Variations in the susceptibility to lysis of NK target cells

Natural killer (NK) cell activity varied considerably from one subject to another and in the same subject tested on different occasions. In addition to the interindividual variations, considerable variation was also found in the susceptibility to lysis of cultured target cell lines. In this report it is shown that the susceptibility to lysis of NK target cells depends on the growth phase of these cells but is independent of the cell cycle. These results may be important for interpreting NK cell data, may have some implications for transplantation experiments in animals using cultured tumor cells and are in agreement with the data describing the sensitivity of tumor cells to radiation or chemotherapy.