were then introduced into the gene for VP2 using Bal-31 nuclease. Polypeptides shortened at the carboxy terminus of VP2 were obtained from the deletions and were blotted onto nitrocellulose. The samples were then probed with monoclonal antibody 8F5. Recognition by 8F5 was maintained as long as the expressed polypeptide contained the VP2 sequence up to amino acid 164 or beyond. However, when the VP2 sequence was truncated to amino acid 153 or less 8F5 was no longer able to bind. The neutralization epitope (or part of it) recognized by 8F5 on VP2 is therefore located between amino acids 153 and 164.

The effect of pH and different concentrations of added monovalent and divalent cations on translation in poliovirus-infected HeLa cells has been examined. A strong effect on protein synthesis was observed when the concentration of sodium ions was modified. If cells were placed in a hypotonic medium after virus adsorption, no shut-off of cellular translation took place, nor were viral proteins synthesized. An increase in the multiplicity of infection partially overcame this effect. Reversal of the shut-off of cellular translation and inhibition of viral protein synthesis was achieved when cells were placed in hypotonic medium 2 h after infection. Modification of divalent cations (calcium or magnesium) had little or no effect on the pattern of translation. On the other hand, acidic pH (below 6) inhibited both cellular and viral protein synthesis, whereas basic pH had no influence. During infection the synthesis of poliovirus proteins reached a maximum at about 4 to 6 h and then declined. This inhibition of viral translation was partially prevented if cells were placed in a medium containing a high concentration of potassium although the cytopathic effect was prevented. These results indicate that viral protein synthesis and the cytopathic effect were, to a large extent, influenced by the external monovalent ion concentration.

Poliovirus-infected HeLa cells increased their permeability to monovalent ions from the third hour post-infection. At that time infected cells lost their content of potassium ions as measured by efflux of the potassium analogue 86Rb+. The rate of release of 86Rb+ from cells increased as infection proceeded, and was not sensitive to ouabain or quinidine, inhibitors of the Na+/K+ ATPase and Ca2+-induced K+ release system, respectively. The leakage of 86Rb+ was only slightly sensitive to furosemide, an inhibitor of the Na+/K+/Cl− cotransport system, suggesting that the mechanism of release involved an increased passive permeability of the cell membrane. The calcium content or its efflux did not vary significantly in the infected cells. Neither were there alterations in the intracellular pH throughout infection.

Twelve Dutch isolates and the M41 strain of infectious bronchitis virus (IBV), a coronavirus of chickens, were characterized by cross-neutralization and T1 fingerprinting to elucidate their evolutionary relationship. The T1 fingerprinting showed that the Dutch isolates formed two clusters. The first cluster contained strains H52, H120, D387, V1259, V1385 and V1397; the estimated sequence homology is 99%. Cluster two comprised strains D207, D274, D212, D1466, D3128 and D3896, which have about 95% sequence homology. The M41 virus did not belong to either cluster. The four different serotypes which arose in the late 1970s belonged to cluster two and appeared to be different from the vaccine strains (H52 and H120) used at that time. This indicates that the strains were newly introduced and could have arisen from a common virus. On the other hand, three recently isolated field strains were genetically closely related to the vaccine strains H120 and H52 (cluster one), suggesting that these live vaccine strains themselves could have given rise to these serologically altered field isolates. The data are relevant to the development of new vaccine strategies.

