KINETICS OF IN-VITRO NATURAL-KILLER ACTIVITY AGAINST K562 CELLS AS DETECTED BY FLOW-CYTOMETRY

Natural killer (NK) cells bind to K562 tumor target cells in vitro and kill them. The binding and cytotoxic activities of NX cells are tight ly related to each other: degranulation of the cytotoxic effector is t he basis for target cell damage and a consequence of effector-target r ecognition and binding. However, the two phases of NK activity, bindin g and killing, have always been measured separately by various methodo logies and under different experimental conditions, because of the lac k of a comprehensive methodology able to measure both of them at one t ime. Here we describe the simultaneous measurement of the binding and killing activities against K562 of resting and cytokine (IL-2 or IL-12 )-stimulated MC cells by flow cytometry. NK, K562 and conjugates can b e identified and measured by flow cytometry on the basis of NK mAb sta ining and target cells autofluorescence (Binding Plot). Within each po pulation of the binding plot, killed targets can be identified and mea sured by their scatter characteristics (Cytotoxicity Plot). We show th at i) the conjugate formation is enhanced in cytokine-stimulated cells , even at relatively short co-incubation times; ii) the conjugate rele ase is also accelerated by cytokines; iii) the conjugate release is al ways quicker than the induction of the morphological changes in the ta rget cell that generate its modified scattering properties. Cytometry 32:280-285, 1998, (C) 1998 Wiley-Liss, Inc.