Acceleration of erythrocyte aggregation with in vivo aging

The cell-age associated acceleration of erythrocyte aggregation at low shear rate was proved with a rheoscope (composed of a cone-plate viscometer and an inverted microscope), combined with a video camera, an image analyzer and a computer. Human erythrocytes were fractionated by density gradient centrifugation with Percoll. Compared with the low-density erythrocytes (4.0–6.6 % of total erythrocytes, presumably rich in young erythrocytes), the high-density erythrocytes (5.0–6.7 %, rich in aged erythrocytes) were characterized by (1) high velocity of erythrocyte aggregation at low shear rate (7.5 s⁻¹ ) in diluted plasma and in medium containing fibrinogen and albumin, (2) decrease of cellular deformability at high shear stress (10–98 dyn/cm² ) (3) small cell volume, and (4) low content of sialic acid with no alteration of electrophoretic mobility. The mechanism and the physiological meaning of increased erythrocyte aggregation of aged erythrocytes are discussed.