Bronchial subepithelial fibrosis correlates with airway responsiveness to methacholine

To evaluate the relationships between airway subepithelial collagen deposition and epithelial desquamation with airflow obstruction and hyperresponsiveness in different types of asthma and other respiratory conditions such as chronic cough and allergic rhinitis.

We compared the histopathologic features observed on bronchial biopsy specimens obtained from 80 subjects: 38 with different types of asthma, 19 with chronic cough, 13 with allergic rhinitis, and 10 normal control subjects. Each subject had a questionnaire on respiratory symptoms and medication needs, measurements of expiratory flows and methacholine responsiveness, allergy skin prick tests, and a bronchoscopy with bronchial biopsies. None of the subjects studied used bronchial anti-inflammatory agents.

Different degrees of bronchial subepithelial fibrosis were present in asthmatic subjects, the most intense being observed in occupational asthma; a subepithelial deposition of collagen was also found in subjects with allergic rhinitis, although it was less intense than in asthma and irregularly distributed under the basement membrane. On global analysis, we found a significant correlation between individual provocative concentration of methacholine inducing a 20% fall in FEV1 (PC20) and subepithelial fibrosis intensity (rs=-0.70, p<0.001). The degree of epithelial desquamation was correlated with that of subepithelial fibrosis (rs=0.36, p=0.02) in subjects with normal airway responsiveness, but it was not correlated with the PC20 (rs=0.10, p>0.05). Neither the degree of subepithelial fibrosis nor epithelial desquamation was correlated with the FEV1.

These results suggest that structural airway changes such as subepithelial collagen deposition may be significant determinants or markers of a process that results in airway hyperresponsiveness.