Antigenic diversity of the glycoprotein and nucleocapsid proteins of rabies and rabies-related viruses: implications for epidemiology and control of rabies

Rabies virus-specific monoclonal antibodies (MAbs) have served to describe operationally the topography of the antigenic structure of the glycoprotein and nucleocapsid proteins of rabies virus. With the use of nucleocapsid protein-specific MAbs and cleavage fragments of the nucleoprotein and phosphoprotein, it has been possible to identify the chemical structure of two antigenic sites of the nucleoprotein and one antigenic site of the phosphoprotein. Antisera produced to synthetic peptides that make up the structure of these antigenic sites exhibited reactivities similar to those of MAbs. Analysis of a large number of isolates of rabies virus from different animal species and from different geographic locations revealed that rabies viruses differ considerably in their antigenic structure and can be identified according to their characteristic reactivity patterns with MAbs. Analysis of field virus isolates has also revealed that strains of rabies virus generally are associated with only one or a few major mammalian hosts within any given geographic area. Protection experiments in mice have not demonstrated correlations between protective activity and degree of antigenic difference between the vaccine strain and the challenge virus. Therefore, changes in antigenic structure, as determined by analysis with rabies virus-specific MAbs, cannot predict whether a given rabies vaccine will protect against a particular field virus.

Epidemiology of rabies virus variants. Differentiation using monoclonal antibodies and discriminant analysis

Rabies virus was isolated by cell culture from the brains of 104 confirmed rabies cases diagnosed by the fluorescent-antibody staining technique in the United States during 1974-1984. Eighty-seven isolates were obtained from wild-life species, 10 from humans, and seven from domestic animals. These isolates were tested in virus neutralization and immunofluorescence assays using a panel of 34 monoclonal antibodies specific for rabies virus nucleocapsid protein, 44 monoclonal antibodies specific for rabies virus glycoprotein, and two monoclonal antibodies specific for rabies virus nucleocapsid-associated phosphoprotein. Using discriminant analysis, a distinctly different reactivity pattern was revealed between virus isolates from terrestrial (raccoon, skunk) and nonterrestrial (bat) reservoir hosts. The usefulness of this approach for studying the epidemiology of rabies and for predicting the source of infection when this information is unknown is discussed.

Immune response in skunks to a vaccinia virus recombinant expressing the rabies virus glycoprotein

Striped skunks (Mephitis mephitis) were vaccinated with a vaccinia virus recombinant expressing the rabies virus glycoprotein. Virus neutralizing antibodies to rabies virus were present at 14 days postvaccination by the following routes: scarification (6/6), intramuscular (4/4) and intestinal (5/8). Six out of seven skunks that ate vaccine filled baits had virus neutralizing antibodies at 28 days. When challenged intramuscularly with street virus, the survival rates were 5/7 for the bait-fed group, 4/8 for the intestinal group, 3/4 for the intramuscular group, 5/6 for the animals that were scarified, and 0/8 for controls. This is the first report of a high rate of immunization of skunks with a rabies vaccine administered orally.

Oral immunization and protection of raccoons (Procyon lotor) with a vaccinia-rabies glycoprotein recombinant virus vaccine

Animal rabies control has been frustrated by the existence of multiple wildlife reservoirs and the lack of efficacious oral vaccines. In this investigation, raccoons fed a vaccinia-rabies glycoprotein recombinant virus in a sponge bait developed rabies virus-neutralizing antibody (0.6-54.0 units) and resisted street rabies virus infection 28 and 205 days after feeding. Additional raccoons immunized by oral infusion with attenuated antigenic variants of rabies virus strains CVS-11 and ERA failed to develop rabies virus-neutralizing antibody. This work demonstrates the feasibility of a recombinant virus vaccine containing the rabies glycoprotein gene for immunization of raccoons, and possibly other wildlife, to obtain long-term protection against rabies.

Isolation and characterization of human T cell lines and clones reactive to rabies virus: antigen specificity and production of interferon-gamma

By using a preparation of inactivated rabies virus, the blood mononuclear cells from five rabies vaccine recipients were stimulated in vitro in the presence of interleukin 2. T cell lines that displayed significant proliferative responses to whole rabies virus and to preparations of rabies glycoprotein and nucleocapsid were obtained from all the individuals. Other antigens, such as diphtheria and tetanus toxoids, influenza A virus, hepatitis B surface antigen, and serum albumin, failed to induce the proliferation of the T cell lines. One of these rabies-specific T cell lines was found to proliferate in response to rabies antigens only when the antigen-presenting cells expressed homologous HLA-DR antigens. The use of mouse monoclonal antibodies specific for human T cell surface markers revealed that most of the cells of these rabies-reactive lines were of the helper/inducer class of T lymphocytes. Stimulation of the T cell lines with the rabies antigens induced the production of interferon-gamma, a lymphokine with potent antiviral activity. Several T cell clones were isolated from two of these cell lines, and most of them appeared to be specific for the antigenic components of the viral nucleocapsid. Two T cell clones specific for the rabies glycoprotein were also isolated from one of these lymphocyte interleukin 2-dependent lines. Further in vitro studies with rabies-specific T cells could help us to understand in more depth the role of regulatory T cells in the human immune response to rabies virus.

