Influence of serum on interaction of Porphyromonas gingivalis ATCC 33277 and Aggregatibacter actinomycetemcomitans Y4 with an epithelial cell line

Background and Objective: The purpose of this study was to investigate the influence of serum on the interaction of periodontal pathogens with epithelial cells using an epithelial cell line (KB cells). This is important because serum is a key component of gingival crevicular fluid and may influence inflammatory responses in epithelial cells exposed to periodontal pathogens. Material and Methods: Porphyromonas gingivalis ATCC 33277 and Aggregatibacter actinomycetemcomitans Y4 were co-cultured with KB cells either with or without the addition of up to 10% human serum or 50 mg/mL human serum albumin. The numbers of free-floating, adherent and intracellular bacteria were determined up to 18 h after exposure of the epithelial cells to the pathogens. Additionally, the concentrations of interleukin (IL)-6 and IL-8 produced by the epithelial cells in response to exposure to the bacteria were determined. Results: Serum and human serum albumin reduced the number of internalized A. actinomycetemcomitans Y4 organisms in the epithelial cells, increased the levels of IL-6 and IL-8 in the supernatants of infected cells (those with internalized A. actinomycetemcomitans) and influenced non-infected epithelial cells. Increased IL-6 and IL-8 concentrations were also detected in the supernatants of KB cells infected with P. gingivalis ATCC 33277. Interleukin-6 and IL-8 were detectable after addition of serum, probably as a result of inhibition of the activity of P. gingivalis cysteine proteinases by serum. Conclusion: Serum promotes the release of the cytokines IL-6 and IL-8 by epithelial cells. This mechanism is influenced by periodontal pathogens and may maintain clinical periodontal inflammation.