Natural killer cells and interferon.

Natural killer cells are cytotoxic lymphocytes found in all examined vertebrates and implicated as mediators of tumor surveillance in experimental animal models. Normally cytotoxic for a selective group of tumor target cells, NK cells can be dramatically activated to a level of high cytotoxicity by interferon and interferon-inducing agents, such as viruses, bacteria, lectins, and synthetic polynucleotides. These interferon-activated cells differ physically and antigenically from nonactivated precursor cells. All types of interferon (alpha, beta, and gamma) are capable of activating NK cells. Conversely, interferon treatment of target cells renders them resistant to NK cell-mediated cytotoxicity. Tumor cells induce interferon synthesis in leukocyte cultures, and the interferon-producing cell has properties in common with NK cells. The complexities of these effector cell-target cell-interferon interactions will be discussed.