Molecular mimicry: frequency of reactivity of monoclonal antiviral antibodies with normal tissues

More than 600 monoclonal antiviral antibodies made against 11 different viruses were screened against 14 different organs from normal uninfected mice. Of these antiviral antibodies, 21, or approximately 3.5%, reacted with specific cells in these organs. Several of these antibodies were of the multiple-organ-reactive type and recognized antigens in more than one organ. It was concluded that the reactivity of monoclonal antiviral antibodies with normal tissues is a common phenomenon.

Isolation and characterization of human T cell lines and clones reactive to rabies virus: antigen specificity and production of interferon-gamma

By using a preparation of inactivated rabies virus, the blood mononuclear cells from five rabies vaccine recipients were stimulated in vitro in the presence of interleukin 2. T cell lines that displayed significant proliferative responses to whole rabies virus and to preparations of rabies glycoprotein and nucleocapsid were obtained from all the individuals. Other antigens, such as diphtheria and tetanus toxoids, influenza A virus, hepatitis B surface antigen, and serum albumin, failed to induce the proliferation of the T cell lines. One of these rabies-specific T cell lines was found to proliferate in response to rabies antigens only when the antigen-presenting cells expressed homologous HLA-DR antigens. The use of mouse monoclonal antibodies specific for human T cell surface markers revealed that most of the cells of these rabies-reactive lines were of the helper/inducer class of T lymphocytes. Stimulation of the T cell lines with the rabies antigens induced the production of interferon-gamma, a lymphokine with potent antiviral activity. Several T cell clones were isolated from two of these cell lines, and most of them appeared to be specific for the antigenic components of the viral nucleocapsid. Two T cell clones specific for the rabies glycoprotein were also isolated from one of these lymphocyte interleukin 2-dependent lines. Further in vitro studies with rabies-specific T cells could help us to understand in more depth the role of regulatory T cells in the human immune response to rabies virus.

Amplification of rabies virus-induced stimulation of human T-cell lines and clones by antigen-specific antibodies

The effect of antigen-specific antibodies on the response of human T-cell lines and clones to rabies virus was studied. Plasmas from rabies-immune vaccine recipients, but not those from nonimmune individuals, enhanced the proliferative response of rabies-reactive T cells to whole inactivated virus or to the purified glycoprotein and nucleocapsid from the rabies virion. Rabies-immune plasma also increased the antigen-induced production of gamma interferon by the rabies-specific T-cell lines. Experiments performed on T-cell clones specific for either rabies glycoprotein or nucleocapsid showed that immune plasma as well as antiglycoprotein and antinucleoprotein murine monoclonal antibodies possessed the capacity to increase significantly the antigen-induced proliferative responses of these clones. The overall results indicate that this in vitro effect of antigen-specific antibodies on the response of regulatory T lymphocytes to rabies virus could be an important factor in the development of effective immune responses in vivo to rabies virus.

Antigenic sites on the ERA rabies virus nucleoprotein and non-structural protein

Thirty-one monoclonal antibodies, specific for either the nucleoprotein (N) or the non-structural protein (NS; nucleocapsid-associated protein) of the nucleocapsid of the ERA strain of rabies virus, were used to investigate the topography of antigenic sites on the nucleocapsid complex. Based on the results of a competitive enzyme immunoabsorbent assay using these antibodies, five spatially distinct antigenic sites were defined: three on the N protein (groups N I, N II and N III) and two on the NS protein (groups NS I and NS II). Antigenic variations among various street and laboratory strains of rabies virus were analysed by indirect immunofluorescence assay with the monoclonal antibodies specific for the nucleocapsid. Some correlation between the natural nucleocapsid variation and the antigenic topographical map was observed.

Differences in cell-to-cell spread of pathogenic and apathogenic rabies virus in vivo and in vitro

Pathogenic parental rabies virus and apathogenic variant virus were shown to differ in their ability to infect neurons in vivo and neuroblastoma cells in vitro. After intracerebral inoculation, the distribution of infected neurons in the brain was similar for both viruses, but the rate of spread throughout the brain, the number of infected neurons, and the degree of cellular necrosis were much lower in the case of apathogenic virus. After adsorption to mouse neuroblastoma cells, apathogenic virus was less rapidly internalized than pathogenic virus, and cell-to-cell spread of apathogenic variant virus was completely prevented by the addition of rabies virus-neutralizing antibody, whereas the spread of pathogenic virus was not affected.

