Soluble Cytotoxic Factors and the Mechanism of NK Cell Mediated Cytotoxicity
The mechanism of lysis by natural killer (NK) cells has been delineated into three discrete steps, namely binding or recognition, programming for lysis or the lethal hit, and target cell disintegration independent of the killer cell. This delineation closely resembles the mechanism of lysis by cytotoxic T lymphocytes (1). However, unlike the T cell system, lysis by NK cells is not antigen restricted and a wide range of target cells is sensitive to the NK lytic attack. These results may be best explained if a common denominator is intimately involved in the mechanism of lysis by NK cells. What is the nature of this common denominator and how can it be verified experimentally? We have proposed a model which could accommodate the known features of the NK cytotoxic system. This model suggests that the initial recognition and interaction between an NK effector cell and a target cell leads to activation of the lytic step. This activation step may result in the release of cytotoxic mediators which can lyse the sensitive NK targets. Data presented in this communication support the proposal that it is the target cell’s sensitivity to the lytic activity of the cytotoxic mediators that is the “common denominator” of the NK system.
KeywordsNatural Killer Natural Killer Cell Natural Killer Activity Innocent Bystander Mouse Spleen Cell
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