Structural studies of the O-antigen oligosaccharides from two strains of Moraxella catarrhalis serotype C

Formation and immunological evaluation of Moraxella catarrhalis glycoconjugates based on synthetic oligosaccharides

Published work has shown that glycoconjugate vaccines, based on truncated detoxified lipopolysaccharides from Moraxella catarrhalis attached through their reducing end to a carrier protein, gave good protection for all three serotypes A, B, and C in mice immunisation experiments. The (from the non-reducing end) truncated LPS structures were obtained from bacterial glycosyl transferase knock-out mutants and contained the de-esterified Lipid A, two Kdo residues and five glucose moieties. This work describes the chemical synthesis of the same outer Moraxella LPS structures, spacer-equipped and further truncated from the reducing end, i.e., without the Lipid A part and containing four or five glucose moieties or four glucose moieties and one Kdo residue, and their subsequent conjugation to a carrier protein via a five‑carbon bifunctional spacer to form glycoconjugates. Immunisation experiments both in mice and rabbits of these gave a good antibody response, being 2-7 times that of pre-immune sera. However, the sera produced only recognized the immunizing glycan immunogens and failed to bind to native LPS or whole bacterial cells. Comparative molecular modelling of three alternative antigens shows that an additional (2 → 4)-linked Kdo residue, not present in the synthetic structures, has a significant impact on the shape and volume of the molecule, with implications for antigen binding and cross-reactivity.

Characterization of a novel exopolysaccharide from Acinetobacter rhizosphaerae with ability to enhance the salt stress resistance of rice seedlings

We here describe the isolation of a novel exopolysaccharide from Acinetobacter rhizosphaerae, named ArEPS. The structure of ArEPS was characterized by analysis of the monosaccharide composition, molecular weight, infrared spectrum, methylation, and nuclear magnetic resonance spectrum. ArEPS was found to be an acidic heteropolysaccharide composed of glucose, galactose, galacturonic acid, glucuronic acid, mannose, and glucosamine; the molecular weight was 1533 kDa. Structural analysis showed that the main-chain structure of ArEPS predominantly comprised 1,3,6-β-Glcp, 1,3,4-α-Galp, 1,2-β-Glcp, 1,4-β-GlcpA, 1,4-β-GalpA, and the side-chain structure comprised 1,6-β-Glcp, 1,3-β-Galp, 1-α-Glcp, 1-β-Galp, 1-α-Manp, 1,4,6-α-Glcp, 1,2,4-β-Glcp, 1,2,3-β-Glcp, and 1,3-β-GlcpN. ArEPS significantly enhanced the tolerance of rice seedlings to salt stress. Specifically, plant height, fresh weight, chlorophyll content, and the K+/Na+ ratio increased by 51 %, 63 %, 29 %, and 162 %, respectively, and the malondialdehyde content was reduced by 45 % after treatment with 100 mg/kg ArEPS compared to treatment with 100 mM NaCl. Finally, based on the quadratic regression between fresh weight and ArEPS addition, the optimal ArEPS addition level was estimated to be 135.12 mg/kg. These results indicate the prospects of ArEPS application in agriculture.

Preferred conformations of lipooligosaccharides and oligosaccharides of Moraxella catarrhalis

Moraxella catarrhalis (M. catarrhalis) is a pathogenic gram-negative bacterium that causes otitis media and sinusitis in children. Three major serotypes A, B and C are identified to account for approximately 95% of the clinical isolates. Understanding the conformational properties of different serotypes of M. catarrhalis provides insights into antigenic determinants. In this work, all-atom molecular dynamics simulations were conducted for M. catarrhalis lipooligosaccharide (LOS) bilayer systems and oligosaccharides (OS) in water solution to investigate the conformational similarities and differences of three serotypes. For up to 10 neutral monosaccharides in the core part, the conformational ensembles described by the pair-wise root mean square deviation distributions are similar among the three serotypes of either the LOS or OS. At the central β-($1\to4$)-linkage, anti-$\psi$ conformation in conjunction with the gauche-gauche (g-) conformation of the central trisubstituted glucosyl residue is observed as the dominant conformation to sustain the structural characteristics of M. catarrhalis three types, which is further supported by calculated transglycosidic ${}^3{J}_{C,H}\Big({\psi}_H\Big)$ of serotype A in comparison to experimental data. Interestingly, the conformational variability of three serotypes is more restricted for the OS in water solution than that in the LOS bilayer systems. The LOS-LOS interactions in the bilayer systems are responsible for the increased conformational diversity despite of tight packing. Solvent-accessible surface area analysis suggests that a trisaccharide attached to the β-($1\to 6$)-linked sugar in all three serotypes of LOS could be the common epitope and have the possibility to interact with antibodies.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

