The structure of group II adenoviruses

Recombinant virus-like particles as a carrier of B- and T-cell epitopes of hepatitis C virus (HCV)

The major aim of the project was the development of virus-like particles (VLP) displaying B- and T-cell epitopes of hepatitis C virus (HCV) proteins. To this end, hepatitis B virus core (HBc) particles were used as a carrier of HCV epitopes. Fragments of HCV genes encoding core (aa 98) and NS3 (aa 155) proteins were fused to the 3' terminus of the truncated HBV core gene. All recombinant plasmids led to relatively high levels of expression of chimeric proteins in E. coli, which resulted in the formation of complete "mature" VLP. Chimeric HBc/HCV VLPs were purified by combination of gel filtration and sucrose gradient centrifugation, and used for immunogenicity studies in mice. All variants of hybrid particles induced high humoral and cellular responses to HBcAg. Immunization with the HBc/HCV core particles led to relatively low antibody and T-cell proliferative responses to HCV core epitopes. The HBc/HCV NS3 particles were able to induce high levels of anti-NS3 antibodies in the absence of proliferative responses to HCV epitopes. Thus, the results of the current study have demonstrated the principal possibility of using VLP on the basis of HBcAg for creation of a new type of HCV-specific immunogen.

An amino-terminal segment of hantavirus nucleocapsid protein presented on hepatitis B virus core particles induces a strong and highly cross-reactive antibody response in mice

Previously, we have demonstrated that hepatitis B virus (HBV) core particles tolerate the insertion of the amino-terminal 120 amino acids (aa) of the Puumala hantavirus nucleocapsid (N) protein. Here, we demonstrate that the insertion of 120 amino-terminal aa of N proteins from highly virulent Dobrava and Hantaan hantaviruses allows the formation of chimeric core particles. These particles expose the inserted foreign protein segments, at least in part, on their surface. Analysis by electron cryomicroscopy of chimeric particles harbouring the Puumala virus (PUUV) N segment revealed 90% T = 3 and 10% T = 4 shells. A map computed from T = 3 shells shows additional density splaying out from the tips of the spikes producing the effect of an extra shell of density at an outer radius compared with wild-type shells. The inserted Puumala virus N protein segment is flexibly linked to the core spikes and only partially icosahedrally ordered. Immunisation of mice of two different haplotypes (BALB/c and C57BL/6) with chimeric core particles induces a high-titered and highly cross-reactive N-specific antibody response in both mice strains.

Puumala (PUU) hantavirus strain differences and insertion positions in the hepatitis B virus core antigen influence B-cell immunogenicity and protective potential of core-derived particles

Hepatitis B virus (HBV) core-derived chimeric particles carrying a Puumala (PUU) hantavirus (strain Vranica/Hällnäs) nucleocapsid (N) protein sequence (aa 1-45), alternatively inserted at three distinct positions (N-, C-terminus, or the internal region), and mosaic particles consisting of HBV core as well as core/PUU (Vranica/Hällnäs) N (aa 1-45) readthrough protein were generated. Chimeric particles carrying the insert at the N-terminus or the internal region of core induced some protective immune response in bank voles (Clethrionomys glareolus) against a subsequent PUU virus (strain Kazan) challenge; 40-50% of the animals showed markers of protection. In contrast, internal insertion of PUU strain CG18-20 N (aa 1-45) into the HBV core caused a highly protective immune response in the bank vole model. Immunizations with particles carrying aa 75-119 of PUU (CG18-20) N at the C-terminus of core verified the presence of a second, minor protective region in the N protein. A strong PUU N-specific antibody response was detected not only in bank voles immunized with chimeric particles containing internal and N-terminal fusions of PUU N protein but also in animals immunized with the corresponding mosaic particles. Except for the exclusive occurrence of antibodies directed against aa 231-240 of N in non-protected animals post virus challenge, there was no additional obvious difference in the epitope-specificity of N-specific antibodies from immunized animals prior and post virus challenge.

Interaction of wild-type and naturally occurring deleted variants of hepatitis B virus core polypeptides leads to formation of mosaic particles

The simultaneous presence of hepatitis B virus (HBV) genomes carrying wild-type (wt) and in-frame deleted variants of the HBV core gene has been identified as a typical feature of HBV-infected renal transplant patients with severe liver disease. To investigate possible interactions of wt and deleted core polypeptides a two-vector Escherichia coli expression system ensuring their concomitant synthesis has been developed. Co-expression of wt and a mutant core lacking 17 amino acid residues (77-93) within the immunodominant region led to the formation of mosaic particles, whereas the mutant alone was incapable of self-assembly.

