High-affinity receptor for immunoglobulin epsilon/IgE. Mediates IgE effector functions in myeloid cells. Upon IgE binding and antigen/allergen cross-linking initiates signaling pathways that lead to myeloid cell activation and differentiation. On mast cells, basophils and eosinophils stimulates the secretion of vasoactive amines, lipid mediators and cytokines that contribute to inflammatory response, tissue remodeling and cytotoxicity against microbes. Triggers the immediate hypersensitivity response to allergens as a host defense mechanism against helminth parasites, pathogenic bacteria and venom toxicity. When dysregulated, it can elicit harmful life-threatening allergic and anaphylactic reactions.