Histopathological Analysis of SARS-CoV-2 in Lung Tissues

Histopathology and detection of SARS-CoV-2 virus antigen were performed as previously described (15 (link), 24 (link), 38 (link)). Briefly, lung tissue sections were processed and stained with hematoxylin and eosin (H&E) for pathological analysis and with a rabbit polyclonal anti-SARS-CoV-2 anti-nucleocapsid antibody in immunohistochemistry (IHC) staining the presence of virus antigen. The polyclonal antibody (GeneTex, GTX135357) was used at a dilution of 1:2000. The tissue sections used for gross histology examination include the left cranial lobe (Lc), right middle lobe (Rmid), and right caudal lobe (Rc). The extent and severity of alveolar inflammation were characterized by the criteria the number of lung lobes affected, type 2 pneumocyte hyperplasia, alveolar septal thickening, fibrosis, perivascular cuffing, peribronchiolar hyperplasia, inflammatory infiltrates, and hyaline membrane formation. Each lung lobe was assessed individually for animals with multiple affected lung lobes, and then the scores were by presence and absence of signs for inflammation and virus antigen. Tissue sections were analyzed by a blinded board-certified veterinary pathologist using an Olympus BX43 light microscope. Photomicrographs were taken on an Olympus DP27 camera.