Problems in the definition of meningococcal serotypes

Neisseria meningitidis serogroup B lipooligosaccharide genotyping reveals high prevalence of L2 strains in Spain and unexpected relationship with factor H-binding protein expression

Neisseria meningitidis may be classified according to the lipooligosaccharide immunotype. We show that this classification can be achieved by PCR genotyping of the genes involved in the lipooligosaccharide inner-core biosynthesis, lpt3, lpt6, lgtG and lot3. Genotyping data correlated well (90-100%) with mass spectrometry data and was, therefore, applied to screen a random subset of recent N. meningitidis serogroup B isolates from Europe. Analysis of the proportion of the different lipooligosaccharide types highlighted the predominance of L3 strains. Surprisingly, high rates of L2 type strains were found in Spain (17%, versus 2.5% in Germany and 1.9% in the United Kingdom). Therefore, we also investigated further these Spanish L2 strains in an attempt to explain such prevalence despite the known sensitivity of L2 immunotype to complement. We explored the hypothesis that these strains express high amounts of factor H-binding protein (fHbp), but we found, on the contrary, that L2 strains express low or undetectable amounts of fHbp. Our findings suggest that, in addition to a genetic analysis, a multivalent approach may be necessary to estimate the effectiveness of a N. meningitidis serogroup B vaccine.

Measurement of functional anti-meningococcal serogroup a activity using strain 3125 as the target strain for serum bactericidal assay

Functional anti-N. meningitidis serogroup A (MenA) activity in human serum is detected by serum bactericidal assay (SBA), using either rabbit (rSBA) or human (hSBA) complement, with F8238 as the recommended MenA SBA target strain. However, the F8238 strain may not be optimal for this purpose because, as we show here, it expresses the L11 immunotype, whereas most MenA invasive strains express the L(3,7)9 or L10 immunotype. Moreover, SBA results may be strain dependent, because immunotypes differ in their sensitivity to complement, emphasizing the need to choose the most appropriate strain. Sera from random subsets of infants, toddlers, children, and adolescents in clinical trials of MenA conjugate vaccines were tested by rSBA using strains 3125 (L10) and F8238 (L11). In unvaccinated subjects from all age groups, the percentages of seropositive samples (rSBA-MenA titer, ≥1:8) was lower using strain 3125 than using strain F8238. However, in toddlers and adolescents immunized with a conjugate MenA vaccine, the percentages of seropositive samples generally were similar using either strain in the rSBA. In two studies, sera also were tested with hSBA. Using hSBA, the differences in the percentages of seroprotective samples (hSBA-MenA titer, ≥1:4) between strains 3125 and F8238 was less apparent, and in contrast with rSBA, the percentage of seroprotective samples from unvaccinated subjects was slightly higher using strain 3125 than using strain F8238. In adults vaccinated with plain MenA polysaccharide, the percentage of seroprotective samples was higher using strain 3125 than with strain F8238, and the vaccine response rates using strain 3125 were better aligned with the demonstrated efficacy of MenA vaccination. In conclusion, SBA results obtained using the MenA L10 3125 strain better reflected vaccine-induced immunity.

Genetically modified L3,7 and L2 lipooligosaccharides from Neisseria meningitidis serogroup B confer a broad cross-bactericidal response

Currently available Neisseria meningitidis serogroup B (MenB) vaccines are based on outer membrane vesicles (OMVs) that are obtained from wild-type strains. They are purified with the aim of decreasing the lipooligosaccharide (LOS) content and hence reduce the reactogenicity of the vaccine even though LOS is a potential protective antigen. In <2-year-old children, these MenB vaccines confer protection only against strains expressing homologous PorA, a major and variable outer membrane protein. Our objective was to develop a safe LOS-based vaccine against MenB. To this end, we used modified porA knockout strains expressing genetically detoxified (msbB gene-deleted) L2 and L3,7 LOSs, allowing the production of LOS-enriched OMVs. The vaccine-induced antibodies were found to be bactericidal against nearly all invasive strains, irrespective of capsular serogroup. In addition, we have also demonstrated that LOS lacking the terminal galactose (with a lgtB mutation; truncated L3 LOS), but not LOS produced without the galE gene, induced a bactericidal antibody response in mice similar to that seen for LOS containing the full lacto-N-neotetraose (L3,7 LOS). In conclusion, a bivalent detoxified LOS OMV-based vaccine demonstrated the potential to afford a broad cross-protection against meningococcal disease.

