A monoclonal antibody study of the receptor area of the Venezuelan encephalitis virus]

The receptor region for virus-cell interaction in Venezuelan equine encephalomyelitis (VEE) and Eastern equine encephalomyelitis (EEE) viruses was studied using a panel of 17 monoclonal antibodies (MCA). They were able to block agglutination of goose erythrocytes. The dominant role of glycoprotein E2 in the formation of viral receptor for EEE and VEE viruses was demonstrated. Competitive radioimmunoassay identified three antigenic sites in this region. These sites were also responsible for virus neutralization. MCAs to these sites protected outbred mice against lethal infection. The presence of a highly conservative region in VEE (site E2-3) and EEE (site E2a) which produced cross-reacting antibodies blocking hemagglutination of Western equine encephalomyelitis, Semliki Forest, Sindbis, Getah, Aura, Chikungunya, and Pixuna viruses was established. A hypothesis is suggested concerning the existence of similar regions for the entire alphavirus genus, and the role of this region in virus-cell interaction.     

Glycoproteins E2 of the Venezuelan and Eastern equine encephalomyelitis viruses contain multiple cross-reactive epitopes

Summary Enzyme immunoassay (EIA) with sixty types of monoclonal antibodies (MAbs) was used to study cross-reactive epitopes on the attenuated and virulent strains of the Eastern equine encephalomyelitis (EEE) and Venezuelan equine encephalomyelitis (VEE) viruses. All three structural proteins of the EEE and VEE viruses were demonstrated to have both cross-reactive and specific antigenic determinants. The glycoprotein E1 of EEE and VEE viruses possesses three cross-reactive epitopes for binding to MAbs. The glycoprotein E2 has a cluster of epitopes for 20 cross-reacting MAbs produced to EEE and VEE viruses. Cross-reactive epitopes were localised within five different sites of glycoprotein E2 of VEE virus and within four sites of that of the EEE virus. There are no cross-neutralising MAbs to the VEE and EEE viruses. Only one type of the protective Mabs was able to cross-protect mice against lethal infection by the virulent strains of the VEE and EEE viruses. Eight MAbs blocked the hemagglutination activity (HA) of both viruses. Antigenic alterations of neutralising and protective sites were revealed for all attenuated strains of the VEE and EEE viruses. Comparative studies of the E2 proteins amino acid sequences show that the antigenic modifications observed with the attenuated strains of the VEE virus may be caused by multiple amino acid changes in positions 7, 62, 120, 192 and 209–213. The escape-variants of the VEE virus obtained with cross-reactive MAbs 7D1, 2D4 and 7A6 have mutations of the E2 protein at positions 59, 212–213 and 232, respectively. Amino acid sequences in these regions of the VEE and EEE viruses are not homologous. These observations indicate that cross-reactive MAbs are capable of recognising discontinuous epitopes on the E2 glycoprotein.     

Monoclonal antibodies capable of distinguishing epizootic from enzootic varieties of subtype 1 Venezuelan equine encephalitis viruses in a rapid indirect immunofluorescence assay.

We used previously characterized murine monoclonal antibodies to develop a panel useful in subtyping Venezuelan equine encephalitis (VEE) viruses by an indirect fluorescent antibody assay. This panel worked well with either prototype VEE viruses or a series of more recent VEE virus isolates. The panel is particularly useful for rapidly differentiating VEE viruses with epidemic-epizootic potential from other endemic varieties of this virus. Using this panel, we identified an antigenic variant of prototype VEE subtype 1E virus currently present in Mexico. This antigenic change in the E2 glycoprotein was confirmed by enzyme-linked immunosorbent assay. Because VEE virus virulence has been associated in part with the E2 glycoprotein, this observed antigenic change in the 1E virus E2 glycoprotein may explain the apparent equine virulence of this unusual VEE 1E virus.     

