PAR1 is expressed by endothelial cells41,42 and lung cells.43 It is highly expressed in both intra- and extravascular compartments of the injured lung, being associated with endothelial dysfunction and a prothrombotic state.35,39,42 In fact, in lung tissue, additionally to endogenous enzymes (i.e., thrombin, matrix metalloproteinase-1 (MMP-1), and APC), PAR1 activity can also be regulated by exposed pathogen-derived proteinases, playing both pro and anti-inflammatory roles depending on the activator. This evidence concerns the gene MMP1 and endothelial dysfunction.