The plasminogen activating system in periodontal health and disease.

The plasminogen activating system is important for extracellular proteolysis and plays a regulatory role in interactions with other tissue degrading systems. Studies on the plasminogen activating system in gingival crevicular fluid (GCF) as well as gingival tissue are reviewed. t-PA, u-PA, PAI-1 and PAI-2 have all been detected in GCF. Especially t-PA and PAI-2 are found in high concentrations. In tissue studies fibrinolytic activity has been found in the gingival pocket epithelium in humans and in animal studies. t-PA and PAI-2 have been detected there immunohistochemically. Local production of the PAs and PAls has been verified with in situ hybridization. In inflammation, a more intense and widespread immunohistochemical staining of t-PA and PAI-2 is seen. Higher concentrations of t-PA and PAI-2 are found in GCF but the balance between them seems to be constant. A systemically disturbed balance of the plasminogen activating system in GCF has been observed during pregnancy, with a possible protective function of PAI-2. In studies of periodontitis, the production of PAI-2 seemed to be locally lowered at impaired sites. In a study of children, a higher inflammatory response to bacterial plaque was accompanied by a higher fibrinolytic ativity in GCF samples. Bacterial LPS has been found to change the ratio of t-PA to PAI-2 in cultured gingival fibroblasts. Interactions between PAI-2 and a protease in the gingival epithelium has been verified through the immunohistochemical detection of relaxed PAI-2.