[Localization and functions of mesenchymal stromal cells in vivo]

Studying mesenchymal stromal cells (MSC) is a very topical problem. Numerous experiments in vitro promoted understanding of MSC biology to a great extent. However, many aspects of their behavior in vivo still remain unclear. This review deals with MSC localization and functioning in an organism. MSC are present in various tissues, changing their numbers and traits during ontogenesis. Pericytes, or adventitial cells, can be considered as possible equivalents of MSC in vivo. Self-maintenance, proliferation, and differentiation of MSC are controlled by their tissue microenvironment that includes surrounding cells, soluble molecules, and extracellular matrix. At early stages of ontogenesis, MSC, probably, migrate throughout an organism. The migration occur also through a mature organism when tissues happen to be damaged. MSC move pointedly to the damaged parts and render a reparative effect which is due, first of all, to paracrine production of bioactive molecules. Immunomodulatory properties of MSC also play their role in tissues regeneration. An important function of MSC consists in creation of hematopoietic microenvironment. They secrete humoral regulators of hemopoiesis such as cytokines and chemoattractants. In addition, they interact with hemopoietic cells via surface molecules. Possibly, MSC sustain the stable functioning of other tissues as well. Their unique features make them quite attractive for clinical use, although successful introduction of MSC into medical practice requires their further studying.