Isolation and molecular characterization of a novel cytopathogenic paramyxovirus from tree shrews

A cytopathic infectious agent was isolated from the kidneys of an apparently healthy tree shrew (Tupaia belangeri) that had been captured in the area around Bangkok. The infectivity was propagated in Tupaia fibroblast and kidney cell cultures. Paramyxovirus-like pleomorphic enveloped particles and helical nucleocapsids were observed by electron microscopy and accordingly the infectious agent was termed Tupaia paramyxovirus (TPMV). However, no serological cross-reactions were detected between TPMV and known paramyxoviruses. For the molecular characterization of TPMV an experimental strategy that allows the random-primed synthesis of relatively large cDNA molecules from viral genomic RNA was applied. Nucleotide sequence analysis of a TPMV-specific cDNA fragment (1544 bp) revealed two nonoverlapping partial open reading frames corresponding to paramyxoviral N and P transcription units. Using modified rapid amplification of cDNA ends techniques, a substantial contiguous portion of the viral genome (4065 nt) was elucidated including the complete N and P/V/C genes. The coding strategy of TPMV as well as significant amino acid sequence homologies clearly indicates an evolutionary relationship between TPMV and members of the genus Morbillivirus. Highest homologies were detected between TPMV and Hendra virus (equine morbillivirus), which recently emerged in Australia, causing outbreaks of fatal respiratory and neurological disease in horses and humans.

HBV core particles allow the insertion and surface exposure of the entire potentially protective region of Puumala hantavirus nucleocapsid protein

Core particles of the hepatitis B virus (HBV) potentiate the immune response against foreign epitopes presented on their surface. Potential insertion sites in the monomeric subunit of the HBV core protein were previously identified at the N- and C-terminus and in the immunodominant c/e1 region. In a C-terminally truncated core protein these sites were used to introduce the entire 120 amino acid (aa)-long potentially immunoprotective region of the hantavirus (serotype Puumala) nucleocapsid protein. The N- and C-terminal fusion products were unable to form core-like particles in detectable amounts. However, a suppressable stop codon located between the HBV core and the C-terminally fused hantavirus sequence restored the ability to form particles ('mosaic particles'); in contrast to the C-terminal fusion product the mosaic construct allowed the formation of particles built up by the core protein itself and the HBV core-Puumala nucleocapsid-readthrough protein. The mosaic particles exposed the 120 aa region of the PUU nucleocapsid protein on their surface as demonstrated by ELISA and immuno electron microscopy applying different monoclonal antibodies. Insertion of the hantaviral sequence into the c/e1 region not only allowed the formation of chimeric particles, but again the surface accessibility of the sequence. HBV core antigenicity itself was, however, reduced in the particles carrying insertions in the c/e1 region, probably due to a masking effect of the 120 aa long insert.

Bacteriophage diversity in the North Sea

In recent years interest in bacteriophages in aquatic environments has increased. Electron microscopy studies have revealed high numbers of phage particles (10(4) to 10(7) particles per ml) in the marine environment. However, the ecological role of these bacteriophages is still unknown, and the role of the phages in the control of bacterioplankton by lysis and the potential for gene transfer are disputed. Even the basic questions of the genetic relationships of the phages and the diversity of phage-host systems in aquatic environments have not been answered. We investigated the diversity of 22 phage-host systems after 85 phages were collected at one station near a German island, Helgoland, located in the North Sea. The relationships among the phages were determined by electron microscopy, DNA-DNA hybridization, and host range studies. On the basis of morphology, 11 phages were assigned to the virus family Myoviridae, 7 phages were assigned to the family Siphoviridae, and 4 phages were assigned to the family Podoviridae. DNA-DNA hybridization confirmed that there was no DNA homology between phages belonging to different families. We found that the 22 marine bacteriophages belonged to 13 different species. The host bacteria were differentiated by morphological and physiological tests and by 16S ribosomal DNA sequencing. All of the bacteria were gram negative, facultatively anaerobic, motile, and coccoid. The 16S rRNA sequences of the bacteria exhibited high levels of similarity (98 to 99%) with the sequences of organisms belonging to the genus Pseudoalteromonas, which belongs to the gamma subdivision of the class Proteobacteria.

