High affinity receptor that binds to the Fc region of immunoglobulins epsilon. Aggregation of FCER1 by multivalent antigens is required for the full mast cell response, including the release of preformed mediators (such as histamine) by degranulation and de novo production of lipid mediators and cytokines. Also mediates the secretion of important lymphokines. Binding of allergen to receptor-bound IgE leads to cell activation and the release of mediators responsible for the manifestations of allergy. Tetramer of an alpha chain, a beta chain, and two disulfide linked gamma chains. Binds LILRB1. Interacts with FGR, FES/FPS and LYN (By similarity). Found on the surface of mast cells and basophils. Phosphorylated on tyrosine residues by LYN. Variant Glu-237 has been found to be present in about 5.3% of a 1004 individuals population sample in Australia (PubMed:8817330). Belongs to the MS4A family.