Fig 1: Upregulation of PAI‐1 and Neuroserpin in the lungs of patients with fatal SARS‐CoV‐2 infection, and controls. (A) Control case #1. H&E shows preserved alveolar structures. (B) COVID‐19 case #2. H&E shows loss of normal lung architecture and changes associated with the disease. The arrows indicate the alveolar epithelium. (C) Control case #1. PAI‐1 expression determined with anti‐PAI‐1 polyclonal antibody is minimally detected in the alveolar epithelium. (D) COVID‐19 case #2. Upregulation of PAI‐1 in epithelial cells (arrows) and macrophages (asterisk). (E) Control case #1. Anti‐Neuroserpin polyclonal antibody shows scattered macrophages, but is negative in other cell types. (F) COVID‐19 case #2. Expression of Neuroserpin in intra‐alveolar macrophages (asterisk) but not in epithelial cells (arrows). (G) Control case #1. Anti‐CD68 shows few intra‐alveolar macrophages. (H) COVID‐19 case #2. Anti‐CD68 reveals abundant intra‐alveolar macrophages (asterisk). (I) Control case #1. Anti‐cytokeratin antibody stains alveolar epithelium. (J) COVID‐19 case #2. Anti‐cytokeratin highlights alveolar epithelium (arrrows). All images (x200). Bar represents 100 μm.
Fig 2: Cellular sources of PAI‐1 and Neuroserpin in the lung of SARS‐CoV‐2 infection. COVID‐19 case #2. (A) H&E shows the accumulation of reactive pneumocytes (short arrow) and intraalveolar macrophages (arrowhead) (x500). (B) Upregulation of PAI‐1 in epithelial cells (arrows) [29] and in macrophages (arrowheads) [30, 31, 32], with variable/weak staining in endothelial cells (long arrow) [33] (x500). (C) Neuroserpin expression in macrophages (arrowheads) is typically associated with the plasma membrane as reported [34], but not in epithelial cells (arrows) (x500). (D) As a comparison for staining specificity, anti‐tissue factor (TF) polyclonal antibody shows staining for TF in epithelial cells only (arrows), but not in macrophages (arrowheads)(x400), as reported [5]. The inset shows negative staining in the absence of a primary antibody. (E) Cytokeratin staining of epithelial cells with AE1/AE3 (arrows), but negative for macrophages (arrowheads) (x500). (F) CD68 confirms abundant intra‐alveolar macrophages (arrowheads) and is negative for epithelial cells (arrows) (x500). Bar represents 50 μm.
Fig 3: Inhibitors, components of fibrinolytic cascade and Vaspin in SARS‐CoV‐2 infection and controls. (A) PAI‐1, (B) t‐PA/PAI‐1, (C) Neuroserpin, (D) α2‐Antiplasmin, (E) PAP (Plasmin‐α2‐Antiplasmin complex), (F) TAFI, (G) TAFIa, (H) HRG (Histidine‐rich glycoprotein), (I) Factor XIII, and (J) Vaspin plasma concentrations were determined by ELISA in controls and COVID‐19 patients. Each symbol corresponds to one patient. Means and SEM are indicated. NS, non‐significant; **p ≤ 0.01, ***p ≤ 0.001 ****p ≤ 0.0001 (Kruskal‐Wallis test).
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