Immunohistochemical localization of nitric oxide synthase and the oxidant peroxynitrite in lung transplant recipients with obliterative bronchiolitis

Background Obliterative bronchiolitis (OB) is a disease affecting a large percentage of lung and heart-lung transplant recipients. Histologically, the disease is characterized by inflammation, cellular proliferation, and obliteration of terminal airways. Methods. We investigated the production of inducible and constitutive nitric oxide syntheses and peroxynitrite by immunohistochemistry in the lungs of control subjects (n=14) compared with those of transplant recipients with OB (n=8). Results. Strong immunoreactivity for inducible nitric oxide synthase and nitrotyrosine, a marker of protein nitration by peroxynitrite, was seen in inflammatory cells, airway epithelium, and vascular endothelium of patients with OB, compared with little immunoreactivity in control lungs. Immunoreactivity for constitutive nitric oxide synthase was abundant in the airway epithelium and vascular endothelium of control lungs, however,it was decreased in airway epithelial cells and arterial endothelial cells of patients with OB. Conclusions. We conclude that increased formation of the potent oxidant peroxynitrite and decreased production of endothelial nitric oxide may contribute to the functional and morphological abnormalities of OB.