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Characterization of the IgE Fc receptors on monocytes and macrophages
Abstract:
Subpopulations of human monocytes (15%) and alveolar macrophages (AM phi, 8%) and rat and mouse AM phi (89%) and peritoneal M phi (57%) bear Fc receptors for IgE (Fc epsilon R) as shown by IgE-specific rosette formation. Cells from M phi-like cell lines of human, rat, and mouse origins also express Fc epsilon R. Monomeric IgE binds to Fc epsilon R on M phi with an equilibrium association constant Ka congruent to 10(7) M-1. The Fc epsilon R on human monocytes and M phi are antigenically similar to Fc epsilon R on lymphocytes but differ from Fc epsilon R on basophilic granulocytes. The Fc epsilon R on human and mouse M phi promote phagocytosis and lysis of IgE-coated erythrocytes. Patients with active IgE-mediated allergic diseases have elevated percentages of Fc epsilon R(+) monocytes (56%) that show allergic increased lytic activity against IgE-coated erythrocytes as compared to monocytes from normal humans. M phi from rats infested with Nippostrongylus brasiliensis parasites express more Fc epsilon R than normal M phi. The data indicate that Fc epsilon R expressed on M phi differ from those on mast cells and basophils, increase in number during IgE immune responses, and are likely to play an important role in the host's defense against parasites and in the pathogenesis of allergic diseases.
Insights
Macrophages and monocytes express IgE Fc receptors (Fc epsilon R), mediating phagocytosis and lysis. These Fc epsilon R are crucial in allergic diseases and host defense against parasites.
Area of Science:
- Immunology
- Cell Biology
Background:
- Fc receptors for IgE (Fc epsilon R) are expressed on various immune cells.
- The role of Fc epsilon R on macrophages and monocytes in immune responses is not fully understood.
Purpose of the Study:
- To investigate the presence and function of Fc epsilon R on human and animal macrophages and monocytes.
- To explore the involvement of Fc epsilon R in IgE-mediated allergic diseases and host defense.
Main Methods:
- IgE-specific rosette formation assay to detect Fc epsilon R.
- Binding studies using monomeric IgE to determine association constants.
- Functional assays measuring phagocytosis and lysis of IgE-coated erythrocytes.
- Comparison of Fc epsilon R expression in healthy individuals, allergic patients, and parasite-infested animals.
Main Results:
- Subpopulations of human monocytes and alveolar macrophages, as well as rat and mouse macrophages, express Fc epsilon R.
- Fc epsilon R on macrophages bind monomeric IgE with a high affinity (Ka ≈ 10(7) M-1).
- Fc epsilon R on human and mouse macrophages facilitate phagocytosis and lysis of IgE-coated erythrocytes.
- Elevated Fc epsilon R expression and increased lytic activity were observed in monocytes from allergic patients and parasite-infested rats.
Conclusions:
- Fc epsilon R on macrophages are distinct from those on mast cells and basophils.
- Fc epsilon R expression on macrophages increases during IgE immune responses.
- These Fc epsilon R play a significant role in host defense against parasites and in the pathogenesis of allergic diseases.