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ABSTRACT
In this paper we make a short overview of our experimental work on the effect of different factors influencing the red blood cell (RBC) aggregation induced by the neutral polymers dextran (Dx) and polyethylene glycol (PEG). Suspensions of washed RBC in phosphate buffered saline (final hematocrit = 0.40 v/v, pH=7.4) were used throughout this study. The Zeta sedimentation technique was applied to quantify RBC aggregation. It gives the opportunity to modify the RBC-RBC interactions pressing them toward each other under relative centrifugal forces (RCF) of various magnitudes. The dependence of the aggregation index (AI) on the concentration of the neutral polymers free in solution was complicate. For both polymers the extent of aggregation increases with molecular mass—in the range 70000–50000 for Dx, in the range 20000–200000 for PEG. The PEG was a more powerful aggregating agent as compared to Dx. The role of the electrostatic factors for the aggregation process of RBC was proved in two ways. Decreasing the ionic strength of the suspending medium lowered the aggregation. This effect was reversed to some extent increasing the mechanical force pressing the RBC to each other. Reducing the surface electric charge of the RBC by neuraminidase (Neu) increased aggregation. We have proved the role of the steric factors for the aggregation process modifying the cell surface with covalently bound PEG. Increase in chain length and concentration of PEG linked to RBC surface reduces the aggregation probably via elevation of the steric repulsion, which counteracts the aggregating force generated by the free polymer. This effect was reversed to some extent by elevation of free polymer concentration and centrifugation forces. Hardening the RBC with glutaraldehyde or by temperature decreased the aggregation. In general the role of the cellular factors for the aggregation was masked increasing the aggregating force between RBC.