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Updated: Jul 20, 2026
Mesenchymal Stem Cell Regulation of Macrophage Phagocytosis; Quantitation and Imaging
Published on: July 16, 2021
Platelet binding and phagocytosis by macrophages
Bahram A Badlou1, Ya Ping Wu, W Martin Smid
1Thrombosis and Hemostasis Laboratory, Department of Hematology, University Medical Center Utrecht, the Netherlands.
Background:
Earlier it was reported that metabolic arrest followed by incubation at 4 degrees C reduces the platelet (PLT) storage defect. Here it is reported that this treatment also reduces binding and phagocytosis by macrophages.
Study Design And Methods:
Phagocytosis of mepacrine-labeled PLTs by macrophages changes the latter into bright fluorescent particles easily detected by fluorescence-activated cell sorting.
Results:
In combination with conventional binding analysis it was found that binding to phorbol 12-myristate 13-acetate-matured THP-1 cells is primarily regulated by PLT P-selectin expression and phagocytosis by combined phosphatidylserine (PS) exposure and glycoprotein (GP) Ibalpha clustering. It was found that trapping of PLT Ca2+ and raising cAMP reduces phagocytosis by lowering PS exposure. Chilling of PLTs leads to an increase in binding and PS- and GPIbalpha-mediated phagocytosis. Prior depletion of PLT energy stores prevents this increase by preserving low Ca2+ concentration, PS exposure, and PS-mediated phagocytosis.
Conclusion:
These data characterize the individual factors that control PLT binding and phagocytosis and might help to define conditions that improve the survival of stored PLTs after transfusion.
Insights
Metabolic arrest and chilling reduce platelet storage defects by decreasing macrophage binding and phagocytosis. This improves platelet survival after transfusion by controlling key cellular interactions.
Area of Science:
- Hematology
- Immunology
- Cell Biology
Background:
- Platelet (PLT) storage defects are a significant issue in transfusion medicine.
- Metabolic arrest and cold incubation (4°C) have been previously shown to reduce PLT storage defects.
- This study investigates the effect of this treatment on PLT interaction with macrophages.
Purpose of the Study:
- To elucidate the mechanisms by which metabolic arrest and chilling affect platelet binding and phagocytosis by macrophages.
- To identify factors regulating platelet-macrophage interactions during storage.
- To inform strategies for improving stored platelet viability.
Main Methods:
- Utilized mepacrine-labeled platelets for phagocytosis detection via fluorescence-activated cell sorting.
- Employed binding assays with phorbol 12-myristate 13-acetate-matured THP-1 cells.
- Investigated the roles of P-selectin, phosphatidylserine (PS) exposure, and glycoprotein (GP) Ibalpha clustering.
Main Results:
- Platelet binding is primarily regulated by P-selectin expression.
- Phagocytosis is mediated by a combination of PS exposure and GPIbalpha clustering.
- Trapping platelet Ca2+ and increasing cAMP reduced phagocytosis by decreasing PS exposure.
- Chilling increased binding and PS/GPIbalpha-mediated phagocytosis, an effect prevented by depleting PLT energy stores.
Conclusions:
- Characterized individual factors controlling platelet binding and phagocytosis.
- Identified metabolic arrest and chilling as methods to reduce macrophage-mediated clearance of stored platelets.
- Findings may guide the development of improved conditions for stored platelet transfusion survival.
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