Fc-Receptors for IgE on Human Lymphocytes. Detection with a Rosetting Assay Using a Recombinant Human/Mouse IgE Antibody and Characterization with Monoclonal Antibodies

Two monoclonal antibodies, M-L25 and M-L47, were produced against the human lymphoid Fc receptor for IgE (Fc_εR). These antibodies were identified by their ability to selectively inhibit the binding of IgE to Fc_εR⁺ lymphoid cells as demonstrated by a newly developed IgE rosetting assay. In this method, NIP coated ox erythrocytes were complexed with a NP-specific recombinant chimeric human/mouse IgE antibody and employed as indicator cells for the detection of Fc_εR⁺ cells. The anti-Fc_εR antibodies stained 4.6 ± 2.3% of normal peripheral blood mononuclear cells, 0-4 ± 0.3% of T cells, 22.2 ± 11.7% of the non-T cell fraction, and 34.9 ± 2.9% of tonsil cells. Less than 0.1% of monocytes, basophilic and eosinophilic granulocytes, platelets, and thymus cells were labelled. This indicates an antigenic heterogeneity of the low affinity FcεR on lymphocytes and the Fc_εR found on monocytes, platelets, and eosinophilic granulocytes. The lymphoid Fc_εR was immunoprecipitated by M-L25 from the lysate of surface iodinated lymphoid cells. Three polypeptide chains were identified having an apparent MW of 40, 82, and 100 kd under non-reducing, and of 42, 115, and 145 kd under reducing conditions, suggesting a multichain structure of the human lymphoid Fc_εR.