Effects of Porphyromonas gingivalis infection on human gingival epithelial barrier function in vitro

The gingival epithelium plays an important role in the protection of oral tissues from microbial challenge. Oral keratinocytes form various cellular contacts, including tight junctions, and thus are able to create an epithelial barrier. A measurable indicator of barrier function in vitro is the transepithelial electrical resistance (TER). Porphyromonas gingivalis is recognized as a major aetiologic agent of periodontal disease and exhibits a variety of virulence factors. The aim of the study was to investigate the effect, in vitro, of infection with P. gingivalis on gingival barriers composed of primary and immortalized human keratinocytes. Primary and immortalized human gingival keratinocytes were infected with different strains of P. gingivalis. The impact of the bacterial challenge on the barrier was analysed by measuring the TER. The destructive effects of gingipains were blocked by specific enzyme inhibitors. After an initial increase of about 20-30% in infected wells, the TER decreased to zero. Gingipain inhibitors delayed the destruction of the barrier by 12 +/- 4 h. In all cases, the loss of TER was accelerated if the system was infected from the basolateral side. A distinct effect of P. gingivalis on the epithelial barrier function of three-dimensional cultured epithelial cell models was demonstrated, which can partly be attributed to the activity of gingipains.