Fc receptors for IgE on a subpopulation of human peripheral blood monocytes.

Peripheral blood monocytes (latex-ingesting cells) from healthy human donors were analyzed for their capacity to form rosettes with chicken erythrocytes (Ec) coated with IgE Fc fragments (Ec-FcIgE) and for release of 51Cr from Ec target cells coated with an IgE myeloma protein (Ec-IgE). For coating of the Ec with FcIgE or IgE, the proteins were coupled to rabbit Fab′ anti-Ec fragments with glutaraldehyde, and the resulting complexes were added to Ec. A mean ± S.D. of 18.6 ± 6.5% monocytes from 15 donors formed IgE rosettes, which were specific for the native IgE or IgE Fc fragment. IgE myeloma proteins but not myeloma proteins of the other Ig classes inhibited rosette formation. Ec coated with reduced and alkylated FcIgE failed to form rosettes. Of various mononuclear cell fractions tested, only those enriched for monocytes induced significant 51Cr release from Ec-IgE. The 51Cr release was inhibited by soluble IgE but not IgG and was significantly reduced when Ec were coated with heated or reduced and alkylated IgE. There was a high correlation (r = 0.83) between the percentage of 51Cr release from Ec-IgE and the percentage of Ec-Fc IgE rosetting monocytes, whereas the correlation to the total percentage of monocytes in the preparations was only r = 0.46. The data indicate that a subpopulation of human monocytes have Fc receptors for IgE that presumably mediate phagocytosis and lysis of IgE-coated target cells.