Immunopotentiation of the antibody response against influenza HA with apoptotic bodies generated by rabies virus G-ERA protein-driven apoptosis

Apoptosis is considered to be a way of eliminating unwanted cells without causing major inflammation. Nevertheless, several lines of evidence show that apoptotic cell-derived antigens can be strong immunogens. The rabies virus glycoprotein G-ERA is an apoptotic molecule. We tested the ability of G-ERA to potentiate a B cell response against an exogenous antigen (influenza hemagglutinin, HA). We found that co-expression of G-ERA and HA in apoptotic bodies increased both the primary and memory HA-specific immune responses. The immunopotentiation of G-ERA is apoptosis-mediated but not necrosis-mediated. Our data indicate that G-ERA-mediated apoptosis might be useful to improve the immunogenicity of live vaccines.

Recombinant Ebola virus nucleoprotein and glycoprotein (Gabon 94 strain) provide new tools for the detection of human infections

After cloning and sequencing the glycoprotein (GP) gene of one of the Gabonese strains of Ebola virus isolated during the 1994-1996 outbreak, it was shown that the circulating virus was of the Zaire subtype. This was confirmed in this study by cloning and sequencing the nucleoprotein (NP) gene of this strain. These two structural proteins were also expressed as recombinant proteins and used in ELISA tests. NP was expressed as a His-tagged fusion protein in Escherichia coli and was purified on resins charged with nickel ions. GP was expressed by means of recombinant baculoviruses in Spodoptera frugiperda cells. Both recombinant proteins reacted positively in ELISAs for the detection of IgG antibodies in convalescent human sera from Gabon and Zaire. The difference in the relative titres of anti-NP and -GP antibodies was variable, depending on the sera. In addition, the recombinant NP reacted with heterologous sera from Côte d'Ivoire and was used successfully to detect IgM antibodies by mu-capture ELISA in sera from Gabonese patients.

Mapping of the mutations present in the genome of the Rift Valley fever virus attenuated MP12 strain and their putative role in attenuation

The MP12 attenuated strain of Rift Valley fever virus was obtained by 12 serial passages of a virulent isolate ZH548 in the presence of 5-fluorouracil (Caplen et al., 1985. Mutagen-directed attenuation of Rift Valley fever virus as a method for vaccine development. J. Gen. Virol., 66, 2271-2277). The comparison of the M segment of the two strains has already been reported by Takehara et al. (Takehara et al., 1989. Identification of mutations in the M RNA of a candidate vaccine strain of Rift Valley fever virus. Virology 169, 452-457). We have completed the comparison and found that altogether a total of nine, 12 and four nucleotides were changed in the L, M and S segments of the two strains, respectively. Three mutations induced amino acid changes in the L protein but none of them was located in the recognized motifs conserved among RNA dependent polymerases. In the S segment, a single change modified an amino acid in the NSs protein and in the M segment, seven of the mutations resulted in amino acid changes in each of the four encoded G1, G2, 14 kDa and 78 kDa proteins. Characterization of the MP12 virus indicated that determinants for attenuation were present in each segment and that they were introduced progressively during the 12 passages in the presence of the mutagen (Saluzzo and Smith, 1990. Use of reassortant viruses to map attenuating and temperature-sensitive mutations of the Rift Valley fever virus MP-12 vaccine. Vaccine 8, 369-375). Passages 4 and 7-9 were found to be essential for introduction of temperature-sensitive lesions and attenuation. In an attempt to correlate some of the mutations with the attenuated or temperature-sensitive phenotypes, we determined by sequencing the passage level at which the different mutations appeared. This work should help to address the question of the role of the viral gene products in Rift Valley fever pathogenesis.

