E | SARS-CoV-2-infection manifests histological changes in patients' lungs as demonstrated by H&E staining. 1)For comparison, the normal lung of an elderly individual is shown, containing air-filled empty looking alveolar spaces and thin alveolar septae/gas-exchange membranes. Note that there are almost no inflammatory cells and that capillaries are only merely visible since not congested. 2) Diffuse (proliferative) alveolar damage showing evidence of cell death. An alveolar space filled with desquamated pneumocytes and macrophages, lymphocytes and focal erythrocyte extravasation as well as one multinucleated pneumocyte type II. The still recognizable epithelial lining is detached. Cells and surfactant are lost creating perforations in the alveolar wall, allowing migration of blood cells and fluid to enter inside the alveolar space. The adjacent interstitial space is significantly widened, showing an increase of mononuclear inflammatory cells and extravasation of erythrocytes. On the top and the lower right, dilated and congested capillaries can be seen (Hematoxylin and Eosin (H&E) stain, 200x). Abbreviations: a- Alveolar structure destroyed by lymphocytes, desquamated epithelium, as well as extravasated blood; The alveoli should be empty, but here it is filled with a combination of degenerated cells and fibrin; b- Next alveoli; c- Expanded pulmonary interstitium. The interstitium should be as thin as 10um, but here it is 100um; d- Extravasation of erythrocytes; e- Lymphocytes; f- Congested capillaries and arterioles; g- Multinucleated alveolocyte/pneumocyte type II; h- Detached epithelium; i- A histiocyte with a kidney-shaped nucleus at the bottom of the circle has ingested erythrocytes (left-handed), representing the first step of cellular elimination. Round inlet with encircled karyopyknotic, karyorrhectic and "ghost-cell" figures indicative of apoptosis. 3) Presence of type II pneumocyte syncytial giant cells in a collapsing alveolar space with detached epithelial lining. The adjacent interstitial space shows analogous changes to 2A1. At the bottom, there is a prominently dilated and congested capillary (H&E, 200x). Abbreviations: a- Alveoli with detached epithelium; b- Next alveoli; c- E Extravasation of erythrocytes; d- Expanded interstitium; e- Lymphocytes; f- Multinucleated pneumocyte type II. 4) Diffuse alveolar damage showing massive extravasation of fibrin (homogeneous eosinophilic material in the center of the alveolar space). The lining pneumocytes are almost all apoptotic/necrotic. The fibrin exudate is intermingled with mononuclear inflammatory cells and cellular debris (H&E, 200x). Abbreviations: a- Alveola; b- Congested capillaries; c- Fibrin; d- Remnants of degenerated / dying epithelium; e- Expanded interstitium; f- Cellular debris consisting of macrophages, detached epithelial cells and lymphocytes; g- Fully degenerated / lacking epithelial coverage within the alveoli. Round inlet with encircled karyopyknotic, karyorrhectic and "ghost-cell" figures indicative of apoptosis. 5) Immunohistochemical stain (IHC) for fibrin showing microthrombi caused by dysfunction of endothelial cells in capillaries of the alveolar membranes/lung interstitium leading to obstruction of the microcirculation (IHC for fibrin, 200x). Abbreviations: a- All small alveolar septal capillaries are filled out with worm-like fibrin thrombi hampering / obstructing circulation; b- Normal interstitium.