Evidence for three separate antigenic sites on the G1 protein of La Crosse Virus

Competitive binding assays with monoclonal antibodies have been used to show that there are a minimum of three nonoverlapping antigenic sites on the G1 glycoprotein of La Crosse virus. One of these sites contains the epitopes for three of the five monoclonal antibodies employed and is involved with both hemagglutination and neutralization. A second site contains the epitope for an antibody that inhibits hemagglutination but has no neutralizing activity. The third site encompasses the epitope for an antibody that at present has no identified biological role.     

Alternative forms of a strain-specific neutralizing antigenic site on the Sindbis virus E2 glycoprotein

Experiments with monoclonal antibodies raised against two laboratory strains of Sindbis virus, SB and SIN, suggested the existence of a strain-specific neutralizing antigenic site (E2-b) on the E2 glycoprotein. A comparison of monoclonal antibody binding patterns and E2 glycoprotein gene sequences of six laboratory strains distinguished three different configurations of E2-b that correlated with specific amino acid substitutions at position 216 of the E2 glycoprotein. Further study of neutralization escape mutants selected with E2-b-specific antibodies confirmed that amino acid 216 is a major determinant of the E2-b antigenic site. Eight of nine mutants showed a coding change at position 216. One neutralization escape mutation created a new glycosylation site at position 213 and resulted in an E2 protein with an altered migration rate in SDS-PAGE. The neutralization escape mutants studied included amino acid substitutions not found in the laboratory strains that revealed differing binding requirements for two E2-b-specific monoclonal antibodies. The E2-b site is contrasted with the E2-c neutralizing antigenic site described previously (R.A. Olmsted, W.J. Meyer, and R.E. Johnston, 1986, Virology 148, 245-254).     

Localization of functional sites on the hemagglutinin-neuraminidase glycoprotein of Sendai virus by sequence analysis of antigenic and temperature-sensitive mutants

To locate the various functions associated with the hemagglutinin-neuraminidase (HN) glycoprotein of Sendai virus in the primary structure of the protein, a temperature-sensitive (ts) mutant and seven antigenic mutants were sequenced. The ts mutant was defective in its ability to agglutinate erythrocytes and infect host cells, while its neuraminidase activity was normal. Its sequence revealed two closely spaced amino acid substitutions (residues 262 and 264) and one distant substitution (residue 461). Revertants could not be isolated, suggesting that more than one of the substitutions is responsible for the defective hemagglutinating activity. The antigenic mutants were selected with monoclonal antibodies that delineate four nonoverlapping antigenic sites (I-IV) and separately inhibit hemagglutinating, neuraminidase, and hemolysis activities. Mutants selected with antibodies to antigenic sites I-III were used to map these functions on the primary sequence of HN. Each antigenic mutant had a single point mutation in the HN gene that resulted in an amino acid substitution in the protein. A site II mutant selected with an antibody which inhibits hemolysin activity had a substitution at amino acid 420, while a mutant selected with antibody that inhibits only erythrocyte binding (site III) had a substitution at amino acid 541. Two antigenic mutants selected with an antibody that inhibits hemagglutination and neuraminidase activities (site I) had amino acid substitutions in close proximity (residues 277 and 279) to the two closely spaced substitutions of the ts mutant. These findings suggest that the region defined by the ts mutant and these two antigenic mutants is involved in host cell binding. Antigenic mutants selected with another site I antibody had amino acid changes at residue 184, indicating that antigenic site I is discontinuous in the primary sequence. This antibody blocks only hemagglutination, but mutants selected with it had a decreased neuraminidase activity. This finding supports the idea that the neuraminidase site is close to, but distinct from, the hemagglutination site.     

Synthetic peptides of Venezuelan equine encephalomyelitis virus E2 glycoprotein. I. Immunogenic analysis and identification of a protective peptide

Fourteen peptides representing 67% of the extramembranal domain of the Venezuelan equine encephalomyelititis (VEE) virus E2 glycoprotein were synthesized and analyzed to determine their antigenic, immunogenic, and protective capacities. Thirteen of 14 peptides elicited antibody for the homologous peptide. Thirteen peptides elicited antiviral antibody that recognized either the Trinidad (TRD) strain of VEE virus or the TC-83 vaccine derivative, or both. Two peptides, VE2pep01(TC-83) and VE2pep01(TRD), protected significant numbers of mice from TRD virus challenge. The majority of the peptides were reactive with antisera from mice immunized with the various subtypes of VEE virus. A competition assay using antipeptide antibodies to block virus binding of anti-VEE virus monoclonal antibodies corroborated previous studies on the spatial relationship of E2 epitopes and provided evidence for a spatial overlap of the E2 amino terminus with a domain composed of residues 180-210.     

