Flow cytometric measurement of NK cell cytotoxicity

A simple and fast method to measure the natural killer (NK) cell cytotoxicity has been established. In our novel assay, following the incubation of K562 target and effector cells, the cells were stained with FITC-conjugated anti-transferrin receptor (CD71) mAb. The K562 targets alone were labeled with anti-CD71 mAb, since CD71 is highly expressed on K562 cells but not on mononuclear cells. The fluorescence intensity of CD71 on K562 cells were analyzed using flow cytometry, and the cytotoxicity was evaluated. In our assay, designated as a "CD71 assay", no spontaneous release of anti-CD71 mAb was observed from labeled K562 cells and living K562 cells were able to be divided from dead K562 cells. The data obtained by this assay was well correlated with that by the standard 51Cr-release assay as well as the C-FDA assay. In addition, the CD71 assay is a safe and simple analytic procedure since no isotope is required.