Antigenic heterogeneity associated with pilus aggregation and autoagglutinability in Neisseria gonorrhoeae

A type-specific antigen of Neisseria gonorrhoeae was previously demonstrated by two-dimensional immunoelectrophoresis, and was produced by strains adapted to growth in subcutaneous chambers in guinea pigs. This antigen was also present in 'smooth' (non-autoagglutinating) variants selected directly from the first agar cultures of three clinical isolates, without chamber passage. The type-specificity of this antigen paralleled the reactions of pili in immune electron microscopy, suggesting that the type-specific antigens were pili. However, 'rough' (autoagglutinating) variants lacking this type-specific antigen were nevertheless pilated. Examination of one strain by immune electron microscopy showed that the pili of the rough variant differed antigenically from those of the smooth variant. Pili on the rough variant tended to form extensive parallel aggregates, whereas pili on the smooth variant radiated individually from the gonococci. This physical difference might relate to the behaviour of the gonococci in suspension. The significance of pilus variation in immunity to gonococcal infection is discussed.