Standardization of a micro-cytotoxicity assay for human natural killer cell lytic activity

Abstract

Cytotoxicity assays are widely used to evaluate the functional activity of NK and T cells against tumour target cells and the release of radioactive sodium chromate from labelled target cells is still the most commonly used market of target lysis in culture supernatants. We describe here the standardization of a micro-cytotoxicity test in which the number of cytolytic effector and tumour target cells have been decreased by a factor of 10. The release obtained by 500 tumour target cells was compared with the release obtained by 5000 target cells in the standard cytotoxicity assay for target: effector cell ratios from 1:1 to 1:100. Both γ and β emissions of the 51Cr isotope were evaluated to determine the assay release. The results obtained by the micro-cytotoxicity assay (500 target cells) were comparable to those of the standard assay (5000 target cells) and 51Cr release evaluation using the γ counter was the most sensitive method of determining lytic activity using 500 tumour target cells. β counter evaluation using solid phase scintillation was found to be a reproducible alternative method, even if the lytic curves cannot be compared with those obtained using the traditional method.