Immune responses to linear epitopes on the PorB protein of Neisseria meningitidis in patients with systemic meningococcal disease

Neisserial porins, the major protein constituents of the outer membrane capable of inducing antibody responses in humans, are considered to be meningococcal vaccine candidates, so it is important to map the relevant B-cell epitopes. For B-cell epitope analyses of the serotype 15 PorB protein in Neisseria meningitidis, paired sera from selected patients with systemic meningococcal disease (SMD) were screened with synthetic 12mer peptides spanning the PorB protein sequence, and/or its variable region 1 (VR1). A 'SMD-related' linear B-cell epitope was found within the VR1 region consisting of 14 residues ((17)svFHQNGQVTEvtt(30)). A 23mer soluble peptide (D63b2) that covered the VR1 region, including the complete (17)svFHQNGQVTEvtt(30) sequence, was recognized, whereas no detectable binding was observed to a 16mer peptide (D63a1) containing most of the essential sequence ((19)FHQNGQVTEVtt(30)). A low frequency of IgG responses specific for the PorB linear epitopes was found in convalescent-phase sera from 132 SMD patients studied, as judged from both immunoblotting studies (24/132; 18.2 %) and reactivity with peptide D63b2 (18/132; 13.6 %). Peptide D63b2 significantly inhibited IgG binding to the denatured PorB protein on immunoblots, suggesting that this B-cell epitope was one of the main linear epitopes on the PorB protein recognized by sera from some SMD patients.