CD226 (Cluster of Differentiation 226), also known as PTA1 (outdated term, 'platelet and T cell activation antigen 1')[5] or DNAM-1 (DNAX Accessory Molecule-1), is a ~65 kDa glycoprotein expressed on the surface of natural killer cells, platelets, monocytes and a subset of T cells. It is a member of the immunoglobulin superfamily. This protein is involved in intercellular adhesion, lymphocyte signaling, cytotoxicity and lymphokine secretion mediated by cytotoxic T-lymphocyte (CTL) and NK cell. It is the cell surface receptor for NECTIN2 and its main ligands are CD112 and CD155. It stimulates T-cell proliferation and cytokine production, including that of IL-2, IL-5, IL-10, IL-13, and IFNγ upon ligand binding.

> 90% as determined by SDS-PAGE