Dynamic Detection of Natural Killer Cell-Mediated Cytotoxicity and Cell Adhesion by Electrical Impedance Measurements

Measurement of electrical impedance is a relatively new real-time and label-free method for monitoring cell adhesive properties. Impedance measurements are performed in tissue culture wells in which the bottom is equipped with gold electrodes. The extent of electrode coverage by living cells as well as the strength of the bond between the cell membrane and the electrode surface determines the impedance, which in real-time cell electrical sensing (RT-CES™, ACEA Biosciences, San Diego, CA) is measured as the cell index (CI). We showed for carcinoma cells that CI was linearly correlated to the number of cells and that CI also was related to the amount of coating (laminin-5) of the wells. When natural killer (NK) cells were added to adherent carcinoma cells (target cells) CI declined rapidly dependent on the NK cell:target cell ratio. The initial decrease of CI was much more pronounced than target cell death as measured by [3H]thymidine incorporation assay. Such a rapid fall of CI was due to changes in the ad...