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 membran e capable of inducing antibody responses in humans, are considered to be meningococcal vaccine candidates, so it is important to map the rel evant B-cell epitopes. For B-cell epitope analyses of the serotype 15 PorB protein in Neisseria meningitidis, paired sera from selected pati ents with systemic meningococcal disease (SMD) were screened with synt hetic 12mer peptides spanning the PorB protein sequence, and/or its va riable region 1 (VR1). A 'SMD-related' linear B-cell epitope was found within the VR1 region consisting of 14 residues ((17)svFHQNGQVTEvtt(3 0)). A 23mer soluble peptide (D63b2) that covered the VR1 region, incl uding the complete (17)svFHQNGQVTEvtt(30) sequence, was recognized, wh ereas no detectable binding was observed to a 16mer peptide (D63a1) co ntaining most of the essential sequence ((19)FHQNGQVTEVtt(30)). A low frequency of IgG responses specific for the PorB linear epitopes was f ound in convalescent-phase sera from 132 SMD patients studied, as judg ed from both immunoblotting studies (24/132; 18.2 %) and reactivity wi th peptide D63b2 (18/132; 13.6 %). Peptide D63b2 significantly inhibit ed IgG binding to the denatured PorB protein on immunoblots, suggestin g that this B-cell epitope was one of the main linear epitopes on the PorB protein recognized by sera from some SMD patients.