Regulation of natural killer activity.

Cells mediating natural killer (NK) activity mediate lysis against a variety of tumor cells and may serve as important effector cells in host resistance to infection. NK active cells are present in virtually all individuals and can be rapidly activated by a wide range of stimuli. Their activities are non-MHC restricted and do not depend on sensitization by antigens, a prerequisite for specific immunity. Several important components of the immunoregulation of NK active cells are: 1) positive or negative signals that regulate the expression of NK activity, and 2) the ability of these cells to function as immunoregulatory cells. The majority of the agents that activate NK activity fall into two basic categories; the interferons and interleukin-2. This review will concentrate on studies regarding these two agents, and will primarily discuss the results obtained with recombinant molecules.