Monoclonal antibodies directed to E1 glycoprotein of rubella virus

Summary We have prepared four monoclonal antibodies to rubella virus E1 glycoprotein. Three nonoverlapping antigenic sites were delineated on E1 protein by competitive binding assays. Antibodies binding to one site were characterized by high hemagglutination inhibition (HI) titer but poor neutralizing activity. The addition of antiglobulin conferred neutralizing activity. Antibodies directed to two other antigenic sites had modest hemolysis inhibition but little or no HI and neutralizing activities. The addition of antiglobulin markedly augmented HI activity but had little effect on neutralizing activity. Epitopes defined by three antibodies were conserved among four rubella virus strains examined.With 4 Figures     

Correlation between the reactivity patterns of monoclonal antibodies to distinct antigenic sites on HN glycoprotein and their protective abilities in Sendai (6/94) virus infection

The relative importance of the host immune response to various antigenic and functional sites on the HN glycoprotein of Sendai (6/94) virus for protection in vivo, was evaluated in mice passively immunized with monoclonal antibodies to HN and then intranasally challenged with infectious virus. Five neutralizing monoclonal antibodies reacting with distinct antigenic sites and exhibiting different reactivity patterns were selected. All of them were able to prevent entirely the growth of virus in the lungs of experimental animals injected with appropriate dilutions of monoclonal antibody. The calculation of correlation coefficients between the reduction of virus in the lungs of immunized mice and the amount of antibody, expressed in terms of hemagglutination inhibition, hemolysis inhibition or neutralizing units, showed a high degree of correlation (r = 0.89) with neutralization and a lack of correlation (r = 0.44) with hemagglutination inhibition. In parallel a minimum threshold value for protection equivalent to 2 x 10(3) neutralizing units per mouse was determined independently of the mechanism(s) by which monoclonal antibodies mediated the neutralization of the infectivity. On the HN glycoprotein of Sendai (6/94) virus we could not individualize a critical site for successful immune recognition by antibodies although the characteristics of an "ideal protective monoclonal antibody" have also been defined.     

The biological and immunochemical properties of monoclonal antibodies to the Venezuelan equine encephalomyelitis virus]

Five strains of hybrid cells producing highly active monoclonal antibodies (MCA) to Venezuelan equine encephalomyelitis (VEE) virus were generated. VEEC6 MCA had high virus-neutralizing and hemagglutinating activities attesting to their direction to the "critical" site of E2 glycoprotein. MCA VEEA5 directed to the same glycoprotein did not overlap spatially with the previous one. MCA VEEB5 and VEEA4 interacted with conformational virus determinants taking part in hemagglutination.     

Monoclonal antibodies to bovine coronavirus: characteristics and topographical mapping of neutralizing epitopes on the E2 and E3 glycoproteins

Monoclonal antibodies to the Quebec isolate of bovine coronavirus were produced and characterized. Monoclonal antibodies to both the E2 and the E3 glycoproteins were found to efficiently neutralize virus in vitro. None of the monoclonal antibodies directed against the E1 glycoprotein neutralized virus infectivity. Neutralizing monoclonal antibodies to the E2 glycoprotein were all found to immunoprecipitate gp190, gp100, and their intracellular precursor protein gp170. Neutralizing monoclonal antibodies to the E3 glycoprotein immunoprecipitated gp124 and showed differential reactivity to its precursor proteins gp59 and gp118. These monoclonal antibodies also showed differential reactivity to an apparent degradation product of E3. Neutralizing monoclonal antibodies to E2 bound to two distinct nonoverlapping antigenic domains as defined by competitive binding assays. Neutralizing monoclonal antibodies to the E3 glycoprotein also bound to two distinct antigenic sites as defined by competitive binding assays plus a third site which overlapped these regions. Other results indicated that one domain on the E3 glycoprotein could be further subdivided into two epitopes. Thus four epitopes could be defined by E3-specific monoclonal antibodies.     

