Induction of Natural Killer Cell Activity and Allocytotoxicity in Human Peripheral Blood Lymphocytes after Mixed Lymphocyte Culture

The k‐562 tumour cell is a highly susceptible target for natural killer (NK) cell lysis by lymphocytes of human peripheral blood. We have studied the antigenic relationship between the recognition sites for lysis or lymphoid and various tumour target cell by cytolytic T lymphocytes (CTL) and NK cells induced in mixed lymphocyte cultures (MLC). The characteristics of these two effector cell types have also been investigated. It was demonstrated that fresh NK cells lose their NK lytic activity when cultured alone. Cell lines not susceptible to lysis by fresh NK cells are lysed by MLC‐induced NK cells. There is no antigenic relationship between the recognition sites for the alloreactive T lymphocytes and MLC‐generated NK cells expressed on the lymphoid target cells and the tumour target cells, respectively. The MLC‐generated alloreactive T cells and NK cells are not identical. The MLC‐generated NK cells arc different from the fresh NK cells present in the peripheral blood.