PI3 and acute respiratory distress syndrome: By comparing expression between the acute-stage and recovery-stage of ARDS, we identified an ARDS-related gene encoding a potent human neutrophil elastase inhibitor (PI3, peptidase inhibitor 3, also known as elastase specific inhibitor, skin-derived antileukoprotease, or elafin), which was down-regulated during the acute-stage of ARDS.