Chimaeric HBV core particles carrying a defined segment of Puumala hantavirus nucleocapsid protein evoke protective immunity in an animal model

Hantaviruses are rodent-born agents which are pathogenic in humans causing haemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome. To induce a protective immunity against a European hantavirus (Puumala) we constructed chimaeric hepatitis B virus (HBV) core particles carrying defined fragments of the Puumala virus nucleocapsid protein. After immunisation of bank voles, the natural host of Puumala virus, with core particles possessing an insertion of the N-terminal part of Puumala virus nucleocapsid protein, four of five animals were protected against subsequent virus challenge. The results show that the major protective region of the nucleocapsid protein is located between amino acids 1 and 45 and that chimaeric HBV core-like particles are useful carriers of foreign protective epitopes.

Adenovirus dodecahedron, a new vector for human gene transfer

Recombinant adenovirus is one of most efficient delivery vehicles for gene therapy. However, the initial enthusiasm for the use of recombinant adenovirus for gene therapy has been tempered by strong immune responses that develop to the virus and virus-infected cells. Even though recombinant adenoviruses are replication-defective, they introduce into the recipient cell, together with the gene of interest, viral genetes that might lead to fortuitous recombination if the recipient is infected by wild-type adenovirus. We propose the use of a dodecahedron made of adenovirus pentons or penton bases as an alternative vector for human gene therapy. The penton is a complex of two oligomeric proteins, a penton base and fiber, involved in the cell attachment, internalization, and liberation of virus into the cytoplasm. The dodecahedron retains many of the advantages of adenovirus for gene transfer such as efficiency of entry, efficient release of DNA from endosomes, and wide range of cell and tissue targets. Because it consists of only one or two adenovirus proteins instead of the 11 contained in an adenovirus virion and it does not contain the viral genome, it is potentially a safer alternative to recombinant adenovirus.

Biological and physicochemical characterization of the major (1.40) and minor (1.45) component of infectious avian adeno-associated virus

Two infectious components with buoyant densities of 1.40 g/cm3 and 1.45 g/cm3, designated as major (1.40) and minor (1.45) component, were detected by banding avian adeno-associated virus (AAAV) isopycnically in CsCl. In metrizamide, however, infectious AAAV banded only as a single peak at a density of 1.32 g/cm3. Biological as well as physicochemical properties of the two AAAV components recovered from CsCl density gradient were described. Concerning the minor (1.45) component, three experimental findings may suggest that the capsid structure of this AAAV population is altered in comparison with that of the major (1.40) component: (i) the sedimentation pattern characterized by an additional peak containing slower-sedimenting noninfectious material (16 S); (ii) the specific infectivity decreased by the 3.5 fold; (iii) the ready disintegration when exposed to gently denaturing conditions.

HBcAg expressed on the surface of circulating Dane particles in patients with hepatitis B virus infection without evidence of anti-HBc formation

Circulating immune complexes composed of HBcAg and anti-HBc have been demonstrated recently in patients with hepatitis B virus replication. After dissociation of immune complexes by chaotropic ions, HBcAg was quantified radioimmunologically. In the present study, we describe 10 patients with hepatitis B virus replication, absent or delayed anti-HBc formation and exposed HBcAg in serum. Four of the 10 patients had acute hepatitis, and six patients had chronic persistent hepatitis. In seven of 10 patients, a secondary immune defect was apparent due to acquired immunodeficiency syndrome, leukemia, histiocytosis X, sarcoidosis or end-stage renal disease. Electron microscopy demonstrated that Dane particles from anti-HBc-negative patients were agglutinated after addition of monoclonal anti-HBc antibodies, whereas Dane particles from anti-HBc-positive sera did not show agglutination. Monoclonal HBsAg-specific antibodies aggregated Dane particles independent of the presence of anti-HBc. Circulating HBcAg was always associated with the Dane particle fraction after density gradient separation. Hepatitis B virus core proteins from patients with and without anti-HBc studied by immunoblotting after sodium dodecyl sulfate-gel electrophoresis showed identical patterns. Hepatocytes from anti-HBc-negative patients were positive for HBcAg but negative for immunoglobulin G by immunofluorescence technique. The data indicate that HBcAg may also be expressed on the surface of Dane particles, where it is commonly masked by anti-HBc.

Morphological characterization of chicken anaemia agent (CAA)

Chicken anaemia agent (CAA) was characterized as a virion with 25 nm in diameter, with a buoyant density in CsCl of 1.36-1.37 g/cm3, and containing a circular, single-stranded DNA genome. The virus is composed of 32 hollow morphological units representing a regular T = 3 icosahedron.

