Production and characterization of monoclonal antibodies to type 8 lipooligosaccharide of Neisseria meningitidis

Detection of lipopolysaccharides blotted on nylon membranes

A sensitive method for the detection of Gram-negative bacterial lipopolysaccharide (LPS) blotted on nylon membranes is described. LPSs are separated by SDS-PAGE and then electrophoretically transferred to nylon membranes. Immobilized LPS is oxidized with periodate and then reacted with a hydrazide conjugated to the steroid, digoxigenin. LPS is visualized by alkaline phosphatase labelled antibodies against the steroid and the enzyme substrate 5-bromo-4-chloro-3-indolyl phosphate/nitro blue tetrazolium. LPS banding patterns of both rough (R-) and smooth (S-) type LPSs from over 15 different bacterial species are similar to those of silver stained companion gels, but without nonspecific staining of proteins. The detection of S-LPS from Pseudomonas aeruginosa F-D type 1 and R-LPS from Escherichia coli K12 is sensitive to 10-20 ng per lane. The use of this detection system in combination with antibody or lectin studies on identical blots can provide an effective tool in locating the precise position of certain epitopes or sequences in both R- and S-type LPSs on the blots.

Lipooligosaccharide Structures of Invasive and Carrier Isolates of Neisseria meningitidis Are Correlated with Pathogenicity and Carriage

The degree of phosphorylation and phosphoethanolaminylation of lipid A on neisserial lipooligosaccharide (LOS), a major cell-surface antigen, can be correlated with inflammatory potential and the ability to induce immune tolerance in vitro. On the oligosaccharide of the LOS, the presence of phosphoethanolamine and sialic acid substituents can be correlated with in vitro serum resistance. In this study, we analyzed the structure of the LOS from 40 invasive isolates and 25 isolates from carriers of Neisseria meningitidis without disease. Invasive strains were classified as groups 1-3 that caused meningitis, septicemia without meningitis, and septicemia with meningitis, respectively. Intact LOS was analyzed by high resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Prominent peaks for lipid A fragment ions with three phosphates and one phosphoethanolamine were detected in all LOS analyzed. LOS from groups 2 and 3 had less abundant ions for highly phosphorylated lipid A forms and induced less TNF-α in THP-1 monocytic cells compared with LOS from group 1. Lipid A from all invasive strains was hexaacylated, whereas lipid A of 6/25 carrier strains was pentaacylated. There were fewer O-acetyl groups and more phosphoethanolamine and sialic acid substitutions on the oligosaccharide from invasive compared with carrier isolates. Bioinformatic and genomic analysis of LOS biosynthetic genes indicated significant skewing to specific alleles, dependent on the disease outcome. Our results suggest that variable LOS structures have multifaceted effects on homeostatic innate immune responses that have critical impact on the pathophysiology of meningococcal infections.

Improvement of immunogenicity of meningococcal lipooligosaccharide by coformulation with lipidated transferrin-binding protein B in liposomes: implications for vaccine development

Among various meningococcal antigens, lipooligosaccharide (LOS) and recombinant lipidated transferrin-binding protein B (rlip-TbpB) are considered to be putative vaccine candidates against group B Neisseria meningitidis. In the present work, we report the development of a new liposome-based vaccine formulation containing both rlip-TbpB and L8 LOS. The endotoxic activity of the liposomal LOS was evaluated in vitro using the Limulus Amebocyte Lysate assay and compared to the endotoxic activity of free LOS. Above a 250:1 lipid/LOS molar ratio, liposomes were shown to effectively detoxify the LOS as the endotoxic activity of the LOS was reduced by more than 99%. Immunogenicity studies in rabbits showed that the presence of rlip-TbpB dramatically increased the immunogenicity of the LOS. While the formulation raised a strong anti-TbpB response, it elicited a higher anti-LOS IgG level than the liposomal LOS alone. Sera from rabbits immunized with rlip-TbpB/liposomal LOS displayed increased ability to recognize LOS on live bacteria expressing the L8 immunotype and increased anti-LOS-specific bactericidal activity compared to sera from rabbits immunized with liposomal LOS alone. Measurement of interleukin-8 (IL-8) produced by HEK293 cells transfected with Toll-like receptor (TLR) after stimulation with rlip-TbpB showed that the protein is a TLR2 agonist, which is in accordance with the structure of its lipid. Furthermore, an in vivo study demonstrated that the lipid moiety is not only required for its adjuvant effect but also has to be linked to the protein. Overall, the rlip-TbpB/LOS liposomal formulation was demonstrated to induce an effective anti-LOS response due to the adjuvant effect of rlip-TbpB on LOS.