Mannose-binding lectin binds to two major outer membrane proteins, opacity protein and porin, of Neisseria meningitidis

Human mannose-binding lectin (MBL) provides a first line of defense against microorganisms by complement activation and/or opsonization in the absence of specific Ab. This serum collectin has been shown to activate complement when bound to repeating sugar moieties on several microorganisms, including encapsulated serogroup B and C meningococci, which leads to increased bacterial killing. In the present study, we sought to identify the meningococcal cell surface components to which MBL bound and to characterize such binding. Outer membrane complex containing both lipooligosaccharide (LOS) and proteins and LOS from Neisseria meningitidis were examined for MBL binding by dot blot and ELISA. MBL bound outer membrane complex but not LOS. The binding to bacteria by whole-cell ELISA did not require calcium and was not inhibited by N-acetyl-glucosamine or mannose. With the use of SDS-PAGE, immunoblot analysis, and mAbs specific for meningococcal opacity (Opa) proteins and porin proteins, we determined that MBL bound to Opa and porin protein B (porB). The N-terminal amino acid sequences of the two MBL binding proteins confirmed Opa and PorB. Purified PorB inhibited the binding of MBL to meningococci. Escherichia coli with surface-expressed gonococcal Opa bound significantly more MBL than did the control strain. The binding of human factor H to purified PorB was markedly inhibited by MBL in a dose-dependent manner. Meningococci incubated with human serum bound MBL as detected by ELISA. We conclude that MBL binds to meningococci by a novel target recognition of two nonglycosylated outer membrane proteins, Opa and PorB.

Structural and immunochemical characterization of the lipooligosaccharides expressed by Neisseria subflava 44

Neisserial lipooligosaccharides (LOSs) are a family of complex cell surface glycolipids. We used mass spectrometry techniques (electrospray ionization, collision-induced dissociation, and multiple step), combined with fluorophore-assisted carbohydrate electrophoresis monosaccharide composition analysis, to determine the structure of the two low-molecular-mass LOS molecules (LOSI and LOSII) expressed by Neisseria subflava 44. We determined that LOSI contains one glucose on both the alpha and beta chains. LOSII is structurally related to LOSI and differs from it by the addition of a hexose (either glucose or galactose) on the alpha chain. LOSI and LOSII were able to bind monoclonal antibody (MAb) 25-1-LC1 when analyzed by Western blotting experiments. We used a set of genetically defined Neisseria gonorrhoeae mutants that expressed single defined LOS epitopes and a group of Neisseria meningitidis strains that expresses chemically defined LOS components to determine the structures recognized by MAb 25-1-LC1. We found that extensions onto the beta-chain glucose of LOSI block the recognition by this MAb, as does further elongation from the LOSII alpha chain. The LOSI structure was determined to be the minimum structure that is recognized by MAb 25-1-LC1.

Production and characterization of a new monoclonal antibody against Neisseria meningitidis: study of the cross-reactivity with different bacterial genera

We have generated a hybridoma cell line which produces an 8C7Br1 clone of the IgM antibody isotype. It recognizes the 50-, 65-, and 60-kDa antigens and is reactive with strains of N. meningitidis in the 98% of local Neisseria genera by Dot-ELISA assays. Two percent of the strains of N. meningitidis B do not present reactivity with the 8C7Br1 monoclonal antibody (MAb). The antibody reacted against N. meningitidis of serogroups A, B, C, X, Y, Z, and different serotypes and subtypes of N. meningitidis B and C by means of Dot-ELISA and Immunoblot. It cross-reacted with Neisseria gonorrhoeae, Neisseria lactamica, Haemophilus influenzae type b, Escherichia coli, Salmonella typhimurium, Salmonella typhi, Shigella flexneri, Bordetella pertussis, and Bacillus subtilis. The 8C7Br1 MAb reacted with the 65-kDa protein present in the prototype meningococcal strains B:16:B6(B2a:P1.5.2) and 2996 (B2b:P1.5.2). In H. influenzae type b, E. coli and B. subtilis, the MAb recognized the protein of 60, 65, and 70 kDa, respectively. FACS analysis showed that 8C7Brl MAb could recognize the 50-kDa protein on the surface of N. meningitidis homologous (B:4:P1.9) strain. These results, together with the bactericidal activity of 8C7Br1, and an experiment of passive protection in mice, demonstrated the potential importance of the cross-reactive protein as a candidate antigen for N. meningitidis B vaccine composition.

