The natural killer system in the rat: the relationship between natural and immune cell-mediated lysis of fibroblast targets.

Natural killer (NK) cell cytotoxic activity is thought to operate as an early defence system before the expression of specific cytotoxic immune effectors (Leibold & Peter, 1978). Apart from this temporal relationship it is likely that other mechanisms exist to regulate these two forms of host defence and their relationship to one another. Present studies firstly substantiate evidence that normal and immune effector cells represent different cell types even though they share many functional characteristics in vitro. Normal effector cells (NEC) cytotoxic for normal dermal-derived fibroblasts in vitro were present in rats 3-36 weeks old, were tissue-dependent (with low levels in lymph nodes and thymus, unrelated to cellular suppression), were nylon wool and glass non-adherent and sensitive to 400 rad of X-irradiation in vitro. Secondly, discrimination between normal and immune cell-mediated cytotoxicity by factor(s) present in normal rat serum (Lindsay & Allardyce, 1981) allowed various aspects of their in vitro and in vivo relationship to be examined. These studies suggested that the expression of NEC cytotoxicity was temporally related to the in vivo generation of immune cytotoxic effector cells.