Receptors for IgE on macrophages have been characterized by binding assays (1-3), but to date there has been only one report on the isolation of this receptor from macrophages, with use of the cell line U937 (4). In that report the receptor was isolated by using a heavily absorbed polyclonal antibody raised against lymphocytes bearing receptors for IgE (5). Monomeric IgE binds so weakly to macrophages that affinity chromatography of IgE-receptor complexes, such as has been used for isolation of the receptors for IgE on basophils (6) and for IgG on macrophages (7), cannot be readily accomplished. We have used oligomers of IgE to enhance the binding of IgE to macrophages (3), but this alone would not be sufficient because--depending on whether the receptors are multi- or univalent--once the cells are solubilized, multipoint attachment would again be reduced if not abrogated. In this report we describe the use of cross-linking reagents to stabilize further the interaction between IgE and its receptor on peritoneal macrophages. With this approach we have found that the receptor is likely to be composed of two chains whose gross properties are similar to the polypeptides constituting the receptor with high affinity for monomeric IgE on rat basophilic leukemia cells and mast cells.

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