title: Antibodies to N-terminal peptides of gonococcal porin are bactericidal when gonococcal lipopolysaccharide is not sialylated.
abstract: Six synthetic 25-mer peptides corresponding to certain presumed surface-exposed regions of gonococcal porin protein I (PI) were made from strains FA19 (PIA) and MS11 (PIB). Four peptides were immunogenic in rabbits. Affinity-purified antisera against both PIA and PIB N-terminal peptides were bactericidal for homologous gonococci and many heterologous PI serovars. However, sialylation of gonococcal lipopolysaccharide (LPS) by growth of gonococci in the presence of cytidine monophosphate-neuraminic acid (CMP-NANA) abrogated the bactericidal activity of these antisera. Binding of anti-PI monoclonal antibodies to whole gonococci was reduced two- to fourfold by sialylation of LPS, suggesting that sialylation may inhibit bactericidal activity by masking porin epitopes. However, binding of anti-PII (Opa) monoclonal antibodies was not inhibited, yet complement-mediated killing was inhibited by sialylated LPS. Binding of complement components C3 and C9 was inhibited in the presence of either anti-PI or anti-PII monoclonals when gonococci were grown in the presence of CMP-NANA. Thus sialylation inhibited both anti-PI antibody binding and complement deposition, with a resultant decrease in bactericidal activity.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology / Q000633:toxicity*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D001483:Base Sequence; D003165:Complement System Proteins / Q000276:immunology; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D000939:Epitopes / Q000276:immunology; D008070:Lipopolysaccharides / Q000737:chemistry*; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid; D009344:Neisseria gonorrhoeae / Q000145:classification / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology*; D018272:Porins; D011817:Rabbits; D012794:Sialic Acids / Q000502:physiology*
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D000939:Epitopes; D008070:Lipopolysaccharides; D010446:Peptide Fragments; D018272:Porins; D012794:Sialic Acids; C057699:porin protein, Neisseria; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D003165:Complement System Proteins; D019158:N-Acetylneuraminic Acid