Comprehensive analysis of NK cell function in whole blood samples

Natural killer (NK) cells represent the first line of defense against transformed or virally infected cells. Upon triggering of activating receptors NK cells can respond by secreting cytokines such as interferon-gamma or tumor necrosis factor-alpha and by the release of cytotoxic granules, resulting in the lysis of susceptible target cells. The importance of NK cells becomes clear in patients with impaired NK cell function or development. These patients suffer from recurrent illness and have particular problems in controlling viral infections despite their functional adaptive immune response. A detailed analysis of NK cell function is therefore of great importance. Here we describe a fast and comprehensive NK cell assay. The assay is performed in whole blood samples, eliminating the need for the isolation of PBMC or pure NK cells, while still allowing for the stimulation of the samples with cytokines. In each sample the absolute NK cell number is determined. The cytolytic activity is assayed by the lysis of (51)Cr labeled target cells and by determining the externalization of CD107a in the NK cells. Furthermore, cytokine production is detected by intracellular FACS analysis. Due to the strong reduction of required material this approach utilizes less than 3.5 ml of heparinized whole blood and is particularly applicable for frequent monitoring the immune function of adult and especially of pediatric patients.