Figure 3.
Histopathology in hamsters on day 4 following SARS-CoV-2 infection
Lung tissue from hamsters infected with 5 × 104 PFU SARS-CoV-2 WA1/2020 (top) and 2.5 × 105 PFU Omicron (middle) compared with uninfected hamsters (bottom) was stained with H&E.
(A–C) Low power-representative images of lung. There are multifocal to locally extensive areas of interstitial inflammation and consolidation associated with bronchioles in WA1/2020-infected animals that are reduced in Omicron-infected animals.
(D–L) Medium power-representative images of bronchioles and lumina showing presence of intraluminal necrotic epithelium in both WA1/2020- and Omicron-infected animals (J–L) and perivascular edema and marginating inflammatory cells along the endothelium of medium-sized arterioles (arrowheads).
(M–O) High magnification images of bronchiolar epithelium showing cellular atypia, hypertrophy, and loss of basal nuclear polarity in degenerative bronchiolar epithelium that is more pronounced in WA1/2020-infected hamsters compared with Omicron-infected hamsters.
(P) Cumulative pathology scoring of (1) airways (bronchi, bronchioles), (2) interstitium, (3) alveoli, (4) vessels, (5) edema, and (6) regeneration. Each feature received a score of 0–3 with a maximum possible score of 18 per animal.
(Q–S) Quantitative image analysis of immunohistochemistry using HALO (Indicalabs)-optimized algorithms to enumerate (Q) SARS-N-positive (R), Iba-1-positive (macrophages), and (S) myeloperixade-positive (neutrophils) cells per unit area. ∗p = 0.0048, two-tailed Mann-Whitney test. Scale bars: 2 mm (A–C), 200 μm (D–F), 100 μm (G–I), and 50 μM (J–O).