Figure 2.

Histological study of the lungs of mice infected with H3N2 avian influenza viruses. Mice were euthanized on day 3 post-inoculation with 10⁶ EID₅₀ of test virus, and the lungs were collected. a. The lung of PBS-inoculated control mice (H&E staining). Mild histopathological changes, including infiltration of lymphocytes near the bronchiole (b, c), moderate capillary congestion, hyperplasia of pneumocytes, infiltration of lymphocytes, and widening of alveolar septa were observed (d–f). Viral antigens were mainly detected in the alveolar macrophages and intraseptal alveolar macrophages (h, i), or the bronchiolar epithelial cells (j–l). a–f, H&E staining; g–l, immunohistochemical staining. a and g, control mice; b and h, DK/HuB/S1072/09 infected mice; c and i, DK/HuN/S31479/12-infected mice; d and j, DK/FJ/S2186/11-infected mice; e and k, DK/GX/S4011/14-infected mice; f and l, DK/GX/S4234/14-infected mice. Images were taken at 400X magnification.