Figure 3.

Immunostaining I. Exemplary histological morphology using hematoxylin-eosin (HE) staining in a patient who succumbed to COVID-19 3 days after hospital admission (A) showing a perivascular lymphocytic infiltrate and focal hyaline membranes/intraalveolar fibrin deposits (arrow) in line with diffuse alveolar damage; to compare, (B) shows another patient who died 14 days after hospitalization due to COVID-19 with intra-alveolar mesenchymal proliferation (arrow) and adjacent thickened alveolar septae indicating a pattern of acute fibrinous organizing pneumonia; (C) healthy lung tissue that was donated, but not used for lung transplantation; integrin subunit beta 1 (ITGB1) showed a specific but moderate staining of the internal and external elastic lamina of pulmonary artery branches as well as alveolar basement membranes (arrow) in the early group (D); in the late group, ITGB1 was enhanced in the same structures but in comparison to (E) these structures appeared distinctly thickened resulting in a higher staining intensity; matrix metalloproteinase 14 (MMP14) showed a broad but moderate staining of several extracellular matrix (ECM) structures in the early group (G) compared with an extensive high intensity enrichment in ECM structures in the late group (H); compared to the autopsy samples, staining appeared more intensive in healthy controls (C,F,I), presumably due to the higher tissue integrity; scale bars equal 300 µm in all panels except for (B) and (H) (500 µm each).