Multiple binding of antibodies to antigens: effect on radioimmunoassay binding curves

Factors affecting the binding curves measured by radioimmunoassay are examined by comparing theoretical binding curves calculated for ideal populations of homogeneous antibodies and antigens in order to test the conclusions of Berzofsky et al. [Berzofsky, J. A., Curd, J. G., & Schechter, A. N. (1976) Biochemistry 15, 2113--2121] about the effect of multiple antigenic determinants on the shapes of such curves. When such ideal binding curves with the same midpoints and limiting values expected for univalent and multivalent antigens are compared, it is clear that multivalent antigens do not produce abnormally steep binding curves but rather tend somewhat to produce less steep curves. Under practical experimental circumstances, the binding curves for univalent and multivalent antigens are predicted to be indistinguishable in shape. Some alternative causes of abnormally steep binding curves are suggested.