An Unusual Carbohydrate Conformation is Evident in Moraxella catarrhalis Oligosaccharides

Oligosaccharide structures derived from the lipooligosaccharide of M. catarrhalis show that the highly branched glucose-rich inner core of the oligosaccharide has an altered conformation compared to the most truncated tetra-glucose-Kdo lgt1/4Δ oligosaccharide structure. Addition of one residue each to the (1-4) and (1-6) chains to give the lgt2Δ oligosaccharide is the minimum requirement for this conformational change to occur. Extensive molecular modeling and NMR investigations have shown that the (1-3), (1-4), and (1-6) glycosidic linkages from the central α-d-Glcp have significantly altered conformational preferences between the two structures. For the lgt1/4Δ oligosaccharide the (1-3) and (1-4) linkage populates predominantly the syn minimum on the conformational free energy map and for the (1-6) linkage conformational flexibility is observed, which is supported by ¹H-NMR T1 measurements. For the lgt2Δ oligosaccharide the unusual “(1-4)anti-ψ(1-6)gg” conformation, which could be confirmed by long-range NOE signals, is a dominant conformation in which the oligosaccharide is very compact with the terminal α-d-GlcNAc residue folding back towards the center of the molecule leading to an extensive intra-molecular hydrophobic interaction between the terminal residues. Comparing effective H-H distances, which were calculated for conformational sub-ensembles, with the NOE distances revealed that typically multiple conformations could be present without significantly violating the measured NOE restraints. For lgt2Δ the presence of more than one conformation is supported by the NOE data.

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) as a characteristic component of bacterial endotoxin — a review of its biosynthesis, function, and placement in the lipopolysaccharide core

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is a characteristic component of bacterial lipopolysaccharide (LPS, endotoxin). It connects the carbohydrate part of LPS with C6 of glucosamine or 2,3-diaminoglucose of lipid A by acid-labile α-ketosidic linkage. The number of Kdo units present in LPS, the way they are connected, and the occurrence of other substituents (P, PEtn, PPEtn, Gal, or β-l-Ara4N) account for structural diversity of the inner core region of endotoxin. In a majority of cases, Kdo is crucial to the viability and growth of bacterial cells. In this paper, the biosynthesis of Kdo and the mechanism of its incorporation into the LPS structure, as well as the location of this unique component in the endotoxin core structures, have been described.

Characterization of a trifunctional glucosyltransferase essential for Moraxella catarrhalis lipooligosaccharide assembly

The human respiratory tract pathogen Moraxella catarrhalis expresses lipooligosaccharides (LOS), glycolipid surface moieties that are associated with enhanced colonization and virulence. Recent studies have delineated the major steps required for the biosynthesis and assembly of the M. catarrhalis LOS molecule. We previously demonstrated that the glucosyltransferase enzyme Lgt3 is responsible for the addition of at least one glucose (Glc) molecule, at the β-(1-4) position, to the inner core of the LOS molecule. Our data further suggested a potential multifunctional role for Lgt3 in LOS biosynthesis. The studies reported here demonstrate that the Lgt3 enzyme possesses two glycosyltransferase domains (A1 and A2) similar to that of other bifunctional glycosyltransferase enzymes involved in surface polysaccharide biosynthesis in Escherichia coli, Pasteurella multocida and Streptococcus pyogenes. Each Lgt3 domain contains a conserved DXD motif, shown to be involved in the catalytic activity of other glycosyltransferases. To determine the function of each domain, A1 (N-terminal), A2 (C-terminal) and double A1A2 site-directed DAD to AAA mutants were constructed and the resulting LOS phenotypes of these modified strains were analyzed. Our studies indicate that the Lgt3 N-terminal A1 catalytic domain is responsible for the addition of the first β-(1-3) Glc to the first Glc on the inner core. The C-terminal catalytic domain A2 then adds the β-(1-4) Glc and the β-(1-6) Glc, confirming the bifunctional nature of this domain. The results from these experiments demonstrate that Lgt3 is a novel, multifunctional transferase responsible for the addition of three Glcs with differing linkages onto the inner core of M. catarrhalis LOS.

