Expression of Rhizobium leguminosarum CFN42 genes for lipopolysaccharide in strains derived from different R. leguminosarum soil isolates.

Two mutant derivatives of Rhizobium leguminosarum ANU843 defective in lipopolysaccharide (LPS) were isolated. The LPS of both mutants lacked O antigen and some sugar residues of the LPS core oligosaccharides. Genetic regions previously cloned from another Rhizobium leguminosarum wild-type isolate, strain CFN42, were used to complement these mutants. One mutant was complemented to give LPS that was apparently identical to the LPS of strain ANU843 in antigenicity, electrophoretic mobility, and sugar composition. The other mutant was complemented by a second CFN42 lps genetic region. In this case the resulting LPS contained O-antigen sugars characteristic of donor strain CFN42 and reacted weakly with antiserum against CFN42 cells, but did not react detectably with antiserum against ANU843 cells. Therefore, one of the CFN42 lps genetic regions specifies a function that is conserved between the two R. leguminosarum wild-type isolates, whereas the other region, at least in part, specifies a strain-specific LPS structure. Transfer of these two genetic regions into wild-type strains derived from R. leguminosarum ANU843 and 128C53 gave results consistent with this conclusion. The mutants derived from strain ANU843 elicited incompletely developed clover nodules that exhibited low bacterial populations and very low nitrogenase activity. Both mutants elicited normally developed, nitrogen-fixing clover nodules when they carried CFN42 lps DNA that permitted synthesis of O-antigen-containing LPS, regardless of whether the O antigen was the one originally made by strain ANU843.     

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.     

The epitope structure in lipopolysaccharide recognized by the serotype 2-specific monoclonal antibody of Actinobacillus pleuropneumoniae.

The polysaccharide structure recognized by a monoclonal antibody specific to serotype 2 lipopolysaccharide of Actinobacillus pleuropneumoniae was investigated using an enzyme-linked immunosorbent assay inhibition test. Lipopolysaccharide obtained from serotype 2, strain SH-15, was hydrolysed with acetic acid to liberate the polysaccharide portion, and the polysaccharide mixture was fractionated by gel filtration. The longer polysaccharide, composed of O-antigenic polysaccharide and core, fully inhibited the binding of monoclonal antibodies to a whole cell antigen of strain SH-15, whereas the core oligosaccharide without O-polysaccharide did not. No inhibition was observed with the monosaccharides which were the components of serotype 2 LPS. Enzyme-linked immunosorbent assay inhibition ability of O-polysaccharide was completely lost only by O-deacetylation. These results demonstrate that the epitope of the serotype-specific monoclonal antibody resided in O-polysaccharide of LPS and that the O-acetyl group was essential for the epitope structure.     

Immunological characterization of Rhizobium leguminosarum outer membrane antigens by use of polyclonal and monoclonal antibodies.

Surface antigens of Rhizobium leguminosarum biovar viciae strain 248 were characterized by using polyclonal and monoclonal antibodies. With Western immunoblotting as the criterion, an antiserum raised against living whole cells recognized mainly flagellar antigens and the O-antigen-containing part of the lipopolysaccharide (LPS). Immunization of mice with a peptidoglycan-outer membrane complex yielded eight monoclonal antibodies, of which three reacted with LPS and five reacted with various sets of outer membrane protein antigens. The observation that individual monoclonal antibodies react with sets of related proteins is discussed. Studies of the influence of calcium deficiency and LPS alterations on surface antigenicity showed that in normally grown wild-type cells, the O-antigenic side chain of LPS blocks binding of an antibody to a deeper-lying antigen. This antigen is accessible to antibodies in cells grown under calcium limitation as well as in O-antigen-lacking mutant cells. Two of the antigen groups which can be distinguished in cell envelopes of free-living bacteria were depleted in cell envelopes of isolated bacteroids, indicating that the monoclonal antibodies could be useful tools for studying the differentiation process from free-living bacteria to bacteroids.     

