Progressive Immunologic Dysregulation with Exposure to Tobacco Smoke in a Model of Chronic Obstructive Pulmonary Disease (COPD)

Our research objective is to examine the role of dysregulated immune responses in disease progression and changes in lung physiology in a rat model of COPD. Spontaneously hypertensive rats were exposed to tobacco smoke (TS) (90 mg/m3) or filtered air (FA) for up to 12 weeks. Necropsy timepoints of 4, 6, 8, 10 and 12 weeks were chosen to define the immunological and pathophysiological changes in the lung. Rats exposed to TS showed significant increases in macrophage, neutrophil and lymphocyte number in bronchoalveolar lavage compared to FA at all weeks examined. Proinflammatory cytokines IL-1β, IL-6 and IFN-γ in whole lung homogenates were significantly increased following exposure to TS compared to FA controls. Physiological airway obstruction due to TS exposure was noted by significant elevations in central airway resistance and tissue damping. Central airway resistance was significantly increased at 4 weeks, decreased at 6 weeks, but returned to significantly elevated levels at 10 and 12 weeks following TS exposure. Tissue damping showed a peak at 4 weeks, then a decreasing trend, although remaining significantly elevated through 12 weeks of TS exposure. Strong positive correlations were noted between proinflammatory cytokines IL-1β, IL-6, IFN-γ, TNF-α and the degree of tissue damping. These changes were associated with increases in central airway squamous epithelial metaplasia and distal airway mucous metaplasia. These findings suggest progressive airway obstruction with an abnormal inflammatory response to TS exposure in this rodent model of COPD. We conclude a dysregulated immunologic response, along with airway inflammation are strongly associated with the impairment of physiological lung function in TS-exposed rats.