MSCs: The Sentinel and Safe-Guards of Injury. 
Mesenchymal stem cells (MSCs) were originally named because they could differentiate in a variety of mesenchymal phenotypes in culture.  Evidence indicates that MSCs arise from perivascular cells, pericytes, when the blood vessels are broken or inflamed.  These pericyte/MSCs are situated on every blood vessel in the body.  The MSCs sense the micro-environment of the injury site and secrete site-specific factors that serve several important reparative functions: first, a curtain of molecules from the front of the MSCs provide a barrier from the interrogation of the over-aggressive immune system.  Second, from the back of the MSCs, a different set of bioactive agents inhibit scar formation and establish a regenerative micro-environment.  Third, if bacteria are sensed by the MSCs, they produce powerful protein antibiotics that kill the bacteria on contact.  Last, the MSCs surround and encyst intruding solid objects like a piece of wood (a "splinter") or other foreign objects.  The MSCs act as a combination paramedic and emergency room (ER) staff to survey the damage, isolate foreign components, stabilize the injured tissues, provide antibiotics and encysting protection before a slower, medicinal sequence can be initiated to regenerate the damaged tissue.  The MSCs, thus, act as sentinels to safeguard the individual from intrusion and chronic injury.  A societal treatment system has evolved, paramedics and ER procedures, which mirror in a macro-sense what MSCs orchestrate in a micro-sense.  Key to this new understanding is that MSCs are not "stem cells," but rather as Medicinal Signaling Cells as the therapeutic agents.