Application of Non-Radioactive Europium(EU³⁺) Release Assay to a Measurement of Human Natural Killer Activity of Healthy and Patient Populations

Abstract

Europium (Eu³⁺) release assay is a non-radioactive method for a measurement of cytotoxicity of lymphocytes and has several advantages compared with a conventional ⁵¹Cr release assay. However, the Eu³⁺ release assay has not been applied to a natural killer (NK) activity measurement of a large number of the human population mainly due to a lack of comparability with the ⁵¹Cr release assay. With some modifications of the procedures and careful manipulation of cells, constant and reproducible results were obtained by the Eu³⁺ release assay. NK activity of several individuals was measured by the Eu³⁺ release assay and was compared with data obtained by ⁵¹Cr release assay performed simultaneously. The obtained values by the two methods were almost identical. We applied the Eu³⁺ method to measure NK activity of a large number of individuals, including 68 apparently healthy donors and 36 autoimmune and 21 cancer patients. Some of these diseases are known to show abnormal NK activity. The obtained cytotoxicities were mostly consistent with the previously reported data obtained by the ⁵¹Cr release assay. These results indicated that the Eu³⁺ release assay could be used as an alternative method for a measurement of human NK activity of mass population including patients.