Conservation and Accessibility of an Inner Core Lipopolysaccharide Epitope ofNeisseria meningitidis

Abstract

We investigated the conservation and antibody accessibility of inner core epitopes of Neisseria meningitidislipopolysaccharide (LPS) because of their potential as vaccine candidates. An immunoglobulin G3 murine monoclonal antibody (MAb), designated MAb B5, was obtained by immunizing mice with agalE 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 β-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. meningitidisLPS. 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 byN. meningitidis.

Identification of a gene (lpt‐3) required for the addition of phosphoethanolamine to the lipopolysaccharide inner core of Neisseria meningitidis and its role in mediating susceptibility to bactericidal killing and opsonophagocytosis

“…L3 strain MC58) or absent (L7-L12 immunotypes), the phenotype was B5+. We were also able to shed light on a previous and puzzling observation of phase variation of the B5+ serogroup B strain BZ157 (Plested et al, 1999). Sequencing of the homopolymeric tract within the lgtG gene of colony variants of this strain revealed that the lgtG gene was out of frame (nine C residues) in a B5+ colony and in frame (11 C residues) in a B5-colony (Table 1).…”

“…About 70% of Nm strains have an inner core LPS structure that binds mAb B5. An essential structural requirement of the epitope recognized by mAb B5 is PEtn attached specifically at the 3-position (PEtn-3) of HepII (Plested et al, 1999). To investigate further the genetic basis of this inner core LPS epitope and, in particular, the gene(s) required for the addition of PEtn-3, a recently developed method for mutagenesis was used (Tang et al, 2001) to identify mutants with either gain or loss of mAb B5 reactivity using appropriate Nm strains.…”

“…Previous studies have established that mAb B5 recognizes an epitope of Nm LPS for which PEtn-3 is an absolute requirement (Plested et al, 1999). The structural evidence on which this was based included specific chemical modification of LPS in order to result in complete loss of LPS reactivity with mAb B5.…”

“…As the lpt-3 gene is required for bacteria to react with mAb B5, and this reactivity is dependent on the presence of PEtn at the 3-position of HepII, we investigated the functional effects of mAb B5 on wild type or the isogenic lpt-3 mutant using OP and BC assays. For these experiments, we used the galE mutants of MC58 and MC58::lpt-3, as mAb B5 was raised against a galE strain (H44/76::galE) (Plested et al, 1999), and we reasoned that any differences mediated by the presence or absence of lpt-3 might be detected most easily in a galE background because of the greater accessibility of mAb B5 to the truncated LPS expressed by galE mutants.…”

Identification and localization of glycine in the inner core lipopolysaccharide of Neisseria meningitidis

“…Strains BZ157 and NGH15 are from the culture collection of E. R. Moxon. LPS was extracted by the hot phenol/water method as described previously and purified from the aqueous phase by ultracentrifugation (45K, 4°C, 5 h) [11] yielding 200 mg in each case. O-deacylated LPS was prepared as described previously [13] in 50% yield from the LPS.…”