death-ligand 1 (PD-L1), through which MSCs can suppress T cells. The secreted substances MSCs release an inflammatory response is stimulated include for example nitric oxide (NO), indoleamine 2,3-dioxygenase (IDO), prostaglandin E2 (PGE2), programmed death-ligand 1 (PD-L1) and many more. Inflammatory cytokines like IFN-gamma can stimulate the expression of these immunoregulatory mediators like IDO. IDO catalyzes the conversion of tryptophan into kynurenine inhibiting T cell proliferation and activity by tryptophan depletion and by kynurenine-mediated suppression. Pro-inflammatory Stromal cells are most often looked at for their hypoimmunogenic response but they are actually non specific immunomodulating. MSCs can flip the switch between anti-inflammatory and pro-inflammatory based on their levels of IFN-gamma, TNF-alpha, and either +IL-6 or -IL-6. Pathogens are initially recognized by toll-like receptors (TLR's). This triggers inflammatory mediators and activates either pro- or anti-inflammatory MSCs. If IFN-gamma and TNF-alpha are present in high levels the MSCs will stimulate an anti-inflammatory response by activating CD4, CD25, FoxP3, and Treg cell instead of cytotoxic T-cells. However, if the levels of IFN-gamma and TNF-alpha are low the MSCs produce low levels of IDO and therefore can activate T-cells normally and the inflammation process takes place. MSCs with +IL-6 in the presence of monocytes induce M2-macrophages and CCL-18 which inhibits T-cells from being activated. However, MSCs with -IL-6 in the presence of monocytes induce M1-macrophages and can activate T-cells and produce high levels of IFN-gamma and TNF-alpha which regulates the inflammation through the previously mentioned mechanism. Role in hematopoiesis Before differentiation a majority of MSCs are housed within the bone marrow which is also where lymphocytes and other blood elements are formed. Stromal cells play a large role in the distinction of hematopoietic cells (cells that can differentiate into other blood cells). MSCs act as a physical support for differentiating hematopoietic cells in conjunction with the extracellular matrix. Stromal cells also provide nutrients and growth factors for the hematopoietic cell to continue to develop. Lastly, MSCs express adhesion molecules that influence the hematopoietic cells differentiation. The body tells the MSCs what blood elements are needed and it conveys those adhesion molecules to the differentiating cell. Stroma (disambiguation) Stroma of ovary Multipotent stromal cells Use in future therapies MSCs have the potential to be used in multiple disease interventions. One important feature of MSCs is that they can go virtually undetected by the immune system. The stromal cells possess serine proteases which are an inhibitor of the