In addition to these studies that were mainly performed in mice with ALI, in a recent observational clinical study the researchers reported that an increased ratio of CD4 + CD25 + Foxp3 + Treg cells to all CD4+ cells in BALF obtained from ARDS patients on admission is an independent risk factor for 30-day mortality, although the ratio of Treg to all CD4+ cells in the blood was not associated with 30-day mortality and did not differ between patients with ARDS and controls [8]. This evidence concerns the gene CD4 and acute respiratory distress syndrome.