Antigenic variants of rabies virus in isolates from eastern, central and northern Canada

Street rabies virus isolated from 51 specimens from Ontario, Quebec, Manitoba and the Northwest Territories have been typed by a panel of 36 antinucleocapsid monoclonal antibodies. Three main groups were found. The first group comprised those terrestrial mammals originating in Ontario, Quebec and the Northwest Territories. The second group was found in terrestrial mammals from Manitoba. The third heterogenous group was made up of bats from Ontario.

Protection from rabies by a vaccinia virus recombinant containing the rabies virus glycoprotein gene

Inoculation of rabbits and mice with a vaccinia-rabies glycoprotein recombinant (V-RG) virus resulted in rapid induction of high concentrations of rabies virus-neutralizing antibodies and protection from severe intracerebral challenge with several strains of rabies virus. Protection from virus challenge also was achieved against the rabies-related Duvenhage virus but not against the Mokola virus. Effective immunization by V-RG depended on the expression of a rabies glycoprotein that registered proline rather than leucine as the eighth amino acid from its NH2 terminus (V-RGpro8). A minimum dose required for effective immunization of mice was 10(4) plaque-forming units of V-RGpro8 virus. beta-propiolactone-inactivated preparations of V-RGpro8 virus also induced high levels of rabies virus-neutralizing antibody and protected mice against intracerebral challenge with street rabies virus. V-RGpro8 virus was highly effective in priming mice to generate a secondary rabies virus-specific cytotoxic T-lymphocyte response following culture of lymphocytes with either ERA or PM strains of rabies virus.

T cell responses to cleaved rabies virus glycoprotein and to synthetic peptides

The antigenic structure of the rabies virus glycoprotein has been studied. A limited number of fragments were obtained by cyanogen bromide (CNBr) cleavage of viral glycoprotein, and eight large peptides were isolated by using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. These were tested for their capacity to stimulate the proliferation of nylon wool-purified T cells obtained from spleens of rabies-immune A/J mice. Three peptides (Cr1, Cr2 plus Cr2A, and Cr3) stimulated antigen-specific proliferation, indicating that at least three T cell determinants of the native molecule are sequential or continuous in nature. Stimulation was also obtained with 27-residue and 13-residue synthetic peptides (designated R21 and R20, respectively) that included sequences towards the carboxy terminal end of Cr1, but not with synthetic peptides that included sequences of Cr2 and Cr3 (which are both glycosylated in virus-derived material). The intact viral glycoprotein and synthetic peptide R21 stimulated T lymphocytes with surface characteristics of helper cells, and induced the production of interleukin 2 by these lymphocytes. Synthetic peptides R20 and R21 also stimulated a minor population of Lyt-2-positive cells, which were not yet identified as either suppressor or cytotoxic T lymphocytes.

T cell responses to cleaved rabies virus glycoprotein and to synthetic peptides

The antigenic structure of the rabies virus glycoprotein has been studied. A limited number of fragments were obtained by cyanogen bromide (CNBr) cleavage of viral glycoprotein, and eight large peptides were isolated by using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. These were tested for their capacity to stimulate the proliferation of nylon wool-purified T cells obtained from spleens of rabies-immune A/J mice. Three peptides (Cr1, Cr2 plus Cr2A, and Cr3) stimulated antigen-specific proliferation, indicating that at least three T cell determinants of the native molecule are sequential or continuous in nature. Stimulation was also obtained with 27-residue and 13-residue synthetic peptides (designated R21 and R20, respectively) that included sequences towards the carboxy terminal end of Cr1, but not with synthetic peptides that included sequences of Cr2 and Cr3 (which are both glycosylated in virus-derived material). The intact viral glycoprotein and synthetic peptide R21 stimulated T lymphocytes with surface characteristics of helper cells, and induced the production of interleukin 2 by these lymphocytes. Synthetic peptides R20 and R21 also stimulated a minor population of Lyt-2-positive cells, which were not yet identified as either suppressor or cytotoxic T lymphocytes.

