Immunological and serological diversity of Neisseria gonorrhoeae: gonococcal serotypes and their relationship with immunotypes

Characterization of Neisseria gonorrhoeae reference strains used in development of serologic classification systems

Certain strains of Neisseria gonorrhoeae have been used by numerous investigators to develop serologic classification systems. Some of these strains have been used by investigators to study gonococcal virulence. A reference consisting of strain classification by auxotype and serovar, a strain history, and a selected bibliography are provided cohesively.

Panel of reference strains for evaluating serologic reagents used to identify gonococci

A panel of strains for evaluating Neisseria gonorrhoeae serologic reagents was developed. The strains selected for the panel were antigenically diverse and representative of strains isolated worldwide and had been isolated from a variety of anatomic sites. A few strains with characteristics that can cause problems in serologic tests were included. The panel of 52 gonococcal and 20 nongonococcal strains was used to evaluate two commercially produced kits with monoclonal antibody reagents, GonoGen and Phadebact, and one Phadebact kit with absorbed rabbit antiserum. The GonoGen reagent correctly identified all gonococcal strains and did not react with any of the nongonococcal strains. The Phadebact absorbed antiserum reagent correctly identified 47 of 48 gonococcal strains but reacted with 2 of the 20 nongonococcal strains. The Phadebact monoclonal antibody reagent correctly identified all the gonococcal strains; however, it gave positive reactions with 8 and trace reactions with 4 of the 20 nongonococcal strains.

Characterization of the immune response in subcutaneous chambers of guinea pigs immunized with a ribosomal preparation from Neisseria gonorrhoeae

Immunization of guinea pigs with ribosomal preparations has been previously shown to be protective against chamber infection with Neisseria gonorrhoeae, and this protection could be correlated with the presence of serum bactericidal antibody. Analysis of the chamber fluids from ribosome-immunized and nonimmunized guinea pigs has demonstrated that the chamber fluid may accurately reflect serum antibody levels and proteins. At least one major population of antiribosomal antibodies is present in both immune serum and chamber fluid as revealed by lines of identity between these components. Antibody- and complement-mediated bactericidal assays revealed that matched chamber fluids and sera from immune animals had comparable bactericidal titers. These results suggest that the antibody-complement-mediated bactericidal activity plays a major role in the protection against N. gonorrhoeae infection. Protection could not be explained on the basis of the cellular components of the inflammatory response since both immune and nonimmune chambers had comparable increases in polymorphonuclear neutrophils, monocytes, and lymphocytes after challenge.

Role of outer envelope contamination in protection elicited by ribosomal preparations against Neisseria gonorrhoeae infection

A recent report (Cooper et al., Infect. Immun. 28:92-100, 1980) demonstrated that immunization of guinea pigs with ribosomal preparations was protective (approximately 90%) against chamber infections with Neisseria gonorrhoeae. Similar protection has been demonstrated with other cellular immunogens such as outer membranes (OM) (92%) or purified lipopolysaccharide (LPS) (83%). Protection of LPS (5 to 100 micrograms) was dose dependent (83% with 100 micrograms). Treatment of LPS with pronase reduced the protection by 50%. Ribosomal preparations contained LPS contamination (3.9%) based on dry weight determinations by 2-keto-3-deoxyoctonate analysis. Analysis of ribosomal preparations isolated from cells after lactoperoxidase-mediated 125I labeling indicated a major OM contamination (Protein I). The ribosomal preparation also contained low levels of succinic and lactic dehydrogenase. Passive hemagglutination tests revealed that sera from guinea pigs immunized with ribosomal preparations also demonstrated antibody to OM proteins and LPS. LPS was able to absorb one line of precipitation seen in immunodiffusion reactions as well as the bactericidal activity of such sera. OM preparations were unable to absorb the remaining precipitin line or remove the bactericidal activity. It appears that LPS is the major antigen responsible for the bactericidal activity seen in ribosome-immune sera.

Immunological and serological diversity of Neisseria gonorrhoeae: identification of new immunotypes and highly protective strains

Gonococci, irrespective of serotype or immunotype, varied significantly in their capacity to induce immunity in animal models, and in vitro serological relatedness did not always insure in vivo cross-protection. By using a serum bactericidal assay followed by in vivo cross-protection studies, new immunotypic strains which were highly protective were identified from cultures isolated in different geographical areas and from patients with various clinical manifestations. Beta-lactamase production and gonococcal immunotype did not appear as related characteristics in that certain penicillin-sensitive strains were highly effective in immunizing animals against infection with beta-lactamase producers. The findings of this study emphasize the importance of using appropriate biological tests and strains for the investigation of gonococcal immunity and vaccine development. Immunization with a combination of a few major gonococcal immunotypic immunogens may provide substantial protection against the majority of penicillin-sensitive and beta-lactamase-producing gonococci. Investigation of isolated immunotypic immunogens is in progress.

