Red cell aggregation by macromolecules: Roles of surface adsorption and electrostatic repulsion

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Abstract
Aggregation of normal and neuraminidase‐treated human red blood cells (RBC) by dextrans of various molecular sizes and concentrations was quantified by microscopic counting and light reflectometry. The influences of variations in the ionic strength and the cationic valency of the dextran solution on RBC aggregation were also investigated. The data on RBC aggregation were correlated with measurements of the zeta potential by cell electrophoresis and the intercellular distance in the rouleaux by electron microscopy. With the use of the classical equations and newly developed knowledge in colloid chemistry, the electrostatic repulsive force between adjacent cell surfaces (Fe) was calculated from the experimental data. The macromolecular bridging force causing RBC aggregation (Fb) has also been derived as a function of dextran concentration. Other forces that cause RBC disaggregation are the mechanical shearing force (Fs) and the RBC membrane bending force (Fm). The net force for RBC aggregation is equal to Fb – Fe – Fm – Fs. This model of aggregation involving force balance at the surface can explain known experimental results on factors influencing cell aggregation. It is proposed that such force balance between cell surfaces may be applicable in other cell or particulate systems and that it may be of fundamental importance in many physiological functions.