Analyses of the immunosuppressive potential of MSCs. MSCs from both female and male donors significantly suppressed the proliferation of activated allogeneic T cells. MSCs from female donors (n = 18) showed a significantly higher potency to suppress T cell proliferation than MSCs from male donors (n = 16). Data are normalized to the proliferation index of PBMNCs alone (A). ANOVA analysis of variance followed by Tukey’s Multiple Comparison Test (*P <0.05; ***P <0.001). Error bars: SD. No correlation of the donor age to the potential to suppress T cell proliferation could be detected (B). Upon co-culturing of MSCs from older donors with activated allogeneic T cells more IL-6 could be detected in the supernatant compared to MSCs from younger donors that were co-cultured with activated T cells (n = 17) (C). Spearman two-tailed correlation test (*P <0.05). Although a trend toward a negative correlation was observed, no significant correlation of IDO 1 mRNA expression to T cell proliferation could be detected (n = 8) (D). Spearman two-tailed correlation test. No difference of IDO 1 mRNA expression from male MSC donors compared to female MSC donors could be detected (n = 22) (E). Two-tailed Student’s t-test. Error bars: SD. No correlation of the IDO 1 mRNA expression to the donor age could be observed (n = 22) (F). Spearman two-tailed correlation test.