Epitope mapping of four monoclonal antibodies recognizing the hexose core domain of Salmonella lipopolysaccharide.

Four murine monoclonal antibodies reactive with distinctive regions of the hexose core domain of Salmonella lipopolysaccharide (LPS) were generated and their epitope specificities were delineated. MAST 56 (IgG1) and MAST 50 (IgG3) antibodies elicited by immunizations with Salmonella typhimurium Rb1 and Rb2 mutants, reacted selectively in enzyme immunoassay with the LPS from rough mutants. In contrast, MATy 1 (IgM) and MATy 2 (IgG2b) antibodies raised by an attenuated Salmonella typhi 620 Ty strain were reactive with LPS from both smooth and rough Salmonellae. Immunoblotting analysis showed that MATy 1 distinguished only the bottom bands (naked LPS core) among the heterogeneous LPS populations, whereas MATy 2 gave a ladder pattern (reactive with both naked and O-chain-substituted LPS cores). Differential binding specificities of MATy 1 and MATy 2 antibodies to the naked and capped LPS cores were further analyzed utilizing S. typhimurium polysaccharide fractions with different O-chain:core ratios which were obtained after separation by Sephacryl S-200 chromatography. Steric effects on the antibody reactivity by the bulky O-polysaccharide chain were detected. The use of chemically defined native and synthetic saccharides as inhibitors, in combination with the conformation of the Salmonella core oligosaccharide, permitted the definition of antigenic determinants carried in the core domain recognized by each antibody: (i) the branches I and VIII are essential for MATy 1 recognition, (ii) the backbone III-IV-V for MATy 2, (iii) the backbone II-III-IV-V for MAST 56, and (iv) the backbone plus the branch III-IV-V-VIII for MAST 50. (formula; see text)     

Antigenic structure of human hepatitis A virus defined by analysis of escape mutants selected against murine monoclonal antibodies.

We examined the antigenic structure of human hepatitis A virus (HAV) by characterizing a series of 21 murine monoclonal-antibody-resistant neutralization escape mutants derived from the HM175 virus strain. The escape phenotype of each mutant was associated with reduced antibody binding in radioimmunofocus assays. Neutralization escape mutations were identified at the Asp-70 and Gln-74 residues of the capsid protein VP3, as well as at Ser-102, Val-171, Ala-176, and Lys-221 of VP1. With the exception of the Lys-221 mutants, substantial cross-resistance was evident among escape mutants tested against a panel of 22 neutralizing monoclonal antibodies, suggesting that the involved residues contribute to epitopes composing a single antigenic site. As mutations at one or more of these residues conferred resistance to 20 of 22 murine antibodies, this site appears to be immunodominant in the mouse. However, multiple mutants selected independently against any one monoclonal antibody had mutations at only one or, at the most, two amino acid residues within the capsid proteins, confirming that there are multiple epitopes within this antigenic site and suggesting that single-amino-acid residues contributing to these epitopes may play key roles in the binding of individual antibodies. A second, potentially independent antigenic site was identified by three escape mutants with different substitutions at Lys-221 of VP1. These mutants were resistant only to antibody H7C27, while H7C27 effectively neutralized all other escape mutants. These data support the existence of an immunodominant neutralization site in the antigenic structure of hepatitis A virus which involves residues of VP3 and VP1 and a second, potentially independent site involving residue 221 of VP1.     

BacS: an abundant bacteroid protein in Rhizobium etli whose expression ex planta requires nifA

Rhizobium etli CFN42 bacteroids from bean nodules possessed an abundant 16-kDa protein (BacS) that was found in the membrane pellet after cell disruption. This protein was not detected in bacteria cultured in tryptone-yeast extract. In minimal media, it was produced at low oxygen concentration but not in a mutant whose nifA was disrupted. N-terminal sequencing of the protein led to isolation of a bacS DNA fragment. DNA hybridization and nucleotide sequencing revealed three copies of the bacS gene, all residing on the main symbiotic plasmid of strain CFN42. A stretch of 304 nucleotides, exactly conserved upstream of all three bacS open reading frames, had very close matches with the NifA and sigma 54 consensus binding sequences. The only bacS homology in the genetic sequence databases was to three hypothetical proteins of unknown function, all from rhizobial species. Mutation and genetic complementation indicated that each of the bacS genes gives rise to a BacS polypeptide. Mutants disrupted or deleted in all three genes did not produce the BacS polypeptide but were Nod+ and Fix+ on Phaseolus vulgaris.     

