Fig. 2

NK cell interaction with pMSCs evaluated by culturing IL-2 unactivated NK cells with pMSCs at different NK to pMSC ratios for 24 h and NK cell cytolytic activity against pMSCs were then evaluated using microscopic examination and the xCELLigence real-time cell system. Representative phase contrast microscopic images showing untreated pMSCs (control) have a spindle-like morphology (arrow) (a), unlysed pMSCs cultured with IL-2-unactivated NK cells (arrow) at ratio 1NK to 1pMSC (b), 15NK to 1pMSC (c), 25NK to 1pMSC (d), 50NK to 1pMSC (e), and 100NK to 1pMSC (f). The results of the xCELLigence showing that after 24 h culture, IL-2-unactivated NK cells did not lyse pMSCs as reflected by the cell index (g) and decreased pMSC proliferation (growth slope), but statistically was not significant, P > 0.05 (h) at all examined NK to pMSCs ratios. Experiments were carried out in triplicate and repeated for ten times using NK cells and pMSCs prepared from the peripheral blood of ten different healthy donors and ten different normal human term placentae, respectively. Scale bars, 50 μm