Fig. 1

Hematoxylin and eosin-stained sections staining from representative regions of the lung parenchyma of post-mortem lung tissue of 8 COVID-19 patients (Patient 1 to 8). A All patients show extensive alteration of lung microstructure in the form of alveolar damage, fibrin exudation into alveolar space, thrombi and fibroblastic proliferation. The septa are thickened and there is presence of hyaline membranes and dense infiltrates. Scale bar is 3 mm. 1: patient 1- Alveolar damage with collagen deposition and exudative pattern of damage, 2. patient 2- Large thrombi and smaller caliber arteries showing fibrin thrombi (arrows), 3. patient 3-Alveolar damage pattern arising from fibroblastic proliferations, 4 and 5. patient 4 and 5- Exudate in the entire lung, 6. patient 6-Necrosis with blood and exudate in the lung parenchyma, 7. patient 7-Hemorrhagic infarction of lung tissue adjacent to a pulmonary artery with thrombotic material, 8. patient 8-Pulmonary hemorrhage with blood and fibrin exudation into the parenchyma. B H and E staining at higher magnification to show representative areas of extensive diffuse alveolar damage, microthrombi and edema in regions of the lungs from various COVID-19 ARDS samples. I. Fibroblastic proliferation, II. Plugged airway due to remodeling, III. Coagulation necrosis with blood in the lung tissue, IV. Proliferative phase of diffuse alveolar damage, V. Patchy distribution of damage, VI. Proteinaceous exudates in alveolar spaces, VII. Blood and fibrin exudation into parenchyma, VIII. Proteinaceous exudates in alveolar spaces, IX. Endotheliitis of small vessel < 100 μm with infiltration of the vessel wall by lymphocytes (arrow shows infiltrated cells). C Thrombi and microthrombi were identified in lung sections of 7 of the 8 patients. Images of vessels were chosen to emphasize the microthrombi. Box is magnified in the right panel. Arrow shows microthrombi on alveolar septa