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Plasmin generation induces neutrophil aggregation: dependence on the catalytic and lysine binding sites
1Department of Physiology and Cell Biology, Albany Medical College of Union University, NY 12208.
Abstract:
We established that plasmin (10(-10) M to 10(-6) M) caused neutrophils (PMN) to aggregate using an in vitro assay. Plasminogen had no PMN aggregatory activity even at a concentration of 2 microM. However, plasminogen caused PMN to aggregate when incubated with plasminogen activators [tissue plasminogen activator (25-200 U/ml) or urokinase (5-500 U/ml)]. Tissue plasminogen activator and urokinase alone had no PMN aggregatory activity. Analysis of these incubation mixtures indicated that plasmin was generated in the process and that the time course of plasmin generation correlated with the aggregation response. Active-site-inhibited plasmin did not induce PMN aggregation, indicating that a functional catalytic site was required for the response. Pretreatment of PMN with either active-site-inhibited plasmin or tranexamic acid prevented PMN aggregation by plasmin, indicating that both binding of plasmin to the cell surface via the lysine binding sites and catalysis were required for the response. The generation of plasmin during activation of fibrinolysis may play a pro-inflammatory role by mediating aggregation of PMN.
Insights
Plasmin, not plasminogen, aggregates neutrophils (PMN). This process requires plasmin
Area of Science:
- Biochemistry
- Immunology
- Hematology
Background:
- Neutrophil (PMN) aggregation is a key inflammatory response.
- Fibrinolysis, the breakdown of blood clots, involves plasminogen and plasmin.
- The role of plasmin in neutrophil aggregation is not fully understood.
Purpose of the Study:
- To investigate the role of plasmin and plasminogen in neutrophil aggregation.
- To determine the mechanisms by which plasmin induces neutrophil aggregation.
Main Methods:
- In vitro neutrophil aggregation assays.
- Incubation of neutrophils with plasmin, plasminogen, and plasminogen activators (tissue plasminogen activator, urokinase).
- Use of active-site-inhibited plasmin and tranexamic acid to probe mechanisms.
Main Results:
- Plasmin directly induced neutrophil aggregation in a dose-dependent manner.
- Plasminogen alone did not cause aggregation, but did so when activated to plasmin.
- Neutrophil aggregation required both plasmin's catalytic activity and its binding to cell surface lysine residues.
Conclusions:
- Plasmin, generated during fibrinolysis, can directly mediate neutrophil aggregation.
- This plasmin-induced neutrophil aggregation represents a pro-inflammatory mechanism.
- Targeting plasmin-neutrophil interactions may offer therapeutic strategies for inflammatory conditions.