A fluorescence NK assay using flow cytometry.

A flow cytometric NK assay was developed in which the K562 targets were labelled with the fluorogenic substrate, carboxyfluorescein diacetate (c'FDA). This new assay compared favourably with results obtained using the conventional 51Cr-release assay. c'FDA was not toxic to target cells and did not inhibit lysis. The assay permits the evaluation of various aspects of NK activity such as the activity of NK-enriched, IFN-alpha-activated, and ALG-inhibited populations. The assay can be used in place of 51Cr-release, and has the advantages of being able to directly monitor target cell lysis of reducing overall assay time, and the avoidance of radioisotope usage.