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In 1983, a gonococcal pilus vaccine failed to show protection in a large, placebo-controlled, double-blind field trial. The epitopic response to this vaccine was investigated in a random subgroup of 20 vaccine recipients. Using Western blot analysis of the immunizing pilus and its cyanogen bromide (CNBr) fragments, IgG antibody to pilin was detected before immunization in all individuals. Preexistent antibody to the CNBr-2 and CNBr-3 fragments of pilin was detected in 65% and 5% of individuals, respectively. Pilus immunization resulted in a vigorous response to the CNBr-2 fragment in 100% of the individuals tested; only 33% developed antibody to the CNBr-3 fragment. Absorptions of postimmunization sera with different gonococcal strains resulted in either complete or partial removal of antibody to the CNBr-2 fragment. In the context of an unsuccessful vaccine trial, these results suggest that antibody to the CNBr-2 fragment of pilin may not be protective.

Local genital antibodies to the infecting strains of Neisseria gonorrhoeae were demonstrated by indirect immunofluorescence (binding antibody) and by their ability to inhibit the attachment of gonococci to epithelial cells (functional antibody). Both IgG and IgA classes of immunoglobulin were involved, and the IgA component were primarily of a secreting (11S) nature. The ability of local genital antibody to inhibit attachment appears to persist for at least a short period of time and to be relatively strain specific.

Antibodies in genital secretions of patients with gonorrhea have been shown to inhibit the attachment of gonococci to epithelial cells. The gonococcal antigens for which these antibodies are specific were studied by adsorption of the genital secretions from a patient infected with gonorrhea with purified lipopolysaccharide, outer membrane complex, or purified pili of homologous Neisseria gonorrhoeae and measurement of the reduction of inhibition of attachment of the gonococci to epithelial cells. The removal of antibodies was documented with the use of a solid-phase radioimmunoassay in which the amount of antibody in the adsorbed secretions that bound to a specific gonococcal antigen was shown to be reduced as compared with the amount of antibody in unadsorbed secretions. The antibody in the secretions that inhibited attachment was removed primarily by adsorption with the homologous pili, not with homologous lipopolysaccharide. A preparation of the homologous outer membrane complex that contained pili, cell-wall proteins, and lipopolysaccharide also blocked the inhibitory antibody.

A parenteral gonococcal pilus vaccine which has previously been shown to be safe and antigenic also results in the production of specific local genital antibody. All three major antibody classes were present in the local secretions, but immunoglobulin A predominated, a portion of which is dimeric 11S immunoglobulin A. This mucosal antibody is also capable of blocking the attachment of gonococci to epithelial cells. The antibody cross-reacted with five heterologous pili in a solid-phase radioimmunoassay. These results are encouraging and suggest that a gonococcal pilus vaccine may be efficacious in preventing gonorrhea.

The bactericidal activity of human sera for Neisseria gonorhoeae was studied. Sera were obtained from a group of patients with gonococcal infections who had acute urethritis, acute pelvic inflammatory disease, disseminated gonococcal infection, or who were asymptomatic carriers. The homologous and heterologous strains were tested with these sera. The development of serum bactericidal antibodies was not a universal event. With few exceptions, the susceptibility of a particular strain to human antibody and complement appeared to be largely independent of the particular person from whom the serum was obtained and was due instead to antigenic properties intrinsic to each individual strain. Lipopolysaccharide appeared to be the predominant antigen against which bactericidal antibodies were directed. The principal bactericidal antibody class was IgM. Blocking antibodies were not found to account for the lack of lytic activity. A correlation of bactericidal antibodies with protection from developing gonococcal infection could not be demonstrated in three pateints.

A latex agglutination test employing serogroup-specific meningococcal polysaccharides as the antigen has been developed. The test has been used to measure serological responses in patients with meningococcal disease, in meningococcal carriers, and in volunteers who received meningococcal vaccines. It has been shown to be a sensitive and highly specific test for the detection of group-specific meningococcal antibody. The advantages of standardized particles and antigens which are simple to prepare and stable make this assay feasible for many nonspecialized or small laboratories.