Natural killer (NK) cell activity against human gingival fibroblasts exposed to dental plaque extracts

Natural killer (NK) cell activity against plaque pretreated human gingival fibroblasts and against the erythroblastoid cell line K562 also pretreated with plaque extract was studied. Supra- and subgingival plaque was collected and extracts prepared by sonication for 10 to 15 minutes at room temperature. The erythroblastoid cell line K562 was given in RPMI (1640) medium, and served as the control. Gingival fibroblasts were grown from an explant of human gingiva. The K562 cells and gingival fibroblasts were incubated in subcytotoxic doses of both supra- and subgingival plaque for 18 hours prior to the NK cell assay in serum free medium. Pretreatment of the K562 cells with both supra- and subgingival plaque was found to reduce NK cell activity. On the other hand pretreatment of the human gingival fibroblasts with plaque extracts seemed to increase their sensitivity to NK cell activity. This suggests that the plaque pretreatment leads to a cytopathic change in the fibroblasts making them more sensitive to NK cell activity, or alternatively that by binding to target cells, plaque modulates the ability of NK cells to bind to, and kill these cells. Nevertheless, these results indicate that NK cell activity could play a role in tissue destruction in chronic inflammatory periodontal disease.