We found MSC-secreted PGE2 to be the key mediator of their immunomodulatory effect in vitro, as reported in infection studies elsewhere.7 11 In comparison, other inflammatory mediators were not significantly changed (such as IDO and GM-CSF) or not specifically modulated by MSCs (such as IL-6 and IL-8 which were also increased by fibroblast cell control). Here, IDO1 is linked to infection.