On the memory of a chronic illness.

The elderly are particularly susceptible to disease, yet the biological mechanisms that bring about this susceptibility remain unclear. Using atherosclerosis as a model chronic illness, we review how recent studies of bone marrow-derived vascular repair systems in mice and humans provide new insights into the causes and potential cures for age-related illness. Organisms are born with a finite capacity for stem cell-mediated repair after chronic exposure to tissue injury. Once that capacity is exhausted, a cycle of pathological inflammation ensues and leads to overt disease manifestations. Augmentation of stem cell-mediated repair systems may provide a novel means of treating or preventing many age-related illnesses.