Gonococcal pili : properties and role in the pathogenesis of Neisseria gonorrhoeae infections

Pili, protein filaments 7 nm in diameter are found only on virulent gonococci and are thought to facilitate gonoccal attachment to the genital epithelia thus preventing the organisms from being flushed from the mucosal surface. Specific antibodies directed against pili might prevent the development of gonorrhoea, therefore. Pili were sheared from the surface of gonococci, selectively disaggregated by sucrose and purified by density gradient centrifugation. The resultant pili were pure by the criteria of analytical electrophoresis, gas-liquid chromatography, and electron microscopy. Pili from six gonococcal strains had buoyant densities of 1.30 - 1.31 g ml -I on caesium chloride. Amino acid composition of pilin from strains P9 and 201 gonococci were similar, consisting of 208 and 212 amino acids respectively with molecular weights of 22,600 and 22,352. 1-2 phosphate groups and 1-2 hexose groups were present. in the P9 pilin subunit but no amino sugars were detected. On isoelectric focusing strain P9 pili two types of pill were resolved, a minor component of PI 4.9 and a major component of PI 5.3. Antisera to pili were raised in rabbits and purified by affinity chromatography. The ability of equivalent amounts of specific IgG antibody directed against pili or against other gonococcal surface components to block gonococcal attachment and invasion in human fallopian tube organ culture or to protect the chick embryo against gonococcal infection was assessed. Pili facilitated attachment of gonococci to human fallopian tube but were not essential for invasion. Pilated gonococci were more virulent than non-pilated variants for the chick embryo. Pilus antibodies abolished the enhanced virulence of pilated gonococci for the chick embryo but failed to block gonococcal attachment and invasion of the fallopian tube. Antibodies to gonococcal outer envelope reduced attachment and invasion in the fallopian tube and were protective for the chick embryo. The implications of these and other findings are discussed.