Role of c-Jun N-terminal protein kinase 1/2 (JNK1/2) in macrophage-mediated MMP-9 production in response to Moraxella catarrhalis lipooligosaccharide (LOS)

Moraxella catarrhalis is a Gram negative bacterium and a leading causative agent of otitis media (OM) in children. Recent reports have provided strong evidence for the presence of high levels of matrix metalloproteinase (MMPs) in effusion fluids from children suffering with OM, however, the precise mechanisms by which MMPs are generated are currently unknown. We hypothesized that MMPs are secreted from macrophages in the presence of M. catarrhalis lipooligosaccharide (LOS). In this report, we demonstrate that in vitro stimulation of murine macrophage RAW 264.7 cells with LOS leads to secretion of MMP-9 as determined by ELISA and zymogram assays. We have also shown that inhibition of ERK1/2 and p38 kinase completely blocked LOS induced MMP-9 production. In contrast, inhibition of JNK1/2 by the specific inhibitor SP600125 actually increased the level of expression and production of MMP-9 at both mRNA and protein levels, respectively by almost five fold. This latter result was confirmed by knocking down JNK1/2 using siRNA. Similar results have been observed in murine bone marrow derived macrophages in vitro. In contrast to and in parallel with the LOS-induced increased levels of MMP-9 in the presence of SP600125, we found a corresponding dose-dependent inhibition of TIMP-1 (tissue inhibitor of matrix metalloproteinase-1) secretion. Results of subsequent in vitro studies provided evidence that when JNK1/2 was inhibited prior to stimulation with LOS, it significantly increased both the extent of macrophage cell migration and invasion compared to control cells or cells treated with LOS alone. The results of these studies contribute to an increased understanding of the underlying pathophysiology of OM with effusion in children.

Intranasal immunization of the combined lipooligosaccharide conjugates protects mice from the challenges with three serotypes of Moraxella catarrhalis

Background

There are no licensed vaccines available against Moraxella catarrhalis, a significant human respiratory pathogen. Lipooligosaccharide (LOS) based conjugate vaccines derived from individual serotype M. catarrhalis only showed partial protection coverage. A vaccine combining LOS conjugates of two or three serotypes might provide a broader protection.

Methods

Mice were immunized intranasally with the combined conjugates consisting of LOS from serotype A and B or serotype A, B, and C followed by challenge with different M. catarrhalis strains of three serotypes. Mouse lungs, nasal washes, and sera were collected after each challenge for bacterial counts, histological evaluation, cytokine profiles, antibody level and binding activity determinations.

Results

Intranasal administration of the combined LOS conjugates not only enhanced pulmonary bacterial clearance of all three serotypes of M. catarrhalis strains in vaccinated mice, but also elevated serotype-specific anti-LOS immunoglobulin (Ig)A and IgG titers in nasal wash and serum respectively. Mice vaccinated with the combined LOS conjugates also showed increased interferon (IFN)-γ, interleukin (IL)-12, and IL-4 in the lungs after challenges. Compared to the control group, mice immunized with the combined LOS conjugates also showed reduced lung inflammation after M. catarrhalis infections. The hyperimmune sera induced by the combined conjugates exhibited a broad cross-reactivity toward all three serotypes of M. catarrhalis under transmission electron microscopy.

Conclusions

The combined vaccine of serotype A and B LOS conjugates provides protection against most M. catarrhalis strains by eliciting humoral and cellular immune responses.

Mutant lipooligosaccharide-based conjugate vaccine demonstrates a broad-spectrum effectiveness against Moraxella catarrhalis

There is no licensed vaccine available against Moraxella catarrhalis, an exclusive human pathogen responsible for otitis media in children and respiratory infections in adults. We previously developed conjugate vaccine candidates based on lipooligosaccharides (LOSs) of M. catarrhalis serotypes A, B, and C, each of which was shown to cover a portion of the clinical strains. To generate conserved LOS antigens and eliminate a potential autoimmune response to a similar epitope between M. catarrhalis LOS moiety Galα1-4Galβ1-4Glc and human P(k) antigen, two LOS mutants from strain O35E were constructed. Mutant O35Elgt5 or O35EgalE revealed a deletion of one or two terminal galactose residues of wild type O35E LOS. Each LOS molecule was purified, characterized, detoxified, and coupled to tetanus toxoid (TT) to form conjugates, namely dLOS-TT. Three subcutaneous immunizations using dLOS-TT from O35Elgt5 or O35EgalE elicited significant increases (a 729- or 1263-fold above the preimmune serum levels) of serum immunoglobulin (Ig)G against O35E LOS in rabbits with an adjuvant or without an adjuvant (an 140- or 140-fold above the preimmune serum levels). Rabbit antisera demonstrated elevated complement-mediated bactericidal activities against the wild type strain O35E. The rabbit sera elicited by O35Elgt5 dLOS-TT were further examined and showed cross bactericidal activity against all additional 19 M. catarrhalis strains and clinical isolates studied. Moreover, the rabbit sera displayed cross-reactivity not only among three serotype strains but also clinical isolates in a whole-cell enzyme-linked immunosorbent assay (ELISA), which was further confirmed under transmission electron microscopy. In conclusion, O35Elgt5 dLOS-TT may act as a vaccine against most M. catarrhalis strains and therefore can be used for further in vivo efficacy studies.

