KLRK1 and hepatocellular carcinoma: The expression of activating receptors (NKG2D, NKp44, NKp30, NKG2C) on the surface of NK cells in a co-culture of HCC cells was increased by the treatment of rhIL-21 (Fig. 6) however, that was not be better than the treatment of IL-6 antibody alone or in combination with rhIL-21 except for NKp30.