Scrapie infectivity, fibrils and low molecular weight protein

The development of a short incubation model of scrapie (strain 263K), in golden hamsters has added impetus to the purification of the infectious agent. Our own attempts have been based on methods pioneered by Millson and developed by Prusiner. We present here results indicating that a purification factor of up to 10(4) with respect to protein may now be possible. Fractions from brain with high infectivity had a sedimentation range of 70-300S and contained an abundance of fibrils closely similar to the scrapie-associated fibrils (SAF) discovered by Merz et al.. Material of molecular weight (Mr) 26,000, which is probably protein, appears to be a major constituent of the fibrils. The association between infectivity and fibrils raises two possibilities: the fibrils are an infectious form of the scrapie agent or they are a pathological response to scrapie infection.

Characteristics of mastadenovirus h 8, the causative agent of epidemic keratoconjunctivitis

Adenovirus 8 (Ad 8, strain 1127) has the general structural features of an adenovirus; it produces the genus-specific hexon antigen. The fiber length of 12 nm corresponds to that of other subgenus D adenoviruses. In hemagglutination-inhibition, Ad 8 is related to Ad9 and Ad 15/H9. The slow multiplication, compared to most other subgenus D viruses, was shown not to be caused by an extended growth cycle, but appears to be due to an inefficient virus release into the medium. After restriction analysis with the enzymes Sma I and Bgl II, the typical fragment patterns of species from subgenus D were obtained, while very different patterns emerged from the analysis with Hind III, Bam HI, and Bst E II endonucleases. Several strains of Ad 8 produced more penton-associated toxin than Ad 15/H9 used as reference virus from subgenus D, which could explain the "clumping CPE" caused by Ad 8. Ad 8 toxin was neutralized by antisera from many adenovirus species. The poor virus yield of Ad 8 was not improved by removing soluble viral or cellular substances; all other attempts to improve virus yield by varying the conditions of cell culture also failed.

Analysis of the genome of fish lymphocystis disease virus isolated directly from epidermal tumours of pleuronectes

Virions of fish lymphocystis disease virus (FLDV), a member of the iridovirus family, were isolated directly from lymphocystis disease lesions of individual flatfishes and purified by sucrose and subsequent cesium chloride gradient centrifugation to homogeneity as judged by electron microscopy. The isolated FLDV DNAs appear to be heterogeneous in size. Contour length measurements of 43 DNA molecules gave an average length of 49 +/- 23 microns, corresponding to 93 +/- 44 X 10(6) D. Molecular weight estimations of FLDV DNA by restriction enzyme analysis resulted in only 64.8 X 10(6) D indicating an excess length of the DNA of about 50%. FLDV DNA was sensitive to lambda 5'-exonuclease and to E. coli 3'-exonuclease III without preference of any one terminal DNA restriction fragment. Denaturation and reannealing experiments of FLDV DNA resulted in the formation of circular DNA molecules of 34.25 microns contour length (= 65.22 X 10(6) D). This result suggests that FLDV DNA contains directly repeated sequences at both ends and that it is terminally redundant. FLDV DNA is methylated in cytosine. FLDV DNA did not hybridize with frog virus DNA indicating that the two iridoviruses are not closely related to each other. Restriction enzyme analysis and Southern blot hybridizations revealed that FLDV isolates can be classified into two different strains: FLDV strain 1 occurs in flounders and plaice, whereas strain 2 is usually found in lesions of dabs.

The fibers of fowl adenoviruses

Purified virions from 14 strains of fowl adenoviruses (FAV) representing 11 serotypes were examined by electron microscopy. Pentons of all strains turned out to have two projections at their penton bases. It is shown that the double fibers also protrude from the intact virion. The length of both fibers was measured on free pentons and is given for each serotype. Double fibers seem to be a common feature of FAV. The serologically unrelated Egg Drop Syndrome (EDS) avian adenovirus strain 127 was confirmed to have single fibers only.

Stabilization of adenovirus infectivity against thermoinactivation by lowered ionic strength

The thermostability of adenovirus 5 increases when the ionic strength is decreased before heating by dilution in distilled water (1 : 100, heating at 50 degrees C). A predilution in Eagle's MEM before heating or a previous dialysis against water had no effect on thermostability. The stabilizing effect was found likewise in crude and purified virus, in heating at 50 degrees C up to 320 min, from 50 degrees C to 56 degrees C, and in dilution from 10(-2) to 10(-5). The degree of stabilization was similar to cationic stabilization in 2M NaCl. The infectivity of heated adenovirus 5 was not sensitivity to DNase digestion. Other adenovirus types were stabilized in a similar manner.

