Understanding the NK Cytolytic Process by Studying Mechanisms of Activation
It has become apparent from recent observations that the definition of the human NK effector cell is more complex then initially suspected. The effector cell which is a lymphocyte has been most accurately defined functionally by its ability to lyse particular “sensitive” target cells (1–4); however, the active NK cell appears to be Fc receptor positive and possibly of T-cell lineage (5), In addition, a large granular lymphocyte has been isolated which has many of these aforementioned characteristics and also possesses most of the NK and activated NK lytic activity (6). Recent observations have shown that NK activity can be augmented by various in vitro modalities. These stimuli appear to be divided into those that can augment NK activity within minutes to 24 hours of culture (Interferon (IF), Poly-IC, viruses) and those that require 48–72 hours of incubation before detectable augmentation (B-cell lines (MLC), pokeweed mitogen, and fetal calf serum) (2, 5, 7–10). The variable length of exposure required for each of these classes of agents to augment NK activity suggest that there may be multiple stages of differentiation and responsiveness of NK cells. Pre-NK cells have been defined as effector cells possessing NK receptors and therefore able to bind target cells, but needing further activation in order to express their lytic capabilities (11). In addition, agents such as interferon can also enhance the lytic abilities of the pre-NK and NK cells to become functionally more efficient killer cells (activated NK cells) (11).
KeywordsNatural Killer Cell Human Natural Killer Cell Lytic Process Interferon Activation Lytic Mechanism
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