Binding of complement component C3b to glycoprotein gC of herpes simplex virus type 1: mapping of gC-binding sites and demonstration of conserved C3b binding in low-passage clinical isolates.

The sites on glycoprotein gC of herpes simplex virus type 1 (HSV-1) which bind complement component C3b were evaluated by using anti-gC monoclonal antibodies and mutants which have alterations at defined regions of the glycoprotein. Monoclonal antibodies were incubated with HSV-1-infected cells in a competitive assay to block C3b binding. Each of 12 different monoclonals, which recognize the four major antigenic sites of gC, completely inhibited C3b binding. With this approach, no one antigenic group on gC could be assigned as the C3b-binding region. Next, 21 gC mutants were evaluated for C3b binding, including 1 which failed to synthesize gC, 4 which synthesized truncated forms of the glycoprotein such that gC did not insert into the cell's membrane, and 16 which expressed gC on the cell's surface but which had mutations in various antigenic groups. Eleven strains did not bind C3b. This included the 1 strain which did not synthesize gC, the 4 strains which secreted gC without inserting the glycoprotein into the cell membrane, and 6 of 16 strains which expressed gC on the cell surface. In these six strains, the mutations were at three different antigenic sites. One hypothesis to explain these findings is that C3b binding is modified by changes in the conformation of gC which develop either after antibodies bind to gC or as a result of mutations in the gC gene. Attachment of C3b to gC was also evaluated in 31 low-passage clinical isolates of HSV-1. Binding was detected with each HSV-1 isolate, but not with nine HSV-2 isolates. Therefore, although mutants that lack C3b binding are readily selected in vitro, the C3b-binding function of gC is maintained in vivo. These results indicate that the sites on gC that bind C3b are different from those that bind monoclonal antibodies, that antibodies directed against all sites on gC block C3b binding, and that C3b binding is a conserved function of gC in vivo.     

Assembly of the OmpF porin of Escherichia coli B. Immunological and kinetic studies of the integration pathway

The different conformations of the outer membrane protein OmpF of Escherichia coli B were studied with immunological probes. The antigenic determinants recognized by one monoclonal (MoF3) and two polyclonal antibodies were investigated under various conditions of solubilization which modify the association of OmpF with other membrane components, such as lipopolysaccharide. Several polymeric forms of the protein could be detected after extraction at 37 degrees C or 56 degrees C. The monoclonal antibody, which is specific to an exposed region of native OmpF, recognized various trimeric forms in an immunoprecipitation assay. Under the same conditions, the binding of polyclonal antibodies apparently induced strong conformational rearrangements, since the pattern of trimeric forms detected was greatly modified. The conversion of newly synthesized monomers of OmpF to the various trimer forms was investigated using these antibodies. The trimerization occurred rapidly but the appearance of the native conformation of OmpF was delayed. Some additional step was required to expose the MoF3-specific antigenic site at the surface of the trimeric form. These results are discussed in relation to the structure of OmpF and its association with lipopolysaccharide in the outer membrane.     