Use of monoclonal antibodies to confirm vaccine-induced rabies in ten dogs, two cats, and one fox

A panel of 8 monoclonal antibodies to rabies glycoprotein antigen was used to characterize the modified-live virus vaccines marketed in the United States during the last 10 years. Thirteen of 14 rabies virus isolates from 11 dogs, 2 cats, and 1 fox suspected of developing vaccine-induced rabies were shown to have reactivity patterns that were identical to the vaccine administered. Reactivity patterns for 20 rabies isolates from human beings, wild animals, or domestic animals with no history of recent vaccination with modified-live virus rabies vaccine were different from those obtained for vaccines.

Anti-idiotypic antibodies induce neutralizing antibodies to rabies virus glycoprotein

Rabbit anti-idiotypic antibodies (alpha Id Ab) were prepared against five murine monoclonal antibodies (mAb) specific for the rabies virus glycoprotein. Four of the mAb were directed against three known, type-specific, neutralizing sites on the glycoprotein, and the other mAb was directed against a topographically uncharacterized, nonneutralizing epitope. An absence of significant cross-reactivity among the alpha Id Ab for heterologous mAb suggested that the alpha Id Ab were highly specific for unique variable region determinants. The binding of three of the five alpha Id Ab to their homologous mAb could be inhibited by rabies virus-soluble glycoprotein, suggesting that the alpha Id Ab possessed subpopulations similar or adjacent to the antigen-binding site of the mAb. Two of the five alpha Id Ab injected into mice elicited a specific virus-neutralizing antibody response. Mechanisms to account for the induction of the virus-neutralizing antibody by alpha Id Ab are discussed.

Epidemiologic analysis of antigenic variations of street rabies virus: detection by monoclonal antibodies

The nucleocapsid antigen of 204 strains of street rabies virus, which originated in Europe, Africa and Asia, was analyzed by fluorescent antibody staining technique with a panel of 20 monoclonal antibodies specific for nucleocapsid of rabies and rabies-related viruses. A definite pattern of reactivity was observed with strains of the same geographic origin with the exception of strains originating from Madagascar, Thailand and Iran which were more diversified. Mice immunized with a vaccine prepared from a Pasteur PV-11 strain of virus were well protected against challenge with representative strains from Europe and Africa, and a partial protection was observed following challenge with strains from Madagascar and Thailand.

Antigenic sites on the CVS rabies virus glycoprotein: analysis with monoclonal antibodies

Antigenic variation in the glycoprotein of rabies (CVS-11) virus was studied. Neutralization-resistant variant viruses were isolated in vitro at high frequency (10(-4) to 10(-5)) in the presence of anti-glycoprotein monoclonal antibody. Analysis of these variants identified at least three functionally independent antigenic sites, based on the grouping of variants that were no longer neutralized by one or more of a panel of 24 monoclonal antibodies. Competition radioimmunoassay suggested that one of these three antigenic sites was topologically distinct, with the other two in close proximity. In addition, it was shown that most (but not all) neutralization-resistant variants failed to bind the relevant monoclonal antibody. Viruses with altered antigenicity were shown to accumulate in virus stocks following several passages in vitro in the absence of antibody. In addition, variants were isolated in vivo following treatment of mice with monoclonal antibody.

Chemical and immunological analysis of the rabies soluble glycoprotein

Soluble glycoprotein (Gs), purified from virion-depleted, rabies-infected tissue culture fluid, was chemically and immunologically analyzed. A comparison of this antigen with the virion-associated glycoprotein showed that Gs lacks 58 amino acid residues from the carboxy terminus of the virion-associated glycoprotein. Analysis with monoclonal antibodies revealed that all the epitopes of the viral glycoprotein are also present in the soluble glycoprotein. However, when tested for its ability to protect mice against a lethal challenge infection with rabies virus, Gs in contrast to viral glycoprotein, showed no protective activity. These results suggest that the carboxy terminus of the rabies virus glycoprotein is necessary for its full protective activity even though this portion of the glycoprotein molecule does not contain any antigenic determinants.

Characterization of an antigenic determinant of the glycoprotein that correlates with pathogenicity of rabies virus

The pathogenicity of fixed rabies virus strains for adult mice depends on the presence of an antigenic determinant on the viral glycoprotein. Two virus-neutralizing monoclonal antibodies have been used to identify this determinant. All pathogenic strains of fixed rabies virus bind to these antibodies and are neutralized by them, whereas nonpathogenic strains fail to react with these monoclonal antibodies and are not neutralized by them. Antigenic variants of the rabies virus with altered glycoprotein were selected by growing virus in the presence of one monoclonal antibody, 194-2. All variants that lost their ability to react with this antibody and an additional antibody, 248-8, were found to be nonpathogenic for adult mice. Analysis of tryptic peptides of the glycoproteins of pathogenic parent virus and nonpathogenic variants and the amino acid sequence of a specific variant tryptic peptide revealed that the change in pathogenicity corresponded to an amino acid substitution at position 333 of the glycoprotein molecule. The nucleotide sequence of the nonpathogenic variant glycoprotein gene contained a base change that confirmed the single amino acid substitution in the tryptic peptide replacing arginine-333 in the parental glycoprotein. We conclude that arginine-333 is essential for the integrity of an antigenic determinant and for the ability of rabies viruses to produce lethal infection in adult mice.

