Presence of antigenic determinants common to Fc IgE receptors on human macrophages, T and B lymphocytes and IgE-binding factors.

The present study indicates that two Mab specific to Fc epsilon R (MabER) on human B lymphocytes also react with Fc epsilon R on macrophage and T-cell lines. More importantly, it is also shown that MabER cross-react with IgE-BFs derived from B, T and macrophage cell lines. This conclusion is supported by the following observations: the binding of MabER to Fc epsilon R-bearing cells is blocked by the CSN of T, B and macrophage Fc epsilon R-bearing cell lines, known to contain IgE-BFs as shown by their inhibition of rosette formation between IgE-coated erythrocytes and Fc epsilon R-bearing cells; the material purified from the CSN of each Fc epsilon R(+) cell lines by affinity chromatography on MabER-Affi-gel blocks the rosetting of U937 cells with IgE but not with IgG-coated erythrocytes; the same affinity-purified material inhibits the binding of 125I-IgE to a selected anti-IgE Mab (Mab 75); and the CSN of Fc epsilon R(+) cells but not of Fc epsilon R(-) cells reacts in a solid-phase sandwich radioimmunoassay with two MabER (135-176), and their reactivity is significantly retained on IgE-Affi-gel from which it may be recovered by glycine elution. This RIA is not influenced by any class of Ig, including IgE, employed at a final concentration of 100 micrograms/ml. Human serum also reacts in the RIA, and parallel dilution curves are obtained with different CSN and human sera. The RIA proved to be a reproducible and sensitive method to quantify human IgE-BFs. The expression of the same antigenic determinants on Fc epsilon R from T, B and macrophages as well as on the IgE-BFs secreted by these cells indicates structural homology between IgE receptors and IgE-FBs and suggests that they are encoded by the same gene.