Distinctive characteristics of bronchial reticular basement membrane and vessel remodelling in chronic obstructive pulmonary disease (COPD) and in asthma: they are not the same disease

Abstract

Aims: This study compared reticular basement membrane (Rbm) and vascular remodelling within the bronchial mucosa of subjects with chronic obstructive pulmonary disease (COPD) with those from patients with asthma, to test the 'Dutch hypothesis' of whether these are essentially the same or different pathological conditions.

Methods and results: Bronchoscopic biopsies were stained with anti-collagen IV antibody; 18 current smoking COPD, 10 symptomatic asthmatics and 13 healthy non-smoking controls were studied. The Rbm in COPD was fragmented, non-homogeneous, variable in thickness and hypervascular, whereas in asthma the Rbm was compact and homogeneous with no evidence of increased vascularity compared to controls. Length of Rbm splitting presented as percentage of Rbm length was used to measure fragmentation; it was greater in COPD than in controls and asthmatics [median (range) 20.7% (0.4-68.5) versus 5.3% (0.0-21.7) versus 1.5% (0.0-15.1), P < 0.001]. The number of Rbm vessels/mm Rbm [median (range) 10.1 (1.6-23.0) versus 4.5 (0.0-26.4) versus 4.4 (0.4-8.1), P < 0.01] and area of Rbm vessels, μm(2) /mm Rbm [median (range) 953 (115-2456) versus 462 (0-3263) versus 426 (32-2216), P < 0.05] was also increased in COPD compared to normal subjects and asthmatics.

Conclusions: The characteristics of Rbm remodelling are quite different in asthma and COPD.

Figure 1

Reticular basement membrane (Rbm) splitting and vessels. A and B represent micrographs from bronchial biopsies in two COPD patients. The Rbm (two-headed arrows) is attached below the true basement membrane; in COPD it is fragmented and shows splitting (white arrows). Black arrows indicate Rbm-associated vessels. Arrow heads indicate vessels in the lamina propria. Bronchial biopsies, anti-Collagen IV antibody staining.

Figure 2

Morphology of the reticular basement membrane (Rbm) in asthma (A & B) compared to COPD (C & D). The Rbm, as indicated in A & B is located immediately beneath the true epithelial basement membrane (black arrows). A & B represent micrographs from airway biopsies in two asthma subjects. The Rbm is compact, homogenous and thickened in asthma. C & D represent micrographs from airway biopsies in two COPD subjects. In COPD the Rbm is non-homogenous, variable in thickness and fragmented. Vessels are seen contacting and partially or completely embedded within the Rbm in D. Vessels in the lamina propria are indicated with arrowheads. Bronchial biopsies, anti-Collagen IV antibody staining.

Figure 3

Length of splitting compared between groups. H-N, healthy nonsmokers; S-COPD, Smokers with COPD; Rbm, reticular basement membrane.

Figure 4

Number of vessels compared between groups. H-N, healthy nonsmokers; S-COPD, Smokers with COPD; Rbm, reticular basement membrane.

Figure 5

Cross-sectional area of vessels compared between groups. H-N, healthy nonsmokers; S-COPD, Smokers with COPD; Rbm, reticular basement membrane.