We showed previously that treatment with the non-cognate CXCR4 agonist ubiquitin protects lung endothelial barrier function during resuscitation from hemorrhagic shock and prevents development of ARDS in pre-clinical lung ischemia–reperfusion injury, endotoxemia and polytrauma models2,5,6,10. Here, CXCR4 is linked to acute respiratory distress syndrome.