STUDYING RECEPTOR-MEDIATED CELL-ADHESION AT THE SINGLE-MOLECULE LEVEL

Cell adhesion is essentially mediated by specific interactions between membrane receptors and ligands. It is now apparent that the mere know ledge of the on- and off-rate of association of soluble forms of these receptors and ligands is not sufficient to yield accurate prediction of cell adhesive behavior. During the last few years, a variety of com plementary techniques relying on the use of hydrodynamic flow, atomic force microscopy, surface forces apparatus or soft vesicles yielded ac curate information on i) the dependence of the lifetime of individual bonds on applied forces and ii) the distance dependence of the associa tion rate of bound receptors and ligands. The purpose of this review i s, first to recall the physical significance of these parameters, and second to describe newly obtained results. It is emphasized that molec ular size and flexibility may be a major determinant of the efficiency of receptor mediated adhesion, and this cannot be studied by conventi onal methods dealing with soluble molecules.