Analysis of the 3' terminal sequence recognized by the Rift Valley fever virus transcription complex in its ambisense S segment

A reconstituted transcription system composed of the Rift Valley fever phlebovirus (Bunyaviridae family) proteins L and N expressed via recombinant vaccinia viruses and an S-like model RNA containing the CAT gene in the antisense orientation, has been described previously by Lopez et al. (J. Virol., 1995, 69, 3972-3979). We extended the use of this in vivo system to determine the sequence at the 3' end of the ambisense S segment recognized by the transcription complex. A mutational analysis of the sequences at the 3' end of the S-like genomic or antigenomic RNA was undertaken. The data indicated that the minimal sequence required for transcription resides in the 13 first 3' nucleotides of the genomic or antigenomic RNA. In these sequences, two regions appeared crucial: the bases at positions 3 to 8 and the purine at position 13. In addition, the terminal repeat ...GU could be deleted without affecting significantly the template activity of the RNA. These data support the prime and realign mechanism proposed recently for Bunya- and Arenaviruses

The L protein of Rift Valley fever virus can rescue viral ribonucleoproteins and transcribe synthetic genome-like RNA molecules

Overlapping cDNAs representing the complete L segment of Rift Valley fever virus were assembled, and the L protein was expressed via a recombinant vaccinia virus. The transcriptase activity of the L protein was assayed with two types of templates: natural ribonucleoproteins (RNPs) and artificial genome-like RNAs. RNPs purified in a CsCl gradient did not retain the RNA polymerase function, but the activity was restored when the L cDNA was expressed in mammalian cells via a recombinant vaccinia virus. Indeed, after transfection of transcriptase-depleted RNPs in cells infected with the recombinant vaccinia virus expressing the L protein, the mRNAs coding for the N and NSs proteins and to a lesser extent, those coding for the glycoproteins were synthesized as well as the corresponding proteins. The transcriptase activity of the recombinant L protein was then investigated by using synthetic templates containing the reporter chloramphenicol acetyltransferase gene in the antisense orientation flanked by the 3' and 5' noncoding region of the S genomic segment. Our results indicate that after transfection of the RNA templates, transcription was achieved in cells coexpressing both the L and N proteins. Together, the experiments demonstrate that the two proteins N and L are absolutely required and sufficient to reconstitute the transcriptase activity.

A liquid-phase blocking ELISA for the detection of antibodies to rabies virus

A liquid-phase blocking ELISA was adapted to the detection and titration of antibodies to principally the nucleoprotein of rabies virus. Sera from animals that had either been vaccinated against rabies or inoculated with street rabies viruses, as well as sera from animals that had no recorded contact with rabies, were tested. These included sera from people, cattle, sheep, goats, dogs, laboratory mice, rabbits, yellow mongooses, wild dogs and lions. Where possible, the results were compared with those obtained with a commercial kit incorporating an indirect ELISA that measures antibody to the rabies glycoprotein. There was a high correlation (r = 0.79) between the two tests. The blocking ELISA provides a single test suitable for the rapid detection of antibodies against rabies virus in the sera of any animal species and for that reason is particularly apt for epidemiological investigations in regions where species diversity is important, as in southern Africa.

Overproduction and purification of Mycobacterium tuberculosis chaperonin 10

The overexpression of the Mycobacterium tuberculosis chaperonin 10 (Cpn10)-encoding gene was accomplished using baculovirus expression vectors. The product was immunoreactive with a Cpn10 monoclonal antibody (mAb) and had an electrophoretic mobility identical to authentic Cpn10. The baculovirus system was most successful in terms of reaching nearly the full expression potential of the system. Recombinant Cpn10 was purified from recombinant baculovirus-infected Spodoptera frugiperda cells by isoelectrofocussing and size-exclusion chromatography. The baculovirus vector and purification methodology described represent a very powerful system for the large-scale production of the M. tuberculosis Cpn10 which may allow us to undertake structure-function analysis.

Membrane fusion activity, oligomerization, and assembly of the rabies virus glycoprotein

The spike glycoprotein (G protein) of rabies virus (CVS strain) expressed in HeLa cells from cloned cDNA mediated membrane fusion after exposure to pHs of 6.1 or below. Chemical crosslinking showed that the rabies G protein, like the vesicular stomatitis virus (VSV) G protein, could be crosslinked to dimers and trimers, indicating that rabies G protein is a trimer. However, unlike the VSV G protein, rabies G protein trimers were not stable to sedimentation in sucrose gradients, even at a mildly acidic pH which stabilizes the VSV G protein trimers. In addition, we report that the expressed rabies virus G protein was functional because it could assemble into VSV particles (tsO45) lacking VSV G protein and rescue infectivity. These VSV (rabies) pseudotypes were neutralized only by an antibody to the rabies G protein. We also examined the properties of a hybrid protein containing the extracellular domain of the rabies virus glycoprotein and the transmembrane and cytoplasmic domains of the VSV G protein. This protein was transported to the cell surface and could be crosslinked to form dimers and trimers, but had little or no detectable membrane fusion activity. The lack of fusion activity was paradoxical because the hybrid protein could rescue VSV infectivity, although the titers were lower than those obtained with the wild-type rabies G protein.

