Density, heterogeneity and deformability of red cells as markers of clinical severity in hereditary spherocytosis

Hereditary spherocytosis originates from defective anchoring of the cytoskeletal network to the transmembrane protein complexes of the red blood cell. Red cells in hereditary spherocytosis are characterized by membrane instability, reduced deformability and a large heterogeneity in disease severity among patients. To unravel this variability in disease severity, we analyzed blood samples from 21 spherocytosis patients with defects in ankyrin, band 3, α-spectrin and β-spectrin using red cell indices, eosin-5-maleimide binding, microscopy and the osmotic fragility test, Percoll density gradients, vesiculation and ektacytometry to assess cell membrane stability, cellular density and deformability. Reticulocyte counts, CD71 abundance, band 4.1 a:b ratio, and HbA1c were used as markers of red blood cell turnover. We observed that patients with moderate/severe spherocytosis have short-living erythrocytes of low density and abnormally high intercellular heterogeneity. These cells show a prominent decrease in membrane stability and red cell deformability and, as a consequence, are quickly removed from the circulation by the spleen. In contrast, in mild spherocytosis less pronounced reduction in deformability results in prolonged red cell life-span and, hence, cells are subject to progressive loss of membrane. Red blood cells from patients with mild spherocytosis thus become denser before they are taken up by the spleen. Based on our findings, we conclude that red blood cell membrane loss, cellular heterogeneity and density are strong markers of clinical severity in spherocytosis