Natural killer cell function in flow cytometry

Background. Natural Killer cells are an important line of defense against newly arising malignant cells and cells infected with viruses, bacteria, and protozoa. They have the ability to mediate a spontaneous cytotoxicity against a variety of cell types including normal allogeneic cells, virally infected cells, and tumor cells. NK cell activity is finely tuned by the opposing activity of stimulatory and inhibitory receptors, with specificity for various MHC-I allotypes. Lysis of the target can be achieved by different mechanisms, including cytotoxic granule exocytosis and production of soluble factors. We studied the possibility offered by flow cytometry to give a comprehensive quantitative evaluation of human NK cell activity. Method. Human MC cells, recognised by specific monoclonal antibodies, and tumor targets were analysed by flow cytometry after the binding and killing phases of their activity. Results. The two phases of NK lytic activity (binding and killing) can be measured by flow cytometry, in a single test tube. The flow cytometry methodologies described here give the quantitative measurement of NK cell binding to tumor targets and of their lytic activity. Conclusions. The measurement of NK cell function should be performed in specific instances, such as on patients experiencing or suspected of autoimmune disorders, chronic fatigue immune dysfunction syndrome (CFIDS), repeated infections, chemotherapy, treatment with biological modifiers such as IL-2. Flow cytometry can measure both binding and killing NK cell functions, and is fast, independent of the operator, statistically reliable, avoids the use of radioactive material and performs the analysis at single cell level rather than on whole PBL.