Quantification of polymer depletion induced red blood cell adhesion to artificial surfaces

Abstract

Cell-cell interactions are governed by interplay of various cell-receptor-mediated interactions and non-specific forces, with non-specific forces such as electrostatic repulsion often allowing or preventing cells approaching close enough to establish adhesion via lock and key forces. One non-specific force that has only recently been suggested as being important for cell-cell interaction is macromolecular depletion interaction. Polymer depletion occurs at cell surfaces if adsorption energy is low, and if depletion zones of adjacent surfaces overlap; osmotic forces move fluid away from the intercellular gap and cell-cell attractive forces develop. In this study interference reflection microscopy (IRM) was employed to study red blood cell (RBC) adhesion to glass surfaces in the presence of dextran in order to elucidate and quantify the underlying mechanism. Our results indicate that adhesion is markedly increased in the presence of dextrans with a molecular weight above 70 kDa. The calculated adhesion energies varied between 0.1 and 1 μJ/m2 and the bell-shaped relation between adhesion energy and both polymer molecular mass and concentration was in qualitative and quantitative agreement with a theoretical depletion model. A strong suppression of membrane undulations was also observed. In overview, our results indicate that depletion interaction plays a significant role in RBC adhesion via initiating close contacts. The results suggest the importance of depletion forces for RBC interactions and its relevance to a wide variety of cell-cell and cell-surface interactions.