Conservation and accessibility of an inner core lipopolysaccharide epitope of Neisseria meningitidis

We investigated the conservation and antibody accessibility of inner core epitopes of Neisseria meningitidis lipopolysaccharide (LPS) because of their potential as vaccine candidates. An immunoglobulin G3 murine monoclonal antibody (MAb), designated MAb B5, was obtained by immunizing mice with a galE mutant of N. meningitidis H44/76 (B. 15.P1.7,16 immunotype L3). We have shown that MAb B5 can bind to the core LPS of wild-type encapsulated MC58 (B.15.P1.7,16 immunotype L3) organisms in vitro and ex vivo. An inner core structure recognized by MAb B5 is conserved and accessible in 26 of 34 (76%) of group B and 78 of 112 (70%) of groups A, C, W, X, Y, and Z strains. N. meningitidis strains which possess this epitope are immunotypes in which phosphoethanolamine (PEtn) is linked to the 3-position of the beta-chain heptose (HepII) of the inner core. In contrast, N. meningitidis strains lacking reactivity with MAb B5 have an alternative core structure in which PEtn is linked to an exocyclic position (i.e., position 6 or 7) of HepII (immunotypes L2, L4, and L6) or is absent (immunotype L5). We conclude that MAb B5 defines one or more of the major inner core glycoforms of N. meningitidis LPS. These findings support the possibility that immunogens capable of eliciting functional antibodies specific to inner core structures could be the basis of a vaccine against invasive infections caused by N. meningitidis.

Monoclonal antibody to serotype 17 of Neisseria meningitidis and their prevalence in Brazilian states

Neisseria meningitidis are gram-negative diplococci responsible for cases of meningococcal disease all over the world. The epidemic potential of N. meningitidis serogroup B and C is clearly a function of their serotype antigens more than of their capsular polysaccharides. Until recently, hiperimmune sera were used to detect typing antigens on the bacteria. The advent of monoclonal antibodies (MAbs) offered the opportunity to eliminate many of the cross-reactions and have improved the accuracy and reproducibility of meningococcal serotyping. We have produced a MAb to the outer membrane protein of the already existent serotype 17 that have been detected by the use of hiperimmune rabbit sera. The prevalence of this serotype epitope is low in the Brazilian strains. By using the MAb 17 we could not decrease the percentage of nontypeable serogroup C strains. However, there were a decreasing in nontypeable strains to 13% into serogroup B strains and to 25% into the other serogroups.

Preparation, characterization, and immunogenicity of meningococcal lipooligosaccharide-derived oligosaccharide-protein conjugates

A method was developed for coupling carboxylic acid-containing oligosaccharides (OS) to proteins. An OS was isolated from Neisseria meningitidis group A strain A1 lipooligosaccharide (LOS). This LOS has no human glycolipid-like lacto-N-neotetraose structure and contains multiple immunotypes, including L8, found in group B and C strains. The carboxylic acid at 2-keto-3-deoxyoctulosonic acid of the OS was linked through adipic acid dihydrazide to tetanus toxoid. The molar ratio of the OS to tetanus toxoid in three conjugates ranged from 11:1 to 19:1. The antigenicity of the OS was conserved in these conjugates, as measured by an enzyme-linked immunosorbent assay (ELISA) and an inhibition ELISA with polyclonal and monoclonal antibodies to A1 LOS. These conjugates induced immunoglobulin G antibodies to A1 LOS in mice and rabbits. The immunogenicity of the conjugates in rabbits was enhanced by use of monophosphoryl lipid A plus trehalose dimycolate as an adjuvant. The resulting rabbit antisera cross-reacted with most of 12 prototype LOSs and with LOSs from two group B disease strains, 44/76 and BB431, in an ELISA and in Western blotting (immunoblotting), which revealed a 3.6-kDa reactive band in these LOSs. The rabbit antisera showed bactericidal activity against homologous strain A1 and heterologous strains 44/76 and BB431. These results indicate that conjugates derived from A1 LOS can induce antibodies against many LOS immunotypes from different organism serogroups, including group B. OS-protein conjugates derived from meningococcal LOSs may therefore be candidate vaccines to prevent meningitis caused by meningococci.

