Neisseria gonorrhoeae were cultured from the urethra of male patients and from the cervix and urethra of female contacts. Isolates from a given group of individuals were of the same strain but differed considerably in terms of the molecular weight of both protein II and pili. Radioimmunoprecipitation assays showed that most patients produced serum antibodies to protein I. Antibodies to pili, when present, showed limited cross-reactivity with the different pili produced by a single strain. Antibodies to protein II were highly specific, reacting with only one of the protein II-types produced by a single strain; this observation suggested that the host immune response may be an important factor in antigenic variation. Several sera also contained antibodies to a common surface protein with a molecular weight of 43,000 that was present in all strains tested.
This paper describes the determination of limits of detection (LODs) of interactions between an antigen, human chorionic gonadotrophin (hCG), and antibodies, anti-alpha-hCG and anti-beta-hCG, using a sandwich assay by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). Randomly biotinylated antibodies were adsorbed onto a structured self-assembled monolayer (SAM)-streptavidin matrix, tethered to gold via a SAM consisting of biotinylated thiol molecules interspersed with hydroxyalkanethiol molecules. The influence of the concentration of biotinylated thiol on the binding of biotinylated antibody and its functionality, in terms of its ability to bind to the hCG antigen, was studied. This allowed determination of the optimum biotin-thiol mole fraction in the mixed thiol solution and consequently in the SAM, to maximize binding of hCG of the streptavidin-bound antibody. SPFS studies of the binding of a secondary fluorescently labeled antibody to hCG immobilized on the optimized SAM-streptavidin-antibody layer showed that a LOD of hCG of 2 mIU mL(-1) (4 x 10(-12) mol L(-1)) could be realized. The system was further optimized by using a more oriented and organized surface by adsorbing monobiotinylated Fab-hCG in place of the whole antibody. A LOD of 0.3 mIU mL(-1) (6 x 10(-13) mol L(-1)) was achieved for this system. This work illustrates the importance of antibody orientation, both on the planar surface and in terms of position of binding site, in maximizing sensor sensitivity.
Several monoclonal antibodies directed against gonococcal outer membrane protein IB have been used in in vitro assays to investigate their potential efficacy in protection against gonococcal infection. In a cytotoxicity assay, virulence of the variant P9-17 for epithelial cells in tissue culture was reduced in the presence of three of the four antibodies which recognized type-specific epitopes. Similarly, virulence of P9-17 as well as a recent isolate was reduced in the presence of the one antibody, SM24, which reacted with a conserved epitope. This antibody was also bactericidal in the presence of complement, and in addition was opsonic for several protein IB-expressing strains as determined by polymorphonuclear leucocyte chemiluminescence measurements. Similarly, all the type-specific antibodies were opsonic for P9 variants. However, only two of these antibodies mediated complement-dependent killing although those which were ineffective were nevertheless complement-fixing antibodies. These results indicate that antibodies to closely positioned epitopes on protein I vary in their biological activities and that the conserved epitope recognized by the antibody SM24 is potentially an effective target on the gonococcal surface for immunoprophylaxis.
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