The high-affinity IgE receptor, also known as FcεRI, or Fc epsilon RI, is the high-affinityreceptor for the Fc region of immunoglobulin E (IgE), an antibodyisotype involved in the allergy disorder and parasites immunity. FcεRI is a tetrameric receptor complex consisting of one alpha (FcεRIα - antibody binding site), one beta (FcεRIβ - which amplifies the downstream signal), and two gamma chains (FcεRIγ - the site where the downstream signal initiates) connected by two disulfide bridges. It is constitutively expressed on mast cells and basophils and is inducible in eosinophils.
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.
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