A recombinant soluble form of the a subunit of the human high-affinity receptor for IgE (rsFceRla), one of the potent IgE-binding molecules, was tested for its ability to regulate IL-4-induced IgE synthesis by human lymphocytes. Addition of rsFcERIc to cultures induced a dose-dependent inhibition of the T cell-dependent and independent synthesis of IgE. The suppression of IgE synthesis was observed at the protein and the mRNA levels, and it was IgE class specific. By flow cytometry, specific binding of rsFceRlei was detected on surface IgE-bearing B cells as well as on U266 cells, and it was completely blocked by preincubation with IgE. rsFcERIac bound to the cell surface IgE could be effectively dissociated not only by a large excess of IgE, but also by an anti-rsFceRfle mAb that competes with IgE for the binding to rsFceRla. This mAb abolished the rsFcERIamediated suppression of IgE synthesis. These data suggest that rsFceRIa may have a function in selectively suppressing IgE synthesis through its interaction with the membrane-bound form of IgE. (J. Clin. Invest. 1994. 94:2162-2165

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