NKp44, a member of Natural Cytotoxicity Receptors (NCRs), is an activating receptor playing a crucial role in most functions exerted by activated NK cells and also by other NKp44+ immune cells. Membrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptorMembrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptor. NKp44 / NCR2 / CD336 may contribute to the increased efficiency of activated natural killer (NK) cells to mediate tumor cell lysis.