The generation of specific cytotoxic responses by human lymphocytes requires antigen and activities provided by a lymphokine supernatant.

The requirements for the generation of specific cytotoxic responses by human lymphocytes have been investigated using as a model system the response to the ultraviolet light-killed mouse tumour P815. These requirements are antigen (P815UV) and activities provided by a human lymphokine (LK) supernatant. Cells that give rise to non-specific cytotoxicity can be separated on discontinuous Percoll density gradients after a 3-day incubation of peripheral blood leucocytes with the lymphokine supernatant. Cells from which specific cytotoxic responses can subsequently be generated in the presence of P815UV and LK sediment at a higher density.