Immunohistochemical staining is shown in red.
Day 1 p.i. (A) SARS-CoV (Urbani)–infected mice: antigen present in occasional ciliated respiratory epithelial cells in bronchioles. (B) MA15-infected mice: diffuse and extensive staining of bronchiolar respiratory epithelium and alveolar pneumocytes.
Day 2 p.i. (C) SARS-CoV (Urbani)–infected mice: staining of occasional bronchiolar epithelial cells and rare alveolar pneumocytes. (D) MA15-infected mice: staining predominantly in intact and detached cells in pulmonary alveoli.
Day 3 p.i. (E) SARS-CoV (Urbani)–infected mice: occasional staining of alveolar pneumocytes and bronchiolar epithelium. (F) MA15-infected mice: extensive staining of abundant, intraalveolar, necrotic debris.
Day 4 p.i. (G) SARS-CoV (Urbani)–infected mice: occasional focus of predominantly pneumocyte staining. (H) MA15-infected mice: extensive staining of abundant, intraalveolar, necrotic debris. Primary antibody, rabbit anti-SARS-CoV antibody; secondary antibody conjugated with alkaline phosphatase with naphthol fast-red and hematoxylin counterstain; original magnifications ×25. Mice were inoculated with 105.6 TCID50 MA15 virus/mouse or 105.0 TCID50 SARS-CoV (Urbani)/mouse.