The influence of the adjuvant Quil A on the epitope specificity of meningococcal lipopolysaccharide anti-carbohydrate antibodies

Rabbits were immunized with immunotype L3,7,9 phosphoethanolamine (PEA) group containing oligosaccharide-tetanus toxoid conjugates both with and without the addition of the adjuvant Quil A. The epitope specificity of the antibodies present in these antisera was analysed in an immunotype L2 and L3,7,9 specific inhibition ELISA using the homologous and heterologous lipopolysaccharide, oligosaccharide and partial dephosphorylated oligosaccharide as inhibitors. Two groups of antisera could be identified. In one group of antisera, at least two antibody populations are present, namely directed against the PEA group containing determinants on immunotype L3,7,9 lipopolysaccharide and against immunotype L2 specific epitopes in which no PEA group is present. In the second group of antisera, one but probably more antibody populations are detected with a similar specificity towards the conserved epitopes of both immunotypes. In general, immunization with the conjugates only resulted in the induction of antibodies against the PEA group containing epitopes on the L3,7,9 lipopolysaccharide (80%). Antibodies directed against the conserved epitopes of both immunotypes are mainly evoked with the conjugates in combination with the adjuvant Quil A (80%). Although these results suggest that the epitope specificity of the antibodies induced depends on the use of Quil A, the influence of genetic factors cannot be excluded. At the moment it is not known whether the differences in epitope specificities are reflected in biological function of these antibodies. However, the induction of antibodies with clearly different epitope specificities after immunization of different rabbits with the same antigen stresses the importance of this kind of analysis when developing a vaccine based on oligosaccharide-protein conjugates.

Minimal oligosaccharide structures required for induction of immune responses against meningococcal immunotype L1, L2, and L3,7,9 lipopolysaccharides determined by using synthetic oligosaccharide-protein conjugates

The 12 types of meningococcal lipopolysaccharide (LPS) (immunotypes) contain immunotype-specific and cross-reactive epitopes situated on the oligosaccharide part of the LPS molecules. To identify useful cross-reactive epitopes and to determine minimal oligosaccharide structures required for the induction of an immune response against the most prevalent immunotypes, L1, L2, and L3,7,9, synthetic as well as native LPS-derived oligosaccharides were conjugated with tetanus toxoid. L3,7,9 phosphoethanolamine (PEA) group-containing oligosaccharide-tetanus toxoid conjugates evoked high immunoglobulin G (IgG) antibody levels in rabbits which were detected by an L2-, L3,7,9-, and, depending on the antiserum, L1-specific enzyme-linked immunosorbent assay (ELISA). Inhibition studies revealed that an identical antibody population was detected by L1 and L3,7,9 ELISA, indicating a similar tertiary structure of the inner core oligosaccharide of these two immunotypes. These antibodies recognize PEA group-containing epitopes present on the L1 and L3,7,9 LPS. An L2 PEA group-containing oligosaccharide-tetanus toxoid conjugate elicited L2- and L3,7,9-specific IgG antibodies, but in contrast with the L3,7,9 conjugates, no L1-specific IgG antibodies were evoked. These results indicate that L1 and L2 LPS do not contain cross-reactive epitopes, whereas both L2 and L3,7,9 LPS and L1 and L3,7,9 LPS possess common determinants. Three linear oligosaccharides and one branched oligosaccharide, representing partial structures of the inner core oligosacchardes of meningococcal LPS, were synthesized. Only the branched synthetic oligosaccharide-containing conjugate was able to induce and L1- and L3,7,9-specific immune response, whereas the linear oligosaccharide-protein conjugates evoked L2-specific immune responses. The branched oligosaccharide (beta-D-Glcp(1----4)-[L-alpha-D-Hepp(1----3)]-L-alpha-D-Hepp ) is therefore considered a minimal structure required for the induction of an immune response against L1 and L3,7,9 LPS and part of a cross-reactive epitope between these two immunotypes. For L2-specific immune responses, oligosaccharide structures terminating in beta-D-Glcp(1----4), alpha-D-GlcNAcp(1----2), or L-alpha-D-Hepp(1----5) are needed. The results suggest that it is possible to prepare an oligosaccharide structure with the ability to evoke an immune response against L1, L2, and L3,7,9 LPS. A feasible structure for such a "hybrid" oligosaccharide is discussed.

