CCL2 and acute respiratory distress syndrome: Although many of its mechanisms remain unknown, researchers have highlighted the importance of the activation of MSCs through receptors such as TLRs, triggering a paracrine action through the release of several molecules: angiopoietin-1 and keratinocyte growth factor that favor the restoration of the alveolocapillary barrier in ARDS, chemokines such as the monocyte chemoattractant protein-1 (MCP-1) and the granulocyte-macrophage colony-stimulating factor (GM-CSF) that attract and activate leukocyte cells, exosomes, and anti-inflammatory molecules [51].