Lipid A and O-chain modifications cause Rhizobium lipopolysaccharides to become hydrophobic during bacteroid development

Modifications to the lipopolysaccharide (LPS) structure caused by three different growth conditions were investigated in the pea-nodulating strain Rhizobium leguminosarum 3841. The LPSs extracted by hot phenol-water from cultured cells fractionated into hydrophilic water and/or hydrophobic phenol phases. Most of the LPSs from cells grown under standard conditions extracted into the water phase, but a greater proportion of LPSs were extracted into the phenol phase from cells grown under acidic or reduced-oxygen conditions, or when isolated from root nodules as bacteroids. Compared with the water-extracted LPSs, the phenol-extracted LPSs contained greater degrees of glycosyl methylation and O-acetylation, increased levels of xylose, glucose and mannose and increased amounts of long-chain fatty acids attached to the lipid A moiety. The water- and phenol-phase LPSs also differed in their reactivity with monoclonal antibodies and in their polyacrylamide gel electrophoretic banding patterns. Phenol-extracted LPSs from rhizobia grown under reduced-oxygen conditions closely resembled the bulk of LPSs isolated from pea nodule bacteria (i.e. mainly bacteroids) in their chemical properties, reactivities with monoclonal antibodies and extraction behaviour. This finding suggests that, during symbiotic bacteroid development, reduced oxygen tension induces structural modifications in LPSs that cause a switch from predominantly hydrophilic to predominantly hydrophobic molecular forms. Increased hydrophobicity of LPSs was also positively correlated with an increase in the surface hydrophobicity of whole cells, as shown by the high degree of adhesion to hydrocarbons of bacterial cells isolated from nodules or from cultures grown under low-oxygen conditions. The implications of these LPS modifications are discussed for rhizobial survival and function in different soil and in planta habitats.     

Premature stop codons in the G glycoprotein of human respiratory syncytial viruses resistant to neutralization by monoclonal antibodies.

Mutants of human respiratory syncytial (RS) virus which escaped neutralization by monoclonal antibodies directed against the G glycoprotein were selected from the Long strain. Most mutants showed drastic antigenic changes, reflected in the lack of reactivity with several anti-G antibodies, including the one used for selection. Sequence analysis revealed the presence of in-frame premature stop codons in the mutated G genes which shortened the G polypeptide by between 11 and 42 amino acids. In contrast, two mutants selected with monoclonal antibody 25G contained two amino acid substitutions (Phe-265----Leu and Leu-274----Pro) and had lost only the capacity to bind the antibody used in their selection. These results demonstrate that the carboxy-terminal end of the G molecule is dispensable for infectivity in tissue culture and indicate the importance of this part of the G protein in determining its antigenicity.     

Evaluation of polysaccharide antigens of Vibrio cholerae O139 of different origin by monoclonal antibodies

The epitope composition of O-polysaccharides in the lipopolysaccharide (LPS) of V. cholerae, serogroup O139, isolated from clinical material and water of surface reservoirs was analyzed with the use of monoclonal antibodies. The analysis demonstrated that these O-polysaccharides were similar in their structure and chemical composition. In LPS of V. cholerae O139 clinical strains O-polysaccharide determinants occurred more often. Among V. cholerae isolated from water strains on whose surface individual epitopes of O-polysaccharide occurred less frequently or were absent appeared to be more numerous. A decrease in the concentration of microbial cells in the process of their testing by immunological methods led to increased percent of negative reactions with specific antibodies. Some V. cholerae O139 strains isolated from water were similar in the epitope composition of their O-polysaccharide and binding activity to cultures isolated from humans. As indicated by the results of these studies, cholera vibrios Bengal and vibrios isolated from river water on the territory of Russia had quantitative differences due to a higher level of the production of O-polysaccharide determinants and their occurrence in V. cholerae of serogroup O139.     

