ABSTRACT
The binding forces involved in the specific interactions between antigens (Ags) and antibodies (Abs), lectins and carbohydrates, ligands and their receptors, and, in most cases, enzymes and their substrates, are of a noncovalent, purely physicochemical nature. The same (attractive) physicochemical forces that govern Ag-Ab binding also constitute the (repulsive) forces that prevent freely suspended cells, such as red blood cells (RBCs), to approach each other more closely than a given minimum distance (1). Because the distance to which RBCs can approach each other is of crucial importance to a variety of hemagglutination techniques, the rate of decay of the various physicochemical forces, as a function of distance, is especially treated. The difference in the rate of decay as a function of distance of the three major physical forces involved in cell interactions as well as in Ag-Ab bonds is one of the prime reasons for treating the three forces (electrodynamic, electrostatic, and electron-acceptor/electron-donor interactions) separately from each other. The difference in the response of the three types of physical interaction forces to various physical and physicochemical measures taken with an aim, e.g., to dissociate Ag-Ab bonds, is another important reason to maintain a clear distinction between these forces.
