Immune-enhanced Phagocytosis of Neisseria gonorrhoeae by Macrophages: Characterization of the Major Antigens to which Opsonins are Directed

Abstract

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.

Role of anti-pilus antibodies in host defense against gonococcal infection studied with monoclonal anti-pilus antibodies

“…Nevertheless, opsonic antibody may be produced during gonococcal infection (1) or by immunization of rabbits with gonococci (19,27). Moreover, pili are the most effective antigen at adsorbing the opsonic activity of homologous antiserum, and antiserum raised against purified pili is opsonic, indicating the importance of anti-pilus antibodies for opsonization (19). Our studies with monoclonal antibodies confirm this role.…”

“…of individual host defense systems provide a preliminary screen for functional activity, although some caution must be exercised in directly extrapolating from such studies to immunity in natural infection. Previous studies have reported a potential protective effect of polyclonal anti-pilus antibodies in both opsonization and complement-mediated bactericidal killing (19,27,44). One possible complicating factor of such studies is the presence in polyclonal sera of low levels of more effective antibodies directed against other components present in pilus preparations.…”

“…The mechanism by which piliated organisms resist phagocytosis is not known, but several factors have been suggested, including a decrease in phagocyte membrane fluidity caused by pili, interference by pili in the interaction between opsonic ligands and PMN receptors, and the inability of PMNs to form a phagocytic vacuole on interaction with piliated gonococci (6). Nevertheless, opsonic antibody may be produced during gonococcal infection (1) or by immunization of rabbits with gonococci (19,27). Moreover, pili are the most effective antigen at adsorbing the opsonic activity of homologous antiserum, and antiserum raised against purified pili is opsonic, indicating the importance of anti-pilus antibodies for opsonization (19).…”

“…Pili therefore appear to be attractive candidates for a gonococcal vaccine, since antipilus antibodies would be expected to prevent colonization and promote killing by host defenses. Pili exhibit considerable interstrain antigenic heterogeneity (4), however, and several in vitro studies have shown a biological effect only with antibody directed against the homologous strain (19,39,41).…”

Structure and function of pili of pathogenic Neisseria species

“…Anti-pilus antisera reduce the adhesion of both piliated gonococci (60) and purified pili (35) to human buccal epithelial cells. Antibodies to pili opsonize pili for phagocytosis by PMN (36) and macrophages (19) and protect tissue culture cells from the cytotoxic effect of challenge with gonococci (67). Anti-pilus monoclonal antibodies also inhibit adhesion, opsonize, and protect against infection (70,71), and immunization with pili can also protect guinea pigs against infection following gonococcal challenge of subcutaneously implanted plastic chambers (24).…”