CD16, a member of the immunoglobulin superfamily, is a 50-65 kDa glycoprotein found as both a transmembrane and GPI-linked form. The transmembrane form of CD16 is expressed on NK cells, granulocytes, macrophages, and mast cells but not on eosinophils. The GPI-anchored type of CD16 is found only on neutrophils. CD16 is involved in NK activation and signal transduction.1-5