Beneficial effects of mesenchymal stem cells (MSCs) in acute lung injury. This figure depicts protein-rich edema fluid and inflammatory cells filling an injured alveolus after endothelial and epithelial injury. MSCs exert immunomodulatory effects on neutrophils, lymphocytes, and macrophages, assist in repair of the injured epithelial and endothelial barriers, improve alveolar fluid clearance, and secrete several molecules including the antibacterial peptide LL-37, angiopoietin-1 (ANG-1), and keratinocyte growth factor (KGF).