NOS2 and chronic obstructive pulmonary disease: In COPD, there is accumulation of inflammatory mucous exudates in the lumen and infiltration of the small airway wall by inflammatory cells, as the disease progresses.[37] There is a high level expression of inducible NO synthase (iNOS) present in sputum macrophages alveolar walls, small airway epithelium and vascular smooth muscle of these patients.[38, 39] This may result in an increased production of NO and NO-related species in the lung periphery.