Moraxella catarrhalis Lgt2, a galactosyltransferase with broad acceptor substrate specificity

The genetic basis of lipo-oligosaccharide (LOS) biosynthesis for the bacterium Moraxella catarrhalis has been elucidated and functions suggested for each of the glycosyltransferases. In this study we have expressed and characterised one of these enzymes, the putative galactosyltransferase Lgt2(B/C). The lgt2(B/C) gene was amplified from M. catarrhalis, expressed in Escherichia coli, and Lgt2(B/C) was purified. Analysis of its glycosyltransferase catalytic activity ascertained the pH and temperature optima. The donor specificity and acceptor specificity were examined and they showed that Lgt2(B/C) is a galactosyltransferase with relatively broad acceptor specificity with optimal activity in the presence of exogenous Mg(2+).

Biochemical analysis of Lgt3, a glycosyltransferase of the bacterium Moraxella catarrhalis

The lipooligosaccharide (LOS) of Moraxella catarrhalis is unusual in that it lacks heptose. The sugar linking oligosaccharide to Lipid A is a trisubstituted glucose. A single enzyme, Lgt3, is suggested to trisubstitute this core sugar. The lgt3 gene encodes two distinct domains with high similarity to glucosyltransferases of the GT-A superfamily, thus encoding a bidomain, multifunctional glucosyltransferase. To characterise Lgt3, the gene was amplified from M. catarrhalis, expressed in Escherichia coli, and purified. Analysis of its glycosyltransferase catalytic activity ascertained the pH and temperature optima for Lgt3. The donor specificity and acceptor specificity were examined. This study confirms that Lgt3 is a glucosyltransferase which catalyses addition of glucose to its cognate receptor, a terminal glucose presented as the core region of LOS.

Use of Moraxella catarrhalis lipooligosaccharide mutants to identify specific oligosaccharide epitopes recognized by human serum antibodies

Moraxella catarrhalis is a causative agent of otitis media in children and lower respiratory tract infections in adults suffering from chronic obstructive pulmonary disease (COPD). This strict human pathogen continues to be a significant cause of disease in this broad spectrum of patients because there is no available vaccine. Although numerous putative vaccine antigens have been described, little is known about the human immune response to M. catarrhalis infection in vivo. Human serum antibodies are directed at a number of surface proteins, and lipooligosaccharides (LOS) and detoxified LOS may be an effective immunogen in mice. In this study, we used a specific LOS-based enzyme-linked immunosorbent assay (ELISA), containing the three major M. catarrhalis serotypes together with a complete series of truncated LOS mutants, to detect the development of new antibodies to specific regions of the oligosaccharide molecule. We compared serum samples from COPD patients who had recently cleared an M. catarrhalis infection to serum samples collected prior to their infection. Variability in the antibody response to LOS was observed, as some patients developed serotype-specific antibodies, others developed antibodies to the LOS of each serotype, others developed broadly cross-reactive antibodies, and some did not develop new antibodies. These newly developed human antibodies are directed at both side chains and core structures in the LOS molecule. This LOS-based ELISA can be used to dissect the human antibody response to both internal and external carbohydrate epitopes, thus providing a better understanding of the humoral immune response to M. catarrhalis LOS epitopes developed during natural infection.

Galactose residues on the lipooligosaccharide of Moraxella catarrhalis 26404 form the epitope recognized by the bactericidal antiserum from conjugate vaccination

Lipooligosaccharide (LOS) from Moraxella catarrhalis has the potential to elicit bactericidal antibodies against the pathogen. We generated LOS-based conjugate vaccines that elicited bactericidal antibodies in animal models. However, epitopes on the LOS recognized by the functional anti-LOS antibodies remain unidentified. In this study, a mutant strain, D4, which lost the recognition by a bactericidal anti-LOS rabbit serum in Western blotting was generated from a serotype C strain 26404 by random transposon mutagenesis. Sequence analysis revealed there was an insertion of a kanamycin resistance gene in the lgt2 gene of D4, which encodes beta(1-4)-galactosyltransferase. An isogenic lgt2 mutant, 26404lgt2, was constructed. Structural analysis indicated that the mutant strain produced a truncated LOS lacking terminal galactoses from 4- and 6-linked oligosaccharide chains of strain 26404. Further studies showed that the antiserum lost the recognition of both mutant cells and LOSs in Western blotting, an enzyme-linked immunosorbent assay (ELISA), or a flow cytometry assay. The antiserum also lost the ability to kill the mutant strain in a bactericidal assay, whereas it showed a bactericidal titer of 1:80 to strain 26404. In an inhibition ELISA, d-(+)-galactose or 26404lgt2 LOS showed no inhibition. However, the 26404 LOS and a serotype A O35E LOS with terminal galactoses on its 6-linked oligosaccharide chain showed >90% inhibition, while a serotype B 26397 LOS showed >60% inhibition. These studies suggest that the terminal alpha-Gal-(1-->4)-beta-Gal on the 6-linked oligosaccharide chain of 26404 LOS plays a critical role in forming the epitope recognized by the bactericidal antiserum induced by immunization with our conjugate vaccine.

