Natural killer cells are responsible for the interferon production induced in human lymphocytes by tumor cell contact

The identity of cells producing interferon among human peripheral blood lymphocytes in contact with tumor cells was investigated. The producer cells were target cell‐adherent lymphocytic cells morphologically similar to natural killer (NK) cells. As interferon is known to augment the cytotoxic activity of initially inactive “pre‐NK” cells, the results suggest an internal positive feedback mechanism in the activation of NK cells.