Plasminogen activators and their inhibitors in human saliva and salivary gland tissue.

The purpose of this study was to identify plasminogen activators (PA) and their specific inhibitors in human cell-free saliva and to investigate their expression in salivary gland tissue. Saliva samples were obtained from 34 patients visiting a neurological out-patient department. The activities of tissue and urokinase plasminogen activators (tPA and uPA, respectively), the relative inhibition of tPA, and the amounts of plasminogen activator inhibitors 1 and 2 (PAI-1 and PAI-2, respectively) in cell-free saliva were studied. The activities of tPA and uPA, and tPA inhibition, were measured using in-house microtiter plate assays, and PAI-1 and PAI-2 levels were measured using commercial enzyme-linked immunosorbent assay (ELISA) kits. Immunohistochemistry was used to evaluate the expression of PAs and PAIs in the salivary gland. Tissue plasminogen activator activity was found in most samples, with a mean activity of 0.63 IU ml(-1). uPA was observed in only a few samples. PAI-1 was not detected, but PAI-2 was present in all samples (with a mean value of 11.1 ng ml(-1)). The mean PAI-2 level in women was 12.4 and in men was 7.6 ng ml(-1). The activity of tPA and the relative inhibition of tPA seemed to be inversely associated. Tissue plasminogen activator, PAI-1, and PAI-2 were evident in salivary gland tissue, whereas the expression of uPA was low. The tPA activity in saliva suggests an active proteolysis. Plasminogen activator inhibitor 2 was found to be the main inhibitor of PAs in saliva.