Expression of the tobacco mosaic virus movement protein using a baculovirus expression vector

A cDNA clone of the tobacco mosaic virus 30K movement protein (MP) gene was constructed and introduced into an Autographa californica nuclear polyhedrosis baculovirus expression vector. Infection of Spodoptera frugiperda cells with the vector resulted in the synthesis of low levels of MP, which was detected by anti-MP serum as two closely related species of Mr approximately 34K and a third species of 32K. The authenticity of the recombinant MP was confirmed by comparison of the protein, on the basis of migration during SDS-PAGE, with authentic MP from several sources. It appeared that the recombinant MP was not modified by N-linked glycosylation, but was phosphorylated. The recombinant MP was produced in both a phosphorylated and an unphosphorylated state and the former species was shown to comigrate with plant-expressed MP during SDS-PAGE.

Immunogenic and protective properties of rabies virus glycoprotein expressed by baculovirus vectors

The gene encoding the glycoprotein of rabies virus (G protein, CVS strain) has been cloned and inserted into the baculovirus transfer vector pAcYM1 derived from the nuclear polyhedrosis virus of Autographa californica (AcNPV). The gene was placed under the control of the AcNPV polyhedrin promoter and expressed to high levels by the derived recombinant virus using a Spodoptera frugiperda cell line. It has been established that the antigenic characteristics of the protein were conserved by comparison with those of the native glycoprotein of rabies virions. The immunogenicity of the expressed product was also demonstrated. Intraperitoneal or intramuscular injection of G antigen conferred protection to mice and was associated with the induction of high titers of neutralizing antibodies. The availability of large quantities of antigenically and immunogenically reactive rabies G protein may make feasible crystallographic studies and the safe preparation of a low cost subunit vaccine for the disease.

Invasion of the peripheral nervous systems of adult mice by the CVS strain of rabies virus and its avirulent derivative AvO1

The penetration of the CVS strain of rabies virus and its avirulent derivative AvO1 into peripheral neurons was investigated after intramuscular inoculation into the forelimbs of adult mice. It was found that CVS directly penetrates both the sensitive and motor routes with equal efficiency, without prior multiplication in muscle cells. Infected neurons became detectable 18 h after infection. The second cycle of infection occurred within 2 days, and at day 3 there was a massive invasion of the spinal cord and sensory ganglia. In sensory ganglia, where it was possible to identify cell outlines, it was evident that the infection did not proceed directly from cell body to cell body. The avirulent strain AvO1 penetrated motor and sensory neurons with the same efficiency as CVS. Restriction of viral propagation was observed from the second and third cycles onwards. No further development of the infection could be seen after day 3, and by that time the lysis of primarily infected neurons seemed to occur.

Antigenic site II of the rabies virus glycoprotein: structure and role in viral virulence

Twelve monoclonal antibodies neutralizing the CVS strain of rabies virus were used to characterize antigenic site II of the viral glycoprotein. Nineteen antigenic mutants resistant to neutralization by some of these antibodies were selected; some continued to normally or partially bind the antibody, whereas others did not. Mutations conferring resistance to neutralization by site II-specific monoclonal antibodies were localized into two clusters, the first between amino acids 34 and 42 (seven groups of mutants) and the second at amino acids 198 and 200 (three groups of mutants). Two intermediate mutations were identified at positions 147 and 184. Four mutations resulted in reduced pathogenicity after intramuscular inoculation of the virus in adult mice. One of the mutants, M23, was 300 times and the others were 10 to 30 times less pathogenic than CVS. In three cases the attenuated phenotype was related to an important modification of antigenic site II, whereas the other known antigenic sites were unchanged.