The class 3 OMP, a porin of Neisseria meningitidis, and the PI porin protein of N. gonorrhoeae have eight predicted surface exposed loops. The gene encoding this protein is different between different serotypes in regions corresponding to several of these loops. Protective antibodies to these porins appear to be raised to conformational not linear epitopes. In order to determine epitopes which induce protective antibodies, we have constructed synthetic cyclic peptides with lipid tails inserted into liposomes in an effort to mimic suspected conformational epitopes corresponding to surface exposed loops. Immunization of mice with peptide loops corresponding to loop 1 of serotypes 4 and 15 of N. meningitidis and to loops 1 and 5 of strain MS 11 N. gonorrhoeae have been completed. Chacterization of the immune responses using ELISA, Western Blot, and bactericidal assays indicate that a strong antibody response to the peptide is seen in some mice. The VR1-4 low dose lipid A preparation stimulated high titer anti-peptide antibodies measured by ELISA, variable region specific antibodies by Western, and in 3 of 7 mice, functional antibodies shown by compliment mediated killing in the serum bactericidal assay. The VR1-15 peptide stimulated high titer antibodies which were not serotype specific suggesting they were directed against the side regions of loop 1. These antibodies, even when found to bind to the native trimeric protein, were not bactericidal. Antibody to the gonococcal MS 11 loop 1 peptide binds only to PI protein from strains with an identical loop 1 sequence suggesting that the antibodies are directed against the tip of the loop where the variable region is located. Anti-gonococcal peptide sera are being evaluated in bactericidal and whole cell binding assays. This project is supported by an FDA Office of Women's Health Grant.
