IgEFcRI

IgEFcRI, also known as FcεRI, is a high-affinity receptor for immunoglobulin E. In humans it is expressed mainly on mast cells and basophils, where it initiates rapid allergic responses, and on various antigen-presenting cells such as dendritic cells and some monocytes in certain tissues. The receptor is a heterotetramer composed of an α chain that binds IgE, and signaling subunits β and two γ chains. On mast cells and basophils FcεRI typically exists as a tetramer (αβγ2), whereas on some dendritic cells a trimeric form (α2γ2) lacking the β chain can be found.

IgE binds FcεRI with high affinity, and cross-linking of the bound IgE by multivalent allergens clusters the receptors, triggering cell activation. This leads to degranulation and the release of mediators such as histamine, leukotrienes, prostaglandins, and various cytokines, driving immediate-type hypersensitivity reactions. The expression level of FcεRI on effector cells is modulated by cytokines, particularly interleukin-4 and interleukin-13, which upregulate receptor transcription and surface stability.

FcεRI–IgE signaling is central to many allergic diseases, including allergic rhinitis, asthma, and chronic urticaria, contributing to inflammation and symptoms. Therapeutic approaches that reduce circulating IgE, such as the monoclonal antibody omalizumab, decrease FcεRI occupancy and expression on effector cells, reducing sensitivity. Beyond allergy, FcεRI participates in parasite defense through eosinophil and dendritic cell–mediated pathways. Ongoing research aims to selectively modulate FcεRI signaling to treat allergic disease while preserving protective immune functions.