Histochemical expression of inducible nitric oxide synthase and inflammatory cytokines in alveolar macrophages in patients with ARDS

To evaluate the role of inducible nitric oxide synthase (iNOS) and proinflammatory cytokines in acute respiratory distress syndrome (ARDS), we immunostained alveolar macrophages (AMs) in the bronchoalveolar lavage fluid (BALF) collected from patients with ARDS, patients in the operating room whose lung function were normal, and non-ARDS patients who were intubated and artificially ventilated for one week in the intensive care unit. We observed the significant expression of iNOS, interleukin-6 (IL-6) and interleukin-8 (IL-8), in AMs obtained from BAL in ARDS patients by the immunocytochemical approach. By comparison, statistically significant elevation was detected in IL-8 levels in BALF supernatant from the ARDS patients compared with the control and the non-ARDS patients. These results suggest that the expression of proinflammatory cytokines and iNOS in AMs as determined by immunocytochemical technique may be an important predictor of the early stage of lung injury in ARDS. We suggest that NO and proinflammatory cytokines produced by AMs might play a pivotal role in acute lung injury. The immunocytochemical approach could be the most sensitive predictor for activated AMs in ARDS patients.