Monoclonal antibodies to Salmonella lipopolysaccharide: anti-O-polysaccharide antibodies protect C3H mice against challenge with virulent Salmonella typhimurium

The present investigation reports the production of monoclonal antibodies to antigenic determinants of the O-polysaccharide of Salmonella typhimurium lipopolysaccharide (LPS), and assesses the effectiveness of these antibodies in protecting C3H mice against the lethal effects of Salmonella infection. Hybridomas were generated by fusing spleen cells from (BALB/c X A/J)F1 (CAF1) mice hyperimmunized by i.v. injection with acetone-killed S. typhimurium SR-11 with X63-Ag8.653 murine myeloma cells. Hybridomas producing antibodies reactive with S. typhimurium SR-11 whole cells were subcloned, and seven of the resulting clones as well as one previously described clone were selected for use in the studies reported here. Monoclonal antibodies from these eight clones were of the IgG1 (1), IgG3 (6), or IgM (1) isotype and were specific for the O-polysaccharide region of Salmonella LPS, reacting with LPS from smooth S. typhimurium SR-11 and LT-2, but not with LPS from rough S. minnesota R60 (Ra), R345 (Rb), or R595 (Re). The effectiveness of each monoclonal antibody in protecting C3H/HeN and C3H/HeJ mice against the lethal effects of Salmonella infection was evaluated by comparing the median length of survival of groups of mice given antibody by i.p. injection before i.p. challenge with virulent S. typhimurium SR-11 to that of animals that received no antibody. Three out of eight monoclonal anti-O-polysaccharide antibodies, ST-1 (IgM), 10-5-47 (IgG3), and 10-5-6 (IgG3), provided significant (p less than 0.01) protection to C3H/HeN mice challenged with approximately 10(4) LD100 of Salmonella. Only antibodies ST-1 and 10-5-6, however, extended the median length of survival of C3H/HeJ mice beyond that of infected controls. Mouse antiserum prepared against S. typhimurium SR-11 was equally protective in C3H/HeJ mice. In an attempt to understand the contribution of antibody specificity to the relative differences in the protective capacities of the monoclonal antibodies, their reactivities with several Salmonella reference strains of different classical serotypes were examined. Although some differences in reactivity against the different strains were apparent, this approach was not adequate for defining the fine specificity of these monoclonal antibodies. The results of this study provide evidence that monoclonal antibodies with specificity to the O-polysaccharide region of Salmonella LPS can protect C3H mice against challenge with the homologous bacterial strain.     

Brucellosis vaccines: assessment of Brucella melitensis lipopolysaccharide rough mutants defective in core and O-polysaccharide synthesis and export

Background

The brucellae are facultative intracellular bacteria that cause brucellosis, one of the major neglected zoonoses. In endemic areas, vaccination is the only effective way to control this disease. Brucella melitensis Rev 1 is a vaccine effective against the brucellosis of sheep and goat caused by B. melitensis, the commonest source of human infection. However, Rev 1 carries a smooth lipopolysaccharide with an O-polysaccharide that elicits antibodies interfering in serodiagnosis, a major problem in eradication campaigns. Because of this, rough Brucella mutants lacking the O-polysaccharide have been proposed as vaccines.

Methodology/Principal Findings

To examine the possibilities of rough vaccines, we screened B. melitensis for lipopolysaccharide genes and obtained mutants representing all main rough phenotypes with regard to core oligosaccharide and O-polysaccharide synthesis and export. Using the mouse model, mutants were classified into four attenuation patterns according to their multiplication and persistence in spleens at different doses. In macrophages, mutants belonging to three of these attenuation patterns reached the Brucella characteristic intracellular niche and multiplied intracellularly, suggesting that they could be suitable vaccine candidates. Virulence patterns, intracellular behavior and lipopolysaccharide defects roughly correlated with the degree of protection afforded by the mutants upon intraperitoneal vaccination of mice. However, when vaccination was applied by the subcutaneous route, only two mutants matched the protection obtained with Rev 1 albeit at doses one thousand fold higher than this reference vaccine. These mutants, which were blocked in O-polysaccharide export and accumulated internal O-polysaccharides, stimulated weak anti-smooth lipopolysaccharide antibodies.

Conclusions/Significance

The results demonstrate that no rough mutant is equal to Rev 1 in laboratory models and question the notion that rough vaccines are suitable for the control of brucellosis in endemic areas.     

