Fig. 1

Acute COVID-19 pneumonia features neutrophil extracellular traps (asterisk) that expand the alveolar wall, thereby increasing pulmonary resistance and impairing diffusion. Neutrophil extracellular traps appear as collections of neutrophils, nuclear debris accompanied engorged and damaged capillaries (A). Small arterial thrombi (asterisk) are frequently present in the lungs of patients with COVID-19 related pulmonary symptoms (B). Capillary beds in the alveolar walls show marked accumulation of platelet-rich thrombi, which is highlighted by immunohistochemistry for CD61. (A, B hematoxylin and eosin stain)