BACKGROUND: Reticular basement membrane (RBM) thickening has been variably associated with asthma and chronic obstructive pulmonary disease (COPD). Even if RBM thickness is similar in both diseases, its composition might still differ.

OBJECTIVE: To assess whether RBM thickness and composition differ between asthma and COPD.

METHODS: We investigated 24 allergic asthmatics (forced expiratory volume in one second [FEV(1)] 92% predicted), and 17 nonallergic COPD patients (FEV(1) 60% predicted), and for each group a control group of similar age and smoking habits (12 and 10 persons, respectively). Snap-frozen sections of bronchial biopsies were stained with hematoxylin/eosin and for collagen I, III, IV, V, laminin and tenascin. RBM thickening was assessed by digital image analysis. Relative staining intensity of each matrix component was determined.

RESULTS: Mean (SD) RBM thickness was not significantly different between asthma and COPD 5.5 (1.3) vs 6.0 (1.8) microm, but significantly larger than in their healthy counterparts, ie, 4.7 (0.9) and 4.8 (1.2) microm, respectively. Collagen I and laminin stained significantly stronger in asthma than in COPD. Tenascin stained stronger in asthma than in healthy controls of similar age, and stronger in COPD controls than in asthma controls (p < 0.05).

CONCLUSION: RBM thickening occurs both in asthma and COPD. We provide supportive evidence that its composition differs in asthma and COPD.