Binding parameters of antibodies: pseudo-affinity and other misconceptions

In order to evaluate and compare monoclonal antibodies (Abs), functional affinities are generally determined. While the equations that define affinity relate to monovalent interactions, it has been considered that the binding of Abs to multivalent antigens such as the cell surface could be described by an apparent, or functional affinity. We demonstrate here that this concept is incorrect, since the binding interactions that occur cannot be described in terms of a functional affinity, and the values that are obtained serve only to obscure the true interactions. Bivalent Ab binding must be considered to be an irreversible reaction, in most cases. A correct understanding of Ab binding will be useful in the further development of Abs for therapeutic purposes.