Vasoocclusion in Sickle Cell Anemia

Abstract

After reviewing a peripheral blood smear from a patient with sickle cell anemia, one might predict that the clinical consequences of sickle hemoglobin would result simply from vascular obstruction by misshapen red cells. In fact, the pathophysiology of sickle cell disease is far more complex. Besides red cell adhesion to vascular endothelium, it includes the participation of leukocytes, blood coagulation proteins, and platelets. See page 1626 More than 25 years ago, Hebbel et al observed that sickle red cells adhere to cultured endothelial cells regardless of their state of oxygenation.1 It was found subsequently that sickle red cells, and in particular sickle reticulocytes, express a number of adhesion receptors including the integrin α4β1, the immunoglobulin receptor family member ICAM-4, basal cell adhesion molecule/Lutheran (BCAM/Lu), and CD36 that are normally present on red cell progenitors in the bone marrow, but disappear as the progenitors mature into circulating red cells.2,3 Their presence on sickle red cells may be a consequence of the accelerated rate of red cell production in sickle cell anemia and the absence of a functioning spleen. But why these proteins are more prevalent on sickle red cells than on red …