No abstract

SummaryWe have identified a gene, lpt-3, that is required for the addition of phosphoethanolamine to the 3-position (PEtn-3) on the b-chain heptose (HepII) of the inner core lipopolysaccharide (LPS) of Neisseria meningitidis (Nm). The presence of this PEtn-3 substituent is characteristic of the LPS of a majority (ª 70%) of hypervirulent Nm strains, irrespective of capsular serogroup, and is required for the binding of a previously described monoclonal antibody (mAb B5) to a surface-accessible epitope. All strains of Nm that have PEtn-3 possess the lpt-3 gene. In some lpt-3-containing strains, the 3-position on HepII is preferentially substituted by glucose instead of PEtn, the result of lgtG phase variation mediated by slippage of a homopolymeric tract of cytidines. Inactivation of lpt-3 resulted in loss of PEtn-3, lack of reactivity with mAb B5 and conferred relative resistance to bactericidal killing and opsonophagocytosis by mAb B5 in vitro. Thus, the identification of lpt-3 has facilitated rigorous genetic, structural and immunobiological definition of an immunodominant epitope that is a L9 (Jennings et al., 1983) have been elucidated. There has been significant success in identifying genes involved in LPS biosynthesis, including lgtA, lgtB, lgtE (Jennings et al., 1995a), lgtC (Gotschlich, 1994), rfaC (Stojiljkovic et al., 1997), lgtF, rfaK (Kahler et al., 1996a,b), rfaF (Jennings et al., 1995b) and lgtG (Banerjee et al., 1998). A characteristic of meningococcal LPS is reversible, highfrequency phase variation of its outer core structures mediated by slippage-like mechanisms in homopolymeric DNA tracts present in LPS biosynthetic genes . These homopolymeric tracts are absent in inner core LPS biosynthetic genes such as rfaC, rfaK, rfaF and lgtF, making this structure relatively stable and an attractive candidate for incorporation into a vaccine.In an attempt to investigate LPS epitopes for potential inclusion into a vaccine against serogroup B meningococcal disease, we have previously identified an inner core LPS epitope defined by a monoclonal antibody designated B5 (mAb B5). The cognate epitope of mAb B5 was found to be present on 70% of all Nm strains (Plested et al., 1999). mAb B5 recognises LPS inner core structures that contain phosphoethanolamine (PEtn) attached specifically at the 3-position (PEtn-3) on the b-chain heptose (HepII). L1, L3, L7, L8 and L9 LPS immunotypes of Nm containing PEtn-3 were mAb B5 reactive (B5+), whereas those containing PEtn in an exocyclic position (L2, L4 and L6 immunotypes) or glycoforms that completely lack PEtn (L5 immunotype) were mAb B5 nonreactive (B5-).Recent studies have revealed that antibodies specific for the mAb B5+ epitope are present in sera from infants recovering from invasive meningococcal disease (Plested et al., 2000). These antibodies exhibited functional activity towards meningococci in an in vitro opsonophagocytic (OP) assay . Taken together, these findings indicate that the mAb B5+ epitope is a target for protective antibodies, and that the inner core...

Inner-core lipopolysaccharide (LPS) from Neisseria meningitidis is under investigation as a vaccine for prevention of meningococcal disease caused by N. meningitidis serogroup B (NmB). We investigated the functional activity of murine monoclonal antibody (MAb) B5 that recognizes a highly conserved (galE) LPS epitope. Three patterns of MAb reactivity were observed in N. meningitidis by Western blot, depending on the relative prevalence of sialylated, nonsialylated, and/or truncated LPS glycoforms. Three representative N. meningitidis strains (8047, M986, and 2996) were investigated with MAb B5 in functional assays in vitro and in vivo. MAb B5 completely protected infant rats against bacteremia caused by 8047, partially protected against 2996, and had no protective activity against M986. Thus, an inner-core LPS epitope can be a target for protective immunity, but the affinity of MAb B5 may only be sufficient to mediate protection against NmB strains possessing at least some truncated glycoforms.