Comparison of antigenic heterogeneity of Neisseria gonorrhoeae strains by micro-immunofluorescence and serum bactericidal tests

The antigenic heterogeneity of Neisseria gonorrhoeae strains was assessed by the micro-immunofluorescence (micro-IF) and the serum bactericidal tests. The micro-IF test verified the antigenic heterogeneity of nine strains received from the Center for Disease Control and placed them into immunotypes A and B. The serum bactericidal system also detected different antigenic determinants among the strains. Although the micro-IF and bactericidal assays did not correspond in each instance, the overall pattern of similarities and differences among these gonococcal strains was similar. The micro-IF pattern obtained with mouse antisera was identical to the pattern revealed with guinea pig antisera. Different colony type organisms showed similar sensitivity in the bactericidal test. The micro-IF test is a rapid technique for the immunotyping of N. gonorrhoeae and has the additional advantages of reproducibility and simplicity.

Effects of iron and culture filtrates on killing of Neisseria gonorrhoeae by normal human serum

Neisseria gonorrhoeae GC9, both colony types T2 and T4, were killed by normal human serum, although populations of colony type T4 were more susceptible. Ferric ammonium citrate prevented the killing of populations of both T2 and T4 colony types. Other iron compounds tested showed no protective effect, nor did ammonium citrate or the divalent cations magnesium or calcium. A filtrate from cultures of an N. gonorrhoeae strain grown in a liquid defined medium showed a similar protective effect in the serum assay. The filtrate appeared to chelate iron, as measured by decreased ability of iron-free transferin to bind iron in the presence of the filtrate. However, the two effects did not appear to be related. Neither ferric ammonium citrate nor the culture filtrate sufficiently inactivated complement to account for protection.

Strain related infectivity of Neisseria gonorrhoeae for the guinea-pig subcutaneous chamber and the variability of the immune resistance in different breeds of guinea-pig

The ability of gonococci to infect the subcutaneous chamber in guinea-pigs is strictly strain related. This ability was usually present in prototrophic strains and auxotrophs requiring proline only which were obtained from patients with uncomplicated gonorrhoea, but it was invariably absent in Neisseria gonorrhoeae auxotypes requiring arginine, uracil, and hypoxanthine, or arginine only for growth. All the strains obtained from disseminated gonococcal infections (all dependent upon arginine, uracil, and hypoxanthine) were unable to infect the guinea-pig chamber. Hence, the high invasiveness of N. gonorrhoeae for man and its infectivity for guinea-pig chambers appear to be unrelated properties. Although guinea-pigs of the same origin (Dunkin-Hartley) were used throughout, the degree of immune resistance was found to differ between the lines supplied by various breeders--that is, after a standard immunisation schedule using whole cell gonococcal vaccines, the homologous immune resistance to challenge varied from weak or non-existent in some lines, to highly resistant in others.

Comparative physical and immunological aspects of the chimpanzee and guinea-pig subcutaneous chamber models of Neisseria gonorrhoeae infection

Physical and immunological characteristics of the chimpanzee and guinea-pig subcutaneous chamber models for Neisseria gonorrhoeae infection were compared to evaluate their usefulness for gonococcal research. Urethral infection in chimpanzees anatomically resembled the human infection; however, individual variation in response, limited availability, and the presence of interfering micro-organisms in the urethra were found to limit the usefulness of the chimpanzee in immunological research. Although the guinea-pig subcutaneous chamber model may not be suitable for studying the attachment of gonococci to host cells or for the local production of IgA, it does have the immunological advantages of being more sensitive to infection, less variable in response, free of interfering micro-organisms, and is readily available to investigators. Except for differences in sensitivity and variability, results with the guinea-pig model paralleled results obtained in experiments with chimpanzees. Unlike chimpanzees, guinea-pigs are a comparatively inexpensive, rapidly replenishable animal, which after subcutaneous implantation with small porous chambers provide a convenient model for studying most immunological aspects of gonococcal infections.