Effects of Bacterial Endotoxin on the Fibrinolytic Activity of Normal Human Leukocytes

Two modifications of Todd’s histochemical fibrin slide technique were used to study the effect of bacterial endotoxin on the plasminogen activator activity of intact normal human leukocytes in vitro. Leukocyte suspensions were obtained from heparinized peripheral blood by dextran sedimentation. Plasminogen activator activity was measured as the percentage of individual cells producing zones of fibrinolysis in plasminogen-rich fibrin. Of the cells from normal individuals, 27 ± 2 per cent were fibrinolytically active. The addition of lipopolysaccharide B from Salmonella abortus equi resulted in a marked increase in the percentage of active cells without impairment of cell viability. The stimulation of plasminogen activator release appeared to be dose-related, since at higher endotoxin concentrations the number of active cells gradually approached the granulocyte level. Maximum effect on leukocytes was observed 2 hours after addition of endotoxin, followed by a steady decline in activity. Plasminogen activator activity in the suspending medium became detectable after 2 hours’ incubation. Simultaneous assays of beta-glucuronidase revealed increasing amounts of this lysosomal enzyme in the suspending medium during incubation. Addition of endotoxin enhanced the rate of this increase. The parallel appearance of plasminogen activator and beta-glucuronidase activities without concomitant cell destruction from unstimulated and endotoxin-treated leukocytes is consistent with the release of both compounds from lysosomes following noncytocidal stimulation.