Identification of a tumour factor inducing resistance to NK cell lysis.

The mechanisms involved in the resistance or susceptibility of tumour cells to NK cytotoxicity are poorly understood. The role of different molecules on the target cell surface which could act as recognition elements by NK effectors has been postulated. However, there are also some tumour cell lines which release factors capable of inhibiting NK cytotoxicity. This paper presents a new factor (NK-RIF), produced and released by different tumour cell lines, making K562 resistant to NK lysis without affecting the cytotoxic function of NK effector cells. This soluble factor is shown to be thermolabile, non-dialyzable and to have a molecular weight of 36,000 daltons. It does not block the binding capacity of the target and effector cells, nor does it affect target susceptibility to LAK or cytotoxic T-cells.