SERPINE1 and acute respiratory distress syndrome: In patients with adult respiratory distress syndrome (ARDS) secondary to sepsis, the fibrinolytic activity of bronchoalveolar fluid was markedly lower than that of patients with interstitial lung disease or normal subjects, due to the appearance of PAI activity.33,110 In situ hybridization on lung biopsies showed that, like in animal models, macrophages rather than ECs were the main source of PAI-1.