Towards understanding the functional role of the glycosyltransferases involved in the biosynthesis of Moraxella catarrhalis lipooligosaccharide

The glycosyltransferase enzymes (Lgts) responsible for the biosynthesis of the lipooligosaccharide-derived oligosaccharide structures from Moraxella catarrhalis have been investigated. This upper respiratory tract pathogen is responsible for a spectrum of illnesses, including otitis media (middle ear infection) in children, and contributes to exacerbations of chronic obstructive pulmonary disease in elderly patients. To investigate the function of the glycosyltransferase enzymes involved in the biosynthesis of lipooligosaccharide of M. catarrhalis and to gain some insight into the mechanism of serotype specificity for this microorganism, mutant strains of M. catarrhalis were produced. Examination by NMR and MS of the oligosaccharide structures produced by double-mutant strains (2951lgt1/4Delta and 2951lgt5/4Delta) and a single-mutant strain (2951lgt2Delta) of the bacterium has allowed us to propose a model for the serotype-specific expression of lipooligosaccharide in M. catarrhalis. According to this model, the presence/absence of Lgt4 and the Lgt2 allele determines the lipooligosaccharide structure produced by a strain. Furthermore, it is concluded that Lgt4 functions as an N-acetylglucosylamine transferase responsible for the addition of an alpha-D-GlcNAc (1-->2) glycosidic linkage to the (1-->4) branch, and also that there is competition between the glycosyltransferases Lgt1 and Lgt4. That is, in the presence of an active Lgt4, GlcNAc is preferentially added to the (1-->4) chain of the growing oligosaccharide, instead of Glc. In serotype B strains, which lack Lgt4, Lgt1 adds a Glc at this position. This implies that active Lgt4 has a much higher affinity/specificity for the beta-(1-->4)-linked Glc on the (1-->4) branch than does Lgt1.

Identification of a novel glycosyltransferase involved in LOS biosynthesis of Moraxella catarrhalis

Moraxella catarrhalis is an important human mucosal pathogen that contributes to otitis media in infants and exacerbates conditions such as chronic obstructive pulmonary disease in the elderly. This study describes the identification of a novel gene, lgt5 that encodes a glycosyltransferase involved in the LOS biosynthesis of M. catarrhalis. Analysis of NMR data of LOS-derived oligosaccharide from a Serotype A lgt5 mutant strain of M. catarrhalis indicate that lgt5 encodes an alpha-(1-->4)-galactosyltransferase.

Multiplex PCR assay that identifies the major lipooligosaccharide serotype expressed by Moraxella catarrhalis clinical isolates

A heterologous cluster of glycosyltransferase genes was identified in the three Moraxella catarrhalis LOS serotype strains. Multiple PCR primers designed to this region amplified products that differentiate between the serotypes more rapidly and efficiently than previously described serological analyses. This assay will be valuable for clinical and research-based studies.

Characterization of a cluster of three glycosyltransferase enzymes essential for Moraxella catarrhalis lipooligosaccharide assembly

Moraxella catarrhalis isolates express lipooligosaccharide (LOS) molecules on their surface, which share epitopes similar to that of the Neisseria and Haemophilus species. These common LOS epitopes have been implicated in various steps of pathogenesis for the different organisms. In this study, a cluster of three LOS glycosyltransferase genes (lgt) were identified in M. catarrhalis 7169, a strain that produces a serotype B LOS. Mutants in these glycosyltransferase genes were constructed, and the resulting LOS phenotypes were consistent with varying degrees of truncation compared to wild-type LOS. The LOS structures of each lgt mutant were no longer detected by a monoclonal antibody (MAb 4G5) specific to a highly conserved terminal epitope nor by a monoclonal antibody (MAb 3F7) specific to the serotype B LOS side chain. Mass spectrometry of the LOS glycoforms assembled by two of these lgt mutants indicated that lgt1 encodes an alpha(1-2) glucosyltransferase and the lgt2 encodes a beta(1-4) galactosyltransferase. However, these structural studies could not delineate the function for lgt3. Therefore, M. catarrhalis lgt3 was introduced into a defined beta(1-4) glucosyltransferase Haemophilus ducreyi 35000glu- mutant in trans, and monoclonal antibody analysis confirmed that Lgt3 complemented the LOS defect. These data suggest that lgt3 encodes a glucosyltransferase involved in the addition of a beta(1-4)-linked glucose to the inner core. Furthermore, we conclude that this enzymatic step is essential for the assembly of the complete LOS glycoform expressed by M. catarrhalis 7169.

