Fig 2.

Characterization of infection of cotton rat with H3N2 A/Duck/HK/375/75. Cotton rats were infected with 10⁷ EID₅₀/rat. The control group (mock) was inoculated with allantoid fluid diluted 1:10 in phosphate-buffered saline (PBS). (A) Viral titers in the lung and nose. (B) Lung pathology scores evaluated for 4 relevant parameters: peribronchiolitis (Peribr.), perivasculitis (Perivas.), interstitial pneumonia (Int. P.), and alveolitis (Alveol.). (C) Representative photographs of hematoxylin and eosin (H&E)-stained lung sections from uninfected rats (panels a and d) and rats at 1 dpi (panels b and e) and 4 dpi (panels c and f). Panels b and c best exemplify the progressive increases in epithelial damage, peribronchiolitis, and perivasculitis. Panels e and f demonstrate the progressive increase in pneumonia and alveolitis. Magnification, is ×100. (D and E) Weight (D) and temperature (E) changes were recorded at different days postinfection. *, P < 0.05. (F) mRNA expression of the type I interferon-inducible gene MX-1 in lung (left panel) and blood (right panel) measured at the indicated dpi. C, group of mock (allantoid)-inoculated animals.