However, Naid60 did not bind to HmenB5 (Fig.2D), which is an isotype-matched anti-NMGB PS MAb cross-reactive with NCAMs (Fig.2C). of a new vaccine against NMGB. Neisseria meningitidisis a gram-negative encapsulated bacterium and is the most common cause of bacterial meningitis.N. meningitidiscan be divided into 13 serogroups on the basis of the structures of their capsular polysaccharides (PSs), which are chemically and immunologically distinct in each group (11,21,41). Moreover, the five serogroups A, B, C, Y, and W135 account for the major meningococcal disease-causing isolates in humans. The capsular PSs ofN. meningitidisare important determinants of virulence, and the presence of serum antibody to capsular PS protects against disease. A meningococcal vaccine that uses capsular PSs fromN. meningitidisserogroups A, C, Y, and W135 is currently licensed; however, no meningococcal vaccines are available to protect against meningococcal diseases caused byN. meningitidisserogroup B (NMGB). The lack of protection against NMGB in a meningococcal vaccine is a serious problem because NMGB may account for Ditolylguanidine about 50% of all meningococcal meningitis infections in Europe and North America (32,37,40). To produce an effective vaccine against NMGB, various approaches have been studied by targeting new bacterial proteins (9,17,29), after whole-genome sequencing of NMGB (45), and lipopolysaccharide (LPS) (36) in addition to outer membrane vesicle (4,43) or N-propionylated PS (5). However, the use of bacterial proteins is problematic in a vaccine because of significant serologic heterogeneity among different strains ofN. meningitidisserogroup B (1). With respect to the capsular PS candidate, NMGB PS is an autoantigen that may elicit autoantibodies that bind both NMGB and neuronal tissue (13,14,31), because NMGB PS expresses a linear (2-8) polymer of sialic acid; thus, NMGB PS has poor immunogenicity due to immune tolerance. The structural modification of capsular PS by the substitution ofN-propionyl forN-acetyl groups proved to be highly immunogenic (15) but showed the possibility of eliciting autoantibodies (2,16,19). In a fine-structure analysis of NMGB PS using MAbs, an immunogenic epitope was found which elicits antibodies that activate complement-mediated bacteriolysis and which has no autoantibody activity (16,42). Thus, this epitope may be a target for molecular mimetics, such as peptide mimicry, for eliciting protective antibody without inducing autoimmunity. Peptide mimicry approaches have been demonstrated with phage display technology for the PS of group B streptococcus type III (35),Cryptococcus neoformans(46,50), and serogroups A and B ofN. meningitidis(7,8,18,42). Another approach to peptide mimicry is offered by anti-idiotypic antibody, and the feasibility of this approach has been demonstrated by an evaluation of peptide mimics of group B streptococcal infection (26) and serogroup C Ditolylguanidine (48) and recently serogroup B (3)N. meningitidis, using a recombinant anti-idiotypic single-chain variable fragment (scFv) methodology. Previously we reported a MAb to NMGB PS, HmenB3, which has complement-mediated bactericidal activity against NMGB but no autoimmunity (42). We now report on a monoclonal anti-idiotypic antibody to HmenB3, Naid60, PKCC which has an immunogenic and protective epitope that elicits antibodies to kill NMGB. We demonstrated that Naid60 has no cross-reactive epitope with neuronal cell adhesion molecules (NCAMs) by using both Naid60 immune sera and anti-anti-idiotypic MAb MoB34. Our experiments show that the anti-idiotype approach offers a means of developing a vaccine for NMGB. == MATERIALS AND METHODS == == Bacterial strains and polysaccharide. == The NMGB strains used were ATCC 13090 (M2092) and H44/76 (B:15:P1.7,16). Bacteria were cultured on chocolate agar plates at 37C in a candle jar and harvested after 6 h. All bacteria were aliquoted in Hanks’ balanced salt solution (HBSS) containing 20% glycerol at 70C. Purified capsular PS ofEscherichia coliK1 containing (2-8)-linked polysialic acid (PSA), which is antigenically and structurally identical to the capsular PS of Ditolylguanidine NMGB (22), was a gift from W. Vann (Center for Ditolylguanidine Biologics Evaluation and Research, Food and Drug Administration). == Preparation of F(ab)2. == HmenB3 immunoglobulin M() [IgM()] is a mouse MAb specific for NMGB PS that kills 50% of NMGB at a concentration of 1 1 ng/ml in the presence of rabbit complement and shows no binding to CHP-134, a.