Objectives: Interleukin-6 (IL-6) is a pleiotropic cytokine that may mediate both beneficial and harmful effects in periodontal disease. IL-6 stimulates immunoglobulin secretion and plays an important role in regulating immune responses to periodontal pathogens. Since IL-6 promotes osteoclastogenesis and induces bone resorption, excessive secretion of IL-6 in response to Porphyromonas gingivalis (Pg) may play a role in inducing alveolar bone loss. Previous studies on the effect of Pg on IL-6 production by oral epithelial cells have shown inconsistent results. The objective of the study was to compare IL-6 responses of three human oral epithelial cell lines to virulent and avirulent strains of Pg.
Methods: Two Pg strains, avirulent 2561 and highly virulent W83, were sub-cultivated on blood agar plates and suspended in Medium 199 (4x108Pg/ml). Non-tumor-derived immortalized oral epithelial GMSM-K cells, and HSC-3 and H413 cells, derived from oral squamous cell carcinoma (OSCC) were exposed to live Pg at 107 bacteria/well, and incubated at 37C for 6 and 24 h. IL-6 was determined by ELISA.
Results: Control, uninfected H413 cells produced higher levels of IL-6 than HSC-3 and GMSM-K cells. Exposure of HSC-3 and GMSM-K cells to Pg-2561 and Pg-W83 for 24 h resulted in a 6- and 8-fold increase in IL-6 secretion, respectively. In H413 cells, Pg-2561 down-regulated IL-6 by 30%, while Pg-W83 up-regulated IL-6 by only 50%.
Conclusions: The amount of IL-6 secreted by uninfected cells was strongly dependent on the cell type. Both Pg strains induced IL-6 secretion at similar levels in HSC-3 and GMSM-K cells. However, H413 cells were not highly responsive to Pg. Our results indicate that conclusions on cytokine responses to Pg should not be based on studies with a single cell type.