Mesenchymal stem cells (MSCs), which evoke only minimal immune reactivity, may have anti-inflammatory and immunomodulatory effects. In this study, we conducted a comparative analysis of the immunomodulatory properties of MSCs derived from adult human tissues including bone marrow (BM), adipose tissues (AT), umbilical cord blood (CB), and cord Wharton's jelly (WJ). Using a multiple cytokine detection assay, we showed that there were no significant differences in levels of secreted factors from non-stimulated MSCs. We compared the immunosuppressive effect of BM-MSCs, AT-MSCs, CB-MSCs, and WJ-MSCs on phytohemagglutinin-induced T-cell proliferation. AT-MSCs, CB-MSCs, and WJ-MSCs effectively suppressed mitogen-induced T-cell proliferation as effectively as did BM-MSCs. Levels of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha secreted from activated T-cells increased over time, but these levels were significantly reduced when cocultured with each type of MSCs. In addition, the expression of hepatocyte growth factor, IL-10, transforming growth factor-beta(1), cyclooxygenase (COX)-1, and COX-2 were unchanged in MSCs treated with IFN-gamma and/or TNF-alpha, while indoleamine 2,3-dioxygenase (IDO) expression increased. IFN-gamma and/or TNF-alpha produced by activated T-cells were correlated with induction of IDO expression by MSCs, which, in turn, suppressed T-cell proliferation. These findings suggest that MSCs derived from AT, CB, or WJ could be substituted for BM-MSCs for treatment of allogeneic conflicts.