Fig. 3

Natural killer (NK) cell interaction with decidua parietalis mesenchymal stem/stromal cells (DPMSCs) evaluated by culturing IL-2-activated NK cells with DPMSCs at different NK:DPMSC ratios for 24 h, and NK cytolytic activity against DPMSCs then assessed using microscopic examination and xCELLigence real-time cell analyzer. Representative phase contrast microscopic images show untreated DPMSCs (control) with typical spindle-like morphology (a), nonlysed DPMSCs cultured with IL-2-activated NK cells (arrows) at ratios of 1:1 (b) and 1:5 (c) DPMSC:NK, and lysed DPMSCs cultured with IL-2-activated NK cells (arrows) at ratios of 1:10 (d) and 1:20 (e) DPMSC:NK. The lysis of DPMSCs was evident as there was no sign of intact adherent DPMSCs, cells were ruptured, and cellular debris was obvious in suspension (arrowheads). The results of the xCELLigence showed that after 24 h culture IL-2-stimulated NK cells did not lyse DPMSCs at ratios of 1:1 and 1:5 DPMSC:NK, but DPMSCs were lysed at 1:10 and 1:20 DPMSC:NK as shown by the cell index (f), which showed the cell adhesion and proliferation of intact cells was reduced almost to zero, and growth slope (g). At a ratio of 1:1 and 5:1 NK:DPMSC, DPMSC proliferation significantly decreased (f and g). Experiments were carried out in triplicate and repeated 10 times using NK cells and DPMSCs prepared from the peripheral blood of 10 different healthy donors and 10 different fetal membranes, respectively. Scale bars = 50 μm. *P < 0.05