NCR1 and erythroleukemia: To assess their cytotoxic activity after 72 h of treatment, NK cells were challenged for 4 h with K562 cells, an erythroleukemia cell line that expresses ligands for several activating receptors (NKG2D, DNAM-1, NKp30, NKp44, NKp46) and is devoid of HLA-I ligands for inhibitory receptors42, hence functioning as a highly susceptible target of NK cell cytotoxicity.