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Updated: Dec 1, 2025
Macrophage Differentiation and Polarization into an M2-Like Phenotype using a Human Monocyte-Like THP-1 Leukemia Cell Line
Published on: August 2, 2021
Platelet-conditioned media induces an anti-inflammatory macrophage phenotype through EP4
Sean P Heffron1,2, Ada Weinstock1, Bianca Scolaro1
1NYU Langone Health, Leon H. Charney Division of Cardiology, New York, NY, USA.
Background:
Platelets are increasingly recognized as immune cells. As such, they are commonly seen to induce and perpetuate inflammation; however, anti-inflammatory activities are increasingly attributed to them. Atherosclerosis is a chronic inflammatory condition. Similar to other inflammatory conditions, the resolution of atherosclerosis requires a shift in macrophages to an M2 phenotype, enhancing their efferocytosis and cholesterol efflux capabilities.
Objectives:
To assess the effect of platelets on macrophage phenotype.
Methods:
In several in vitro models employing murine (RAW264.7 and bone marrow-derived macrophages) and human (THP-1 and monocyte-derived macrophages) cells, we exposed macrophages to media in which non-agonized human platelets were cultured for 60 minutes (platelet-conditioned media [PCM]) and assessed the impact on macrophage phenotype and function.
Results:
Across models, we demonstrated that PCM from healthy humans induced a pro-resolving phenotype in macrophages. This was independent of signal transducer and activator of transcription 6 (STAT6), the prototypical pathway for M2 macrophage polarization. Stimulation of the EP4 receptor on macrophages by prostaglandin E2 present in PCM, is at least partially responsible for altered gene expression and associated function of the macrophages-specifically reduced peroxynitrite production, increased efferocytosis and cholesterol efflux capacity, and increased production of pro-resolving lipid mediators (ie, 15R-LXA4 ).
Conclusions:
Platelet-conditioned media induces an anti-inflammatory, pro-resolving phenotype in macrophages. Our findings suggest that therapies targeting hemostatic properties of platelets, while not influencing pro-resolving, immune-related activities, could be beneficial for the treatment of atherothrombotic disease.
Insights
Platelet-conditioned media promotes macrophage anti-inflammatory functions, enhancing efferocytosis and cholesterol efflux. This suggests potential therapies for atherothrombotic disease by targeting platelet hemostatic properties without affecting immune roles.
Area of Science:
- Immunology
- Cardiovascular Research
Background:
- Platelets, recognized as immune cells, can induce and perpetuate inflammation.
- Atherosclerosis is a chronic inflammatory condition requiring macrophage M2 polarization for resolution.
- Macrophage M2 phenotype enhances efferocytosis and cholesterol efflux.
Purpose of the Study:
- To investigate the effect of platelets on macrophage phenotype and function.
- To determine if platelet-conditioned media (PCM) influences macrophage polarization.
Main Methods:
- Macrophages (murine and human cell lines) were exposed to PCM.
- Macrophage phenotype and function were assessed in vitro.
- Key molecular pathways and mediators were analyzed.
Main Results:
- PCM induced a pro-resolving macrophage phenotype across models.
- This effect was independent of STAT6 signaling.
- Prostaglandin E2 stimulation of EP4 receptors mediated reduced peroxynitrite production, increased efferocytosis, cholesterol efflux, and pro-resolving lipid mediator production.
Conclusions:
- Platelet-conditioned media induces an anti-inflammatory, pro-resolving macrophage phenotype.
- Targeting platelet hemostatic properties may offer therapeutic benefits for atherothrombotic disease without compromising immune functions.