Antigenic structure of rabies virus glycoprotein: ordering and immunological characterization of the large CNBr cleavage fragments

After rabies virus glycoprotein was treated with CNBr, the peptide mixture was fractionated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. CNBr-cleaved peptide fragments were resolved into seven peptide bands under reducing conditions and six peptide bands under nonreducing conditions. The isolated nonreduced polypeptides were further analyzed by electrophoresis under reducing conditions. The N-terminal amino acid sequences were determined for the peptides in each of the isolated bands. The sequence data identified eight CNBr peptides and allowed the peptide fragments to be ordered within the deduced amino acid sequence of the glycoprotein. Analysis of the nonreduced CNBr peptides revealed two conformations of the glycoprotein. Two CNBr peptide fragments were specifically immunoprecipitated with a hyperimmune anti-rabies glycoprotein serum. These two and one other CNBr peptide induced the production of rabies virus-neutralizing antibodies, indicating the existence of at least three distinct antigenic sites on the rabies virus glycoprotein.

Vaccine-induced rabies in four cats

Vaccine-induced rabies in 4 cats was characterized by rigid posterior paralysis. In 3 cats, paralysis began in 1 hindlimb and rapidly spread to the other hindlimb. Later, forelimb and cranial nerve deficits were noticed. Onset of clinical signs was 13 to 17 days after IM vaccination with an ERA-strain modified live-virus rabies vaccine approved for use in cats. Each cat eventually was euthanatized. In each case, brain tissue was found to contain rabies virus on fluorescent antibody and mouse inoculation studies. An antibody titer and mouse inoculation studies. An antibody titer against rabies virus was found in the CSF of 1 cat. In each case, viral isolates were shown to be of an ERA strain rather than natural ("street") rabies.

Antibody responses to human diploid cell vaccine for rabies with and without human rabies immune globulin

One hundred one volunteers with no exposure to rabies were given human diploid cell vaccine (HDCV) for rabies with or without 20 international units of human rabies immune globulin (HRIG)/kg of body weight to evaluate schedules for therapy with HDCV and HRIG after exposure. All of the volunteers who received three or more doses of HDCV alone or four or more doses of HDCV with HRIG developed high titers of neutralizing antibodies by day 35, which persisted for at least 60 days. By day 7, of the 61 volunteers given HRIG and HDCV, 53% had neutralizing antibodies by a mouse neutralization test and 67% had neutralizing antibodies by a rapid fluorescent focus inhibition test. Similar antibody levels were found in volunteers given HRIG alone, a finding which suggests that low or undetectable early titers after administration of HDCV and HRIG were due to inadequate HRIG dosage rather than any interaction between the passive antibody (HRIG) and the vaccine antigen. These results suggest that trials with 30 or 40 international units of HRIG/kg in combination with HDCV are warranted.

Antigenic variants of rabies virus

The authors studied nineteen street virus isolates from different regions of Canada using either anti-nucleocapsid and anti-glycoprotein monoclonal antibodies or cross-protection tests. This study only allowed us to recognize three groups of viruses with different nucleocapsid patterns, and no difference, as far as protection with a Pitmann-Moore vaccine is concerned, between four of these strains.

Rabies mRNA translation in Xenopus laevis oocytes

Two rabies virus-specific mRNA species were identified by analysis of their encoded proteins after translation of the partially purified species in Xenopus laevis oocytes. One of these coded for the virion surface glycoprotein (G protein), and the other coded for the major structural protein of the virion nucleocapsid (N protein). The G-mRNA sedimented in a sucrose density gradient at about 18S, and the N-mRNA had a sedimentation coefficient of approximately 16S. Their respective translation products were identified in a radioimmunoassay with specific monoclonal antibody probes that recognized only G or N proteins. Immunoprecipitates formed between the radiolabeled viral antigens synthesized in programmed oocytes and their respective monoclonal antibodies were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The glycoprotein antigen translated from G-mRNA in oocytes migrated in the gel ahead of the virion G protein with a migration rate that was similar to that of nonglycosylated intracellular glycoproteins from virus-infected cells. The results suggested that the branched-chain carbohydrate of G protein was not required for recognition by the particular monoclonal antibody used. The nucleocapsid antigen translated from N-mRNA in oocytes migrated to the same position in the gel as marker virion N protein. Both the electrophoretic mobility of virus-specific antigens in sodium dodecyl sulfate-polyacrylamide gel and the antibody concentration dependence for immunoprecipitations were criteria for identifying the individual viral proteins encoded by the two rabies mRNA's.

