FLUORESCENT EUROPIUM CHELATES AS TARGET-CELL MARKERS IN THE ASSESSMENT OF NATURAL-KILLER-CELL CYTOTOXICITY

A time-resolved fluorometric assay for the detection of natural killer cell activity against target cells labelled with the fluorescent chelate europium-6,6''-bis[N,N-bis(carboxymethyl)-aminomethyl]-4'-phenyl-2,2',6',2''-terpyridine (EuCAPT) has been developed. In the assay released EuCAPT from lysed K-562 cells is measured in the supernatant after co-incubation of the target cells with effector cells. Thus, the performance of the assay is essentially similar to the previously described EuDTPA assay and the widely used Cr-51 assay. EuCAPT is released from target cells lysed by effector cells faster than (CrO42-)-Cr-51 but somewhat slower than EuDTPA. In contrast to methods based on prompt fluorometry the autofluorescence from culture medium supplemented with serum can be avoided by the use of time-resolved fluorometry. The result shows that fluorescent europium chelates provide an alternative to radioactive markers currently used for the assessment of in vitro cellular cytotoxicity.