Improving methods of assessing natural killer cell cytotoxicity.

Natural killer (NK) cells are a class of lymphocytes important in immune resistance to viral and other serious diseases. The cytotoxic function, or 'killing activity' of NK cells has become important in studies of the effects of stress and other psychosocial factors on physical health. Unfortunately, research on NK cell function has been plagued by discrepancies in the methods of interpreting NK cytotoxicity data. We briefly review some of the variations in measuring NK cell activity and present a new model for interpreting these results, introducing maximal target cell lysis (A) and the slope of the cytolytic curve (k) as parameters that attempt to make full use of the information and the statistical power in NK cell cytotoxicity data. Examples of these interpretation methods are presented using NK cytotoxicity data from a group of metastatic breast cancer patients. This approach will be useful in applications of NK cell measurement in psychoneuroimmunology research.