When and How to Evaluate the Natural Killer Cell Function

Abstract

NK cell dysfunction is observed in a variety of physiological and pathological conditions and cytotoxic assays allow to evaluating in vitro the lytic activity of NK cells against tumors or transformed target cells. Since the earliest cytotoxic tests based on the direct visualization of effector/target cell conjugates and the use of trypan blue to exclude non-viable target cells using a light microscope, a variety of cytotoxic assays have been developed. The 51chromium release assay was the most widely used for a long time, although it has several significant drawbacks, the major disadvantage being the use of radioactive compounds. To overcome this problem, several non-radioactive methods have been described, but none is broadly accepted. Among them, flow cytometry has a potential for providing information about the ability of the NK cells to lyse their targets. We review the clinical conditions associated with NK cell dysfunction as well as the role of the NK cells in immunotherapy and describe the available assays for measuring the activity of NK-cells with emphasis on flow cytometry.