Synthesis and characterization of lipooligosaccharide-based conjugate vaccines for serotype B Moraxella catarrhalis

Moraxella catarrhalis is an important cause of otitis media in children and respiratory tract infections in the elderly. Lipooligosaccharide (LOS) is a major surface antigen of the bacterium that elicits bactericidal antibodies. Serological studies show that three major LOS types (A, B, and C) have been identified among clinical isolates. Our previous studies demonstrated that the type A LOS-based conjugates were immunogenic in animals. In this study, LOS from type B strain 26397 was detoxified and conjugated to tetanus toxoid (TT) or a cross-reactive mutant (CRM) of diphtheria toxin to form detoxified LOS (dLOS)-TT and dLOS-CRM, respectively, as vaccine candidates. The molar ratios of dLOS to TT and CRM in the conjugates were 43:1 and 19:1, respectively, while both weight ratios were around 0.9. The antigenicity of the conjugates was similar to that of the LOS, as determined by enzyme-linked immunosorbent assay using a rabbit antiserum to strain 26397. Subcutaneous immunization with each conjugate elicited a 180- to 230-fold rise of serum anti-LOS immunoglobulin G in mice and >2,000-fold rise in rabbits. In addition, both mouse and rabbit antisera showed elevated complement-mediated bactericidal activity against the homologous strain, and a representative rabbit antiserum showed bactericidal activity against nine of twelve clinical isolates studied. The bactericidal activity of the rabbit antiserum can be fully inhibited by the type B LOS but not the A or C LOS. These results indicate that the type B LOS-based conjugates can be used as vaccine components for further investigation.

Neisseria meningitidis, Neisseria lactamica and Moraxella catarrhalis share cross-reactive carbohydrate antigens

Carriage of commensal bacteria species is associated with the development of natural immunity to meningococcal disease, with lipo-oligosaccharides (LOS) of meningococci being one of the main virulence factors associated with severity of meningococcal disease. Meningococcal reference strains and isolates from the commensal species Neisseria lactamica and Moraxella catarrhalis were assessed for the presence of cross-reactive glycoconjugate antigens. Binding of human blood group antibodies of the P and Ii system to meningococcal immunotype reference strains were in accordance with the presence of known LOS carbohydrate structures. Binding studies with meningococcal immunotyping antibodies and blood group phenotyping antibodies to N. lactamica strains from different European countries showed, that a greater number of isolates obtained from native Greek and Scottish adults and children bound anti-meningococcal L(3, 7, 9) immunotyping (P < 0.001), pK (P = 0.035) and paragloboside (P < 0.001) blood group typing antibodies compared to isolates obtained from children of Russian immigrants in Greece. A greater number of M. catarrhalis strains isolated from children in Scotland bound anti-L(3, 7, 9) antibodies (38.2%) compared to strains isolated from adults (22.2%) (P = 0.017). These findings provide evidence that blood group like glycoconjugate antigens found on the commensal species N. lactamica and M. catarrhalis might be involved in the development of natural immunity to meningococcal endotoxins during childhood, and might be exploited as anti-meningococcal vaccine candidates.

Functional characteristics of a protective monoclonal antibody against serotype A and C lipooligosaccharides from Moraxella catarrhalis

A monoclonal antibody (MAb), designated MAb 8E7 (immunoglobulin G3), specific for Moraxella catarrhalis lipooligosaccharide (LOS) was evaluated for its functional activity in vitro and in a mouse model of colonization. Enzyme-linked immunosorbent assay (ELISA) demonstrated that the MAb 8E7 could be prepared to a high titer against LOS of the homologous strain 035E, and that it had bactericidal activity. MAb 8E7 reacted with M. catarrhalis serotype A and C LOSs but not serotype B LOS, as measured by ELISA and Western blotting. On the basis of published structures of LOSs, this suggests that the epitope recognized by MAb 8E7 is directed to a common sequence of either alpha-GlcNAc-(1-->2)-beta-Glc-(1--> at the branch substituting position 4 of the trisubstituted Glc residue or a terminal tetrasaccharide alpha-Gal-(1-->4)-beta-Gal-(1-->4)-alpha-Glc-(1-->2)-beta-Glc-(1--> at the branch substituting position 6 of the trisubstituted Glc residue. In a whole-cell ELISA, MAb 8E7 reacted with 70% of the 30 wild-type strains and clinical isolates tested. Immuno-electron microscopy demonstrated that MAb 8E7 reacted with a cell surface-exposed epitope of LOS on strain O35E. MAb 8E7 inhibited the adherence of strain O35E to Chang conjunctival epithelial cells by 90%. Passive immunization with MAb 8E7 could significantly enhance the clearance of strain O35E from mouse lungs in an aerosol challenge mouse model. This enhanced bacterial clearance was inhibited when MAb 8E7 was absorbed by M. catarrhalis serotype A LOS, indicating that the M. catarrhalis LOS-directed antibody may play a major role in the enhancement of M. catarrhalis clearance from lungs. These data suggest that MAb 8E7, which recognizes surface-exposed LOS of M. catarrhalis, is a protective antibody against M. catarrhalis.