The morphological, biochemical and growth characteristics of four members of the Reoviridae, three from the fish hosts, golden shiner (Notemigonus crysoleucas), chum salmon (Oncorhynchus keta) and channel catfish (Ictalurus punctatus) and one from American oyster (Crassostrea virginica), were compared. Electron microscopy of negatively stained virions revealed icosahedral particles approximately 75 nm in diameter composed of a double capsid. Complete particles had buoyant densities in CsCl of 1·34 to 1·36 g/ml. The viruses replicated well in several fish cell lines, forming plaque-like syncytia in monolayer cultures. Each virus could be distinguished by the range of cell lines supporting its growth. Polyacrylamide gel electrophoresis showed that the genome of each virus was composed of 11 segments of dsRNA distributed among three size classes. There were three large, three medium and five small segments in each genome and each isolate had a unique electropherotype. The segments ranged from 2·5 × 106 to 0·31 × 106 mol. wt. with a total genome of approximately 15 × 106 mol. wt. Analysis by SDS-PAGE revealed that each virus had five major structural proteins. There were two large polypeptides of approximately 135000 and 125000 mol. wt., one medium size polypeptide of 70000 mol. wt. and two small polypeptides of 45000 and 34000 mol. wt. Of the major structural proteins, those of approximately 70000 and 34000 mol. wt. were consistently present in the highest concentrations. Minor virion proteins were detected but were not characterized. These four viruses, isolated from aquatic animals, were unlike viruses of the six established genera of the Reoviridae.

Vero cells were infected by Kunjin virus and radiolabelled in the presence of the leucine analogue, threo-β-hydroxy-dl-leucine (THL). This analogue is known to prevent preprotein processing in cell-free systems when incorporated into signal peptides. Novel Kunjin virus-specified proteins were detected, namely gpl40, pl20 and gp92; the designations for the proteins indicate their approximate M r × 10−3 and whether they are glycosylated. The glycoproteins gp 140 and gp92 were observed in cells labelled with [3H]mannose and bound to concanavalin A. Limited proteolytic digestion of gpl40, gp92 and gp66 (related to the envelope protein E), and tryptic peptide mapping of these three glycoproteins and p120 indicated that all four were closely related. The glycoproteins gpl40 and gp92 were also detected in cells infected by West Nile virus radiolabelled in the presence of THL. Other effects of THL in Kunjin virus- infected cells were (i) a reduction in the incorporation of radioactive amino acids or mannose, (ii) a decrease in the yield of haemagglutinin and infectious virus, (iii) an inhibition of processing of gp66 to gp53 and (iv) an apparent inhibition of synthesis of P98 and P71. We suggest possible explanations for the THL-induced changes in infected cells based on recent models proposed for the synthesis of the yellow fever and West Nile viral proteins.

Adoptive transfer experiments in athymic nude mice demonstrated that the demyelination seen in the central nervous system (CNS) following Semliki Forest virus (SFV) infection was directly dependent upon sensitized T lymphocytes. Antibodies generated during the infection did not seem to be involved in the demyelination, but thymus-dependent antibodies (IgG) were responsible for the reduction of brain virus titres. In the absence of a T cell response and T cell-dependent antibody production, virus persisted in the CNS for several months. Despite persistence of high virus titres for this time, only mice eventually developing a CNS inflammatory response developed lesions of demyelination. In the absence of an inflammatory response no demyelination was apparent even after several months of persistent infection. Administration of anti- SFV hyperimmune serum intracerebrally to both infected and control mice did not produce demyelination but resulted in CNS tissue degeneration with marked pycnosis.

A biochemical and morphological investigation of the mechanism of entry of vesicular stomatitis virus (VSV) into host cells of mammalian (HeLa), avian (CER), piscine (EPC) and arthropod (Aedes albopictus) origin, is described. VSV was capable of infecting all cell lines tested by a endosome- and/or a lysosome-dependent step since ammonium chloride and amantadine blocked the early stages of infection. Complement-dependent immune lysis of infected host cells provided evidence that in none of the four different cell types examined did insertion of VSV antigens occur from the outside to any great extent on the cell surface. When the entry process was studied by electron microscopy, virus particles were seen to be bound to the cell surface at 0 °C. After warming at 37 °C for homeothermic cells or at 26 °C for poikilothermic cells, virus was detected within coated pits and coated vesicles and, later, in lysosomes. VSV entry was seen to take place by endocytosis in all four cell lines, which were derived from phylogenetically unrelated species.

