NOS2 and acute respiratory distress syndrome: Figure 3H shows that F4/80 and iNOS were significantly expressed in the lung macrophages in the vehicle group, indicating that the macrophages were highly polarized toward the M1 phenotype at the onset of ALI; moreover, the CD206 fluorescence was increased compared with that in the control group, suggesting that the macrophages also polarized toward the M2 phenotype at the onset of ALI to attenuate tissue injury in the vehicle group.