Molecular mimetics of Neisseria meningitidis serogroup B polysaccharide.

Strains of Neisseria meningitidis serogroup B (NmB) are an important cause of meningitis and sepsis. Efforts to develop a NmB vaccine have been hampered by poor immunogenicity of the polysaccharide capsule, which cross-reacts with host polysialic acid, and the danger of eliciting autoantibodies. To investigate the potential of molecular mimetics to circumvent these problems, we prepared murine monoclonal antibodies (mAbs) against the N-propionyl derivative (N-Pr) of NmB polysaccharide. Several mAbs were found that reacted with capsular polysaccharide epitopes, which were distinct from host polysialic acid. These mAbs also passively conferred protection against experimental bacteremia. We used these mAbs to screen novel independently folding peptide phage display libraries, and pools of combinatorial small molecules, each consisting of approximately 30 to approximately 700 small molecules of diverse composition. To date, several mimetic candidates have been identified. One is a peptide selected from a library of independently folding alphabeta peptides, and others are peptoid dimers or trimers selected from the small molecule pools. The peptoids contain an indan-type of ring system, and some of them also contain a large hydrophobic group such as oleyl amine or dehydroabietyl amine, and a positively charged group at the amino-terminus. Both the alphabeta peptide from the phage library, and the peptoids from the small molecule pools, inhibit binding of the mAbs to N-Pr NmB polysaccharide. Future studies will focus on the structure/activity relationship of these mimetics, and the development of immunogens that may be capable of eliciting anticapsular antibody without autoantibody activity.

Bactericidal monoclonal antibodies that define unique meningococcal B polysaccharide epitopes that do not cross-react with human polysialic acid.

The poor immunogenicity of the Neisseria meningitidis group B polysaccharide capsule, a homopolymer of alpha(2-->8) sialic acid, has been attributed to immunologic tolerance induced by prenatal exposure to host polysialyated glycoproteins. Substitution of N-propionyl (N-Pr) for N-acetyl groups on the meningococcal B polysaccharide, and conjugation of the resulting polysaccharide to a protein carrier, have been reported to yield a conjugate vaccine that elicits protective Abs with minimal autoantibody activity. To characterize the protective epitopes on the derivatized polysaccharide, we isolated 30 anti-N-Pr meningococcal B polysaccharide mAbs. These Abs were heterogeneous with respect to complement-mediated bactericidal activity, fine antigenic specificity, and autoantibody activity as defined by binding to the neuroblastoma cell line, CHP-134, which expresses long-chain a(2-->8)-linked polysialic acid. Eighteen of the Abs could activate complement-mediated bacteriolysis. Seven of these 18 Abs cross-reacted with N-acetyl meningococcal B polysaccharide by ELISA and had strong autoantibody activity. Thus, N-Pr meningococcal B polysaccharide conjugate vaccine has the potential to elicit autoantibodies. However, 7 of the 18 bactericidal mAbs had no detectable autoantibody activity. These Abs may be useful for the identification of molecular mimetics capable of eliciting protective Abs specific to the bacteria, without the risk of evoking autoimmune disease.

Human immunoglobulin M paraproteins cross-reactive with Neisseria meningitidis group B polysaccharide and fetal brain.

Three hundred fifty-nine serum samples from patients with immunoglobulin M (IgM) or IgG monoclonal gammopathies were tested for binding to the capsular polysaccharide (PS) of Neisseria meningitidis group B (MenB PS, poly-alpha[2-->8]-N-acetylneuraminic acid). Of 159 IgM paraproteins, 7 (4.4%) were positive, compared with 0 of 200 IgG paraproteins (P < 0.05). Since MenB PS reactivity was limited to the IgM paraproteins, the 159 IgM paraproteins were tested by enzyme-linked immunosorbent assay (ELISA) for reactivity with seven other bacterial PSs. None reacted with meningococcal A or C, Haemophilus influenzae type b, or Streptococcus pneumoniae type 3, 6, 14, or 23 PS. The specificity of the MenB PS-reactive antibodies was confirmed by demonstration of binding to N. meningitidis group B cells but not to a capsular PS-deficient mutant and by specific inhibition of binding to solid-phase MenB PS by soluble MenB PS in an ELISA. Five of five antibodies tested protected infant rats from bacteremia caused by Escherichia coli K1, an organism with a PS capsule that also is composed of poly-alpha[2-->8]-N-acetylneuraminic acid. Each of the seven MenB PS-reactive paraproteins had autoantibody activity as defined by binding to homogenates of calf brain in a radioimmunoassay. For six of the seven antibodies, binding to calf brain was inhibited by the addition of soluble MenB PS. Thus, approximately 4% of human IgM paraproteins have autoantibody activity to poly-alpha[2-->8]-N-acetylneuraminic acid, an antigen expressed in fetal brain and cross-reactive with the MenB capsular PS. The reason for this skewing of the IgM paraprotein repertoire toward reactivity with poly-alpha[2-->8]-N-acetylneuraminic acid antigenic determinants is unknown.

Patrones de sensibilidad de los aislados de Haemophilus de ninos de once países en desarrollo / Antimicrobial susceptibility patterns of Haemophilus isolates from children in eleven developing countries

Antimicrobial susceptibility patterns of Haemophilus isolates from children in eleven developing nations