title: Characterization of diverse subvariants of the meningococcal factor H (fH) binding protein for their ability to bind fH, to mediate serum resistance, and to induce bactericidal antibodies.
abstract: Neisseria meningitidis is a commensal of the human nasopharynx but is also a major cause of septicemia and meningitis. The meningococcal factor H binding protein (fHbp) binds human factor H (fH), enabling downregulation of complement activation on the bacterial surface. fHbp is a component of two serogroup B meningococcal vaccines currently in clinical development. Here we characterize 12 fHbp subvariants for their level of surface exposure and ability to bind fH, to mediate serum resistance, and to induce bactericidal antibodies. Flow cytometry and Western analysis revealed that all strains examined expressed fHbp on their surface to different extents and bound fH in an fHbp-dependent manner. However, differences in fH binding did not always correlate with the level of fHbp expression, indicating that this is not the only factor affecting the amount of fH bound. To overcome the issue of strain variability in fHbp expression, the MC58ΔfHbp strain was genetically engineered to express different subvariants from a constitutive heterologous promoter. These recombinant strains were characterized for fH binding, and the data confirmed that each subvariant binds different levels of fH. Surface plasmon resonance revealed differences in the stability of the fHbp-fH complexes that ranged over 2 orders of magnitude, indicating that differences in residues between and within variant groups can influence fH binding. Interestingly, the level of survival in human sera of recombinant MC58 strains expressing diverse subvariants did not correlate with the level of fH binding, suggesting that the interaction of fHbp with fH is not the only function of fHbp that influences serum resistance. Furthermore, cross-reactive bactericidal activity was seen within each variant group, although the degree of activity varied, suggesting that amino acid differences within each variant group influence the bactericidal antibody response.
authors.affiliation: Molecular Genetics Unit, Novartis Vaccines, Via Fiorentina, 1, 53100 Siena, Italy. Kate.Seib@novartis.com
authors.forename: Kate L
authors.initials: KL
authors.lastname: Seib
authors.forename: Brunella
authors.initials: B
authors.lastname: Brunelli
authors.forename: Barbara
authors.initials: B
authors.lastname: Brogioni
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Palumbo
authors.forename: Stefania
authors.initials: S
authors.lastname: Bambini
authors.forename: Alessandro
authors.initials: A
authors.lastname: Muzzi
authors.forename: Federica
authors.initials: F
authors.lastname: DiMarcello
authors.forename: Sara
authors.initials: S
authors.lastname: Marchi
authors.forename: Arie
authors.initials: A
authors.lastname: van der Ende
authors.forename: Beatrice
authors.initials: B
authors.lastname: Aricó
authors.forename: Silvana
authors.initials: S
authors.lastname: Savino
authors.forename: Maria
authors.initials: M
authors.lastname: Scarselli
authors.forename: Maurizio
authors.initials: M
authors.lastname: Comanducci
authors.forename: Rino
authors.initials: R
authors.lastname: Rappuoli
authors.forename: Marzia M
authors.initials: MM
authors.lastname: Giuliani
authors.forename: Mariagrazia
authors.initials: M
authors.lastname: Pizza
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D017242:Complement Factor H / Q000378:metabolism*; D003165:Complement System Proteins; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008589:Meningococcal Infections / Q000276:immunology / Q000382:microbiology; D051379:Mice; D008969:Molecular Sequence Data; D009345:Neisseria meningitidis / Q000235:genetics* / Q000378:metabolism*; D010802:Phylogeny; D011485:Protein Binding; D011817:Rabbits
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D017242:Complement Factor H; D003165:Complement System Proteins