CD25 (IL-2R) expression correlates with the target cell induced cytotoxic activity and cytokine secretion in human...

Cytotoxic activity is one of the major functions of Natural Killer (NK) cells and is a critical effector mechanism of innate immune responses against infected or cancer cells. A variety of assays have been developed to determine NK cell cytotoxic activity, however a receptor-based screening tool is still lacking. Here, we propose the CD25 receptor as a candidate for NK cell cytotoxicity marker. We have verified that there is a correlation between classic target cell induced cytotoxicity markers and the CD25 expression on NK cells. Non-adherent lymphocyte fractions pre-stimulated with Escherichia coli O55:B5 lipopolysaccharide were co-cultured with settled HeLa targets in a four hour long cytotoxic assay. The cytotoxic effect was evaluated by MTT reduction assay and quantification of soluble cytotoxicity markers (granzyme B, FasL, caspase-8, IFN-γ and IL-2) was done by ELISA. Lymphocytes were stained with anti-CD3-Cy-5, anti-CD56/CD16/Nkp46-FITC and anti-CD25-PE antibodies and analyzed by flow cytometry. We observed that the CD25 expression exclusively on the CD3(-)CD56(+)CD25(+) NK cells was positively correlated with their cytotoxic function evaluated by the MTT test (r = 0.68), the upregulation of granzyme B (r = 0.89), IL-2 (r = 0.78) and IFN-γ (r = 0.57), however, it was not positively correlated with FasL and caspase-8. We conclude that the CD25 expression might serve as an in vitro receptor-based screening tool for NK cell activity.