ABSTRACT
Natural killer (NK) cells have cytotoxic activity in vitro against a variety of tumor cells, against some microorganisms, and against cells which are infected with microbial agents. In addition, there are indications that NK cells serve as important effector cells in in vivo host resistance against disease. NK cells have been associated with a morphological cell type, the Large granular lymphocytes (LGLs), isolated from discontinuous Percoll gradients. Although some minor differences in properties exist between species, certain features have indicated that this unique cell type in the human, mouse, and rat is responsible for NK activity. The levels of NK activity in rodents have a characteristic age-related fluctuation. In studying NK cells, one of the more important aspects of the age-related differences is the determination of the mechanisms responsible for basal levels of cytolytic activity.
