A LIPOSOME-BASED MODEL SYSTEM FOR THE SIMULATION OF LECTIN-INDUCED CELL-ADHESION

A parallel plate flow chamber with defined wall shear rates was develo ped in order to study and simulate cellular adhesion to biological mem branes as mediated by lectin/carbohydrate interactions. Planar bilayer s 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 Concanav alin A as model cells was observed fluorimetrically by confocal laser scanning microscopy. The use of supported membranes made it possible t o study the dependence of adhesion upon different physicochemical para meters 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 lipi d compositions which represent a special balance between charged and p olyethylene glycol-coupled lipids. This is discussed in term of the in terplay between the various attractive and repulsive forces at membran e surfaces. The dependence of liposome adhesion upon the shear rate co uld be detected. These results were used to evaluate binding forces be tween lectin-bearing liposomes and ligand-containing planar bilayers.