The MSC curtain that stops the immune system.

We have evolved cellular mechanisms for protecting us from disabling intruders or injuries. The Mesenchymal Stem Cell, MSC, is derived from perivascular cells, pericytes that are liberated from their basement membrane tethers surrounding blood vessels upon injury or inflammation. These site-activated MSCs produce a curtain of immuno-modulation behind which slow and specific tissue regeneration takes place. In addition, the MSC senses the tissue microenvironment and adjusts the curtain and regenerative activity accordingly. This includes the production of antibiotic proteins like LL37 that both kills intruding bacteria on contact, but calls forth macrophage and other members of the hematopoietic system to further medicate the injury site. Indeed, MSCs appear to be local managers of the tissues' innate regenerative potential. Thus, I propose that MSC should denote "Medicinal Signaling Cells" since these cells are "drug stores" for sites of injury or inflammation.