A liposome-based model system for the simulation of lectin-induced cell adhesion

A parallel plate flow chamber with defined wall shear rates was developed in order to study and simulate cellular adhesion to biological membranes as mediated by lectin/carbohydrate interactions. Planar bilayers containing clustered areas of various long-chain alkyl mannosides as carbohydrate ligands and supported on transparent materials were used as model membranes. Their interaction with liposomes bearing Concanavalin A as model cells was observed fluorimetrically by confocal laser scanning microscopy. The use of supported membranes made it possible to study the dependence of adhesion upon different physicochemical parameters of membranes. The liposomes of this model were able to simulate the lectin-mediated adhesion of cells in a shear flow. Once specific receptor-mediated adhesion had taken place, liposomes tended to attach irreversibly to the membrane. This could be avoided by employing lipid compositions which represent a special balance between charged and polyethylene glycol-coupled lipids. This is discussed in term of the interplay between the various attractive and repulsive forces at membrane surfaces. The dependence of liposome adhesion upon the shear rate could be detected. These results were used to evaluate binding forces between lectin-bearing liposomes and ligand-containing planar bilayers.