Attachment role of gonococcal pili. Optimum conditions and quantitation of adherence of isolated pili to human cells in vitro

Abstract

Gonococcal pili facilitate attachment of virulent Neisseria gonorrhoeae to human cells. To characterize this attachment function, purified gonococcal pili isolated from 4 strains possessing antigenically distinct pili were radiolabeled with 125I and used to measure the attachment of pili to various human cells in vitro. Human buccal and cervical-vaginal mucosal epithelial cells, fallopian tube mucosa, and sperm bound pili in greater numbers per μm2 of surface area (1-10) than fetal tonsil fibroblasts, HeLa M cells, erythrocytes, or polymorphonuclear leukocytes. This cell specificity of attachment suggests a greater density of membrane pili binding sites on cells similar or identical to cells from natural sites of infection. The pili binding sites were quantitated as 1 x 104 per cervical-vaginal squamous cell. Pili of all antigenic types attached equally to a given cell type, implying that the attachment moiety of each pilus was similar. Attachment of gonococcal pili to human cells occurred quickly with saturation of presumed receptor sites within 20-60 min. Attachment was temperature dependent (37°>20°>4°C), and pH dependent (3.5 <4.5>5.5>7.5). Attachment was inhibited by antibody to pili (homologous pili Ab> heterologous Ab). The extent of possible protection against gonococcal infection due to inhibition of pili-mediated attachment might prove limited as a result of the considerable antigenic heterogeneity among pili and the observation that blockage of pili attachment is maximal only with antibody to pili of the infecting strain.