Fine antigenic specificity and cooperative bactericidal activity of monoclonal antibodies directed at the meningococcal vaccine candidate factor h-binding protein.

No broadly protective vaccine is available for the prevention of group B meningococcal disease. One promising candidate is factor H-binding protein (fHbp), which is present in all strains but often sparsely expressed. We prepared seven murine immunoglobulin G monoclonal antibodies (MAbs) against fHbp from antigenic variant group 2 (v.2) or v.3 ( approximately 40% of group B strains). Although none of the MAbs individually elicited bactericidal activity with human complement, all had activity in different combinations. We used MAb reactivity with strains expressing fHbp polymorphisms and site-specific mutagenesis to identify residues that are important for epitopes recognized by six of the v.2 or v.3 MAbs and by two v.1 MAbs that were previously characterized. Residues affecting v.2 or v.3 epitopes resided between amino acids 174 and 216, which formed an eight-stranded beta-barrel in the C domain, while residues affecting the v.1 epitopes included amino acids 121 and 122 of the B domain. Pairs of MAbs were bactericidal when their respective epitopes involved residues separated by 16 to 20 A and when at least one of the MAbs inhibited the binding of fH, a downregulatory complement protein. In contrast, there was no cooperative bactericidal activity when the distance between residues was >or=27 A or

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2519416	PMC
http://dx.doi.org/10.1128/IAI.00367-08	DOI Listing