EQUILIBRIUM BINDING OF MULTIVALENT LIGANDS TO CELLS - EFFECTS OF CELLAND RECEPTOR DENSITY

We study the equilibrium binding properties of multivalent ligands to cell surface receptors. We examine the effects of cell density and num ber of receptors per cell, that is, receptor concentration, on ligand binding. These parameters can significantly affect the formation of re ceptor aggregates and cross-links. We then use our general results to show that ligand-induced cell proliferation may be self-limiting, sinc e ligand depletion reduces the signal received by individual cells onc e the cell population has expanded. We discuss the concept of avidity and show its limitations. As a specific example, we examine the bindin g of haptenated polymers to B cells and reinterpret experiments relate d to the immunon theory of B-cell activation.