Monoclonal antibodies demonstrate multiple epitopes on the O antigens of Salmonella typhimurium LPS

To investigate the complexity of the antigenic determinants presented on the surface of Salmonella typhimurium, a panel of murine monoclonal antibodies was generated and characterized. Hybridomas specific for S. typhimurium (strain TML, O antigens 1, 4, 12) were produced by immunization with acetone-killed and dried bacteria and standard fusion procedures. In this report, 15 such monoclonal antibodies, all of which bind lipopolysaccharide (LPS) extracted from S. typhimurium, are described. The fine specificity of these antibodies was assessed by examining the differential binding of each antibody to a panel of Salmonella strains, which selectively express different O antigenic determinants. This analysis defined several distinct categories of monoclonal antibodies of varying isotypes. Four anti-O:4-specific antibodies were identified. Two were specific for O:1. One antibody appears to react with the core polysaccharide of S. typhimurium LPS. Several of the monoclonal antibodies recognized LPS determinants that are presumably created by a combination of O antigens. For instance, one bound only to Salmonella strains that expressed both O:1 and O:12, whereas another bound only to those strains which expressed both O:4 and O:12. A group of three antibodies bound to any strain that simultaneously expressed O:1, O:4, and O:12. A distinct group of three monoclonal antibodies also bound strains that expressed O:1, O:4, and O:12, but only when the O:5 antigenic determinant was not present. The latter are, in that respect, S. typhimurium strain TML LPS-specific. The results of this analysis suggest that the epitopes of the S. typhimurium LPS molecule that are recognized by the host are considerably more complex than has been previously indicated by classical serology.     

Molecular and structural bases for the antigenicity of VP2 of infectious bursal disease virus

Infectious bursal disease virus (IBDV), a member of the family Birnaviridae, is responsible for a highly contagious and economically important disease causing immunosuppression in chickens. IBDV variants isolated in the United States exhibit antigenic drift affecting neutralizing epitopes in the capsid protein VP2. To understand antigenic determinants of the virus, we have used a reverse-genetics approach to introduce selected amino acid changes-individually or in combination-into the VP2 gene of the classical IBDV strain D78. We thus generated a total of 42 mutants with changes in 8 amino acids selected by sequence comparison and their locations on loops P(BC) and P(HI) at the tip of the VP2 spikes, as shown by the crystal structure of the virion. The antibody reactivities of the mutants generated were assessed using a panel of five monoclonal antibodies (MAbs). Our results show that a few amino acids of the projecting domain of VP2 control the reactivity pattern. Indeed, the binding of four out of the five MAbs analyzed here is affected by mutations in these loops. Furthermore, their importance is highlighted by the fact that some of the engineered mutants display identical reactivity patterns but have different growth phenotypes. Finally, this analysis shows that a new field strain isolated from a chicken flock in Belgium (Bel-IBDV) represents an IBDV variant with a hitherto unobserved antigenic profile, involving one change (P222S) in the P(BC) loop. Overall, our data provide important new insights for devising efficient vaccines that protect against circulating IBDV strains.     

Passive immune protection by herpes simplex virus-specific monoclonal antibodies and monoclonal antibody-resistant mutants altered in pathogenicity.

Virus-neutralizing monoclonal antibodies specific for 13 different genetically defined epitopes of glycoproteins gC, gB, and gD of herpes simplex virus type 1, strain KOS-321, were compared for their ability to provide passive immunity to DBA-2 mice challenged intracranially. Protection was highly specific, since individual monoclonal antibodies failed to protect against infection with monoclonal antibody-resistant (mar) mutants altered in the single epitope recognized by the injected antibody. The dose-response kinetics of passive immunity paralleled the in vitro neutralization titers for each antibody. No correlation was observed between immune protection and antibody isotype or complement-dependent in vitro neutralization titers. This suggests that virus neutralization was not the protective mechanism. In general, antibodies reactive with epitopes of gC were protective at the lowest antibody doses, antibodies specific for gB were less efficient in providing immunity, and antibodies against gD were the least effective. mar mutants with single epitope changes in gC and multiple epitope changes in gB showed highly reduced pathogenicity, requiring up to 5 X 10(6) PFU to kill 50% of infected animals. These findings indicated that antigenic variation affects virus growth and spread in the central nervous system. Thus, mutations which affect antigenic structure also can alter virus pathogenicity. The alteration of these epitopes does not, however, appreciably reduce the development of resistance to infection. Infection of mice with these mutants or inoculation of mice with UV-inactivated, mutant-infected cells before challenge rendered the animals resistant to infection with wild-type herpes simplex virus type 1.     