Comparative evaluation of potential components for group B meningococcal vaccine by passive protection in the infant rat and in vitro bactericidal assay

Seventeen monoclonal antibodies to one of three main cell surface antigens of Neisseria meningitidis group B were tested for protective efficacy in the infant rat using as challenge seven strains of different class 2/3 protein serotypes, class 1 protein (P1) subtypes and LPS immunotypes. Type-specific protection indicated both by a reduction of bacteraemia and meningitis and survival of the animals was regularly obtained with antibodies to the P1 protein and to LPS. By contrast, only one of seven antibodies to the serotype-specific class 2/3 protein was protective, even though four of them were highly bactericidal. The animal protection test and in vitro bactericidal assay were otherwise concordant. These data form important guidelines for the design of vaccines to prevent group B meningococcal infections.

Antibody production to a meningococcal outer membrane protein cloned into liv Salmonella typhimurium aroA vaccine strain

We cloned a 28 kDa outer membrane protein (OMP) of Neisseria meningitidis group B into a live Salmonella typhimurium aroA vaccine strain SL3261. The cloned 28 kDa protein was produced in large amounts in the S. typhimurium transformant SH8182 and located in the outer membrane. A mouse-passaged derivative of SH8182 was used as a live vaccine to immunize mice; with antibiotic pressure the strain survived in the mice as well as the parent strain SL3261 and maintained the plasmid carrying the gene encoding the 28 kDa OMP. The mice produced a high titer of antibodies to the 28 kDa OMP, showing that it had been effectively presented to the immune system. The hyperimmune mouse serum bound in an enzyme immunoassay to whole cells of E. coli and group B meningococci expressing the 28 kDa OMP, but its bactericidal activity towards the meningococci was marginal. In a passive protection study, the antiserum did not protect infant rats from meningococcal infection. The results indicate that the antibodies elicited did not bind to intact meningococcal cells, possibly because of inaccessibility of the 28 kDa OMP.

Clonal diversity of Neisseria meningitidis from a population of asymptomatic carriers

Genetic diversity and relationships among 109 isolates of Neisseria meningitidis obtained from throat cultures of healthy individuals in Norway in 1984 were assessed by analyzing electrophoretically demonstrable allelic variation at 15 enzyme-encoding chromosomal genes. Seventy-eight distinctive electrophoretic types (ETs), representing multilocus genotypes, were identified. The mean genetic diversity per locus among the 78 ETs (0.538) was equivalent to that among 19 ETs represented by 66 isolates collected from patients with meningococcal disease in Norway in the first 5 months of 1984. The clonal composition of the collection of carrier strains was, however, quite different from that of strains from patients. The two groups of clones, the ET-5 complex and the ET-37 complex, that were responsible for 91% of the cases of systemic disease in Norway in 1984 were identified in only 7 and 9%, respectively, of the throat cultures from healthy individuals, and their frequencies in the human population sampled were only 0.7% for clones of the ET-5 complex and 0.9% for those of the ET-37 complex. The complex of clones that was most frequently represented by isolates from carriers (19%) has never been recovered from patients with meningococcal disease in Norway or elsewhere, which suggests that these clones have a low virulence potential. Children attending the same day care center or school seldom harbored the same clone in their throats.

