Nontypeable haemophilus influenzae (NTHi) and lung oxidative stress

Background: COPD is characterized by ongoing airway inflammation that continues after smoking cessation. The production of reactive oxygen species (ROS) to produce oxidative stress and lung damage is a key feature of this ongoing inflammatory process. The lung phagocytes (macrophages and neutrophils) are thought to have a key role in ROS production. Nontypeable Haemophilus influenzae (NTHi) is the dominant bacterium found in the lungs of patients with COPD. It is not known if NTHi has a role in ROS production. Aims: To assess the effect of NTHi on the production of ROS by lung phagocytes. Methods: Bronchoalveolar samples were obtained from 51 patients so far (22 patients with COPD and 29 controls). Cells were stimulated with both live and killed NTHi. Cells were analyzed for ROS production using 3 different methods 1), flow cytometry (neutrophils and macrophages), 2), confocal microscopy (macrophages), and 3), chemiluminescence (macrophages). The effect of the cytokine interferon gamma (IFN-g) on ROS production was measured. The association with the phagolysosome was also assessed by confocal microscopy. Results: NTHi stimulation caused a significant increase in ROS production by lung macrophages (in all 3 methods (p < 0.001)) and neutrophils (p < 0.001). This production of ROS was both intracellular and extracellular and was increased by the administration of IFN-g. NTHi was associated with the phagolysosome for at least 24 hours and with sustained ROS production. Results between the COPD and control subject groups were not significantly different. Conclusions: NTHi causes the release of reactive oxygen species from lung phagocytes and may be an important cause of oxidative stress.