Specific Binding of Red Blood Cells to Endothelial Cells Is Regulated by Nonadsorbing Macromolecules

Abstract

Abnormal adhesion of red blood cells to the endothelium has been linked to the pathophysiology of several diseases associated with vascular disorders. Various biochemical changes, including phosphatidylserine exposure on the outer membrane of red blood cells as well as plasma protein levels, have been identified as being likely to play a key role, but the detailed interplay between plasma factors and cellular factors remains unknown. It has been proposed that the adhesionpromoting effect of plasma proteins originates from ligand interaction, but evidence substantiating this assumption is often missing. In this work, we identified an alternative pathway by demonstrating that nonadsorbing macromolecules can also have a marked impact on the adhesion efficiency of red blood cells with enhanced phosphatidylserine exposure to endothelial cells. It is concluded that this adhesion-promoting effect originates from macromolecular depletion interaction and thereby presents an alternative mechanism by which plasma proteins could regulate cell-cell interactions. These findings should thus be of potential value for a detailed understanding of the pathophysiology of diseases associated with vascular complications and might be applicable to a wide range of cellcell interactions in plasma or plasma-like media. The adhesion of red blood cells (RBC)2 to endothelial cells (EC) is usually insignificant. However, increased RBC adhesion to endothelial cells has been observed in various clinical states such as sickle cell disease, ␤-thalassemia, and diabetes mellitus, and the degree of RBC-EC adhesiveness has been linked to the vascular complications associated with these diseases (1-5). There is now general agreement that various cell surface alterations control the increased RBC adhesiveness in such disease states. For example, an enhanced phosphatidylserine (PS) exposure on the outer leaflet of the RBC membrane has been linked to abnormal RBC-EC adhesion in sickle cell disease, hereditary hydrocytosis, and chronic uremia (6 -8). Usually this anionic phospholipid is located exclusively on the inner leaflet of the RBC membrane but is translocated to the outer leaflet in hemoglobinopathies and oxidative stress states (9). The role of PS in adhesion has not been fully understood, but RBC with enhanced PS exposure have been identified to establish specific interactions with EC or the endothelial matrix via several receptors including thrombospondin, ␣ V ␤ 3 , CD36, and PS receptor (6, 10, 11).Moreover, several plasma factors have been identified to be involved in abnormal RBC adhesion to EC. For example, fibrinogen enhances the adhesion of pathological RBC to EC (12, 13), which is consistent with the observation that the onset of vaso-occlusive crisis in sickle cell disease is always accompanied by a temporally elevated level of this acute phase protein (12,14). However, the underlying mechanisms behind the increased adhesion efficiency in the presence of this acute phase protein remain obscure. It has been suggested that fibrinogen acts...

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Dynamic adhesion of eryptotic erythrocytes to immobilized platelets via platelet phosphatidylserine receptors

“…The interaction could contribute to the previously observed stimulation of blood clotting and thrombosis by phosphatidylserine-exposing erythrocytes (3,14,59). For their interaction with the endothelium, erythrocytes with enhanced phosphatidylserine exposure have been identified to establish specific interactions via several receptors including thrombospondin, ␣ v ␤ 3 , and CD36 (47,54).…”

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