EXPRESSION OF MENINGOCOCCAL EPITOPES IN LAMB OF ESCHERICHIA-COLI AND THE STIMULATION OF SEROSUBTYPE-SPECIFIC ANTIBODY-RESPONSES

The class 1 outer membrane protein (OMP), a major variable surface ant igen of Neisseria meningitidis, is a component of novel meningococcal vaccines currently in field trials. Serological variants of the protei n are also used to serosubtype meningococci. Most of the amino acid ch anges that give rise to antigenic variants of the protein occur in two variable regions (VR1 and VR2) that are thought to form loops on the cell surface. The polymerase chain reaction (PCR) was used to amplify the nucleotide sequences encoding VR1 and VR2 from the chromosomal DNA of N. meningitidis strain M1080. These were cloned in frame into the lamB gene of the Escherichia coli expression vector pAJC264. Whole-cel l enzyme-linked immunosorbent assays (ELISAs), using monoclonal antibo dies, and SDS-PAGE confirmed that, upon induction, strains of E. coli carrying these constructs expressed hybrid LamB proteins containing th e N. meningitidis surface loops. These strains were used to immunize r abbits and the resultant polyclonal antisera reacted specifically with the class 1 OMP of reference strain M1080 (Pl.7). Immunogold labellin g of meningococcal cells and whole-cell dot-blot analyses with these a ntisera showed that the variable epitopes were exposed on the cell sur face and confirmed that this approach could be used to obtain serosubt ype-specific antisera. The binding profiles of the antisera were deter mined from their reactions with overlapping synthetic peptides and the ir reactivity compared with that of relevant serosubtype-specific mono clonal antibodies. This approach was used successfully to raise antise ra against two other class 1 OMP VR2s. A fourth antiserum raised again st a VR2, including the P1.1 epitope, was not subtype specific.