IMMUNOSUPPRESSIVE ACTIVITY OF MESENCHYMAL STEM (STROMAL) CELLS
Mesenchymal stem/stromal cells (MSCs) are able to suppress proliferation and activity of the cells related to innate and adapted immunity acting as tolerogenic and antiinflammatory agents. These properties are nearly equally provided in all stromal cells without dependence on their presence in different tissues, the level of MSCs differentiation and genetic coincidence. For MSCs are typical the absence of surface antigenpresenting molecules of the second type and costimulating ligands which are necessary for interactions with CD4 T-cells. This ensures the hypoimmunogenicity of MSCs, i.e. their low ability for activating allogenic T-lymphocytes. Inhibitory properties of MSCs are dependent on the presence of proinflammatory cytokines which are produced by the contact with immune cells. These cytokines stimulate (prime) the immunosupressive functions of MSCs. The blocking action is determined by intercellural contact between MSCs and their cell targets, as well as by humoral mediators secreted with stimulated MSCs. Suppressive effects of MSCs are able to support the homeostasis of bone marrow hematopoietic cells, to take part in peripheral tolerance to own antigens and to determine tolerogenic contacts in the immunological system «mother-fetus». Hypoimmunogenicity and blocking actions of MSCs play a significant role in cytotherapy ensuring a long-time presence of injected MSCs and their capacity to support the tissue regeneration.