CD16, also known as FcγRIII, is a cluster of differentiation molecule found on the surface of natural killer cells, neutrophils, monocytes, and macrophages. CD16 is the type III Fcγ receptor. In humans, it exists in two different forms: FcγRIIIa (CD16a) and FcγRIIIb (CD16b), which have 96% sequence similarity in the extracellular immunoglobulin binding regions.