(a)FcERI: (b)FceRII (CD23): High-affinity IgE receptor Low-affinity IgE receptor NH2 Soluble CD23 Ig-like domains H2N COOH Proteolytic Extracellular NH2 Y cleavage space Plasma membrane Cytoplasm ITAM COOH COOH NH2 NH2 COOH COOH