Relationships between epitopes on IgE recognized by defined monoclonal antibodies and by the Fc(ε) receptor on basophils

The present study investigated whether the sites on the Fc region of the IgE molecule, recognized by different anti-IgE monoclonal antibodies (mAb), are identical to those recognized by the Fc receptor (Fc(ε)R). The anti-IgE mAb recognize different clusters of epitopes on the Fc region of IgE and could interfere to different degrees with the binding of IgE to mast cells and basophils, but still recognized cellbound IgE. Analysis of the stoichiometry and affinity binding of ¹²⁵I anti-IgE mAb Fab' to free IgE have revealed that anti-IgE mAb of one group (51.3) recognized three repetitive determinants on the IgE Fc portion, and another group (95.3) recognized only one determinant. When these stoichiometric studies were performed with cellbound IgE, it was found that only one of the sites recognized by 51.3 mAb was involved in the Fc(ε)R binding site. On the other hand, the site recognized by 95.3 mAb was not the Fc(ε)R binding site. Such findings establish mAb 51.3 as a useful tool for isolating the IgE peptides involved in the binding site to the receptor.