Porphyromonas gingivalis stimulates interleukin-8 secretion in human oral epithelial cells

Objectives: Infection of epithelial cells with Porphyromonas gingivalis (Pg) results in production of pro-inflammatory cytokines that are involved in the initiation and progression of periodontal disease. The pro-inflammatory cytokine interleukin-8 (IL-8) is a potent chemoattractant inducing the influx of neutrophils into periodontal lesions. IL-8 is the primary focus of this project, since conflicting results have been reported on Pg-induced stimulation of IL-8 in human epithelial cells. Methods: Two Pg strains, avirulent 2561 and highly virulent W83, were sub-cultivated on blood agar plates and suspended in Medium 199. HSC-3 and H413 cells, derived from oral squamous cell carcinoma (OSCC), and non-tumor-derived immortalized oral epithelial GMSM-K cells were challenged with live Pg at 107bacteria/well, and incubated at 37°C for 6 and 24 h. IL-8 was determined by ELISA. Results: Control non-infected HSC-3, H413 and GMSM-K cells produced 920, 2624 and 11 pg IL-8/ml, respectively within 6 h, and 2687, 6564, and 22 pg IL-8/ml, within 24 h. Exposure of HSC-3 to Pg-2561 and Pg-W83 resulted in a 6- and 3-fold increase in IL-8 secretion, respectively. Incubation of GMSM-K cells with these strains increased IL-8 by 21- and 12-fold. In H413 cells, Pg-2561 down-regulated IL-8 by 25%, while Pg-W83 did not modify IL-8. Conclusions: The amount of IL-8 secreted by control cells and their response to Pg were strongly dependent on the cell type. GMSM-K cells secreted significantly less IL-8 than OSCC cells. Both Pg strains induced IL-8 secretion in HSC-3 and GMSM-K cells. Degradation of IL-8 by Pg gingipains may be responsible for the down-regulation of IL-8 observed with H413 cells. The etiology of different epithelial cell responses to Pg is not well known. Supported by Research Pilot Project Award 03-Activity 074 from the University of the Pacific, School of Dentistry (S. Kim)