Sequestrocytes: a manifestation of transcellular cross-bonding of the red cell membrane in sickle cell anemia.

An unusual form of red cells (called sequestrocytes) that circulate in the peripheral blood of patients with sickle cell anemia has been identified. In wetmount light microscopy preparations, sequestrocytes appear as massively vacuolated erythrocytes. We have shown by transmission electron microscopy and scanning electron microscopy that the morphology of sequestrocytes can be accounted for on the basis of transcellular cross-bonding of the cell membrane. Initially, endocytotic vesicles span the cytoplasmic space, forming putative cytoskeletal fusion zones. Points of fusion of the membrane skeleton bridging the cytoplasmic compartment expand laterally to form linear fusion zones that entrap lakes of hemoglobin within pseudovacuoles. Sequestrocytes can be isolated in the densest layer (1.159 g ml-1 or greater) of an arabinogalactan density gradient. These cells can be generated in increased numbers in sickle cell blood by incubating samples in 1.5 mM-acetylphenylhydrazine (APH) solution for two hours at 37 degrees C. Their formation is partially blocked by incubation with the reducing agent, dithiothreitol (DTT). Our results suggest that these cells represent an expression of oxidative membrane injury in sickle cell anemia.