Introduction: Although NK cell activity (NKA) has a variety of measuring markers including chromiun release assay and flowcytometry-based cytolysis, limitations such as radioactivity and lack of standardization prevented it from being routine test. NK cell-specific IFN-gamma-releasing assay (NK-IGRA, NK Vue™), which direct measure the IFN-gamma secretion from NK cells in the whole blood, was recently introduced. In this study, we tested NK-IGRA in healthy donors and pretransplant recipients, and the results were compared with flowcytometric K562 cytotoxicity.

Methods: Patients on transplantation waiting lists (n=36 for kidney and n=17 for liver) and healthy control donors (n=48) were included. One mL of fresh whole blood was immediately stimulated with an engineered recombinant cytokine that specifically activates NK cells for 24 hours. The released IFN-gamma was measured by ELISA. Simultaneously, flowcytometry-based NK cytotoxicity assay was performed with K562 target cells. The effect of cell process time variability on NKA results was also evaluated

Results: In pretransplant KT and LT recipients, NK-IGRA results were 161.0±232.6 and 102.1±194.8 pg/mL, respectively. NKA by IGRA was significantly decreased in pretransplant recipients compared to healthy donors (309.1±337.8 pg/mL) (P< 0.05). Flowcytometric cytotoxicity tests at effector to target ratio of 32 revealed 34.3±4.0 and 33.8±4.6% cytolysis of K562 cells in pre-KT and -LT patients, respectively. Flowcytometric NKA was also significantly decreased in pretransplant recipients compared with healthy donors (49.5±3.7) (P<0.05). However, in both tests, there was no significant difference of NKA results between pre-KT and pre-LT recipients (P>0.05). NK-IGRA levels were not correlated with the frequencies of NK (CD3-CD56+) or NKT (CD3+CD56+) cells. In study of cell processing delay, NK-IGRA results were decreased according to their time delay in processing, and whole blood samples shoud be processed wihin 1 hour after blood draw. For flowcytometric K562 cytolysis, samples need to be processed within 4 hours.

Conclusion: NK-IGRA could be a tool for NKA test using small amount of whole blood in clinical laboratory setting. Further investigations concerning the applicability and sensitivity of NK-IGRA are necessary in variable immunologic diseases.

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