Introduction: 

Cholesterol crystals (CC) are an essential part of the necrotic core in atherosclerotic plaques and increased cholesterol blood levels are an established risk factor for development of coronary artery disease. CLEC4E is a C-type lectin pattern recognition receptor expressed by dendritic cells, macrophages, neutrophils and B-lymphocytes. In a recent study human CLEC4E was identified to bind cholesterol crystals and it is known that CLEC4E plays an essential role in murine atherosclerosis. The aim of this study was to elucidate the role of CLEC4E in human atherogenesis. 

Methods and results: 

We collected blood samples of 189 patients undergoing percutaneous coronary intervention (PCI) to study monocytic CLE4E expression and phagocytosis of CC by RT-PCR, flow cytometry and immunohistochemical staining. We found that circulating monocytes of individuals with coronary artery disease, NSTEMI and STEMI express significantly more CLEC4E than monocytes of healthy controls. Furthermore, flow cytometric experiments revealed that CLEC4E positive monocytes from fresh arterial blood samples phagocyte significantly more CC than CLEC4E negative controls and addition of CC was followed by increased monocytic CLEC4E expression. Subgroup analysis revealed that monocytes isolated from individuals with ACS showed even a stronger CLEC4E expression and increased phagocytosis of CC compared to CLEC4E positive monocytes of healthy controls, which is most likely an effect of the increased inflammatory state under ACS condition. Finally, immunohistochemical staining of human atherosclerotic plaques for CLEC4E discovered increased numbers of CLEC4E positive macrophages in human atherosclerotic plaques compared to healthy controls.

Conclusions:

In this study we were able to identify CLEC4E as a key player in phagocytosis of cholesterol crystals by human monocytes and macrophages. We could show that CLEC4E positive monocytes phagocyte more CC than CLEC4E negative controls. Beyond that, we were able to demonstrate a further increased expression of CLEC4E by circulating monocytes in ACS accompanied with an additional boost of cholesterol crystal phagocytosis. Immunohistochemical staining revealed increased numbers of CLEC4E positive macrophages in human atherosclerotic plaques indicating a crucial participation in foam cell formation. Our data indicate that CLEC4E could serve as a useful target in treatment of atherosclerosis and myocardial infarction.