Background
CD57, also known as HNK-1 and Leu7, is a terminally sulfated glycan carbohydrate epitope (glyco-epitope) expressed on a variety of proteins, lipids, and chondroitin sulfate proteoglycans at the cell surface. CD57 is synthesized by the enzyme B3GAT1 and is present on a subset of peripheral blood lymphocytes, including NK cells and CD8+ T cells, as well as neural cells and striated muscle. Studies have shown that CD57 is not expressed on platelets, monocytes, granulocytes, or red blood cells. The CD57 epitope may play a role in neural cell adhesion, and characterizes unique maturation states in T and NK cells. CD57 is an important marker when studying functional immune deficiency in patients with autoimmune diseases, infectious diseases, and cancers.