The structure of the L9 immunotype lipooligosaccharide from Neisseria meningitidis NMA Z2491

The lipooligosaccharide (LOS) from the Neisseria meningitidis prototype serogroup A strain NMA Z2491, an L9 immunotype LOS, was isolated and structurally characterized using glycosyl composition and linkage determination, mass spectrometry, and both 1- and 2-D nuclear resonance spectroscopy. The results show that the L9 LOS has an identical structure to that of an L4 LOS structure with the exception that it does not contain a sialic acid residue linked to position 3 of the lactoneotetraose terminal galactosyl residue. Further, two oligosaccharides are present in the Z2491 LOS preparation, OS1 and OS2. They differ from one another only in that OS2 contains an added glycine moiety, presumably at O-7 on the inner core Hep II residue. The structures of these oligosaccharides are as follows: where R=H or Gly.

Enhanced factor H binding to sialylated Gonococci is restricted to the sialylated lacto-N-neotetraose lipooligosaccharide species: implications for serum resistance and evidence for a bifunctional lipooligosaccharide sialyltransferase in Gonococci

We isolated serologically identical (by serovar determination and porin variable region [VR] typing) strains of Neisseria gonorrhoeae from an infected male and two of his monogamous female sex partners. One strain (termed 398078) expressed the L1 (Galalpha1 --> 4 [corrected] Galbeta1 --> 4Glcbeta1 --> 4HepI) lipooligosaccharide (LOS) structure exclusively; the other (termed 398079) expressed the lacto-N-neotetraose (LNT; Galbeta1 --> 4GlcNAcbeta1 --> 3Galbeta1 --> 4Glcbeta1 --> 4HepI) LOS structure. The strain from the male index case expressed both glycoforms and exhibited both immunotypes. Nuclear magnetic resonance analysis revealed that sialic acid linked to the terminal Gal of L1 LOS via an alpha2 --> 6 linkage and, as expected, to the terminal Gal of LNT LOS via an alpha2--> 3 linkage. Insertional inactivation of the sialyltransferase gene (known to sialylate LNT LOS) abrogated both L1 LOS sialylation and LNT LOS sialylation, suggesting a bifunctional nature of this enzyme in gonococci. Akin to our previous observations, sialylation of the LNT LOS of strain 398079 enhanced the binding of the complement regulatory molecule, factor H. Rather surprisingly, factor H did not bind to sialylated strain 398078. LOS sialylation conferred the LNT LOS-bearing strain complete (100%) resistance to killing by even 50% nonimmune normal human serum (NHS), whereas sialylation of L1 LOS conferred resistance only to 10% NHS. The ability of gonococcal sialylated LNT to bind factor H confers high-level serum resistance, which is not seen with sialylated L1 LOS. Thus, serum resistance mediated by sialylation of gonococcal L1 and LNT LOS occurs by different mechanisms, and specificity of factor H binding to sialylated gonococci is restricted to the LNT LOS species.

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.