Immunotype epitopes of Neisseria meningitidis lipooligosaccharide types 1 through 8

Lipooligosaccharides (LOS) of the eight immunotypes found in serogroup B Neisseria meningitidis were purified from their prototype strains grown in tryptic soy broth. Rabbit antisera to these LOS were prepared. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining revealed that most of the LOS antigens contained two major components; the larger components had apparent molecular weights (Mrs) in the range of 4,800 +/- 300, and the smaller components had an apparent Mr of 4,300. Immunoblot analysis showed that the larger major component of an LOS, in general, was much more immunogenic because the rabbits produced antibodies exclusively or primarily to this component even though the LOS immunogen contained both large and small major components. Antibodies to the smaller 4,300-Mr components were infrequently observed but, when present, were cross-reactive with the same-size components of all heterologous LOS. Hence, the immunotype epitopes reside in the larger major components of all immunotypes except type 5, in which a smaller major component having an apparent Mr of 4,400 carries the epitope. Rabbit antisera to types 1, 5, and 6 were immunotype specific. Antisera to other types had cross-reactivities with some heterologous LOS, and the larger components, but not the 4,300-Mr components, of the LOS were primarily responsible for the cross-reactivities. This finding suggests that the larger components of cross-reactive LOS have a similar structure in addition to their type-specific sugar moieties. The LOS of N. meningitidis M986, a strain used for the production of a serotype 2a vaccine, was found to contain the immunotype 7 epitope.

Endotoxin release from invasive meningococci related to sulfonamide resistance, serogroup and serotype

The relationship between endotoxin liberation, sulfonamide resistance, serogroups and serotypes was studied in 28 Neisseria meningitidis strains isolated from patients with meningococcal disease. Sulfonamide resistance was present in 15/28 strains. 22 strains belonged to serogroup B, and 5 to group C; 1 strain was non-groupable. Free endotoxin activity in growing cultures of meningococci with endotoxin titre of greater than or equal to 10(2) was found in 27/28 strains. A high endotoxin activity was present in both sulfonamide-sensitive and -resistant invasive meningococci. A high endotoxin release with titre greater than or equal to 10(3) seemed to be more associated with serogroup C than B, and more to the serotypes 2 and 15/16 than to the non-typable strains.

Meningococcal serotypes and serogroup B disease in north-west Europe

Examination of the trends of meningococcal infection in Norway, Iceland, Faroe Islands, Denmark, England and Wales, and the Netherlands, has shown that Neisseria meningitidis B:2b:P1.2 and/or B:2a:P1.2 phenotypes were associated with peaks of infection in the Netherlands in 1966, in Iceland 1976-77, and in England and Wales in 1973-75. These strains were present in all six countries in the decade 1970-80 but their prevalence is now practically negligible. In contrast the prevalence of the B:15:P1.16 phenotype has risen. In the Faroe Islands and northern Norway this change in serotype prevalence has been followed by rises in incidence of meningococcal disease; the same is happening in England and Wales but not yet in the other countries.

Protection against infection with Neisseria meningitidis group B serotype 2b by passive immunization with serotype-specific monoclonal antibody

Hybridomas derived from mice immunized with Neisseria meningitidis serogroup B serotype 2b (B,2b) outer membrane preparations produced monoclonal antibodies (MAbs) specific for major outer membrane proteins of classes 1, 2, and 5. The MAbs were examined by enzyme-linked immunosorbent assay against a selected panel of seven strains of N. meningitidis (B,2b) of different sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns, a serotype 2a, and a nontypable strain. The five MAbs selected were all bactericidal and of different immunoglobulin subclasses. None of the MAbs reacted with other bacterial strains in a dot-enzyme immunoassay. The corresponding antigenic determinant for each MAb was localized on a specific outer membrane protein by immunoblotting of sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of major outer membrane proteins. MAbs M5-11 and M5-30 bound to the class 2 protein and were serotype 2b specific. MAb M2-20 bound to the class 1 protein, and MAbs M5-16 and M5-19 bound to the class 5 protein. A mouse model of infection was established whereby a local infection progressed to lethal bacteremia over 3 days, and 50% of the animals were killed with an intraperitoneal injection of 10 meningococci plus 4% mucin and 1.6% hemoglobin. The ability of the MAbs to provide passive protection against experimental infection with N. meningitidis (B,2b) was examined. Both serotype-specific MAbs M5-11 and M5-30 were highly protective even though they were of different immunoglobulin subclasses. The class 5-specific MAb offered no protection, while the class 1-specific MAb gave limited protection. It may therefore be possible to provide protection against serotype 2b infection by using as vaccine the class 2 serotype-specific surface-exposed outer membrane protein epitopes defined by MAb M5-11 or M5-30.