Lipooligosaccharide P(k) (Galalpha1-4Galbeta1-4Glc) epitope of moraxella catarrhalis is a factor in resistance to bactericidal activity mediated by normal human serum

Moraxella catarrhalis is a respiratory pathogen responsible for acute bacterial otitis media in children and exacerbation of chronic bronchitis in adults. M. catarrhalis strains are frequently resistant to the bactericidal activity of normal human serum. In order to determine if the lipooligosaccharide (LOS) of M. catarrhalis has a role in serum resistance, the UDP-glucose-4-epimerase (galE) gene was identified, cloned, and sequenced and a deletion/insertion mutation was introduced into M. catarrhalis strain 2951. GalE enzymatic activity, measured in whole-cell lysates, was ablated in M. catarrhalis 2951 galE. Mass spectrometric analysis of LOS isolated with hot phenol-water confirmed that strain 2951 produced a type A LOS. These studies showed that the LOS from 2951 galE had lost two hexose residues due to the galE mutation and that the resultant LOS structure lacked the (Galalpha1-4Galbeta1-4Glc) P(k) epitope found on M. catarrhalis 2951. Wild-type M. catarrhalis 2951 is resistant to complement-mediated serum bactericidal activity. In contrast, a greater than 2-log(10)-unit reduction in CFU occurred after incubation of 2951 galE in either 50 or 25% pooled human serum (PNHS), and CFU in 10% PNHS decreased by about 1 log(10) unit. These studies suggest that the P(k) epitope of the LOS may be an important factor in the resistance of M. catarrhalis to the complement-mediated bactericidal effect of normal human serum.

Moraxella catarrhalis: a review of an important human mucosal pathogen

Moraxella catarrhalis has again been recognized as a significant pathogen. The past decade has witnessed an increased amount of research and understanding of the pathogenesis of the organism. This review will summarize the research pertaining to the epidemiology and components of pathogenesis in M. catarrhalis.

The lipopolysaccharide of moraxella catarrhalis structural relationships and antigenic properties

Moraxella catarrhalis has recently been shown to be both widespread and pathogenic, in contrast to previous reports. Several factors have been suggested as virulence factors, lipopolysaccharide (LPS) being one. Recent studies have shown the LPS to be without the O-chain, i.e. the polysaccharide part, and to have specific structural features corresponding to each of the three serogroups, A, B and C. The structures resemble in many respects those present in other Gram-negative nonenteric bacteria, with a galabiosyl element as a prominent common denominator. The presence of such common structures suggests that the LPS of these bacteria might be a part of a mechanism of survival for bacteria colonizing the human host.

Monoclonal antibodies to the epitope alpha-Gal-(1-4)-beta-Gal-(1- of Moraxella catarrhalis LPS react with a similar epitope in type IV pili of Neisseria meningitidis

Murine monoclonal antibodies (MAbs) against the A, B and C LPS serotypes of M. catarrhalis were generated and their binding specificity was examined in an enzyme-linked immunosorbent assay (ELISA). Two broadly cross-reactive monoclonal antibodies (MCA1 and MCC2) against the outer core region of LPS were further characterized. A panel of synthetic glycoproteins and glycolipids was used to determine the binding specificity of the MAbs. MCA1 and MCC2 bound specifically to alpha-Gal-(1-4)-beta-Gal of galabiose and globotriose glycoconjugates. The reactivity of the MAbs with galabiose was higher than that with globotriose. The MAbs could recognize the alpha-Gal-(1-4)-beta-Gal epitope only when it was in a terminal position. MCA1 was further shown to react with a similar epitope in the glycosylated type IV pili of N. meningitidis, which has been shown to contain a 1-4 linked digalactose at the terminal part of the saccharide present in the pili. MCA1 could efficiently recognize this epitope indicating that it was exposed on the surface of the pili.