Intranasal immunization with a lipooligosaccharide-based conjugate vaccine from nontypeable Haemophilus influenzae enhances bacterial clearance in mouse nasopharynx

Nontypeable Haemophilus influenzae (NTHi) is a major cause of otitis media in children. We investigated whether intranasal immunization with a detoxified lipooligosaccharide-tetanus toxoid (dLOS-TT) conjugate vaccine would generate protective immunity against NTHi in a mouse model of nasopharyngeal clearance. The results demonstrated that intranasal immunization with dLOS-TT plus adjuvant cholera toxin (CT) significantly induced LOS-specific IgA antibodies in mouse external secretions, especially in nasal wash (90-fold), bronchoalveolar lavage fluid (25-fold), saliva (13-fold) and fecal extract (three-fold). LOS-specific IgA antibody-forming cells were also found in mucosal and lymphoid tissues with their highest numbers in the nasal passage (528 per 10(6) cells). In addition, the intranasal immunization elicited a significant rise in LOS-specific IgG (32-fold) and IgA (13-fold) in serum. For the immunized mice which had been challenged through the nose with 10(7) live NTHi strain 9274 cells, the vaccine group showed a significant reduction (74-77%) of NTHi, compared to that of control groups with CT alone or dLOS plus CT (P<0.05). Negative correlations were found between bacterial counts and the levels of nasal wash IgA or IgG, saliva IgA and serum IgG. The clearance of five heterologous strains was investigated and revealed a significant clearance of strains 3198, 5657 and 7502 but not of strains 1479 and 2019. These data suggest that intranasal immunization with dLOS-TT vaccine elicits both mucosal and systemic immunity against NTHi and enhances bacterial clearance from nasopharynx in mice. Such a vaccine and vaccination regime may be applicable to humans with an appropriate formulation.

Genetic analysis of conservation and variation of lipooligosaccharide expression in two L8-immunotype strains of Neisseria meningitidis

Neisseria meningitidis strains A1 and M978 both express the lipooligosaccharide (LOS) L8 immunotype [Gu et al., J. Clin. Microbiol. 30 (1992) 2047-2053]. Under different growth conditions, strain A1 did not change its LOS profile whereas strain M978 produced variable LOS profiles on SDS-PAGE. To understand the genetic basis of LOS conservation and variation, their lgt locus encoding glycosyltransferases responsible for the biosynthesis of the alpha-chain of LOS was analyzed. Strain A1 possessed only two genes, lgtA and lgtH, at the lgt locus. The lgtA gene was inactivated due to a frameshift mutation; thus strain A1 expressed only L8 LOS. In contrast, strain M978 contained five genes lgtZ, lgtC, lgtA, lgtB and lgtE at this locus, thus it had a potential to express L1, L3,7 in addition to the L8 LOS. The data showed that strain A1 is a better reference strain for the L8 immunotype because of the stability of L8 LOS expression resulting from its unique lgt locus. In addition, these two strains had two new genetic organizations, lgtAH and lgtZCABE, compared to the reported gene organization at the lgt locus in N. meningitidis.

Mice immunization with gel electrophoresis-micropurified bacterial lipopolysaccharides

Some evidence on the possible use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to elicit antibodies against smooth- or rough-type bacterial lipopolysaccharides (LPS) is shown. Gel-separated LPS were negatively stained with zinc-imidazole to precisely localize the bands of interest under fully reversible conditions. Then the bands of interest were excised and the resulting gel slices washed in a solution of a zinc-complexing agent (e.g., 100 mM EDTA), after which they were extruded through a metal sieve of 32 microm average size contained in a 1 mL syringe, to generate homogeneous gel microparticles. The LPS-containing gel slurries were used directly to immunize female BALB/c mice. Using this procedure, positive mouse polyclonal antibody responses against gel-purified smooth- or rough-LPS forms from Escherichia coli K-235 or Bordetella pertussis were elicited, as tested by a dot-immunoblotting assay. Our results may encourage the use of SDS-PAGE-micropurified LPS to develop optimized immunization procedures for the generation of specific antibodies against LPS bands of defined sizes, and therefore they constitute an intermediate step toward that aim.