Antigenic variants of rabies virus

Antigenic variants of CVS-11 strain of rabies virus were selected after treatment of virus populations with monoclonal antibodies directed against the glycoprotein antigen of the virus. These variants resisted neutralization by the hybridoma antibody used for their selection. Two independently mutating antigenic sites could be distinguished when five variants were tested with nine hybridoma antibodies. The frequency of single epitope variants in a cloned rabies virus seed was approximately 1:10,000. Animals were not or only partially protected when challenged with the parent virus or with another variant, but were fully protected against challenge with the virus used for immunization. Variants were also detected among seven street viruses obtained from fatal cases of human rabies. Animals immunized with standard rabies vaccine were protected against challenge with some but not all street rabies variants. A comparative antigenic analysis between vaccine strain and challenge virus by means of monoclonal antiglycoprotein antibodies showed a slightly closer degree of antigenic relatedness between vaccine and challenge strain in the combinations where vaccination resulted in protection. It remains unknown, however, whether these apparently minor antigenic differences in the glycoproteins account for the varying degrees of protection. The results of this study clearly indicate that the selection of vaccine strains and the methods used to evaluate the potency of rabies vaccines need to be revised.

Use of hybridoma monoclonal antibodies in the detection of antigenic differences between rabies and rabies-related virus proteins. I. The nucleocapsid protein

Twenty-one hybridoma cultures, obtained through the fusion of mouse myeloma cells with splenocytes of BALB/c mice immunized with either rabies virus or Mokola virus, secreted monoclonal antibodies specific for the nucleocapsid of the inducer virus. They displayed different specificities for the nucleocapsids of rabies and rabies-related viruses and could be classified into eight groups which are likely to correspond to different antigenic determinants on the nucleocapsid. Four strains of fixed rabies virus (CVS, ERA, Flury-LEP and Kelev) could not be differentiated by the nucleocapsid-specific hybridoma antibody. The Flury-HEP virus (derived from Flury-LEP) as well as the rabies-related viruses Mokola, Lagos bat and Duvenhage, showed marked differences in their reactivities with hybridoma antibodies to nucleocapsid. A selected panel of three of these hybridomas may be used for a rapid differential diagnosis among all members of the Lyssavirus group.

Use of hybridoma monoclonal antibodies in the detection of antigenic differences between rabies and rabies-related virus proteins. II. The glycoprotein

Twenty-five hybridoma cultures secreted monoclonal antibodies directed against the glycoprotein of rabies or rabies-related viruses. The antibodies had different specificities for the glycoproteins of eight rabies and rabies-related viruses. They could be classified into fourteen groups which probably correspond to different antigenic determinants on the glycoproteins. These hybridomas when used in either radioimmunoassay (RIA) or in neutralization tests allow differentiation of laboratory strains of rabies virus from each other as well as from the rabies-related viruses.

[Characteristics of defective rabies virus particles formed in chronically infected cultures]

Cultural fluids of BHK-21/13S and HEp-2 cells chronically infected with rabies virus were used to determine the structures sedimenting in the sucrose gradient of the slow infectious virus. These structures have a polypeptide composition similar to that of rabies virus and contain subgenome RNA. Morphologically they are spherical virions. After amplification in BHK-21/13S cells the structures protected mice from lethal doses of rabies virus. The results obtained allow designation of the structures as defective interfering particles of rabies virus. The evidence is given on their participation in the establishment and maintaining of the chronic infection.

Comparative study on antibody determination by different methods in sera of persons vaccinated with HDCS-vaccine

The comparative studies undertaken by 7 laboratories in 6 countries show that the calculation I.U.s did not as anticipated minimize but actually enhanced the variability of results of Rabies antibody estaminations in the sera of HDCS vaccines. The high biological variance in the method(s) may not have been considered by individual laboratories and any neglect of fundamental biostatistical laws, unfortunately, diminishes the theoretical advantage of using the "International Standard (I.S.)" as a "tertium comparationis". Perhaps the intrinsic variability of the I.S. should be re-evaluated and it is conceivable that a pure IgG fraction of Rabies antiserum would show less variability. Intralaboratory variation might be reduced by agreeing that only a geometric mean of the I.S., and not a single value obtained in an individual test, should be used for calculation of I.U.s. Application of the principles of biochemical and pharmacological methods, such as test-to-test control of the I.S. and its analytical variances might well enhance the reproducibility of the results. MNT, RFFIT, PRT and CFT were unable to detect antibodies in HDCS vaccinees until 7 days after the first vaccination. The establishment of methods for detecting early antibody requires further investigation.

