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Plasminogen activator and thromboplastin activity from sheep alveolar macrophages
Abstract:
Alveolar lavage cells from normal sheep were found to be composed of over 95% macrophages. When the cells were cultured, fibrinolytic and thromboplastin-like activities could be detected within 2-4 hours of incubation. As the number of cultured cells was increased the two activities in the conditioned medium increased proportionately. The cells were separated into two distinct subpopulations by means of a sedimentation velocity cell fractionation technique. The macrophage subpopulations were examined for differences in size, morphology, esterase staining and ability to release plasminogen activator and procoagulant activity respectively. These activities were confined to the large cell subpopulation. The fibrinolytic activity was shown to be plasminogen-dependent and could be inhibited by DFP. On the basis of this the fibrinolytic activity has been designated as plasminogen activator. The procoagulant activity was shown to be thromboplastin in nature because it was Factor VII dependent, inactivated by phospholipase C and not inhibited by DFP. The procoagulant activity has been designated as macrophage thromboplastin. The two activities could be distinguished on the basis of DFP inhibition.
Insights
Sheep lung macrophages release plasminogen activator and macrophage thromboplastin. These activities, crucial for fibrinolysis and coagulation, are primarily found in larger macrophage subpopulations.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Alveolar lavage cells in sheep are predominantly macrophages (>95%).
- Cultured macrophages exhibit fibrinolytic and thromboplastin-like activities.
- These activities increase proportionally with cell number.
Purpose of the Study:
- To investigate the specific cell subpopulations responsible for fibrinolytic and procoagulant activities.
- To characterize the nature of these released activities.
Main Methods:
- Sedimentation velocity cell fractionation to separate macrophage subpopulations.
- Assays for plasminogen activator and procoagulant activity.
- Characterization using DFP inhibition, Factor VII dependence, and phospholipase C inactivation.
Main Results:
- Two distinct macrophage subpopulations were identified.
- Fibrinolytic activity (plasminogen activator) and procoagulant activity (macrophage thromboplastin) were confined to the larger subpopulation.
- Plasminogen activator was DFP-sensitive, while macrophage thromboplastin was DFP-resistant, Factor VII dependent, and inactivated by phospholipase C.
Conclusions:
- Sheep lung macrophages, particularly a larger subpopulation, produce and release plasminogen activator and macrophage thromboplastin.
- These activities play distinct roles in fibrinolysis and coagulation.
- DFP inhibition effectively distinguishes between plasminogen activator and macrophage thromboplastin.