Monoclonal antibodies defining epitopes on human IgE

Twelve monoclonal antibodies (mAb) were isolated that bound to six clusters of epitopes on the constant region of the epsilon chain of human IgE. Four of the mAb bound to the C epsilon 1 or early C epsilon 2 regions; three of these bound to the IgE myeloma protein PS and to serum IgE but not to the IgE myeloma protein ND. These mAb probably recognize an allotypic marker. Another mAb reacted with heat-denatured, but not native IgE. Four of the mAb failed to release histamine; the epitopes recognized by these mAb are in the C epsilon 1, C epsilon 2 and C epsilon 3-4 regions of IgE. Three of these non-histamine releasing mAb did not bind to IgE on the basophil surface. These mAb recognize epitopes in C epsilon 2 and C epsilon 3-4 that are not accessible when IgE is bound to its receptor. Four mAb inhibited IgE binding to basophils; two of these did not release histamine, and two others that bind to epitopes in the C epsilon 2-4 domain, released histamine and therefore blocked IgE binding by steric hindrance. Inhibition of IgE binding by different mAb suggest that the Fc epsilon RI and Fc epsilon RII bind to partly overlapping regions of the IgE molecule although the sites do not appear to be identical. A number of sites on C epsilon 1 and C epsilon 3-4 were accessible when IgE is bound to its basophil receptor. The data support the concept that only part of the Fc portion of IgE is hidden in the receptor and that portions of C epsilon 1-4 are accessible on the cell surface. These mAb should be useful in determining the domains of IgE that are critical for its biological activity.