Rapid flow cytometry based cytotoxicity assay for evaluation of NK cell function

Assessment of natural killer cells (NK-cell) cytotoxicity is used not only in research settings but is also important in diagnosis of various diseases. NK-cell cytotoxicity assays are based on measurement of target cells killed by cytotoxic cells analyzed either by chromium (51Cr) release assay or flow cytometry. Both these methods use peripheral blood mononuclear cells (PBMC) or pure NK-cell population and hence require large volume of blood sample which is difficult to obtain in pediatric patients and patients with cytopenia. Hence, a flow cytometric assay was designed to determine NK cell activity using whole blood, eliminating the need for isolation of PBMCs or pure NK cells. This assay is based on a dual fluorescent staining of target cells (K562 cell line). The DIOC18 dye labeled K562 cells are incubated with whole blood and then counterstained with 7-AAD enabling the measurement of dead target cell and then percent cytotoxicity is calculated. This study compared the NK cell cytotoxicity using PBMC and whole blood in clinically relevant samples. There was no significant difference between two assays in the measurement of lytic activity or in-reproducibility in the repeated samplings of healthy individuals. The whole blood assay required less volume of blood and also less processing time as compared to PBMC assay. It was also validated by testing patients diagnosed with familial hemophagocytic lymphohistiocytosis expected to have low NK-cell activity. This assay is rapid, sensitive and reproducible and requires significantly less volume of blood which is important for clinical evaluation of NK-cell function.