Gonococcal Pilin Variants in Experimental Gonorrhea by John Swanson,* Kenneth Robbins,* Osmar Barrera,*

Pili appear to promote the pathogenicity of gonococci (Gc)' by mediating their attachment to human hosts' mucosal surfaces (1, 2) . Although all Gc pili are assumed to have adherence-promoting properties, they exhibit structural diversity between strains and among variants of a given strain (3-8). This diversity is due to differences in the amino acid sequences of their pilus subunit (pilin) polypeptides . Such pilin sequence diversity is based on the Gc genome's one complete pilin gene and multiple partial pilin genes that participate in homologous recombination . Through nonreciprocal exchange, a partial pilin gene's sequence undergoes insertion into the complete pilin gene ; the resulting chimeric complete pilin gene expresses a novel pilin polypeptide. The Gc genome contains over a dozen distinct partial pilin genes as a basic repertoire for synthesis of differing pilin polypeptides (9, 10). The pathogenic significance of pilus variants generated by the Gc genome's elaborate intergenic recombination system is not clear . Several experimental findings are consistent with the notion that pilus variants play role(s) in the colonization of different mucosal niches by Gc in vivo ; such a role would be important mainly to the initial stages of gonorrheal infection . Pilus variation influences adherence properties of Gc; this has been demonstrated with pilus' variants of strain P9 that express different pilin polypeptides and show disparate adherence proclivities to selected eukaryotic cells, in vitro (11) . Gc that are isolated from diverse sites in an individual with gonorrhea but represent a single strain express pilin polypeptides of differing electrophoretic mobilities (12) . Pilus variation might also allow Gc to avoid the actions of a human host's antipilus antibodies while they retain an adherence-promoting pilus+ status . It is