Monoclonal antibodies against rabies virus produced by somatic cell hybridization: detection of antigenic variants

Somatic cell hybrids (hybridomas) between mouse myeloma cells and spleen cells derived from BALB/c mice immunized with inactivated rabies vaccine were found to produce antibodies to rabies virus. Monoclonal antibodies with different specificities were obtained either from the mass culture directly after fusion or from clones derived from a single-cell cloning procedure. Several strains of fixed or street rabies virus were analyzed by virus neutralization procedures which demonstrated differences in their antigenic composition. Hybridoma antibodies were able to protect experimental animals from lethal rabies virus infection.

Isolation and purification of a polymeric form of the glycoprotein of rabies virus

Of the three major proteins associated with the rabies virus membrane, only the glycoprotein was found to be located on the external surface of the virus membrane. Glycoprotein prepared by treatment of rabies virus with Triton X-100 and purified by isoelectric focusing was found to be homogeneous with respect to size and isoelectric point. This material, which is free of phospholipids, is able to protect in vaccination experiments against a lethal challenge infection with rabies virus. The apparent mol. wt. of this component isolated under non-denaturing conditions is approx. 400000. The same material analysed by SDS polyacrylamide gel electrophoresis (PAGE) was found to consist solely of polypeptide chains of the G protein (mol. wt. 80000). A minor glycoprotein (gp 50), detected by PAGE of the Triton X-100 released material, appeared to be a breakdown product of the G-protein. Therefore the detergent released material represents homopolymers of the G-protein. Whether the antigenic determinants reside on the monomeric subunit or are a property of the polymeric form of the G-protein is discussed.

Suppression of cell-mediated immunity by street rabies virus

Mice lethally infected with street rabies virus failed to develop cytotoxic T cells specific for rabies virus-infected target cells, whereas high levels of cell-mediated cytotoxicity (CMC) were generated after nonfatal infection with the attenuated high egg passage (HEP) or ERA rabies virus strains. Furthermore concurrent infection with street, but not with HEP, rabies virus suppresses development of a primary (but not a secondary) CMC response specific for influenza virus. No cross-reactivity is found between effector T-cell populations from mice immunized with HEP or with influenza virus. It thus appears that street rabies virus, which is not known to replicate in the cells of immune system, induces some general defect in the primary CMC lymphocyte response, though restimulation of memory T-cell populations is unimpaired and there is no defect in antibody formation. Development of fatal rabies may reflect the operation of this selective immunosuppressive mechanism.

Induction and biological properties of defective interfering particles of rabies virus

A method for obtaining large quantities of defective interfering (DI) rabies virus particles that fulfill all the criteria delineated by Huang and Baltimore (1970) is described. The purified rabies DI virion was found to be much shorter (60 to 80 nm) than the complete virion (180 nm) and to have a viral genome of about half the size of normal rabies RNA but with all of the structural proteins of standard virions. Rabies DI virions were noninfectious for both cells in culture and for animals. As determined by in vitro and in vivo techniques, interference with the replication of standard virus was specific to rabies virus. The possible role of rabies DI virion in the pathogenicity of rabies virus infection and in the establishment of attenuated strains for use as live rabies vaccines is discussed.

In vitro evidence of cell-mediated immunity after exposure of mice to both live and inactivated rabies virus

Mice exposed to live or beta-propiolactone-inactivated rabies virus generated a strong, specific cell-mediated cytotoxic response which was generally maximal 6 days after inoculation. Release of 51Cr was apparently a function of immune thymus-derived lymphocytes (T cells) because it was abrogated by prior incubation of spleen cells with anti-thymus antiserum and complement but was undiminished by passage of spleen cells through nylon-wool columns. Cytotoxicity was always maximal for interactions in which thymus-derived cells and targets shared H-2 genes but, unlike the situation found in other assays of this type, considerable lysis of allogeneic, virus-infected target cells may also occur. Perhaps the most significant finding from these experiments is that an inactivated virus has been shown to stimulate a potent cytotoxic thymus-derived cell response. Manipulation of this experimental model may allow analysis of the antigens required for stimulation of cell-mediated immunity. A more practical consequence may be the development of more rational protocols for postexposure vaccination against rabies. Prior treatment of mice with antirabies antibody severely depressed the generation of cell-mediated immunity.