New human adenovirus (candidate adenovirus 36), a novel member of subgroup D

A new adenovirus (candidate Ad36) was isolated from the feces of a girl with enteritis. It has been biological and biophysical properties of an adenovirus, with a particle diameter of 750 +/- 10 A in thin sections and with a fiber length of 190 A. The virus belongs to subgroup D. It is distinct both in neutralization and hemagglutination-inhibition from all other human adenoviruses; it also shows a unique DNA restriction pattern.

Biological and biophysical characteristics of mouse adenovirus, strain FL

Mouse adenovirus, strain FL (MAV), is best propagated in primary rather than secondary cultures of mouse kidney cells. Virus release from the cells into the medium is fairly efficient; the average yield per cell is about 1000 TCID50. Morphological and other biophysical characteristics are those of a typical adenovirus: the icosahedral shell with a diameter of 74 nm, fiber projections of 29 nm length, its localization inside the infected kidney cells, a buoyant density in CsC1 of 1.34 g/ml, inhibition of multiplication by inhibitors of DNA synthesis. The thermostability is higher than that of human adenoviruses, whereas, in contrast to these, MAV is inactivated to a great extent by trypsin. Complete or incomplete hemagglutinin or toxin-like activity were not detected. The virus shows no cross-neutralization with human adenoviruses and a one-side cross-reaction with another murine adenovirus strain K-87. Soluble complement-fixing antigen of MAX exhibits a sedimentation rate of 12S identical to the hexon component of human adenoviruses; both antigens show a partial antigenic relationship in tests with appropriate antisera.

Cytotoxicity of adenovirus-antibody aggregates: sensitivity to different cell strains, and inhibition by hexon antiserum and by complement

Adenovirus-antibody aggregates under defined conditions are cytotoxic in vitro. All members of adenovirus groups I, II, and III caused toxicity upon aggregation. The toxicity of the clusters is exerted by the virions. Toxicity is temperature dependent and may be caused by a mechanism similar to that used in viral penetration. Cells permitting direct viral penetration were all sensitive to the toxic aggregates. The toxicity seems to be related to hexon antigens on the surface of the virions since antihexon sera neutralized the toxicity. No evidence was obtained showing that pentons are required for this kind of cytotoxicity. Adenovirus types 3, 5, and 9 were used in the experiment. Cytotoxicity was estimated by the (51)Cr release assay. Complement factors could be excluded as mediators of the cytolytic reactions. Instead, complement was shown to prevent the formation of toxic aggregates or to neutralize the toxicity of preformed ones.

Immunological basis of the adenovirus 8-9 cross-reaction

The dedecon and hexon components of adenovirus types 8 and 9 have been extensively purified for use in establishing the basis of the cross-reaction between these types. Dodecons, the complete hemagglutinins, were purified 304- to 362-fold by fluorocarbon extraction, calcium phosphate batch chromatography, and ion-exchange column chromatography. Hexons, the group complement-fixation (CF) antigens, were purified 230- to 240-fold by erythrocyte adsorption, ion-exchange chromatography, and exclusion chromatography. Component antisera prepared in rabbits were tested in reciprocal fashion with crude virus and dodecon and hexon components. By hemagglutination-inhibition (HI), the dodecons of types 8 and 9 demonstrated the same predominantly one-sided relationship characteristic of the crude antigens. Some neutralizing activity was associated with both dodecons and hexons of each type. However, combining anti-dodecon and anti-hexon sera or producing antisera against the combined dodecon-hexon components resulted in neutralizing titers which were identical to titers obtained with antisera against the crude virus harvests. Dedecons of each type appear to share at least one antigenic determinant with hexons of the same type, and this determinant may reside on the vertex capsomere. Hexons possess group- and type-specific determinants, as shown by CF, neutralization, and immunodiffusion tests, and may exhibit some minor relationship between types 8 and 9. The results with the purified components are consistent with the predominantly one-sided antigenic relationship between types 8 and 9 in the conventional HI tests and the largely type-specific relationship by neutralization tests.

Cleavage by formamide of intercapsomer bonds in adenovirus types 4 and 7 virions and hemagglutinins

When crude preparations of adenovirus types 4 and 7 were treated with solutions of formamide, a complete or nearly complete inactivation of infectivity could be achieved without affecting the complement fixation titers of the same preparations. Studies on purified virions showed that the intersubunit bonds within the viral capsid were broken and single capsomers were released as the result of treatment by formamide. When subjected to the same treatment, hemagglutinins were sequentially converted into incomplete hemagglutinins (pentons), which were in turn converted into penton bases and fibers.