The neutralization site on the E2 glycoprotein of Venezuelan equine encephalomyelitis (TC-83) virus is composed of multiple conformationally stable epitopes

The neutralization (N) site on the gp56 (E2) surface glycoprotein of the TC-83 vaccine strain of Venezuelan equine encephalomyelitis (VEE) virus has been characterized using monoclonal antibodies. Five new epitopes (E2d-h) were identified three of which could be mapped into the critical N site by using a competitive binding assay (CBA). Antibodies reactive with these three epitopes had either N or N and hemagglutination-inhibition activity. All epitopes contained within this N site elicited monoclonal antibodies that could protect mice from peripheral virus challenge. Antibodies reactive with the N site on other subtypes of VEE virus (IC and II) bound to, but failed to neutralize, TC-83 virus. Epitopes defined by these antibodies could be located outside of the N site on TC-83 virus by CBA. Antigenic activity of all epitopes except E2d was resistant to treatment with 2% SDS, 3% beta-mercaptoethanol, or cleavage with Staphylococcus aureus V8 protease. Those antibodies which defined epitopes located within the N site of TC-83 with CBA bound the same V8 fragments in immunoblots. Those antibodies which defined epitopes not located within the N site bound a different set of fragments than neutralizing antibodies. These results indicate that there is a specific N site on the E2 of VEE virus which undergoes significant antigenic drift while maintaining structural and functional integrity.     

Distinct functions of antigenic sites of the HN glycoprotein of Sendai virus

Monoclonal antibodies specific for the hemagglutinin-neuraminidase (HN) glycoprotein of Sendai virus were used to examine the antigenic structure of HN and its role in the initiation of infection and immunity. Using 10 anti-HN antibodies, four distinct antigenic sites designated I-IV were topographically mapped on the HN molecule by competitive-binding assays. To relate the biological functions of HN to its antigenic structure, anti-HN antibodies were analyzed for their inhibitory activity in neuraminidase, hemagglutination, and hemolysis inhibition tests. Antibodies to antigenic site I inhibited hemagglutination and one of these antibodies also inhibited neuraminidase activity. Antibodies to site II inhibited neither activity. However, hemolysis an F protein activity was inhibited, suggesting that these antibodies which bind to HN interfere with F-mediated fusion. Antigenic sites III and IV had different effects on the hemagglutinating and neuraminidase functions of HN: Site III antibodies inhibited hemagglutination while antibodies to site IV only inhibited neuraminidase activity. Antibodies to each antigenic site inhibited virus production. Since antibodies to sites I and III inhibited hemagglutination, it is likely that they block virus adsorption. Antibodies to HN site II only inhibited hemolysis, and therefore, may prevent virus penetration. Antibodies reacting with site IV inhibited virus production after virus penetration. Since neuraminidase activity was the only function inhibited, the viral enzyme may be involved in virus release. The fact that site IV antibodies inhibited neuraminidase but not hemagglutination suggests that these sites are distinct.     

Biochemical and biological characteristics of epitopes on the E1 glycoprotein of western equine encephalitis virus

Antigenic determinants identified by monoclonal antibodies (Mabs) on the E1 glycoprotein of western equine encephalitis (WEE) virus have been characterized by their serological activity, requirements for secondary structure, expression on the mature virion, and their role in protecting animals from WEE virus challenge. On the basis of a cross-reactivity enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition assay, eight antigenic determinants (epitopes) on the E1 glycoprotein have been identified, ranging in reactivity from WEE-specific to alphavirus group reactive. No neutralization of virus infectivity was demonstrable with any of the Mabs. An alphavirus group-reactive hemagglutination (HA) site, a WEE complex-reactive HA site, and a WEE virus-specific HA site were identified. Spatial arrangement of these epitopes was determined by a competitive binding ELISA. Four competition groups defining three distinct antigenic domains were identified. Antibodies directed against four E1 epitopes were capable of precipitating the E1/E2 heterodimer from infected cells or purified virus disrupted with nonionic detergents. These same antibodies precipitated only E1 in the presence of 0.1% SDS. That E1 conformation was important was shown by the inability of antibodies specific for seven of the epitopes to bind to virus denatured in 0.5% SDS. As determined by equilibrium gradient analysis of virus-antibody mixtures, four epitopes were found to be fully accessible on the mature virion, three epitopes were inaccessible, and one epitope was partially accessible to antibody binding. Antibodies specific for three epitopes were able to passively protect mice from WEE virus challenge.     

