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Figure 1: Simplified overview of the mammalian plasminogen system and its utilization by bacteria. Bacterial plasminogen receptors immobilize plasminogen on the surface, which enhances activation of plasminogen to the active serine protease, plasmin, by host plasminogen activators uPA, tPA and/or bacterial plasminogen activators like streptokinase (SK). Both tPA and uPA can be inhibited by plasminogen activator inhibitors (PAI), while plasmin activity is controlled by its major inhibitor, 2-antiplasmin, and to a lesser extent by 2-macroglobulin. Plasmin degrades fibrin clot (fibrinolysis) and various ECM components which enables bacterial migration through tissue barriers.