Evidence that induction and regulation of lymphokine-activated killer (LAK) activity are mediated by changes in tumour-binding potential of lymphocytes after activation by interleukin-2 (IL-2).

The changes in the tumour-binding potential of human peripheral blood lymphocytes (PBL) after activation by interleukin-2 (IL-2) was investigated by directly counting the number of lymphocytes bound to lined hepatoma cell monolayers. A significant increase in the tumour-binding potential of PBL was found after activation by more than 100 U/ml of IL-2. Maximal tumour-binding potential was achieved at 1000 U/ml of activation, and an overdose of IL-2 activation slightly decreased this potential. These changes were almost exactly the same as the changes in anti-tumour cytotoxicity as measured by a 4-hr 51Cr-release assay. In addition, the kinetics of tumour binding by lymphokine-activated killer (LAK) cells was shown to be almost identical to that of tumour cell lysis. These results thus provide evidence that induction and regulation of LAK activity are mediated by changes in tumour-binding potential of lymphocytes after activation by IL-2.