Variants of Venezuelan equine encephalitis virus that resist neutralization define a domain of the E2 glycoprotein.

Stable neutralization (N) escape variants of Venezuelan equine encephalitis (VEE) virus were selected by anti-E2 glycoprotein monoclonal antibodies (MAbs) that neutralize viral infectivity, block viral hemagglutination, and passively protect mice. The nucleotide sequence of the E1, E2, and E3 genes of four variants revealed a clustering of single mutations in a domain spanning E2-182 to E2-207. The conformation of this short linear sequence affects antigenicity in the N domain because reduction and alkylation of virus disrupted binding of some E2 neutralizing MAbs. Serologic evidence for interaction of E2 epitopes also was obtained. Mutations in the N domain of VEE virus did not alter the kinetics of binding to Vero cells. They did, in some cases, produce attenuation of virulence in mice.     

Characterization of monoclonal antibodies raised against recombinant respiratory syncytial virus nucleocapsid (N) protein: identification of a region in the carboxy terminus of N involved in the interaction with P protein.

To investigate structure and biological properties of the nucleocapsid (N) protein of respiratory syncytial virus (RSV), we have generated a panel of 16 monoclonal antibodies, raised against recombinant N protein, and epitope mapped seven of these to three antigenic sites (Site I aa 16-30; Site II aa 341-350; Site III aa 351-365). Characterization by immunofluorescence and by immunoprecipitation assay demonstrated that a monoclonal antibody to antigenic site I can detect N protein complexed with phospho (P) protein. Antibodies to antigenic sites II and III, which are adjacent to each other near the carboxyl terminus of the N protein, have distinct properties. A site III monoclonal antibody detected N protein in cytoplasmic inclusion bodies and in the cytosol, but not when N was complexed to P protein, while the site II antibody reacted with N protein in the nucleocapsid fraction but did not detect cytosolic N protein. Further investigation into the reactivities of the antibodies after binding of P to N in vitro demonstrated that antigenic sites II and III were blocked by the interaction, indicating an involvement for the carboxy domain of N in the N-P interaction. This was confirmed by the ability of peptides from the carboxy terminus of N to inhibit the N-P interaction in vitro.     

Monoclonal antibodies identify a strain-specific epitope on the HN glycoprotein of Newcastle disease virus strain Australia-Victoria

A panel of monoclonal antibodies raised against the hemagglutinin-neuraminidase glycoprotein (HN) of the Australia-Victoria strain of Newcastle disease virus has been used to compare that strain and eight other strains of the virus. The ability of the antibodies to neutralize infectivity, inhibit hemagglutination and neuraminidase, and bind to purified virions in solid-phase radioimmunoassays was determined for each strain. Of the four antigenic sites delineated by these antibodies on the HN of the homologous strain, site 1 (that with the greatest neutralizing susceptibility), is apparently conserved in all the strains tested as revealed by neutralization assays. The least neutralizing site, number 4, is also conserved in most of the strains tested. Site 2, which lies at or near the neuraminidase site, appears to be conserved in the avirulent strains but not in the virulent strains. An antibody to site 3 is unable to bind to a significant extent to any of the heterologous strains tested, and thus recognizes a strain-specific epitope. Inhibition of hemagglutination and neuraminidase by antibodies to each site were also examined and the results suggest that antibodies to sites 1 and 2 may distinguish virulent and avirulent strains at least with respect to these functions.     

