Figure 3. Loss of elastin found replaced with collagenous fibrosis in alveolar interstitium and perivascular regions.
The density of collagen distribution in the lung parenchyma was measured in (A) COVID-19 negative and (B) COVID-19 positive patients using Masson’s trichrome collagen specific staining. (C) The density of collagen in the lung was quantified using ImageJ analysis as described in the methods. The values of collagen density were represented as means ± SD in lung sections from 8 COVID-19 patients and 6 non-COVID-19 patients. (D) Necrotic and denuded alveolar epithelial lining displayed elastolysis and (E) dense collagen deposition (red arrows - loss of elastin in the alveolar walls; red asterisk - epithelial denudation; black arrows - collagen accumulation). (F, G, H) Collagen replacing elastin fibers in formation of interstitial fibrotic changes in COVID-19 patients evident by H&E, collagen deposition, and elastin degradation respectively (red frame). (I, J) Lung parenchyma shows alveolar collapse (red asterisks) and fibrotic development and reduction of elastin fibers. Scale bar=100 μm.