Adherence properties of sickle erythrocytes in dynamic flow systems

Sickle (SS) erythrocytes have been demonstrated to be more adherent to cultured endothelial cells than normal (AA) erythrocytes when incubated under the static conditions of the culture dish. We studied the adherence of erythrocytes to vascular endothelium under various conditions of controlled perfusion to determine whether the increased adherence of SS erythrocytes has pathophysiologic relevance to the development of vaso-occlusive crises. Freshly procured human umbilical veins were perfused once with chromium 51-labeled washed erythrocytes at a flow rate of 1 ml/min under ambient oxygen tension. After a 10-minute washout procedure, there was no significant difference in the adherence of either SS or AA cells (0.53% vs. 0.54%) to undamaged endothelium. Continuous closed-loop perfusion of labeled cells for 20 minutes also showed minimal adherence for both cell types. Scanning electron microscopy confirmed that adherence was sparse and focal. Endothelial cells were then cultured in fibronectin-coated glass capillary tubes, which served as conduits for perfused erythrocytes. Again, adherence was minimal and not significantly different for SS or AA cells (0.057% vs. 0.065%). To introduce hemodynamic variables into the system, erythrocytes were perfused into fibronectin- and endothelial cell-coated capillary tubes constructed to have multiple bends. Scanning electron microscopy showed that SS erythrocytes were significantly more adherent than AA cells in these convoluted tubes. Our findings support the notion that SS erythrocytes become trapped in the microcirculation because of a complex combination of hemodynamic forces and plasma factors as well as red cell membrane peculiarities, rather than the simple propensity of these cells to adhere to the vascular endothelium.