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 (By similarity). Interacts with FGR and FES/FPS. Interacts with LYN. Phosphorylated on tyrosine residues by LYN. Belongs to the MS4A family.