The animals were euthanized 28 days after bleomycin challenge. Early treatment with allogeneic MSCs protected the lung architecture and significantly reduced fibrosis, apoptosis and IL1-production, while delayed MSC treatment failed to protect the mice from bleomycin-induced lung fibrosis. Of note, this is the first study to definitively show the importance of naturally derived HFG in MSC protection in the bleomycin model. Here, IL1B is linked to pulmonary fibrosis.