A New Method to Determine Natural Killer Cell Activity Without Target Cells

Abstract

Natural killer (NK) cell activity is a conventional parameter used to determine the per- formance lytic activity against tumor as well as virus-infected cells in innate immunity. However, use of this parameter has several problems related to bioassay measurements. To measure NK cell activity, target cells and cell culture equipment are required and ade- quate pre-culture of target cells is needed to maintain constant sensitivity for NK cells. NK cell-activating receptors play an important role in the recognition of targets, which transduce the signals necessary for cellular machinery to induce target injury and cyto- kine production. We statistically examined the parameters related to the NK cell activity of human peripheral blood mononuclear cells (PBMCs) by multiple regression analysis, and obtained a formula with NK cell % and RNA levels of two genes in isolated NK cells. The score calculated using this formula with the three measured values showed signifi- cant correlation with NK cell activity. This prediction score, named the non-incubating natural killer (NINK) score, which is independent of target cells, is not affected by inap- propriate preparation of those targets, and allows us to accurately compare the perfor- mance of NK cell activity among specimens.