VACCINE-INDUCED IGG ANTIBODIES TO THE LINEAR EPITOPE ON THE PORB OUTER-MEMBRANE PROTEIN PROMOTE OPSONOPHAGOCYTOSIS OF NEISSERIA-MENINGITIDIS BY HUMAN NEUTROPHILS

The serotype 15 PorB protein of Neisseria meningitidis contains an N-t erminal linear immunodominant B-cell epitope located on the putative l oop 1 (VR1) region, This epitope has previously been shown to stimulat e antibody formation in 74% of the vaccinees after three doses of the Norwegian group B outer-membrane vesicle (OMV) vaccine, In the present study, the purified PorB protein and the 23mer synthetic peptide D63b 2 covering VR1 region were immobilized onto N-hydroxysuccinimide-activ ated matrix and used for affinity purification of the specific IgG ant ibodies from sera of three selected vaccinees, PorB- and peptide D63b2 -specific IgG; preparations bound to the PorB protein on immunoblots a nd reacted with strain 44/76 and OMV complexes expressing the serotype 15 PorB protein, but not with the PorB-deficient mutant, suggesting h igh specificity for the PorB protein. Both PorB- and peptide D63b2-spe cific IgG were marginally bactericidal, but enabled strong opsonophago cytosis measured as respiratory burst response of human neutrophils an d internalization of opsonized FITC-labeled meningococci. The data ind icate that about 30-57% of the bulk serum opsonic activity for the 44/ 76 bacteria could be ascribed to linear epitope-specific IgG1, thus co ntributing to vaccine-induced protection against systemic meningococca l disease via the opsonophagocytic route of pathogen clearance. (C) 19 97 Academic Press.