Bacterial antigens induce collagenase and prostaglandin E2 synthesis in human gingival fibroblasts through a primary effect on circulating mononuclear cells

Abstract

Our previous work suggests that one mechanism through which connective tissue breakdown might occur in periodontal diseases is the production of metalloproteinases, including collagenase, by gingival fibroblasts. In this study we investigated whether highly purified preparations of lipopolysaccharide (LPS) and lipoteichoic acid (LTA) from a number of putative periodontal pathogens could induce monolayer cultures of human gingival fibroblasts to synthesize collagenase and prostaglandin E2. Using both biochemical assays and immunocytochemical techniques, we found that cells synthesized only very small amounts of collagenase in direct response to LPS or LTA (0.1 to 20.0 micrograms/ml). At the highest dose of both antigens, prostaglandin E2 production was increased. We then studied whether LPS and LTA could signal collagenase production by interacting primarily with a different cell type. Our results show that LPS and LTA were each able to stimulate cultures of human blood mononuclear cells (greater than 95% monocytes) to release collagenase-inducing cytokines. By indirect immunocytochemistry, we found that a large proportion of human gingival fibroblasts was activated to produce collagenase by supernatants from LPS- and LTA-stimulated mononuclear cells, whereas gingival fibroblasts cultured with supernatants from unstimulated mononuclear cells were not. Furthermore, in a population of activated fibroblasts we demonstrated, using a double-labeling technique, that some cells made collagenase and the specific tissue inhibitor of metalloproteinases (TIMP) simultaneously. As yet, the collagenase-inducing signals remain poorly characterized but the interleukins-1 and tumor necrosis factors seem likely candidates.