1784 Monoclonal Antibodies to Gonococcal

The attachment of gonococci to mucosal surfaces is of primary importance in their interactions with the genito-urinary tract of the human host. This process may be, in part, mediated by pili, which are proteinaceous appendages emanating from the bacterial cell surface. Observations by Kellogg et al. (1) suggested that certain colonial morphological phenotypes are associated with virulence. Subsequently, Swanson et al. (2) demonstrated that gonococci giving rise to the colonial phenotype associated with virulence carry pili on their surface. Subsequently, piliated gonococci have been shown to agglutinate erythrocytes (3), and attach to spermatozoa (4), epithelial cells (5), and human fallopian tubes in organ culture (6, 7). Pili are filaments, 1-4 ~m in length, composed of repeating, identical subunits of the protein pilin. Pilin demonstrates a variable apparent molecular weight, depending on type, of 17,500-21,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (8). Gonococcal pilins possess a single intramolecular disulfide bond and two methionine residues, which allows for cleavage by cyanogen bromide into three peptide fragments (CB-1, 2, and 3) (9). The CB-2 fragment (residues 8-92 in strain MS11 pilin) possesses the erythrocyte-binding domain, as evidenced by its ability to compete with intact pili in a hemagglutination assay. Peptide mapping of CB-2 fragments from serologically distinct pilin (strains MS11 and R10) demonstrates homology in this area of the protein (9). The complete amino acid sequence of MS 11 pilin has been obtained, as well as the first 59 amino acids of R10 pilin (10). Comparison of these sequences demonstrates identity through amino acid 59, providing additional evidence that the amino-terminal half of gonococcal pilin is highly conserved. Conversely, peptide mapping of CB-3 fragments (residues 93-159 in MSl l pilin) demonstrates significant differences between pilin types, indicating that the carboxy-terminal portion of the protein contains the variable domain (9). The distinct serological heterogeneity of gonococcal pili has been demonstrated by a number of investigators (8, 11). Immunization of rabbits and mice with purified pili elicits immune responses that are strikingly type specific (8). Vaccination of humans with purified pili produced primarily type-specific anti-