Four types of activating NK receptors recognize the different ligands: CD16 enables NK cells to exert antibody-dependent cell cytotoxicity; natural killer group 2 member D (NKG2D) recognizes a family of stress-induced ligands; natural cytotoxicity receptors (NCRs) are able to recognize pathogen-derived or induced ligands and tumor ligands; and the other receptors, including 2B4 (CD244), NKG2C, DNAM1 (CD226) and NKp80, recognize self-molecules [4]. Here, CD226 is linked to neoplasm.