Filter radioimmunoassay, a method for large-scale serotyping of Neisseria meningitidis

A simple and rapid filter radioimmunoassay method can be used to serotype meningococcal strains on a large scale. The technique consists of simultaneous inoculation of 96 strains on nitrocellulose filters. The resulting colonies can be processed in situ, by extraction and fixation, incubation with antibodies and 125I-labeled protein A, and, finally, autoradiography. Processing many filters simultaneously, one person can serotype thousands of meningococci in a week. Multiple filters with identical strain patterns can be stored after the fixation step for future screening. The use of monoclonal antibodies is essential; polyclonal antisera, even after extensive absorption, were not specific in this assay. When results from filter radioimmunoassay and Ouchterlony microprecipitation were compared for the serotyping of 201 Neisseria meningitidis strains for serotypes 2a and 2b, filter radioimmunoassay was sufficiently sensitive and specific to be useful in mass screening.

Conjugation of meningococcal lipopolysaccharide R-type oligosaccharides to tetanus toxoid as route to a potential vaccine against group B Neisseria meningitidis

Oligosaccharides were obtained by the mild acid hydrolysis of the lipopolysaccharides from a number of different strains of Neisseria meningitidis, serotypes L2, L3, L4, L5, and L10. The dephosphorylated oligosaccharides were conjugated to tetanus toxoid as their 2-(4-isothiocyanatophenyl)-ethylamine derivatives, which resulted in the incorporation of from 18 to 38 oligosaccharides per molecule of tetanus toxoid. When injected in rabbits, the conjugates produced oligosaccharide-specific antibodies which were predominantly serologically specific but which also exhibited some cross-reactivity. These serological results can be attributed to regions of structural dissimilarity and similarity within the oligosaccharides. The oligosaccharide-specific antibodies were also lipopolysaccharide serotype specific, thus indicating that the oligosaccharides are the determinants associated with this serotype specificity. Consistent with the serological results, the conjugate antisera were bactericidal for the homologous serotype meningococcal organisms and in some cases for heterologous serotype organisms.

Virulence markers in patient and carrier strains of Neisseria meningitidis

Patient and carrier strains of Neisseria meningitidis from 2 different periods were compared with respect to serogroups, serotypes and sensitivity to sulphadiazine. The majority of 249 patient strains were resistant to sulphadiazine, and belonged to the groups A, B or C. The group B and C strains were mainly type 15/16 and 2, respectively. In contrast, most of the 400 carrier strains belonged to serotypes other than 2 or 15/16, or were non-typable, and most strains were sensitive to sulphadiazine. Among the resistant group B and C carrier strains there were more type 2 and 15/16 strains than would have been expected from the average. The virulence markers: serogroup A, B and C, serotype 2 and 15/16, and resistance to sulphadiazine, coexist in more carrier strains than would be expected if the distribution of these markers was random.

Monoclonal antibodies against Neisseria meningitidis lipopolysaccharide

A cell line producing monoclonal antibodies directed against a lipopolysaccharide component of Neisseria meningitidis group A has been established. These antibodies reacted with only one of three lipopolysaccharide serotyping strains of group A meningococci by coagglutination, enzyme-linked immunosorbent assay, and Western blotting techniques. A Western blot analysis showed that a NaOH digest of lipopolysaccharide was detectable by the serotype-specific antibody. The monoclonal antibodies cross-reacted with a group B meningococcal strain in an enzyme-linked immunosorbent assay. The immunoblotting analysis also showed that these antibodies reacted with the lipopolysaccharides of a group B meningococcus as well as Haemophilus influenzae type B, but not with the lipopolysaccharides of several strains of Salmonella typhi, Escherichia coli, Streptococcus pneumoniae, and Neisseria gonorrhoeae.

The structure of an R-type oligosaccharide core obtained from some lipopolysaccharides of Neisseria meningitidis

The main structure of a lipopolysaccharide R-type core oligosaccharide common to a number of different strains of Neisseria meningitidis has been elucidated. Methylation analysis, specific degradations, and nuclear magnetic resonance spectroscopic analysis of the dephosphorylated cores indicated that they all have the following structure. (formula see text) The determinants responsible for the L3, L7, and L9 meningococcal lipopolysaccharide serotypes are situated in this oligosaccharide.