Post-exposure use of human diploid cell culture rabies vaccine

880 individuals, 120 of which were exposed to rabid animals, were immunized pre- or post-exposure with 2 different BPL-inactivated and concentrated rabies vaccines prepared in HDC strains WI-38 and MRC-5. The vaccines were well tolerated and no major side effects were observed after primary immunization with 3-10 doses or 1 booster vaccination. The dynamics of neutralizing, antibody formation and persistence of antibodies in 4 different groups of vaccinees are described. The groups were vaccinated pre-exposure (I) on days 0, 28 and 56; (II) on days 0, 7 and 14; (III) on days 0, 3, 7 and 21; and (IV) post-exposure on days 0, 3, 7, 14, 30 and 90. High antibody levels--persisting for at least 30 months--were obtained in all patients. The CFT, using a concentrated and purified virion antigen, was highly specific for rabies virus antibody demonstration. Since in some 50 patients under severe risk, after having been bitten and/or scratched by proven rabid animals, not a single breakthough of immunity was observed during an observation time between 1/2 and 3 years, the protective effect of the HDCS-rabies vaccines seems to be excellent. With regard to their high immunogenicity and extremely low reactogenicity, the new HDCS-vaccines can be recommended for prophylactic and post-exposure immunization of man without any reserve. Data on simultaneous application of homologous anti-rabies gammaglobulin from man (20 I.E./kg body-weight) and HDCS-vaccines are also presented and discussed.

Production and control of rabies vaccines made on diploid cells

Introductory remarks on the advantages of antirabies vaccines obtained from human diploid cell cultures in comparison with brain tissue vaccine and duck embryo vaccine. The characteristics of these new types of vaccine are: (i) high antigenicity, (ii) rapid development of antibodies, (iii) absence of adverse reactions even when the booster inoculation was given two years later. The disadvantage is the high cost of production to obtain a highly purified product.

Role of interferon in prophylaxis of rabies after exposure

Rhesus monkeys were completely protected from rabies by a single dose of experimental, highly concentrated, rabies virus vaccine prepared from virus propagated in cultures of human diploid cells and administered several hours after infection with street rabies virus. Protection seemed to be related to the high antigenicity of the vaccine and to its ability to induce interferon in vaccinated animals. Only partial protection was afforded by one or three inoculations of less concentrated vaccines that were prepared from cultures of human diploid cells or primary hamster kidney cells and that were not capable of inducing interferon. The level of virus-neutralizing antibody induced by vaccination could not be correlated with the final outcome of the disease. The simultaneous inoculation of vaccine and interferon inducers (polyribocytidylic acid homopolymer pair or Newcastle disease virus) did not improve the results obtained with vaccine along, a fact which indicates that factors other than interferon and antibody may play an important role in the treatment of rabies after exposure.

Immunization schedules for the new human diploid cell vaccine against rabies

Clinical and antibody responses of human volunteers to four different serial production lots of human diploid cell vaccine (HDCV) each with a different antigenic value are described. Three to four doses of HDCV administered over a period of 14 days produced high levels of virus neutralizing antibodies with an average titer up to 20 times higher than the titer elicited by four doses of duck embryo vaccine. Antibodies were still present one year after completion of vaccination. Only minimal differences in antibody response could be observed between groups receiving vaccines of different antigenic values. Untoward reactions to the vaccine were few. The possibility of using the vaccine as part of postexposure human prophylaxis against rabies is discussed.

Pathogenesis of Rabies in Immunodeficient Mice

The HEP and ts2 strains of rabies virus inoculated intracerebrally into adult mice normally cause clinically inapparent infection. In the experiments described, this is converted into a lethal infection by immunosuppression with cyclophosphamide, which also prevented induction of immunity with vaccine. Lethal infection of HEP-inoculated mice was also observed in mice treated with antithymocytic serum, and in athymic (BALB/c-nu) nude mice.

Pathogenesis of rabies in immunodeficient mice

The HEP and ts2 strains of rabies virus inoculated intracerebrally into adult mice normally cause clinically inapparent infection. In the experiments described, this is converted into a lethal infection by immunosuppression with cyclophosphamide, which also prevented induction of immunity with vaccine. Lethal infection of HEP-inoculated mice was also observed in mice treated with antihymocytic serum, and in athymic (BALB/c-nu) nude mice.

Rhabdovirus replication in enucleated host cells

Infection of enucleated TC-7 monkey cells with rabies virus resulted in the synthesis of virus-directed RNA and the production of rabies antigens but not of infectious virus. The yield of infectious vesicular stomatitis virus from enucleated TC-7 cells, on the other hand, was almost as high as that from intact cells. Inhibition of the mitochondrial functions of enucleated cells by treatment with ethidium bromide did not influence the development of rabies antigens or the production of infectious vesicular stomatitis virus.