The host component of control of scrapie incubation period in the mouse is manifested largely through the action of the Sine gene. Only one mouse strain (VM) has been found that is p7p7 (prolonged incubation for ME7 agent) and two other strains have been derived from VM. All other strains, designated s7s7, have a short incubation for ME7. In the present study, the I strain was shown to fulfil the criteria that are characteristic of mouse strains with the p7 allele of Sine: (i) a comparatively long incubation period for ME7 and a short incubation period for 22A, (ii) the incubation period for F, hybrid mice (s7s7 x p7p7) either fell between the incubation periods for the parental strains (with ME7) or were longer than either parent (with 139A and 22A), (iii) amyloid plaques occurred following injection of ME7 and 87V but not after 22A or 139A, (iv) lesion profiles for four scrapie strains were similar in I mice and p7p7 mouse strains, and (v) injection of 87V led to disease in less than 300 days. Finally, allelism tests using F, hybrid mice (I × a p7p7 mouse strain) and progeny of backcrosses between these F, mice and I mice failed to reveal the segregation of additional major genes affecting scrapie incubation period.

Monoclonal antibodies to the envelope glycoproteins, HN and F, of human parainfluenza virus type 3 were coupled to a Sepharose 4B matrix and used for affinity purification of the viral glycoproteins. The purity of the glycoproteins was demonstrated by SDS-PAGE followed by fluorography or silver staining. The antigenicity of the glycoproteins was determined by immunization of rabbits; polyclonal rabbit antisera demonstrated inhibition of functional activities of the virus glycoproteins. The F glycoprotein, when reconstituted into lipid vesicles, showed distinct spike-like projections similar to those of intact virions.

The contribution of phagocytes to the early protection of mice inoculated intravenously with influenza virus was investigated in phagocyte-depleted mice. Following the inoculation of a sublethal dose of influenza virus, virus titres in the liver and lung of both untreated and carrageenan-treated mice were reduced rapidly by day 1 and decreased slowly to reach an undetectable level by day 7. The titres in γ-irradiated mice decreased transiently by day 1 and increased progressively thereafter to kill all of the hosts by day 8. The clearance of virus from blood at the early stage of infection was retarded by γ-irradiation but not by carrageenan treatment. In addition, increase in virus titres in the liver and lung in the early stage of the infection was prevented by adoptive transfer with syngeneic polymorphonuclear leukocytes into γ-irradiated mice. No significant rise of neutralizing antibody was detectable by day 3 after the inoculation, in any of the three groups of mice. These observations imply that γ-sensitive and carrageenan-resistant polymorphonuclear leukocytes play a protective role at the early stage in the infection, whereas fixed macrophages or natural killer cells, both of which are carrageenan-sensitive and γ-resistant, scarcely participate in the early phase.

The relative contribution of polymorphonuclear leukocytes and macrophages in the early protection against intranasal infection of mice with influenza virus was investigated. Virus multiplication in the lung in the early phase of infection with less than 1·5 × 103 plaque-forming units was enhanced by X-ray irradiation. The intranasal administration of carrageenan did not influence the titre of virus. However, when mice were infected with 1·5 × 104 plaque-forming units, the virus titre was elevated by intranasal administration of carrageenan as well as by X-ray irradiation, but not by intraperitoneal administration of carrageenan. The intranasal administration of carrageenan not only inhibited the phagocytic activity of alveolar macrophages but also enhanced susceptibility to the virus. On the other hand, polymorphonuclear leukocytes were capable of phagocytosing the virus in vitro and were non-permissive for virus infection. Neutralizing antibody and interferon were not detectable in the early stage of the infection. These results suggested that polymorphonuclear leukocytes (X- ray-sensitive, carrageenan-resistant) were the cells primarily responsible for early protection in influenza virus infection and that after infection with a high dose of the virus alveolar macrophages (X-ray-resistant, carrageenan-sensitive) also played a protective role in the early phase.