Epitopes of the G1 glycoprotein of La Crosse virus form overlapping clusters within a single antigenic site

Antigenic sites on the G1 glycoprotein of La Crosse bunyavirus were defined by constructing a panel of neutralizing and nonneutralizing monoclonal antibodies (F. Gonzalez-Scarano, R. E. Shope, C. H. Calisher, and N. Nathanson (1982), Virology 120, 42-53). To analyze the relationship between the individual epitopes delineated by monoclonal antibodies, 11 neutralizing antibodies were used to select variant viruses. These variant viruses were tested against the panel of anti-G1 protein monoclonal antibodies by neutralization and by ELISA. The neutralization tests assigned the 11 epitopes to five groups, consisting of 6, 2, 1, 1, and 1 epitopes. ELISA tests gave a similar pattern, but also demonstrated interrelationships between four of the five epitope groups, suggesting that there may be a single immunodominant antigenic site on the G1 protein. When eight nonneutralizing anti-G1 monoclonal antibodies were tested in ELISA, they fell into three of the five epitope groups defined by neutralization; there was no evidence of a separate noneutralizing antigenic site on the G1 protein.     

Enumeration of antigenic sites of influenza virus hemagglutinin.

The antigenic sites on the hemagglutinin of X-31 (H3) influenza virus have been defined by using a competitive radioimmunoassay with a panel of monoclonal antibodies which includes those known to select variants with substitutions of particular amino acids. The capacity of each monoclonal antibody to block the binding of other radioiodinated monoclones to purified hemagglutinin permitted classification of the panel into four separate groups, each of which defined a particular antigenic site on the hemagglutinin molecule. Three of these are located on the polypeptide backbone and correspond to the "hinge," the "loop," and the "tip/interface" of the X-ray crystallographic model of Wiley et al. (Nature [London] 289:373-378, 1981). Nonreciprocal blocking of certain anti-interface antibodies by anti-loop antibody suggests that much of the exposed surface of the head of the hemagglutinin molecule extending from the loop to the interface may be a continuum of epitopes. A fourth antigenic site is carbohydrate in nature, presumably situated on the antigenic oligosaccharide side chains. These four domains are in addition to two antigenic sites defined by monoclonal antibodies that inhibit neither hemagglutination nor infectivity (Breschkin et al., Virology 113:130-140, 1981;' Yewdell et al., Nature [London] 279:246-248, 1979).     

Biological activities of monoclonal antibodies reactive with antigenic sites mapped on the G1 glycoprotein of La Crosse virus

Monoclonal antibodies have been prepared which are specific for the G1 glycoprotein of La Crosse virus. By competitive radioimmunoassay, 20 IgG-producing clones were found to map in eight antigenic sites; three distinct and five which showed individual patterns of partial competition indicating they may be in close proximity. Unique in situ trypsin cleavage sites on G1 have helped in orienting these defined epitopes relative to the viral membrane. Antibody molecules belonging to one epitope (H) mapped on the trypsin-resistant part of G1 and had negative or extremely low neutralizing and hemagglutination inhibition activities. Seven epitopes were located on the trypsin-sensitive part of G1, a 25,000-Da region which is probably the amino terminus of the protein. Antibodies binding to six of these seven epitopes (A, B, D, E, F, and G) were positive for neutralization and inhibition of hemagglutination, but exhibited a wide range of activities. Epitopes A, F, and G seem to be in an immunodominant region containing the primary site(s) for attachment to cell receptors. Antibody specific for the remaining epitope (C) was unique in that it bound to a site closely adjacent to neutralizing antibody sites, enhanced antibody binding to epitopes A and G, but lacked the capacity to neutralize viral infectivity or inhibit hemagglutination. Enhancement of antibody binding also occurred between two other closely adjacent sites (B and D) and one other distinct epitope (G). In addition, antibody from an IgM-producing clone competed with antibodies to these same four epitopes (B, C, D, and G), indicating they are in close proximity. These data have been used to construct an antigenic map that may now be used as a working model for the study of virus neutralization.