Synthesis and characterization of lipooligosaccharide-based conjugates as vaccine candidates for Moraxella (Branhamella) catarrhalis

Moraxella (Branhamella) catarrhalis is an important cause of otitis media and sinusitis in children and of lower respiratory tract infections in adults. Lipooligosaccharide (LOS) is a major surface antigen of the bacterium and elicits bactericidal antibodies. Treatment of the LOS from strain ATCC 25238 with anhydrous hydrazine reduced its toxicity 20,000-fold, as assayed in the Limulus amebocyte lysate (LAL) test. The detoxified LOS (dLOS) was coupled to tetanus toxoid (TT) or high-molecular-weight proteins (HMP) from nontypeable Haemophilus influenzae through a linker of adipic acid dihydrazide to form dLOS-TT or dLOS-HMP. The molar ratios of dLOS to TT and HMP conjugates were 19:1 and 31:1, respectively. The antigenicity of the two conjugates was similar to that of the LOS, as determined by double immunodiffusion. Subcutaneous or intramuscular injection of both conjugates elicited a 50- to 100-fold rise in the geometric mean of immunoglobulin G (IgG) to the homologous LOS in mice after three injections and a 350- to 700-fold rise of anti-LOS IgG in rabbits after two injections. The immunogenicity of the conjugate was enhanced by formulation with monophosphoryl lipid A plus trehalose dimycolate. In rabbits, conjugate-induced antisera had complement-mediated bactericidal activity against the homologous strain and heterologous strains of M. catarrhalis. These results indicate that a detoxified LOS-protein conjugate is a candidate for immunization against M. catarrhalis diseases.

The structures of oligosaccharides isolated from the lipopolysaccharide of Moraxella catarrhalis serotype B, strain CCUG 3292

The oligosaccharides from the lipopolysaccharides of Moraxella catarrhalis serotype B, strain CCUG 3292, were isolated after mild acid hydrolysis and separated by high-performance anion-exchange chromatography. The structures of the oligosaccharides were established by fast atom bombardment mass spectrometry and nuclear magnetic resonance spectroscopy. It is concluded that the oligosaccharides comprise a mixture of mainly a nona- and a deca-saccharide. [formula: see text] Smaller amounts of undeca-saccharides and of truncated forms, namely, hexa-, hepta-, and octa-saccharides, were also detected.

Synthesis of Oligosaccharide Structures from the Lipopolysaccharide of Moraxella catarrhalis

The synthesis of the octasaccharide [p-(trifluoroacetamido)phenyl]ethyl 4-O-[2-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-beta-D-glucopyranosyl]-6-O-[2-O-[4-O-(4-O-alpha-D-galactopyranosyl-beta-D-galactopyranosyl)-alpha-D-glucopyranosyl]-beta-D-glucopyranosyl]-3-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside, representing the outer part of the lipooligosaccharide from Moraxella catarrhalis serotype A, is described, together with a hepta-, a hexa-, and a pentasaccaride, composing parts thereof with shorter oligosaccharide chains substituted in the 6-position of the central 3,4,6-branched glucose moiety. The versatility of the use of thioglycosides in oligosaccharide synthesis is shown, since throughout the synthesis thioglycosides are used as glycosyl donor precursors, either directly in dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling reactions or after conversion to the corresponding glycosyl bromide in silver triflate-promoted couplings. The effects of different protecting groups, anomeric leaving groups, and solvents used in the various coupling reactions are often substantial, which necessitates the use of easily convertible intermediates.

Structural studies of the exocellular polysaccharide from Sphingomonas paucimobilis strain I-886

The exocellular polysaccharide from Sphingomonas paucimobilis strain I-886 has been studied using methylation analysis, Smith degradation, partial acid hydrolysis, NMR spectroscopy, and mass spectrometry as the principal methods. It is concluded that the repeating unit has the following structure: [formula: see text] The absolute configuration of the uronic acid was deduced from 1H NMR chemical shifts and is most likely D. Some preparations of the polysaccharide also contain phosphate and O-acyl groups which have not been identified or localised.

A monoclonal antibody reactive with a common epitope of Moraxella (Branhamella) catarrhalis lipopolysaccharides

A hybrid cell line producing a monoclonal antibody (MAb) against Moraxella (Branhamella) catarrhalis lipopolysaccharide (LPS) was established. The specificity of the MAb 1B12 to purified rough LPSs from six strains of M. catarrhalis was ascertained by enzyme-linked immunosorbent assay (ELISA), competitive-inhibition ELISA, and immunoblotting. MAb 1B12 bound to live bacterial cells and culture supernatants from a total of 34 strains of M. catarrhalis, including 12 strains with different LPS serotypes. No cross-reactions with smooth and rough LPSs from selected enterobacterial and nonenterobacterial strains, with other respiratory pathogens, or with Neisseria species were observed. These data suggest that MAb 1B12 recognizes a common epitope of M. catarrhalis LPS which differs from serotype determinants.