Identification of common lipooligosaccharide types in isolates from patients with otitis media by monoclonal antibodies against nontypeable Haemophilus influenzae 9274

Twenty-one murine monoclonal antibodies (MAbs) were induced by nontypeable Haemophilus influenzae (NTHi) 9274. Nineteen MAbs were specific for the lipooligosaccharide (LOS) as determined by enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. When the MAbs were assayed with five LOS prototype strains by ELISA, all bound to strain 3198 LOS (type III), while six of the MAbs were also reactive with LOSs from strain 1479 (type I), 5657 (type IV), or 7502 (type V). Ten MAbs had complement-mediated bactericidal activity, and three MAbs were opsonophagocytic against the homologous strain. Five LOS MAbs with different specificities were used to analyze 155 NTHi clinical isolates from the United States and from Japan. These isolates were classified into nine groups by ELISA. Only four isolates (2.6%) were not recognized by any of the five MAbs. Most of the isolates (91.6%) were in four groups which bound three of the five MAbs. One of three MAbs, 6347C11, had strong activity against the homologous strain and was also bactericidal to 45 clinical isolates (29%) which belonged to the four common patterns (25 belonged to pattern 1). These data indicate that these MAbs can be used for LOS typing in which almost all NTHi strains can be typed according to the LOS antigenicity. Among NTHi, at least one conserved LOS epitope which is a target of bactericidal antibodies exists. We conclude that strain 9274 LOS, which is the target for bactericidal antibodies, is a candidate for LOS-based NTHi vaccines.

Purification of meningococcal lipo-oligosaccharide by FPLC techniques

A rapid and efficient method for the preparation of highly pure meningococcal lipo-oligosaccharide (LOS) was developed. This used a Superose 6 column on a FPLC system to purify LOS from phenol-water extracts of cell lysates of Neisseria meningitidis. The purest LOS preparations, with no detectable protein contamination and less than 0.5% (w/w) residual RNA, were obtained when cell lysates had been treated with RNase ONE before phenol extraction and chromatographic separation. Preparations that had received no ribonuclease treatment had 2-3% residual RNA contamination and predigestion of samples with RNase A, which only partially degraded the RNA present in the crude extracts, resulted in LOS samples contaminated with 15-20% residual RNA. The LOS purified from RNase ONE-treated extracts was highly endotoxic, and showed no reduction in antibody binding or specific endotoxin activity compared to unpurified material. Approximately 80% of the LOS applied to the chromatography column was recovered as purified material.

Detection and quantitation of the glucuronoxylomannan-like polysaccharide antigen from clinical and nonclinical isolates of Trichosporon beigelii and implications for pathogenicity

Sera from patients with systemic infections caused by the opportunistic fungus Trichosporon beigelii have been shown to cross-react with anticryptococcal antibodies. We quantitatively compared the amounts of antigen produced and examined the expression of O-acetyl epitopes from 35 strains of T. beigelii isolated from deep and superficial infections. By counterimmunoelectrophoresis, 10 of 10 isolates from deep infections were positive for polysaccharide, compared with 7 of 13 isolates from superficial infections (P = 0.02). All 23 strains tested were positive for polysaccharide when screened by immunodot. By enzyme immunoassay, the cross-reactive antigen produced by deep isolates (n = 9) had a mean titer of 1:5,500. In contrast, superficial isolates (n = 22) produced significantly less antigen than the deep isolates (P < 0.001), with a mean titer of 1:700. Isolates from environmental sources (n = 3) were similar to the superficial isolates, with a mean titer of 1:600. The mean concentrations +/- standard errors of cross-reactive polysaccharide released by deep isolates and superficial isolates were 3.09 +/- 0.44 and 1.74 +/- 0.30 micrograms/ml, respectively, when measured by rocket immunoelectrophoresis (P = 0.02). O-Acetyl epitopes were detected on polysaccharide from 8 of 9 strains of T. beigelii isolated from deep sources, while only 2 of 12 superficial isolates expressed detectable O-acetyl epitopes (P = 0.01). Thus, while all isolates of T. beigelii tested were capable of producing glucuronoxylomannan-like cross-reactive antigen, pathogenic isolates produced significantly more antigen than superficial or environmental isolates. Furthermore, significantly more pathogenic isolates than superficial or environmental isolates expressed antigen that was O acetylated.

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.