Infection-induced airway fibrosis in two rat strains with differential susceptibility

Chronic infections play a significant role in the morbidity and mortality of patients with chronic airflow limitation. By stimulating airway inflammation, persistent infection has the potential to cause airway fibrosis. However, in patients this condition is most typically found in lungs damaged by other factors, such as smoking, abnormal secretions, or barotrauma. We report the characterization of Mycoplasma pulmonis infection- induced lung fibrosis in two immunocompetent rat strains with no preexisting lung disease. The fibrosis was predominantly in the airways, as demonstrated by the findings for infected animals of increased airway inflammation, airway fibrosis, and airway wall thickness, which correlated with the collagen content of the lungs. Also, the physiological alterations were the opposite of those found in interstitial fibrosis, with a positive correlation between lung compliance and collagen content. The airway fibrosis was noted earlier and to a greater extent in Lewis rats than in Fisher rats, and this result apparently was related to regulation of the inflammatory response. Airway wall thickness, airway inflammation, and airway fibrosis are commonly reported in tissue specimens from patients with chronic airway diseases and have been shown to correlate with airflow limitation in patients with chronic obstructive pulmonary disease. Thus, this model may be useful in furthering our understanding of the role of chronic infection and airway inflammation in airflow obstruction.