Local administration of nucleoprotein purified from X31 (H3N2) influenza A virus primed for A virus cross-reactive cytotoxic T cells and resulted in substantial protection (75 %) of mice from a lethal challenge with the heterologous mouse-adapted A/PR/8/34 (H1N1) virus. By following the course of a lethal virus challenge we found that nucleoprotein priming did not prevent virus infection but rather aided recovery. Nucleoprotein-primed mice suffered initial symptoms of infection, i.e. weight loss and surface temperature changes, but started to recover after approximately 7 days. We suggest that such heterotypic protection can be attributed to priming of A virus crossreactive cytotoxic T cells.

In a series of experiments performed in hamsters and mice, administration of mixtures of detergent-disrupted (SV) influenza A X49 (H3N2) virus and inactivated X49 whole virus (WV) vaccine induced lower serum antibody titres than equivalent or lower doses of WV vaccine alone. This reduction in antibody titre was also observed using influenza A (H1N1) and influenza B (B/Hong Kong/8/73) SV and WV vaccine preparations. The results suggested that SV preparations can suppress the serum antibody response to WV vaccine. A suppressive effect of SV influenza virus on WV vaccine was also observed in an in vitro antibody-forming system, using primed mouse spleen cells. In this system, SV induced markedly lower IgG and IgM antibody responses than WV vaccine, and mixtures of SV with WV reproducibly resulted in lowered antibody responses compared to those elicited by WV alone. Possible reasons for these findings are discussed in the light of the known low immunogenicity observed for split and subunit influenza virus vaccine preparations in animals and in unprimed human populations.

A number of genital cancer biopsy samples were screened for the presence of human papillomavirus type 16 (HPV-16) DNA sequences. One of these samples (a vulvar carcinoma in situ) was found to contain more than 100 copies of HPV-16 DNA sequences per cell. Using this tumour DNA, a genomic library was constructed in bacteriophage lambda and the library was screened for recombinant phage containing HPV-16 sequences. Five recombinant phage clones were isolated and their DNA was analysed by restriction endonuclease digestion and blot hybridization. All five recombinants contained two copies of the HPV-16 genome present in a head-to-tail arrangement. The data are consistent with the presence of HPV-16 sequences in the tumour DNA arranged as genomic dimers in a circular episomal configuration. The HPV-16 genomes contained a deletion within the non-coding region, a region which includes the viral origin of DNA replication and transcriptional control sequences. Possible consequences of this deletion for viral replication and transcription are discussed.

Malignant rabbit fibroma virus (MV) is a lymphocytotropic leporipoxvirus which produces profound immunological dysfunction and lethal fibromyxosarcoma. We examined virus recovery from splenic lymphocytes as a function of time after inoculation in vivo, and correlated this with both immunological function and expression of virus-induced host suppressor activity. MV was most abundant in lymphocytes obtained 4 days following inoculation. At that time, immune function was relatively normal and host suppressor activity was not observed. By 7 days after infection, when active host immunosuppressor functions were observed, virus recovery was decreased. Eleven days post-inoculation host immune function began to recover despite increasing virus-induced tumours and developing opportunistic infection. Simultaneously, MV was no longer recoverable from spleen cells. Spleen cells from day 11 tumour-bearing rabbits did not support MV replication as efficiently as did normal or day 4 or 7 splenic lymphocytes, but they did not alter the ability of MV to grow in the latter cells. By fluorescence examination and cytofluorography, splenic lymphocytes bearing MV antigens were abundant 7 days after infection but disappeared by 11 days. This was temporally related to production of neutralizing antibody to MV, and development of virus-specific lymphocyte proliferative activity. The composition of splenic lymphocytes changed as well: the normal ratio of about 1:1 for B and T cells changed to 1:2 by day 7, and then inverted to almost 2 :1 by day 11. Rabbits infected with MV thus appear to recover their immune function, concurrently eliminate virus-infected lymphocytes, and elaborate high titres of neutralizing serum antibodies despite progressive infections and tumour development.