Variable region sequences and idiotypic expression of a protective human immunoglobulin M antibody to capsular polysaccharides of Neisseria meningitidis group B and Escherichia coli K1.

We determined the heavy (H)- and light (L)-chain variable (V) region nucleotide and translated amino acid sequences of the human immunoglobulin M(kappa) monoclonal antibody (MAb) 5E1, which is specific for the polysaccharide capsule of Escherichia coli K1 and Neisseria meningitidis group B (poly[alpha(2-->8)-N-acetylneuraminic acid]) and which is protective in animal models of infection. The 5E1 VH gene is a member of the VHIIIb family and is 97% homologous to the 9.1 germ line gene. The 5E1 VL gene is a member of the kappa I subgroup and is 98% homologous to the germ line gene, 15A, also known as KLO12. The VL and/or VH genes used by 5E1 are highly homologous to the V genes encoding antibodies to the Haemophilus influenzae type b polysaccharide and to antibodies reactive with self-antigens such as erythrocyte "i," DNA, and thyroid peroxidase. We also produced three murine anti-idiotype (Id) MAbs against 5E1. All three anti-Ids recognize a minor subset of antimeningococcal B polysaccharide antibodies present in serum from normal adults. Two of the anti-Ids define distinct Ids associated with antibodies having kappa I-15A V regions. These 15A-associated Ids are expressed by some heterologous human antimeningococcal B polysaccharide MAbs, and they also are independently expressed by two human MAbs that are specific for either the H. influenzae b polysaccharide or the i erythrocyte antigen and that utilize the kappa I-15A V region. Taken together, these data indicate that the 5E1 antibody uses V regions that recur in the human antibody repertoires to this polysaccharide and to structurally dissimilar polysaccharides and autoantigens. Thus, the poor immunogenicity of poly[alpha(2-->8)-N-acetylneuraminic acid] cannot be explained by the unavailability of certain critical VH and VL genes required for generation of antibody response.