Ultrastructure of the reticular basement membrane in asthmatic adults children and infants

¹ Lung Pathology, Dept of Gene Therapy, Imperial College at the Royal Brompton Hospital, London, UK; and Respiratory Paediatrics, Imperial College at the Royal Brompton Hospital, London, UK
² Lung Pathology, Dept of Gene Therapy, Imperial College at the Royal Brompton Hospital, London, UK
³ Dept of Paediatrics, Skin and Allergy Hospital, University of Helsinki Central Hospital, Helsinki, Finland
⁴ Dept of Respiratory Medicine & Allergy, Umea University Hospital, Umea, Sweden
⁵ Respiratory Paediatrics, Imperial College at the Royal Brompton Hospital, London, UK

^* To whom correspondence should be addressed. E-mail: p.jeffery{at}imperial.ac.uk.

	Abstract

Reticular basement membrane (RBM) thickening in asthma is considered the result of subepithelial fibrosis. Thus the RBM in asthma should contain an excess of fibrils identified as interstitial collagen and the ratio of fibril to matrix should be increased above normal.

Electron micrographs of the RBM were compared with those of interstitial collagen deeper in the bronchial wall using endobronchial biopsies from adult asthmatics (n=10; 18-41 years), children with difficult asthma (n=10; 6-16 years), wheezy infants with reversible airflow limitation (n=10; 0.3-2 years) and age-matched, non-asthma controls: 10 adults, 9 children and 9 symptomatic infants with normal lung function.

Fibrils in the RBM were significantly thinner (median width 0.039 [0.03-0.052]µm vs 0.059 [0.048-0.073]µm, p<0.001) and fewer fibrils were "banded" than in the interstitial collagen (median ratio of banded to non-banded fibrils 0.08 [0-0.17] vs 0.22 [0-1.3] p<0.001). The ratio of fibrils to matrix in the thickened RBM of asthmatics did not differ from that of their respective controls (median 1.34 [0.63-2.49] vs 1.18 [0.31-2.6] NS).

The ratio of fibril to matrix in the thickened RBM of asthma is as normal and, contrary to what is expected in fibrosis, the fibrils do not resemble those of interstitial collagen.

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