Test of a theory relating to the cross-linking of IgE antibody on the surface of human basophils

Recent mathematical models of bivalent hapten-induced histamine release from basophils predict that under appropriate conditions histamine release is maximum when cross-link formation is maximum, at a hapten concentration equal to 1/(2K(a)), where K(a) is the average affinity constant of the hapten for a single IgE binding site. To test this prediction we sensitized human basophils with a monoclonal anti-dinitrophenol IgE and generated histamine release dose-response curves with a bivalent hapten, α,ε-DNP-lysine. The monoclonal IgE has a published affinity constant of 7.1 x 10⁷ M^-1 for ε-DNP-lysine as determined by equilibrium dialysis. From the position of the maximum of the histamine dose-response curves, both in the presence and in the absence of monovalent DNP hapten, we determine that the sensitizing IgE has an intrinsic affinity constant of 6.9 ± 0.5 x 10⁷ M^-1 for ε-DNP-lysine and 1.2 ± 0.6 x 10⁶ M^-1 for α-DNP-lysine. The agreement between the two estimates of the ε-DNP-lysine affinity constant, one from histamine release experiments involving surface bound IgE and one from binding experiments involving IgE free in solution, 1) is consistent with a central prediction of the theory of cross-linking and 2) indicates that the hapten-binding properties of the IgE are unaffected by its being bound to Fcε receptors on the basophil surface.