Natural Killer Cells: Characteristics and Regulation of Activity

Recently there has been increasing recognition of natural cell-mediated cytotoxicity as a potentially important antitumor effector mechanism in addition to that of specifically immune T cells and of activated macrophages. Although natural cellular cytotoxicity was first recognized only a few years ago (Herberman et al. 1973,1974, McCoy et al. 1973b, Oldham et al. 1973, Rosenberg et al. 1972,1974), there has already been extensive research in many laboratories on the nature of the effector cells, the possible mechanisms of cytotoxicity, the factors regulating the levels of reactivity, and the relevance of natural immunity to in vivo resistance against tumor growth and immune surveillance. A principal component of natural cell-mediated cytotoxicity in rodents and man has been found to be a particular subpopulation of lymphocytes which have been termed natural killer (NK) cells. We have recently reviewed in detail much of the available information on NK cells (Herberman & Holden 1978). In this paper we will only summarize our views on the characteristics of NK cells and focus on a few issues of current interest in our laboratory.