The antigen-specific basis of human serum immunoglobulin G antibody response to complicated gonococcal infection was studied in 13 patients by using the Western blot technique for transfer of proteins from sodium dodecyl sulfate-polyacrylamide gels to nitrocellulose paper. Of 13 patients (8 with disseminated gonococcal infection, 4 with pelvic inflammatory disease, 1 with gonococcal epididymitis), 12 reacted with protein I antigens and 9 with lipopolysaccharide (LPS). Sera from eight patients reacted with both protein I and LPS, whereas sera from four reacted only with protein I, and one sera reacted with LPS alone. One serum with antibody to both protein I and LPS by Western blot analysis was tested for bactericidal activity before and after adsorption of antibody to LPS. Removal of antibody to LPS reduced the bactericidal titer of this serum from 1:100 to 1:50, indicating that antibody to both antigens may be bactericidal for Neisseria gonorrhoeae.
Antisera were prepared in rabbits against whole organisms of colony type 1 Neisseria gonorrhoeae strains F62 and B (from gonococcal urethritis) and 7122 (a strain typical of those associated with disseminated gonococcal infection), and against purified outer membrane components from the same strains including pili and principal outer membrane protein. Antibody levels to pilj, principal outer membrane protein and lipopolysaccharide were determined using a quantitative enzyme-linked immunosorbent assay. Each antiserum was heat-inactivated and tested for opsonic activity in a quantitative assay of phagocytosis. Each whole-organism antiserum was opsonic for its homologous strain, and this immuneenhanced phagocytosis was decreased by adsorption with homologous purified outer membrane components : pili B lipopolysaccharide P principal outer membrane protein.Opsonic activity was approximately equal for antiserum to purified pili and antiserum to the whole organisms for each of the three strains, and purified antibody to pili was highly opsonic. The F(ab'), fragments of antibody to pili were not opsonic, indicating a role for the Fc receptor on the phagocyte membrane in immune-enhanced phagocytosis of gonococci.
In a phase I clinical trial, 39 volunteers received an initial and booster subcutaneous injection of 100 or 112 microgram of a pili vaccine prepared from Neisseria gonorrhoeae strain F62 in Tris buffer with an aluminum phosphate adjuvant (alum) or 220 microgram of the F62 pili vaccine prepared in ethanolamine, with or without alum. Antibody responses were quantitated with an enzyme-linked immunosorbent assay. All four groups had significant (P less than 0.0001) responses to the vaccine preparations with peak mean antibody responses one to three weeks after the booster. Differences in antibody responses among the groups were due to the administration of alum and not to use of Tris buffer vs. ethanolamine. In vitro, postimmunization sera enhanced phagocytosis of piliated strain F62 organisms by human polymorphonuclear leukocytes; preabsorption of the sera with strain F62 pili blocked this activity. Thus, gonococcal pili given subcutaneously are immunogenic and lead to production of functional serum antibodies.
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