Antigenic variants of herpes simplex virus selected with glycoprotein-specific monoclonal antibodies.

Monoclonal antibodies specific for herpes simplex virus type 1 (HSV-1) glycoproteins were used to demonstrate that HSV undergoes mutagen-induced and spontaneous antigenic variation. Hybridomas were produced by polyethylene glycol-mediated fusion of P3-X63-Ag8.653 myeloma cells with spleen cells from BALB/c mice infected with HSV-1 (strain KOS). Hybrid clones were screened for production of HSV-specific neutralizing antibody. The glycoprotein specificities of the antibodies were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitates of radiolabeled infected-cell extracts. Seven hybridomas producing antibodies specific for gC, one for gB, and one for gD were characterized. All antibodies neutralized HSV-1 but not HSV-2. Two antibodies, one specific for gB and one specific for gC, were used to select viral variants resistant to neutralization by monoclonal antibody plus complement. Selections were made from untreated and bromodeoxyuridine- and nitrosoguanidine-mutagenized stocks of a plaque-purified isolate of strain KOS. After neutralization with monoclonal antibody plus complement, surviving virus was plaque purified by plating at limiting dilution and tested for resistance to neutralization with the selecting antibody. The frequency of neutralization-resistant antigenic variants selected with monoclonal antibody ranged from 4 X 10(-4) in nonmutagenized stocks to 1 X 10(-2) in mutagenized stocks. Four gC and four gB antigenic variants were isolated. Two variants resistant to neutralization by gC-specific antibodies failed to express gC, accounting for their resistant phenotype. The two other gC antigenic variants and the four gB variants expressed antigenically altered glycoproteins and were designated monoclonal-antibody-resistant, mar, mutants. The two mar C mutants were tested for resistance to neutralization with a panel of seven gC-specific monoclonal antibodies. The resulting patterns of resistance provided evidence for at least two antigenic sites on glycoprotein gC.     

Isolation and characterization of mutants of Rhizobium leguminosarum bv. viciae 248 with altered lipopolysaccharides: possible role of surface charge or hydrophobicity in bacterial release from the infection thread

Effects of alterations in lipopolysaccharide (LPS) structure of Rhizobium leguminosarum bv. viciae on effective symbiosis and on a number of cell surface characteristics were studied. Tn5 mutants with altered LPSs were screened for their inability to bind monoclonal antibody 3, one of three monoclonal antibodies to the tentative O-antigenic part of the wild-type LPS of strain 248. Ten class I LPS mutants completely lacked the O-antigen-containing LPS species. The class II LPS mutant had a severely diminished amount of an antigenically altered O-antigen-containing LPS. The class III LPS mutant had normal amounts of an altered, O-antigen-containing LPS. Class I and II mutants, but not the class III mutant, showed abnormal nodule development (i.e., blocked in the stage of bacterial release from the infection thread) resulting in nodules in which very few, at the most, plant cells contained bacteroids and which were unable to fix nitrogen. Class I and II mutants were nonmotile and were more sensitive to hydrophobic compounds than the parent strain. The most striking difference between the symbiotically defective class I and II LPS mutants on one hand and the wild-type strain and the class III mutant on the other hand was that the class I and II mutants have a more hydrophobic cell surface and a higher electrophoretic mobility. A role for an O-antigen-containing LPS in bacterial release from the infection thread, through its effects on general physicochemical cell surface characteristics, is proposed.