Traversal of a Polarized Epithelium by Pathogenic Neisseriae: Facilitation by Type IV Pili and Maintenance of Epithelial Barrier Function

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Abstract
Gonococci (GC) and meningococci (MC) are gram-negative bacterial pathogens that infect human mucosal epithelia. We would like to understand the functions of specific bacterial components at each stage of mucosal colonization: adhesion, cell invasion, and traversal into subepithelial tissues. As no animal model of mucosal colonization by GC or MC is available, increasingly sophisticated in vitro approaches have been used to address these issues. We adapted the polarized T84 human epithelial cell system to study GC and MC colonization. Epithelial barrier function was monitored by permeability to soluble tracers and with electrical resistance measurements. Polarized cells were used to assay bacterial traversal of the monolayers, and cells grown on plastic were used to assay adhesion and cell invasion. All pathogenic Neisseriae examined traversed the monolayers. The traversal times were species specific and identical to times established previously in organ culture studies. In contrast to experiments with some enteric pathogens, transmigration by GC and MC was not accompanied by disruption of the epithelial barrier. GC mutants lacking type IV pili were compromised in adhesion, invasion, and traversal of T84 cells. Experiments with polarized T84 cells mimic key features of organ culture infections and reveal additional aspects of neisserial infection. Epithelial barrier function can be retained during bacterial traversal. Experiments with a nonpiliated GC mutant and its wild-type parent indicated an unexpected role for pili in cell invasion. Our results are consistent with the hypothesis that bacterial adhesion, invasion, or both are rate-limiting for traversal across the epithelium.