Meningococcal disease primarily affects infants and very young children. The group B capsule is not immunogenic, and outer membrane protein vaccines provide only short-lived protection, in older children, that is restricted to serotypes in the vaccine. Protection is mediated by bactericidal antibodies that are induced by asymptomatic colonization by organisms that share lipooligosaccharides (LOS). By adolescence most children have LOS IgG that are bactericidal for most meningococcal strains. These antibodies prevent meningococcal disease, regardless of protein serotype. LOS are immunogenic at birth, and LOS antibodies can be induced by vaccination. During disease, infants make bactericidal antibodies against their infecting strains. These antibodies bind to a conserved LOS structure that is expressed well by 126E (L1,8), other L1 strains, and by L3,7 and L4,6 strains. This structure has not been definitively identified. LOS antibodies induced during infancy can prevent the monoclonal antibody (mAb), D6A, from binding to 126E LOS, and we have used this mAb, which binds to meningococci of all groups and types, as a surrogate for the LOS structure. MAb D6A binds the deeply truncated LOS of deltagalE mutants that have only a conserved basal structure, but it is not clear that this truncated LOS is the optimal immunogen. We now propose to affinity purify human IgG that binds the conserved LOS structure by 1) passage of IVIG over deltagalE LOS, and 2) by sequential passage of IVIG over L1, L1,8, L3,7 and L4,6 LOS, each coupled to Sepharose. We will assess how well each IgG kills 34 consecutive and unique endemic meningococcal case strains, and whether they can opsonize these meningococci for PMN killing. We will compare the binding of this pauciclonal IgG (pclgG) to that of mAb D6A and use Mass Spectrometry combined with chemical and enzymatic degradations to confirm the LOS structure recognized by mAb D6A and pclgG. We will immunize transgenic mice that have human immmunoglobulin loci (XenoMouse) with a deltagalE mutant to insure that this LOS structure is immunogenic for the human immune system, and characterize the functional activity of the induced IgG, as for the IVIG IgG. We will use enrichment of a coliphage display library with mAb D6A to identify a peptide mimic of the mAb D6A LOS antigen, use this peptide to immunize XenoMouse mice and functionally charaterize the induced IgG. We also will try to identify a peptide mimic that binds the human pclgG. The resulting data should confirm the suitability of a conserved LOS structure as a vaccine for the prevention of endemic group B disease in infants and young children.
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