FcεRI

The high-affinity IgE receptor, also known as FcεRI, or Fc epsilon RI, is the high-affinity receptor for the Fc region of immunoglobulin E (IgE), an antibody isotype involved in allergy and resistance to parasites. FcεRI is a tetrameric receptor complex consisting of one alpha (FcεRIα), one beta (FcεRIβ), and two gamma chains (FcεRIγ). It is constitutively expressed on mast cells and basophils and is inducible in eosinophils.

Tissue distribution
FcεRI is found on epidermal Langerhans cells, eosinophils, mast cells, and basophils. As a result of its cellular distribution, this receptor plays a major role in controlling allergic responses. FcεRI is also expressed on antigen-presenting cells, and controls the production of important immune mediators called cytokines that promote inflammation.

Mechanism of action
Crosslinking of the FcεRI via IgE-antigen complexes leads to degranulation of mast cells or basophils and release of inflammatory mediators. Under laboratory conditions, degranulation of isolated basophils can also be induced with antibodies to the FcεRIα, which crosslink the receptor. Such crosslinking and potentially pathogenic autoantibodies to the FcεRIα have been isolated from human cord blood, which suggest that they occur naturally and are present already at birth. However, their epitope on FcεRIα was masked by IgE, and the affinity of the corresponding autoantibodies found in healthy adults appeared lowered.