We focused on MMP (and in particular MMP-9 or gelatinase B) as a candidate contributor to macrophage phenotypic switching in ALI since the alveolar basement membrane is extensively remodeled in acute respiratory distress syndrome (ARDS)11, and in the acute phase of ARDS, MMP-9 levels have been noted in BAL fluid25,26. This evidence concerns the gene MMP9 and acute respiratory distress syndrome.