Adult human MSCs inhibit allogeneic responses through HO-1 expression. (A) Immunocytology experiments showing that human MSCs express HO-1. Negative controls were performed using normal rabbit serum at the same dilution (1:1000) as the anti–HO-1 antibody. The results of 1 experiment representative of 4 are shown. Similar results were obtained with 8 different MSC lines. See “Image acquisition” for image acquisition information. (B) PBMCs from healthy donors (5 × 104) were stimulated with irradiated allogeneic PBMCs (5 × 104) in the presence or absence of an MSC line at a MSC/T cell ratio of 1:1. When indicated, the HO-1 inhibitor SnPP was added to the culture at 50 μM. The results shown are representative of 5 experiments. Error bars represent SD.
