Natural killer activity of human lymphocytes against colon cancer cells

A human colon cancer cell line, HCT-8, is shown to be an appropriate target cell for study of natural killer (NK) activity in man. In parallel experiments, effector cell characteristics for NK and antibody-dependent cellular cytotoxicity (ADCC) were found to be vested in a single lymphocyte subpopulation, which bore receptors for the Fc fragment of IgG, but lacked other surface receptors. The effector cell failed to adhere to glass and was inactivated by exposure to 3500 rad x-irradiation. Cells forming rosettes with SRBC and cells bearing receptors for complement were inactive in both systems. A wide distribution of NK activity was noted among individuals that correlated with the distribution of effector cell activity in ADCC (r = 0.8). Preincubation of NK effector cells with antibody-coated ADCC target cells markedly reduced NK activity. Neuraminidase treatment of effector cells led to increased NK and diminished ADCC, while trypsin treatment led to reduced NK activity and showed no effect on ADCC. Thus, NK and ADCC effector cells are highly overlapping if not identical populations, but different structures on the cell membrane may mediate the two activities.