(Duke University Medical Center) Duke Health researchers previously showed that introducing bone marrow stem cells to a bone injury can expedite healing, but the exact process was unclear. Now, the same Duke-led team believes it has pinpointed the ‘youth factor’ inside bone marrow stem cells — it’s the macrophage, a type of white blood cell, and the proteins it secretes that can have a rejuvenating effect on tissue. Nature Communications will publish the findings online on Dec. 5.